Botanical Evidence of Floods and Flood-Plain Deposition ¥ EG E T A TION _ AND HY DROLOG IC PHENOMENA GEOLOGICAL_-SURVEY PROFESSIONAL PAPER 48 5-A A description of botanical methods used to determine dates and occurrences of floods and deposition of sediment on modern flood plains UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 "' C3364 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library has cataloged this publication as follows : Sigafoos, Robert Sumner, 1920- Botanical evidence of floods and flood-plain deposition. Washington, U.S. Govt. Print. Off., 1964. vi, 85 p. illus., map, diagrs. 30 cm. (U.S. Geological Survey. Professional Paper 485-A.) Vegetation and hydrologic phenomena. Bibliography : p. 34-35. 1. Sedimentation and deposition. 2. Floods. I. Title. (Series) For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 - _ Price 35 cents CONTENTS Page ...l _c} c {nel . esc do y | Growth of trees after flood damage-Continued NbDebrach 22.0"... ee nr dice Lek wo asan ane ue enols mo aje anl A1 Evidence of floods and deposition in trees along small .i. . 1 ried se. ._ ice.. 2 Evidence of sequential deposition and erosion on the Mechanism of plant growth- ___.._l~._..__-___._._ 2 flood plain...... .._... Hydrologic concepts.. _. 4 | Botanical phenomena relating to the formation of the Collection of streamflow records._.----------- 4 flood plain. Comparison of 4 Relationship between flood-plain trees and low flow . Floodstage-discharge realtionship.------------ 5 Significance of old trees on banks--__------------- Effects of floods upon trees.__._______________________ 3 Botanical evidence of current processes affecting the Physical effects of high velocity and 6 flood plain Effects of inundation upon trees __________------- 9 | Economic significance of botanical evidence of floods.... Growth of trees after flood damage_______-_--_-._-------- 9 Value of botanical evidence of floods and flood-plain Circumferential growth around trunk scars___--_---.- 9 deposition. c_ ual cae fea ie ms Growth of sprouts from stumps and water-felled trees. 12 | List of Growth of trees following burial by alluvium during References flGods=.:. } suntan 18 Analysis of structure of wood from buried trunk. 20 FrcurRE 24. 25. 26. 27. 28. 29. . Silver maple trees on bank flooded at least 60 times between 1981 and 1960-..____________-_-_-_------------ 31. 32. ILLUSTRATIONS Map of Potomac River near Washington, . Sprouts that strated to grow from ash stem after flood damaged first new }: . View of flood-plain forest showing form of . Floating ice overriding flood plain sears Ice jam on Potomac River, Washington, D.C., February 16, Potomac River, low flow, Washington, D.C. July 1956. . Diagrams representing circumferential growth Of . Parts of a stem of an ash tree damaged by minor ice jam on January 15, Fragments of ice deposited on flood plain of Potomac River on January 15, 1958---.-.-----_------_------------ Cross sections through stem of damaged ash tree shown in figure 8.1 Potomac River in flood on August 20, 1955. Potomac River at low flow, June 19561.__ L. W- . Sprouts from stump cut off by an ice jam on February 16, 19481. . Vertical sprout growing from inclined trunk that was felled by 1948 iG@ . Trunk of tree suggesting origin as a sprout which started to grow in . Ash sprouts of four ages growing from a . Diagrams showing events that produced the form of the ash tree illustrated in figure 16-.-------------------- . Diagram of tree bases postulated as result of different rates of . Ash tree party uprooted prior to growing season of 1936 and subsequently buried__________--_-------------- itnelined buried ash tree. : -_. -_. ILLER yt an sa brew - un a alo ale - ale aloe Clara i ame in at ie me . Drawing showing basal sprout, location of samples, and approximate level of flood plain prior to 1986.-..---- . Photomicrograph of wood from buried trunk of ash tree. . Ratio of difference between mean of early wood and late wood vessel diameters to the mean of early wood vessel diameters: ":.. . ;s aia o not Otero to en iin ie tn d a ide ae ole a a oe a ap a ars in ans io o ales » aie mate ele alee Sear on channel side of river birch on Difficult Run, V&A Alder sprout growing from parent stem knocked over in 1956, Scott RUn, Ash sprout growing from inclined trunk knocked over prior to 1928, Seott Run, V&_---_-L---_----------------- Ash from flood plain, Tripps Run, Va., showing flood-damage Drawing of buried part of ash tree in figure 191 Ash tree knocked over by one flood, partly buried by another, and exposed by a third_______---------------- Diagrams representing establishment of trees on flO0d Cut bank of Potomac River showing newly exposed roots and recently fallen trees.__________-_-------------- III Page A23 24 26 27 29 31 32 32 34 34 Page AMB GLOSSARY Annual ring.-A layer of wood resulting from one season's growth of a tree; appears as a ring when seen in a cross section of a tree trunk. Apical dominance.-The inhibiting effect of hormones produced in buds at the apex of a stem which, as long as this growing tip remains intact, prevents the development of buds farther down on the stem. Bark.-A general term for the tissues outside the vascular cambium in tree trunks and stems. Callus.-A tissue of thin-walled cells that grows over a scar. Cambium.-A layer of meristematic cells which by dividing forms new tissues. Vascular cambium divides, producing xylem toward inside and phloem toward outside beneath bark in woody plants. Cork cam- bium lies outside the phloem and produces layers of cork that constitute most of the outer bark. Coniferous trees.-Trees that produce naked seeds in cones, as opposed to fruits, and are typically needle- leaved evergreens. Pine, hemlock, and Douglas-fir are examples. Crest.-The highest elevation of a flood. Deciduous trees.-Trees whose leaves turn brown and die or fall in the autumn. Baldeypress (Tazodium distichum) and larch (Lariz laricina) are examples of deciduous coniferous trees. Diffuse porous.-Wood in which vessels are all about the same size across an annual ring, as in maple or birch. Discharge.-In this report, discharge refers to the amount of flow in a stream or river. It is measured in cubic feet per second (cfs). One cfs is equivalent to 7.48 gallons per second, about 646,000 gallons per day, or 28.32 liters per second. Evergreen trees.-Trees that retain green leaves all winter. Live oak (Quercus virginiana) and American holly opaca) are examples of broad-leaved, evergreen trees. Most coniferous trees are evergreen. Flood.-Any flow of a stream or river that overtops the banks of the channel and spreads across the flood plain. Flood damage.-Generally considered to mean the economic loss resulting from floods. In this report, the physical effects of floods upon trees and other plants are also considered as flood damage. Growth.-The process of adding new cells or cellular material by the conversion of organic and inorganic materials. Growth increment.-The amount of new material added as a result of growth. One season's increment is the annual increment, which approaches the shape of a hollow cone in a tree trunk. Hardwood trees.-A general term, used mostly in the lumber industry, referring to broad-leaved deciduous trees. Wood of some hardwood trees is softer than that of some softwood trees. Hormone.-A substance, produced in a plant, that influences specific physiological processes and is often called a growth regulator. Meristem.-Living tissue in which new cells form by division and grow by the addition of synthesized pro- toplasm. Vascular cambium is a lateral meristem. : Parenchyma.-Tissue composed of thin-walled, nearly spherical cells Pith in the center of corn cobs is parenchyma. Peak.-The highest discharge attained during a flood. Crest and peak stage are synonomous. Peak pertains also to the maximum discharge. Phloem.-Food-conducting tissue of most plants; forms on outside of vascular cambium and constitutes most of inner bark. Pith.-Tissue in the center of stems composed of a mass of parenchyma cells. Rays.-A layer of cells extending radially in the wood and inner bark of tree trunks. Ring-porous.-Wood in which vessels in earlywood are larger than those in latewood, as in a hickory or oak. Root.-As used in this report, the underground parts of plants on which, as opposed to stems, there are no buds, leaves, or leaf scars. Most roots of woody plants do not have pith in the center. v VI GLOSSARY Sedimentation.-The complete series of processes that includes the removal of particles from bedrock, their transportation, deposition, and consolidation as another rock. ; Softwood trees.-A general term used mostly in lumber industry referring to coniferous trees. Wood of some softwood trees is harder than that of some hardwood trees. Stage.-The elevation of the surface of a body of water. Stem.-Plant organ which has buds, leaves, or leaf scars. Most stems grow above ground, but some are subterranean. Streamflow.-Flow of water, or discharge, in a natural channel. Tissue.-Group of cells that have a similar structure or function or both. Trunk.-A general term referring to a large, single, woody stem of a tree. Vessels.-Specialized tissue in wood or xylem of plants, consisting of cells of different shape and size in different species. Vessel cells are alined vertically, and end walls are absent or are perforated by holes or slits.. Water or sap flows in vessels. - Xylem.-Water-conducting tissue of most plants and supporting tissue (wood) of trees. Develops from cells formed toward inside of cambium. VEGETATION AND HYDROLOGIC PHENOMENA BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION By RosErt S8. Staaroos ABSTRACT Methods of identifying past floods have been developed from a study of the form and age of parts of trees growing on the flood plain of the Potomac River near Washington, D.C. The date of deposition of sediment can be learned from the study of the structure of wood in the buried part of tree trunks, and the approximate thickness of the deposit can be determined by measuring to the level of the original tree base. An- atomical characteristics of the wood of roots exposed by erosion of the banks and the flood plain provide data for ascertaining the year that the roots were first exposed. The methods can be used to determine the occurrence of floods and flood-plain deposition on streams draining areas at least as small as 4 square miles. The establishment and maturation of trees on a flood plain are the result of an interrelated sequence in the timing of seed dissemination and germination, suitable environmental condi- tions, and the flow regime of the river. The channelward limit of perennial woody plants-tree species in the humid Eastern 'United States-represents either the level of the maximum discharge during extended periods of low flow or the edge of the channel that is encroaching on a flood plain as the result of lateral corrasion. This line, separating the flood-plain forest from the channel, can be regarded as the bank of the river or the limit of the flood plain, because it is related to the complete range of river discharges and can be readily seen and mapped. Erosion and deposition on densely tree-covered surfaces away from the bank are characteristic processes and thus are effective in the formation and modification of flood plains in the humid Eastern United States. Although evidence of lateral corrosion and accretion has been found along the Potomac River, the presence of many old trees on the vertical face of banks indicates that some banks have been stable for more than 100 years. The botanical evidence shows that on forested flood plains, certainly on those of rivers which are moving laterally only slowly, alluvium is interchanged rapidly by local erosion during overbank flows and by subsequent deposition either during the same flood or during following floods. This process of 'vertical trading of flood-plain sediments without interven- tion of channel movement may affect large amounts of material. In the absence of streamflow data, engineers must rely on indirect methods of analysis to determine the magnitude and frequency of floods. Like most hydrologic data, these analyses are strange to many who are directly concerned with flood- plain phenomena. Evidence of floods and flood-plain deposition as seen in trees is easy to comprehend and presents an irrefutable record of past floods. The methods can be used, therefore, along reaches for which no discharge records exist. Because the methods have proved to be valid on small streams for which streamflow data are inadequate or nonexistent, they can be of help in planning flood-plain use in expanding cities. The age and form of flood-damaged trees may provide the date of the minimum stage of a flood that occurred prior to the pe- riod of record. The botanical phenomena will, at least, indicate the year in which a severe flood occurred, thereby providing valuable assistance in a further search for other kinds of evidence. INTRODUCTION The growth and form of trees along rivers permit the dating of flood occurrences in the last 100 years and the dating of deposition of sediment on flood plains. Floods scar the bark, prune the tops and branches, or knock over or destroy most of the trees on the flood plain. Most trees, however, are not killed; new wood and bark grow over the sears, and sprouts grow from decapitated branches and inclined trunks. The trees continue to grow. The number of annual rings that have grown since scarring of the bark or the age of the sprouts is equal to the number of growing seasons that have elapsed since the trees were damaged. The year when the flood occurred, therefore, can be ascertained. Some trees are partly buried by deposition of sedi- ment, but only a few are killed. If a tree survives par- tial burial, the new wood formed in the buried part of the trunk is more like root wood than like stem wood ; thus it is possible to date the year of burial. The surface upon which the trees were growing prior to burial can be identified by digging to the roots growing from the flared base of the trunk; thus the approximate depth of alluvium that has been deposited can be measured. Floods are characteristic of nearly all rivers; and although severe floods have been recorded, measured, and mapped in recent years, they occur unnoticed or are soon forgotten by most people. A flood is any flow of a stream or river that overtops the banks of the channel and spreads across the flood plain. On the average, A1 A2 flows of this size or larger occur about once every 2 years (Hoyt and Langbein, 1955, p. 15). Flood-control problems are discussed in a recent comprehensive book by Leopold and Maddock (1954). The purpose of this report is to demonstrate, by examples drawn principally from work in progress in the Potomac River basin, how botanical evidence can be used to deduce information on floods and flood-plain deposition. The examples used are important to this report only to the degree that they facilitate the illus- tration of methodology. The larger study, concerned with the relationship of vegetation to the hydrology of streams, has been confined largely to the Poto- mac River flood plain in the vicinity of Washington, D.C. (Fig. 1), primarily because of the long record of streamflow available for this reach. From a study of trees, the flood history of a reach can be extended in time prior to the period of the streamflow record, or a history can be reconstructed for reaches for which there are no records. The depth of fluvial sediment can be measured, and the period of time since deposi- tion can be determined; consequently, the botanical evidence will aid in distinguishing between flood plains and terraces. ACKNOWLEDGMENTS During the course of this study, many of the author's colleagues visited the study areas and offered invalua- ble encouragement and suggestions. Thanks are given to personnel of Region 6, National Park Service- 78°15’ MARYLAND f § é g y Index map of Maryland and Virginia 39°|- -|39° "As CHAIN BRIDGE VIRGINIA 0 5 10 MILES Mecer slc _LL________;__| | 78°15" FIGURE 1.-Map of part of Potomac River near Washington, D.C., show- ing study area. Base from Washington and Baltimore 1 : 250,000 quadrangles. VEGETATION AND HYDROLOGIC PHENOMENA especially to W. Drew Chick, Jr., and T. Sutton Jett- for permission to make studies in the Chesapeake and Ohio Canal and Palisades Parks, and to Maurice Sulli- van for help and suggestions resulting from visits to the field areas. Joe Brown and James Watt, Fairfax County Park Authority, were most helpful with phases of the study at Great Falls Park, Va., and they recently provided a canoe and other facilities at River View Park. Without the permission and enthusiastic interest of several persons who own land along the Potomac River, this study would not have been possible. These include S. P. Spalding, O. V. Carper, Misses Olga A. Larsgaard and Doris K. Stevenson, H. D. Weant, the staff of Madeira School, and E. B. Burling. The author also wishes to thank Ethel W. Coffay, W. J. Conover, and N. C. Matalas for help in making the statistical analysis of vessel diameters. MECHANISM OF PLANT GROWTH Trees grow in height as a result of the division of a few cells just below the tip of each twig. These cells retain the ability to divide, and the tissue is called the apical meristem. Toward the base of the tree, just below the expanding tip and essentially continuous with the apical meristem, is the vascular cambium, which extends as a cylinder down the trunk to near the tips of the roots. This tissue also is meristematic, having the ability to divide, whereby cells formed to the outside differentiate into phloem, or part of the bark; and cells formed inside the tissue differentiate into xylem, or wood. Growth activity of the vascular cambium probably begins at about the time that apical growth starts in the spring, and the activity proceeds downward in the trunk and into the roots. Trees increase in diamater in a general way rather rapidly in early spring; their growth slows later in the season and ceases near the end of the summer. The wood formed early in the growing season is different structurally from that formed later in the summer. Because a different kind of wood, here called early wood, is produced outside the late wood formed at the end of the previous summer, a distinct line is formed between wood that marks the end of one growing season and wood that marks the start of another. The concentric cylinders of wood between successive lines are quite distinct in cross sections of most trees and are known as annual rings. Rings seen in the cross sections of small branches and twigs of some trees, on the other hand, are not formed annually (Glock and others, 1960). Growth activity and anatomy are less well known for the tree roots than they are for aerial parts. A few studies, summarized by Kramer and Kozlowski (1960, BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION p. 52-53), suggest that diameter growth of roots starts later in the spring than does diameter growth of the trunk; however, growth continues for a longer period in the summer in roots. Some evidence also suggests ~ that root growth is rapid in the spring and again in the autumn. Rings are visible in cross sections of roots, but many of these rings are incomplete and may not represent annual growth (Brown and others, 1949, v. 1, p. 252). The wood, or xylem, of stems and roots is composed of different kinds of cells; and because the size, number, and distribution of the cells are different in _ the two organs, stem and root wood will be described separately. Only the wood of trees belonging to the class Angiospermae, flowering plants, as opposed to that of trees belonging to the class Gymnospermae, cone-bearing plants, is described here because conif- - erous trees occur only rarely on flood plains in the _- latitude of Washington, D.C. Wood of trees of flowering plants, the broad-leaved trees, is sometimes called porous because it contains cells in the shape of small tubes, called vessels, that appear as pores when viewed in cross section. Two kinds of porous woods have been defined on the basis of the size and distribution of vessels. In ring-porous woods the vessels formed early in spring are larger than those formed later in the growing season, and the change between them is abrupt. Viewed in cross section, a series of concentric rings are seen which are the rings of large vessels (figs. 10, 21). Oak used for furniture and ash and hickory used for small tool handles are examples of ring-porous woods. Vessels in diffuse-porous woods are about the same diameter and more or less evenly distributed across the annual rings. Some examples of diffuse-porous woods used in furni- ture manufacturing are cherry, maple, and birch. Other cells that constitute wood of broad-leaved trees are tracheids, fibers, and parenchyma (Brown and others, 1949, v. 1, p. 193; Esau, 1953, p. 250). The size and arrangement of these kinds of cells distinguish root wood from stem wood. In root wood, fewer fibers are present; diameters of the cells are larger; and a larger volume of parenchymatous tissue, consisting of rays and cells, surrounds the vessels (Esau, 1953, p. 512-513). Brown and others (1949, v. 1, p. 251-255) concurred with these differences. They also stated that the specific gravity of root wood averages about 20 percent lower than that of stem wood, and that root wood tends to be diffuse-porous in ring porous species. Physiological processes within the apical meristems play a major role in controlling the form of trees from which evidence of floods is discovered. Vegetative buds and flower buds start to form early in the 782-764 O-64--2 A8 growing season on the current year's twig-about the time that twig elongation stops. The buds mature well before the end of the summer. New twigs and leaves grow from the vegetative buds during the following spring. Plant scientists have known for nearly half a century that a growth hormone is produced in the growing tips of plants and is translocated to other areas where it affects physiological processes within the plant. Much of the following discussion is based on Leopold's (1955) review of the existing knowledge of hormones and their use in agriculture. The func- tion of growth hormones which concerns the work reported here is the inhibitive effect upon lateral bud growth and, as a corollary, the effect of light and gravity upon hormone distribution in a trunk (Leo- pold, 1955, p. 96-102). As a result of the inhibitive effect of growth hormones in lateral bud growth, plants possess an apical dominance as long as the terminal buds remain alive. Removal of growing terminal buds results in growth of lateral buds. Subsequent application of hormones to the abscised tip will inhibit growth of lateral buds, thus restoring apical dominance. Both the force of the water and the debris carried by the water during floods decapitate trees and shrubs in their path, thereby destroying the growing tips of the plants and, with them, the source of the growth hormones. The result is the initiation of growth of lateral buds (fig. 2) and the development of one or more sprouts. In addition to lateral buds that start to grow upon loss of apical dominance, adventitious buds are stimu- lated, and their growth gives rise to new stems. Growth of some adventitious buds is initiated by spontaneous cell division in several tissues within the stem (Esau, 1960, p. 229), whereas growth of others is believed to arise from preexisting dormant bud cells (Eames and MacDaniels, 1947, p. 63; Kramer and Kozlowski, 1960, p. 387). Growth of sprouts starts from adventitious buds on mature parts of trunks that have been severely damaged by floods and that remain as stumps or as decapitated water-felled trees. Gravity and light have been demonstrated to affect the movement of growth hormones in stems and thus affect the growth behavior of plants. Hormones be- come concentrated in the lower side of inclined stems because of gravity and migrate toward the shaded side of unilaterally lighted stems; thus the inhibiting effect of hormones on growth of buds on the lighted side is lost. For these reasons, stems normally grow almost vertically upward. Migration of hormones toward the shaded side of stems also explains the phenomenon, familiar to many, of the growth of branches on a previously clear tree trunk after it has been exposed by A4 FicUrE 2.-Sprouts that started to grow from ash stem after flood of May 1, 1958, damaged first growth of 1958 growing season. Photo- graph taken in vicinity of Chain Bridge, Washington, D.C., May 22, 1958. the removal of surrounding trees. Even if some quantity of hormones is produced in water-felled trees, much of it will migrate to the lower, shaded side of an inclined tree; this results in a loss of the inhibiting effect upon adventitious buds on the upper surface. HYDROLOGIC CONCEPTS COLLECTION OF STREAMFLOW RECORDS Although the methods used in the collection .of streamflow records are well described in the literature | (Corbett and others, 1945; Linsley and others, 1958; Johnstone and Cross, 1949), a brief summary of U.S. Geological Survey methods is presented here for those unfamiliar with hydrologic techniques. The U.S. Geological Survey is responsible for the collection and analysis of basic water facts and for research on hydrologic principles which will lead to a better understanding of water in its natural environment. Part of the basic data is collected at more than 7,000 gaging stations where continuous records of streamflow are obtained. In addition, partial records of lowflow or of floodflow are collected at many other points. At the gaging stations the elevation of the water surface, which is ordinarily called the stage, is recorded. Periodically, generally about once a month, each gaging station is visited, the recording instrument is VEGETATION AND HYDROLOGIC PHENOMENA serviced, and a discharge or streamflow measurement is made. The discharge is computed from the mean velocity of the water, measured with a current meter at many points across the stream, and from the area of the cross section of the channel at the measuring section. Discharge measurements are made during low stages and flood stages as well as at times when the gage is regularly serviced ; thus, data are accumulated that permit the development of a stage-discharge rela- tion. The stage, as recorded on the gage, is plotted as the ordinate against the simultaneous measurement of discharge. The continuous record of stage, according- ly, can be transformed into a continuous record of discharge, or the amount of water flowing in the stream. The daily mean discharge, expressed in cubic feet per second for all gaging stations, is published annually in the U.S. Geological Survey Water-Supply Papers. A cubic foot per second (cfs) is defined as the discharge of water in a section 1 foot wide and 1 foot deep flowing at a velocity of 1 foot per second. More detailed information on streamflow, including peak flood discharges, is available at the U.S. Geological Survey district offices. COMPARISON OF FLOODS A record of the crest stage or of the instantaneous peak discharge of a flood is of limited value if the flood . cannot be related to other floods. One method of comparing floods is based on their frequency of occur- rence in time. The concept of frequency of events in time is familiar to all who have an interest in natural history, even if that interest is merely avocational. The vacation camper knows he should not camp overnight in an arroyo because of the danger of frequent floods. Picnickers often state, when a thun- derstorm breaks just after the food is spread, that it always rains when they have a picnic, implying that such events are frequent. The analysis of floods that compares one with another is called flood-frequency analysis and tells the average interval between floods that exceed a given magnitude. The frequency of floods and their relative magni- tude, as one would expect, are inversely related. The smaller floods, which most people never recognize, are frequent; and such floods may recur once every year or two. The severe floods, the ones described by news media, are infrequent; and these may happen on the - average only once in 50 or 100 years. If many classes of mean daily discharge, ranging from the minimum to the maximum, are chosen and the number of days on which each of these flows occurred is tabulated, then a plot of their frequency distribution would tend to be normal. Minimum and maximum flows would occur BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION A5 on the least number of days, and median and average flows would occur on a larger number of days. Several methods of analyzing flood events have been used (Benson, 1962); the method of flood-frequency analysis based on peak discharge as used by the U.S. Geological Survey (Dalrymple, 1960, p. 5-21) will be outlined briefly. The annual flood, which is the highest peak discharge between October 1 of one year and September 30 of the following year (the water year), is listed, and the array is called the annual flood series. Another series, the partial-duration series, requires listing of all floods above a base discharge- that is, all independent peak discharges greater than a selected discharge. From either of these listings, the average recurrence interval can be calculated. A flood having a recurrence interval of 2 years, for example, has one chance out of two, or a 50 percent chance, of occurring in any one year. A flood having a recurrence interval of 50 years, the 50-year flood, has a 2 percent chance of occurring in any one year. Neither method was used in its entirety in this study, but floods having peak discharges above a base of 33,100 cfs were listed. This discharge is the minimum flow for which evidence of damage to trees has been found along the Potomac River. Some difficulty was encountered in determining the independence of flood peaks in the lower range of discharges, and some of the floods listed might not have been independent of preceding floods. However, as suggested by Dalrym- ple (1960, p. 11-12), only those peaks were recorded that were separated by a trough that was 25 percent lower than the lower flood peak. The recurrence interval of only those floods above 82,100 cfs was calculated, using graphical methods outlined by Darl- ing (1959). This base flow was chosen because it is the discharge of the flood that just cover the buried tree (discussed on p. 18-23) that was analyzed to develop a method of dating deposits on flood plains. FLOODSTAGE-DISCHARGE RELATIONSHIP At a gaging station the crests of floods, as well as the stages of all other flows, are recorded. Because in many studies, as in this one, the part of the flood plain involved is remote from the station, other techniques are used to record the elevation of flood crests. These employ visual reading of various types of gages, recording the crest on a crest-stage gage, and mapping } of flood marks. In the present study, crests were - determined by using crest-stage gages and by mapping flood marks. _-_ A crest-stage gage (Ferguson, 1942) consists of a length of 2-inch pipe fastened to a tree near the bank -of a river. The pipe, which has a vented cap at the top and a perforated cap at the bottom encloses a stick equal to the length of the pipe. A small amount of ground cork is placed in the bottom cap, so that when the river rises around the pipe, the holes in the bottom cap permit the water to rise in the pipe, thereby floating the cork. When the water recedes, the cork adheres to the stick at the highest level reached by the water, and the elevation of the ring of cork is readily determined. Flood marks can be found on the flood plain after recession of the water, and these are variously mapped. In this study, bench marks were installed at many points along the river-study reach in connection with installation of the crest-stage gages and other instru- ments, so elevations of flood marks at any point in the reach can be determined readily by leveling. Also, flood marks on banks delimiting inundated areas of flood plain were mapped on aerial photographs. The peak discharge of the various floods in question can be obtained from the gaging-station record and a correlation defined between stage at the various sites under study and the rate of flow at the reference gaging station. (In this study the station record is that of Potomac River near Washington, D.C., located near the Washington, D.C.-Maryland boundary [Fig. 1].) The complete gaging-station record is then ex- amined, and the dates and quantities of all discharg- es that have equaled or exceeded the floods of interest are listed. The peak discharge of the flood, rather than stage, is used in listing flood events and in subsequent analyses. Separate floods on a given river having the same peak discharge do not attain exactly the same relative elevation throughout the reach of the river owing to variations in distribution of tributary flow or changes in physical character of channel and flood-plain sections. Conversely, separate floods that attain the same elevation at a given section do not always have the same discharge. EFFECTS OF FLOODS UPON TREES The high velocity of water and the large quantity of transported debris: are the two characteristics of floodflow most damaging to flood-plain trees. With an increase in discharge, or streamflow, during a flood, the velocity of the water usually increases. Discharge measurements at the reference gaging station are made most of the time from Chain Bridge, which spans the Potomac River in Washington, D.C., where velocities are so high during floods that current meters, if used, would be damaged or destroyed (L. W. Lenfest, oral commun., 1956) ; in fact, velocities higher than 20 feet per second have been recorded at Chain Bridge during minor floods (Leopold, 1953, p. 608). Discharge measurements of the peak flow during floods that occur A6 VEGETATION AND HYDROLOGIC PHENOMENA about once every 2 years and during larger ones that occur less frequently are made from a highway bridge over the tidal estuary about 7 miles downstream where velocities are lower. The velocities of water along the banks, over low brush-covered islands, and at the upstream ends of larger islands, therefore, are exceed- ingly high, and the force of the water is sufficient to injure trees. in the flood path. The water alone will bend small trees, break off tops, and remove leaves if the flood occurs in the summer. Anyone who has walked along a river after a flood is keenly aware that all manner of debris is carried by flood water. This debris consists of logs, branches, leaves, and other fragments from flood-plain vegeta- tion, and of all kinds of human accouterment. Float- ing ice during late winter and spring floods are par- ticularly damaging to trees and other flood-plain vegetation. PHYSICAL EFFECTS OF HIGH VELOCITY AND DEBRIS The physical damage caused by floods and floating ice has been described by many observers. Lindsey and others (1961, p. 125) stated that ice floes during the February 1959 flood along the Wabash River in Indiana abraded the bark and broke branches from trees along the river bank. They noted a line of scarring in vegetation for a considerable distance along the bank, and they believed it represented the crest of the flood. I observed a similar crest line of scarring in plants along the banks of the Potomac River after floods and along banks of the Ohio River near St. Marys, W. Va., in June 1959. I attribute this line on the Ohio River to damage to trees by floating ice in February 1959. Damage to trees by floating ice has been reported in other areas (Cribbs, 1917, p. 148), and on rare occasions in the Southeastern United States (Putnam and others, 1960, p. 20). The results of uprooting, breaking, shearing, and scarring of trees by high water during floods are commonly seen in flood-plain forests and have been reported by several workers. Lindsey and others (1961, p. 124) observed these types of damage to trees along the Wabash River following the February 1959 flood. They also noted that small willow trees (Saliz interior) showed deformation similar to that of wind- trained trees and suggested calling this a "flood- trained" form. Shrubs in the arroyos in the Rio Grande valley in New Mexico are knocked over and partly buried by high water (Gardner, 1951, p. 398). Shull (1944, p. 774-775) observed that willows along the banks of the Mississippi River suffer damage dur- ing high water and that although the tops of many trees may be killed, the roots of most will survive. Dore and Gillett (1955, p. 15) stated that ice on the St. Lawrence River kills tree seedlings and perennial plants along the shore in the International Rapids see- tion. Ware and Penfound (1949, p. 478) observed that most plants on sand bars in the channel of the South Canadian River in central Oklahoma are killed by an- nual floods. Severe floods of extremely rare occurrence at any one place will destroy all trees on parts of the flood plain (Hack and Goodlett, 1960, p. 49). This type of destruction of flood-plain vegetation along small streams in the Appalachian Mountains may occur more commonly than is generally believed; in fact, Hack and Goodlett (1960, p. 55) suggested that such damage may be more frequent in the southern Appalachians than in the northern Appalachians. Landslides that occurred in the southern Appalachian Mountains in August 1940 destroyed large swaths of forests on hillsides and in stream valleys below (Water Resources Branch, 1949, p. 14). Similar slides occurred in central Pennsylvania on July 18, 1942, and destroyed stands of trees on slopes and in stream valleys (Eisen- lohr, 1952, p. 78). Such catastrophic hydrologic events occur in Western United States as well. A most striking debris flow occurred during the night and early morning of October 2-3, 1947, on Kautz Creek in Mt. Rainier National Park when an estimated 50 million cubic yards of rock, gravel, sand, and logs moved down the valley (Grater, 1947, 1948), destroy- - ing and inundating an extensive area in a mature coniferous forest. Accounts of damage to vegetation are included in most flood reports published by State agencies, the U.S. Geological Survey, and other Feder- al agencies. The larger study, concerned with the relationship of vegetation to the hydrology of streams, of which the one reported here is a part, is being made in areas along the Potomac River where stands of trees have survived several major floods. The magnitude and dates of occurrence of these floods are discussed on p. 29. Individual trees have been found that were growing prior to floods in 1861, 1889, and 1924. Several stands that contain trees that were growing prior to the 1936, 1937, and 1942 floods have been studied. Most of the forest along one reach of the river in the vicinity of Chain Bridge near the north- western boundary of Washington, D.C., consists of trees growing from stumps of trees that were cut off or felled by a severe ice jam on February 16, 1948 (fig. 5). The relationship between flood frequency and sedimen- tation and the form, distribution, and age of the trees in this part of the river is under investigation and study. BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION All flood-plain trees that were growing prior to floods of record have, of course, experienced subsequent floods. The majority of flood-plain trees, as a result of this experience, show varying degrees of damage; so that most are small and have poor form or are, in forestry terms, of low quality (fig. 3). The trees are bent and twisted and consist of several sprouts grow- ing from different sizes and forms of stumps. Trunks of trees along the banks of a channel and on upstream ends of islands commonly exhibit scars that have resulted from repeated abrasion by debris and ice carried by high water (fig. 4). The only concentra- tions of large and straight, single-stemmed trees grow _ on the higher ridges of the flood plain and at consider- able distances from the river channel. Severe floods such as the ones that crested on March 19, 1936, and October 17, 1942, and the ice jam that occurred on February 16, 1948, (figs. 5, 6) inflict great damage to a large number of trees. Most of the trees in the paths of these floods or of the ice jam were bent over or partly uprooted, and the crowns were heavily pruned. As long as 25 years after such an event, the trunks of trees are still bent and inclined in a downstream direction and have scars on the upstream side. High wind also fells flood-plain trees, but wind- thrown trees on flood plains, as well as on uplands, are oriented at random and not in a general downstream Fisurs 3.-View of flood-plain forest showing poor form and sprout origin of trees. AT Ice frag- ment lodged in small ash tree that shows light-colored wood exposed by ice abrasion on January 15, 1958. FicUrE 4.-Floating ice overriding flood plain scars trees. direction; furthermore, many wind-thrown trees are broken into a decapitated trunk and the top, which eventually dies. In contrast, most trees felled by high water are partly uprooted. Adventitious roots start to grow from the part of trunk in contact with the soil, and the fallen tree continues to live. The percentage of stems showing evidence of flood damage was determined in December 1962 in seven plots located at random along the Potomac River. The plots were approximately 50 by 50 feet square. Six of them are in areas underlain by bedrock or fine-grained alluvium and are flooded at different frequencies. The surface of the seventh plot, plot 2, consists of alternate ridges of alluvium and flood channels in which bedrock is exposed in the bottom. Plots 1-4 are upstream from Washington, D.C., near the Maryland State line; plots 5-7 are on an island approximately 16 miles upstream from plot 4, near Seneca Falls (fig. 1). All woody stems in two plots, numbers 3 and 4, grow as sprouts from stumps or root crowns with the exception of silver maple * seedlings less than 1 year old. In these two plots, bedrock crops out and the surface is flooded on the average about 5 percent of the time. In the other plots, the percentage of stems showing damage ranges from 52 to 85; the 1 Nomenclature of trees follows that used by Little (1953). AS VEGETATION AND HYDROLOGIC PHENOMENA FiqUzRE 5.-Ice jam on Potomac River at Chain Bridge, Washington, D.C., February 16, 1948. The Washington Post photograph. F1GURE 6.-Low flow on Potomac River at Chain Bridge, Washington, D.C., July 1956. BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION data are summarized as follows : Number Number | Percent Plot Area Surface ! of Total | of stems | of stems floods? | stems | damaged | showing damage Chain Bridge.... Alluy..-.- 17 53 41 77. 4 oedd ace. All. Br.___ D17 52 44 84.7 2 KB 155 227 227 100 155 260 260 100 +15 33 28 84. 8 >15 16 14 87.5 ©15 20 15 51.7 1 Alluy., fine-grained alluvium; All. Br., ridges of fine-grained alluvium and channels having rock bottoms; Br., bedrock. 2 Period of record, 3/1/30-4/1/62, 32 years, 1 month. 3 Approximate. General observation at many places throughout the area of study leaves the impression that the proportion of damaged trees is of the magnitude measured in the plots. EFFECTS OF INUNDATION UPON TREES The presence of living trees that have been flooded at least 20 times in more than 32 years and still survived is sufficient proof that high water alone does not kill them. In fact, detailed quantitative study along one part of the Potomac River shows no signif- icant difference between vegetation that was covered by high water from February to May 1961 and similar vegetation studied during the preceding year, prior to high water. The quantitative studies have been briefly summarized, and the results of the measurements made prior to the high water are discussed (Sigafoos, 1961, p. C 248-250). This phase of the larger study is the subject of a second report that is in preparation. Other workers have reported that high water alone during floods does not kill flood-plain trees but that extended periods of flooding and heavy sedimentation will kill them. Willow thickets along streams in Wyoming are believed to withstand repeated flooding for many years (Reed, 1952, p. 708). Taller trees, whose crowns extend above the crests of floods, were found to survive along the Mississippi River (Shull, 1944, p. 773); however, Shull (1922, p. 205-206) believed that young trees would be killed if submerged for a long time. Several workers have noted that submergence during the dormant season will not kill flood-plain tree spe- cies (Putnam and others, 1960, p. 11, 13, 20, fig. 15; Harper, 1988; Turner, 1936, p. 693; Wistendahl, 1958, p. 150; Silker, T. H., 1948, p. 482433, p. 436), and Lindsey and others (1961, p. 122-123) found that high water during two floods on the Wabash River in Indiana in June 1958 killed only the inundated leaves. Cribbs (1917, p. 148) stated that the period of submer- gence by floods on streams in western Pennsylvania is usually too brief and the amount of sediment deposited is generally too small to injure trees. Putnam and others (1960, p. 13, 17) stated t spring will not kill most bottom- that many will remain dormant A9 hat flooding even in and tree species and until the water re- cedes; however, total submergence for long periods after breaking of dormancy will kill seedlings and small saplings. High water on th September to December 1926, in from April to mid-June 1927 is b an estimated 90 percent of the n flood plain (Turner, 1930). Tur e Illinois River from January 1927, and elieved to have killed nature timber on the ner believed that the high water from April to mid-Ju in killing the trees. flooding by the Kentucky Rese River, Hall and Smith (1955) ne was most effective oir on the Tennessee In a stzjiy of the effects of ound that all woody species were killed if flooded about 60 percent of the time during the growing season. Bottomland species survived, they found, if flooded less than 42 percent of the time. Submergence even for short growing season, however, will ki periods during the 1 some trees and, for extended periods of several years, will kill all species. Flooding as a result of a beaver dam built across Carp Creek in Michigan killed all upland species in 1 year; however, black ash and Americ teristic of flood plains, were elm, species charac- t killed during this interval (Gates and Woollett, 1926). Inundation for a period of 5 to 6 years by backwater of a dam on the Mississippi Riv killed all flood-plain tree species; and a study made during this period showed that young, rapidly growing trees evinced the greatest resistance to death, whereas old trees and young saplings were the first to die (Yeager, 1949, p. 87). GROWTH OF TREES AFTER FLOOD DAMAGE Trees continue to grow after they are damaged during floods; and subsequent growth, in a sense, preserves the injury. The identification and interpre- tation of this growth and of the flood-inflicted damage are the subjects of this section. | It will be shown that parts of the bark and underlying tissues are killed and that scar tissue grows over the damaged area. Initia- tion of growth of the scar tissue can be dated. It will be shown also that sprouts grow from the residual stumps of flood-felled and decapitated trees and that the start of growth of these sprouts can be dated. The dates obtained from all specimens are those of the first growing season following the flood event. CIRCUMFERENTIAL GROWTH AROUND TRUNK SCARS A sharp blow to a tree trunk, whether made by a lawn mower, by a baseball bat in the hands of a small boy, or by debris carried by high water, will crush, and thus kill, the living tissues between the bark and the wood. One of these living tissues beneath the bark is A10 the vascular cambium, composed of thin-walled meris- tematic cells that divide, causing the tree to increase in diameter and circumference by the growth of annual rings. If the external force is sufficiently strong, or if prolonged, as during a flood, the bark is abraded and the wood becomes exposed. Upon death of the cambium, a homogeneous tissue, called callus, forms around the margin of the scar and across it if the scar is small. New wood is not formed VEGETATION AND HYDROLOGIC PHENOMENA over the damaged area upon resumption of growth. Vascular cambium later differentiates within the cal- lus and ultimately bridges the scar. As the cambium is forming, new wood also starts to form around the margin of the scar; and, in time, a new layer of wood will cross the scar, and a complete annual ring will encircle the trunk (Esau, 1953, p. 392, pl. 56, 57). This process of wound healing is illustrated diagram- matically in figure 7. Vascular cambium A Before damage Vascular Callus . cambium Bark C First growth after damage | Senoo e ) Initial scar E After three growing seasons following flood damage FiquRrB 7.-Diagrams representing circumferential growth of trunk after destruction of bark and cambium. B After damage New annual ring D After first growing season Bark Vascular cambium | 3 annual rings Width of the cambium is greatly exaggerated. BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION The extent of healing and the length of time ~ required for the scar to be completely covered with new wood are affected by the size of the initial scar, by the frequency of the event that causes the damage, and apparently by the time of year that the damage is inflicted. Scars that are a few inches long on twigs and stems smaller than about 1 inch in diameter will heal by the end of the growing season following the damage. Thus, small scars made during the spring or early summer generally are covered by new wood and bark by the end of the same summer. Larger scars, which encircle half the circumference of stems as small as half an inch in diameter and extend along most of the length, generally do not heal for several years. Large scars formed by ice abrasion of silver maple trees along the Tippecanoe River in Indiana in 1956 were seen in 1959 to be healing (Lindsey and others, 1961, p. 126). Because floods that damage trees on the lower surfaces of flood plains occur more often, on the average, than once a year, the repeated injury prevents many sears from ever healing. A scar can be dated by taking a section through the trunk, tracing the last ring formed prior to injury along its circumference to the sound part of the stem, and counting the number of rings that lie outside. This number is equal to the number of growing seasons that have elapsed since injury. To count the annual rings in wood directly outside the scar is rarely possible, because the wood consists of callus, which does not contain annual rings, and generally shows an incomplete number of rings. Note in figure TZ that three rings are represented outside the last ring formed before injury, yet only one complete ring overlies the center of the scar. If a large area of the stem is damaged and if damage, furthermore, is severe, part of the wood formed prior to damage may be eroded, so that the outer ring in the scarred area is not the last ring formed. The wood exposed by abrasion of the bark also may rot. and subsequently erode before the scar is healed. _A description of the scars shown in one dissected small tree (fig. 8) and the record of floods will illustrate the relationship between flood damage and subsequent circumferential growth of stemg The tree was collected along the Potomac River near Washing- ton, D.C., in a low area adjoining the channel which had experienced 147 floods in the period of streamflow record of 26 years and 10 months prior to the time of collection. From the spring of 1952, when the oldest part of the stem shown in figure 8 started to grow, to January 20, 1958, when the specimen was collected, the stem was subjected to 28 floods. Since 1954, when the youngest 782-764 0O-64--3 FicurE 8.-Parts of a stem of an ash tree All growing in an area along the Potomac River where a minor ice jam occurred on January 15, 1958. The letters A-F correspond to sections s is 1% inches in diameter at A. part of the main stem included grow, the stem was subjected t these floods are recorded in cros and a fifth is evident in the ste a sprout that grew from a stum downstream direction. Six fig felled the parent tree occurre season of 1951 and before the gi The use of ages of sprouts asJ discussed on pages 12-18. The b by floating ice that covered the hown in figure 10. The stem in figure 8 started to o 12 floods. Four of s sections of the stem, m itself. The stem is p that is inclined in a ods that could have d after the growing rowing season of 1952. evidence of floods is rk (fig. 8) was abraded area on January 15, FIGURE 9.-Fragments of ice deposited on flood plain of Potomac River on January 15, 1958, in area where free in figure 8 was collected. The lightly shaded parts of the stems lare bare wood and are on the upstream side of the stems. A12 1958 (fig. 9). Subsequent observations in this area suggest that some stems of trees similarly damaged in 1958 have died, whereas many others have survived. Indeed, sections of a number of trees collected in late August 1960 show two rings outside a scar that is attributed to the 1958 ice jam. Cross sections through parts of the stem (fig. 104-F') show healed scars on the upstream sides of the sec- tions which are at the top in figure 10. Three annual rings have grown outside the scar in sections A4, 2, and F'; thus the scar was formed before the growing season of 1955. The scar is on the outer part of the ring that grew in 1954; therefore, damage occurred between the fall of 1954 and the spring of 1955 during any one or all of four floods that covered this area during that time. Another sear is present between the 1955 and 1956 rings in section Z'; the fourth highest flood of record on the Potomac River occurred on August 20, 1955 (fig. 11, 12). The scar present within the 1956 ring in sections C and D may have resulted from a sharp rise in the discharge of the Potomac River at Chain Bridge to a peak of 72,500 cfs on July 21, 1956, following an intense local storm which oc- curred in the lower part of the Potomac River basin on July 20-21, 1956 (Water Resources Division, 1964). Summarized below are the types of botanical evidence of flood-induced damage seen in the sections in figure 10, the years when they were created, the dates of the possible floods involved, and the peak discharge. Botanical evidence of Year of growing season Flood dates | Discharge flood damage following damage (1,000 cfs) 1/3/52 59. 2 Sprout from de- Started to grow 1/29/52 66. 0 capitated stump. 1952. 2/6/52 59. 2 3/13/52 108. 0 3/25/52 46. 2 4/29/52 148. 0 10/1/75? I?) 8 1/1/5 . Sear __________---- 1955. 3/7/55 78. 6 3/24/55 99. 5 | "sh. 1 50. 1956-------.------ 3/16/56 62. 0 4/9/56 68. 6 During 1956... 7/21/56 72. 5 Abraded bark.... 1955- .cc 1/15/58 Ice The types of scars described in the preceding dis- cussion are inferred to have been caused by floods: they are on the upstream side of the stem and are dated. Moreover, floods were recorded during the interval when the scars were formed. Many trees from this area have been sectioned, and all show evi- dence of damage that can be related to a flood. Abra- sion of bark by floating ice and debris which had oc- curred during the period of this study was observed VEGETATION AND HYDROLOGIC PHENOMENA during the particular flood, and the effects were sub- sequently seen within a few days after the water had receded. These observations exclude, of course, trees cut by boy‘gfby fishermen, or in lumbering operations. Although many floods occurred for which evidence was not found in the sections of the specific tree discussed here, scars resulting from some of these floods may be embedded in parts of the stem that were not see- tioned. Scars formed during the time of some of these other floods, however, have been found in other trees growing in the same area. GROWTH OF SPROUTS FROM STUMPS AND WATER-FELLED TREES The physical effects upon trees of floods of high magnitude that occur less often than once every 2 years, on the average, and evidence of flood damage have been inferred only from the form of trees grow- ing on surfaces known to have experienced these severe floods (fig. 11,12). Floods of high magnitude have not occurred since this study began. Trees larger in trunk diameter and height than those described in the preceding section show evidence of severe flood damage of a different kind. These trees consist of sprouts growing from a stump or inclined trunk, show a sharp angle near the base, or look, at the base, like a pole implanted in the ground. They have a form that is more treelike, consisting of one or more straight trunks that are unbranched for a third or more of their length. They are not multi- stemmed, much-branched shrubby plants. Wistendahl (1958, p. 140-141, 150) found that willow, river birch, sycamore, and box elder trees produce sprouts follow- ing damage by floods on the Raritan River in New Jersey. Shull (1944, p. 774-775) noted that sprouts grew from root stocks of willow trees whose tops had been killed during floods along the Mississippi River. Heavy flood debris materially damages flood-plain trees and locally breaks the trunks near the ground, leaving a ragged stump. Severe ice jams have cut off most trees in large areas of the Potomac River flood plain. Sprouts start to grow from these stumps during the first growing season following the damage and, if not subsequently damaged by another flood, continue to grow as straight-stemmed trees (fig. 13). The sprouts pictured in figure 13 started to grow in 1948; the parent tree was probably cut off by an ice jam on February 16, 1948, that was about 15 feet deep over the area (fig. 5). Apparently all heavy ice flows do not cut off most trees. Lindsey and others (1961, p. 125-126) reported that floating ice also twisted and bent flood-plain trees during the flood of February 1959 on the Wabash River in Indiana. They observed BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION FiqurE 10.-Cross sections through stem shown in figure 8. The dark dots are large vessels formed during early growth in the spring. One annual ring consists of a ring of vessels and the more or less even-textured wood extending outward to the next ring of ves- sels. In all sections the outer ring was formed in 1957. The outermost tissue, seen only at the bottom of the sections, and especially in F, is bark; it was abraded from the other side of the stems by the ice. The diameter of the section in A is 1% inches. A13 A14 that fast-growing sprouts started to grow from the bent trees and stumps during the following summer. They observed before 1959 that trees on the lower sur- faces of the Wabash River flood plain showed the effects of what they believed to be periodic ice damage. s Many years after a flood, sprout trees can be recog- nized as one or more trunks growing from a common root stock. The old stump can be seen at the base of the sprouts; or with a little digging in the center of the area surrounded by the circle of sprouts, rotten wood can be turned up; or the sprouts may appear as closely grouped trunks, seemingly growing out of the ground, until an excavation around them reveals that they are all connected to the same root system. Such stumps have been buried by alluvium deposited during subsequent floods. This growth form cannot be dis- tinguished with certainty from sprouts growing from FIGURE 11.-Potomac River on August 20, 1955. View is in upstream direction from Chain Bridge. Flood peak discharge was 216,000 cfs at 2:30 p.m. Maximum depth of the water here above low flow is about 35 feet. Photograph by Abbie Rowe, National Park Service. FIGURE 12.-Potomac River, viewed in upstream direction from Chain Bridge, at low flow, June 1956. Two fishermen can be seen standing on a rock to the left of center. This point is just upstream from the large waves in the center of figure 11. VEGETATION AND HYDROLOGIC PHENOMENA FIGURE 13.-Sprouts from stump cut off by an ice jam on February 16, 1948. a sawed stump; but sprouts growing from rotten stumps in a flood-plain area, in which many trees of the same age 'are sprouts growing from inclined trunks, probably date from a severe flood. More commonly, flood-plain trees that have been damaged by high water are partly uprooted or bent over, and the subsequent form consists of vertical sprouts from an inclined trunk (fig. 18). Just as a scar on the side of a trunk can be dated by counting the rings overlying it, so can the year that a tree was felled be determined. The simple form consists of a vertical sprout grow- ing from an older inclined trunk. The roots are up- stream and the trunk is inclined in a downstream di- rection. In line with the axis of the inclined trunk and at the extreme downstream side of the tree, the stub of the parent trunk consists of a protrusion of rotten wood that may be only partly covered with wound tissue (fig. 14). The vertical sprouts start to grow from the inclined trunk during the first growing season after the tree was felled; thus, a count of the annual rings in a core from the base of the sprout that in- cludes the outer- and inner-most rings tells the num- ber of growing seasons since the tree was knocked down. The bark of the older inclined trunk is rougher, the scales or plates are larger, and ridges and grooves are deeper than are those of the sprout. The inclined trunk looks more mature than the sprout, and the two invariably have a visible line of demarcation between them. The L-shaped form and differences in texture of the bark persist for a long period of time (fig. 15). BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION FIGURE 14.-Vertical sprout growing from inclined trunk, showing stub of rotten wood at end of parent trunk that was felled by 1948 ice jam. Difference in texture of bark of sprout and of trunk and line between them are apparent. Downstream is to the left. FIGURE 15.-Trunk of tree that has sharp angle near its base suggesting origin as a sprout from the part inclined in a downstream direction to the right. Trunk above angle started to grow in 1861. Damage from several floods can be seen in the sequential composition of occasional trees: sprouts arising from older, inclined sprouts which in turn arise from the inclined parent trunk (fig. 16). The history of the ash tree illustrated in figure 16 is shown A15 diagrammatically in figure 17 and indicates by way of a case study how botanical evidence of floods can be interpreted from sprouted, flood-felled trees. The two oldest sprouts started to grow in 1930, the first grow- ing season after a flood in October 1929. In the sum- mer of 1929, the tree was probably fairly small and probably consisted of a single vertical trunk. Floods occurred on April 18 and October 23, 1929, prior to the construction of the stream gage near Washington, D.C. From the record of the Point of Rocks gage, 41 miles upstream, I estimated that the discharge at Chain Bridge during these floods was 190,000 cfs and 125,000 cfs. Both, though not large, would have covered the tree and could have damaged it. Evidence that the 1929 floods damaged this tree is somewhat questionable; however, the evidence of sub- sequent floods is more reasonable. The sprouts that started to grow in 1930 were, by the autumn of 1942, small trees having trunks about 5 inches in diameter. On October 17, 1942, the second highest flood of record crested and bent the tree in a downstream direction. FIGURE 16.-Ash sprouts of four ages growing from a stump, to the left out of the photograph, on the Potomac River flood plain near Chain Bridge. The smallest sprouts, in upper half of photograph, are nearly vertical and started to grow in 1956. §econd-age sprouts, shown forming a gentle are and inclined to the right at about 70° from the horizontal, started to grow in 1948. The third-age sprout, the short segment in lower third of photograph, is inclined to the right at about 25° from the horizontal and is growing from a convex split trunk; this sprout started to grow in 1943. The oldest sprouts are a pair that started to grow in 1930. A16 ___ VEGETATION AND HYDROLOGIC PHENOMENA A 1928 D End of summer, 1942 Ey irk Gozo -~ magni- Ai ther -ed Ad A”? B Apr. 18, Oct. 23,1 1929 E Oct. 17, 1942, second highest flood of record; 447,000 cfs C Summer, 1930 F Summer, 1943 FiqURE 17.-Diagrams showing events that produced the form of the ash tree illustrated in figure 16. BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION A17 1948 sprout 1943 sprout G End of summer, 1947 J Early summer, 1955 § g z . f IxAZ -> f- a T ~~ // o F Ser -s"--s ~~~ ea rien -> Naos 3 _ 3 a' ~ ; F a omas --= ee Z eee | # A\ H Feb. 16, 1948, ice jam K Aug. 20, 1955, fourth highest to 34 ft above mean sea level flood of record; 216,000 cfs 1948 sprout 1955 sprout 1943 sprout 1948 sprout 1943 sprout I Summer, 1948 L Present time as illustrated in fig. 16 Two sprouts that started to grow in 1930 persist today ; but, for simplicity, only one is shown. A18 A sprout started to grow in 1948. By the end of the summer of 1947, this sprout was about 1.5 inches in diameter and was bent over or decapitated by the ice jam on February 16, 1948. From this inclined sprout a new sprout started to grow in 1948 and by August 20, 1955, the new sprout was about 1.5 inches in diameter when it was bent over by the fourth highest flood of record. The fact that evidence of the maximum flood of record, on March 19, 1936, and of the third highest, on Apr-11 28, 1937, is mlssmg in this tree points out a major problem in using botanical evidence for recreat- ing a flood history. This tree shows certain evidence of three floods; but like any other one specimen it cannot be expected to yield information on all floods that inundated it during its lifetime. Chance alone can explain why a single tree escaped injury, or the 1942 flood and the. 1948 ice jam could have destroyed evidence of earlier floods. The most abundant evi- dence that has been found in this study stems from the most recent floods. Either other floods which are known to have occurred did not damage trees that show evidence of earlier and later inundation, or the later floods destroyed the earlier evidence. Evidence of nearly every flood on the Potomac River in the vicinity of Washington, D.C., since the flood of 1936 has been found along a reach extending about a mile upstream and a mile downstream from Chain Bridge. Single sprouts of several ages from inclined trunks have been found that date from floods that occurred prior to the period of record. These single sprouts only suggest earlier floods and, in the absence of other evidence, do not date them. If many sprouts of the same age were found, however, they would be offered as proof. The upright trunk of the larger tree shown in figure 15 started to grow in 1861. Sanderlin (1946, p. 220) stated that a "freshet" in April 1861 was reported to have damaged the Chesapeake and Ohio Canal that borders the river. Sprouts of two trees upstream from Great Falls started to grow in 1889, and the maximum flood prior to 1936 occurred in May and June 1889 (Grover, 1937, p. 334). Grover (1937, p. 334) listed another flood in February and March 1902 for which botanical evidence has also been found. In the vicinity of Chain Bridge, a sprout was found that started to grow in 1924. A severe flood occurred on May 13, 1924, that was reported to have overflowed the Chesapeake and Ohio Canal levee for a distance of 1 mile in the vicinity of Chain Bridge (The Washing- ton Post, May 14, 1924). This flood caused such heavy damage throughout the length of the canal that the Canal Company failed to recover, and traffic on the canal finally ended (Sanderlin, 1946, p. 277-278). VEGETATION AND HYDROLOGIC PHENOMENA GROWTH OF TREES FOLLOWING BURIAL BY ALLUVIUM DURING FLOODS The sediment carried by a flood accumulates in places on the flood plain where it may surround the bases of some upright tree trunks or partly cover water-felled trees, giving both a characteristic appear- ance which can be easily recognized. If a tree remains buried through at least one growing season, ring counts and study of wood structure made in the laboratory can determine with accuracy the year in which the burial took place. Trees that grow on fairly stable surfaces have a characteristically flared base, which is buried when the upright trees are subject to aggradation during a flood. Such partly buried trees look like poles or posts stuck in the ground. Hadley (1960, p. 14) noticed this form in trees on flood plains in the Cheyenne River basin in Wyoming and interpreted it as an indication of active aggradation. Jahns (1947, p. 98) learned that the minimum thickness of recent flood-plain sediments could be determined by the depth of buried tree trunks. Digging around the base of a buried tree will expose the roots and may show the flared base that was once above the ground surface. The buried, flared base suggests that the tree grew during much of its life while little or no sediment was deposited around it, and the sediment now above the flared base suggests that aggradation was recent and heavy (fig. 184). rounded or inverted cone-shaped base on a buried tree, on the other hand, may indicate that aggradation occurred early in the life of the tree, before a flared base could form, and that aggradation has continued at repeated intervals (fig. 182). The relationship of the shape of the base to the rate of deposition has not been demonstrated in the field; but a number of individual trees of the same species having the two forms have been found, suggesting the postulated formation. Felled trees, buried or partly buried by alluvium, develop one or more vertical sprouts on the upper side of the part of the inclined parent trunk that protrudes from the ground. This trunk, like those of all water-felled trees, is alined nearly parallel to the direction of streamflow (fig. 19). Sometimes only a row of sprouts or young trunks is visible because the parent trunk is completely buried. Since many living trees of all flood-plain species have been found partly buried in the Potomac River flood plain, it is apparent that severe damage and burial are not necessarily lethal. Adventitious roots commonly start to grow from the buried part of the trunk from tissues, which Eames and MacDaniels (1947, p. 289) called root germs, located close to the vascular cambium. Kramer and Kozlowski (1960, p. _ 391) pointed out that roots grow from branches shll BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN Deposited alluvium dobie saeco FIGURE 18.-Diagram showing forms of tree bases postulated as result of different rates of deposition. \\ / 3 Surface upon which tree started to grow A19 DEPOSITION Adventitious roots ma A, Flared base suggests recent and heavy deposition ; B, inverted cone-shaped base suggests early and repeated deposition. FIGURE 19.-Ash tree partly uprooted prior to growing season of 1936, probably during flood of March 19, 1936, the maximum flood of record. A, Tree, showing parent trunk protruding from flood plain in downstream direction and three vertical sprouts; B, exposed buried trunk, show- ing flared base. Shovel is 4% feet long; point rests about 1 foot below the approximate level of the flood plain prior to 1936. attached to trees when the branches come into contact with moist soil. In the area studied along the Potomac River, I have not discovered any trees that were killed by deposition of sediment as great as 3 feet deep; but Harper (1988, p. 47) found that thick deposits of alluvium resulted in poor drainage which killed trees along Deep Fork of North Canadian River in Oklahoma; he attributed the heavy sedimentation to straightening and dredging of an upstream reach of the channel. Featherly (1941) noted that deposition of alluvium to depths of as much as 10 feet in Oklahoma killed mature forest trees; however, he found a small ash tree that started to grow in 1928 and that, by 1940, it was still alive in spite of the 52 inches of sediment deposited around it. Cotton- wood, willow, baldeypress, and tupelo trees survive A20 heavy siltation on flood plains in the lower Mississippi River valley (Putnam and others, 1960, p. 20). The approximate level of the surface upon which partly buried water-felled trees were growing before being uprooted is determined by interpolating the level of the flared base by figuratively rotating the parent trunk to a nearly vertical position. Application of this system to the tree represented in figure 192 shows that about 244 feet of alluvium lies above the original base level. The fact that the vertical sprouts started to grow in 1936 indicates that the tree was uprooted during the flood of March 19, 1936. The alluvium has been deposited since then. ANALYSIS OF STRUCTURE OF WOOD FROM BURIED TRUNK Because the wood formed in the buried part of the trunk after burial has a structure different from that formed prior to burial, the year of deposition can be determined. Other investigators have found by both experimentation and observation that wood formed in buried or submerged stems structurally resembles the wood of roots. Bannan (1962, p. 15), citing Wieler, stated that wood of the kind found in lateral roots can be produced in a stem by placing it under water. In anatomical studies of stemgrafts in fruit trees, Beak- bane (1941, p. 361) showed that some characteristics of the wood in a stem grown below the ground closely resembled those of root wood; other characteristics were intermediate between those of stems and roots. Wood in the swelled butts of ash trees growing in wet swamps is less dense than wood higher in the trunks, and the cells of the wood in the butts are larger (Koehler, 1983, p. 14-15). Pillow (1939, p. 135-136) found that wood of low density extends farther above ground in deeply flooded trees than in shallowly flooded ones. The method of study and analysis of data used to determine the sedimentation history of buried trees was developed from data collected from an ash tree close to the one shown in figure 19. The site on which these trees grow has been covered by high water at least 26 times between March 19, 1936, and May 10, 1960, and the tree in figure 19 has probably experienced a complex history of alternate burial and exhuming in these 24 years. The tree used to develop the method, however, was merely felled during one flood and buried during another. Its history has been simple. The tree is on the east side of Conn Island approxi- mately 1,000 feet upstream from Washington Aque- duct Dam in Montgomery County, Md. The surface around it has an elevation of 156 feet and is approxi- mately 3.5 feet above low water, which is controlled by the dam. ; VEGETATION AND HYDROLOGIC PHENOMENA The surface around the tree was just covered by the peak flow of 82,100 cfs on May 7, 1958. This discharge has a recurrence interval of 1.25 years, based on the annual flood series. The water was about 1 foot deep during the crest on May 10, 1960, which had a peak discharge of 124,000 cfs and a recurrence interval of 1.9 years. The tree (figs. 20, 21) consisted of a parent trunk that was almost completely embedded in alluvium and a nearly vertical sprout growing from its extreme downstream end. As the sprout started to grow in 1936, the tree must have been felled during the March 19, 1986, flood. Another sprout, already dead and buried when dug, had grown from near the parent base; therefore, the tree was not buried when it was felled. The level of the base shows that about 244 feet of sediment was deposited on the flood plain during one or more of 25 floods after March 19, 1986, and before November 25, 1957, when the tree was studied. In the paragraphs that follow, it will be shown that the tree was buried in 1937, 1 year after it was felled, and that no significant amount of sediment has eroded subsequently from around the tree. To determine when the tree was buried, a laboratory study was made of cores taken from the parent trunk at 1l-foot intervals ("C" in fig. 21) from the base of the sprout, at ground level, to the previously buried base. Microscopic examination of each core showed that the wood lying outside one particular annual ring is softer and more even gggfiured than the wood toward the center from the ring. The ring that marked the change could not be dated directly in each core because some rings, especially those near the outer part of the trunk, are indistinct; so the ring was cross-dated with those in the core taken at the ground surface. The distinctive wood was first formed in 1937 throughout the length of the buried trunk. The third highest flood of record occurred on April 28 of that year. A large wood sample was taken from the buried trunk 21% feet from the vertical sprout and approxi- mately 114 feet below the surface of the ground. Diameters of 1,100 vessels in 11 selected rings, dating from 1930 through 1946, were measured in a prepared cross section that included rings formed in 1936, 1937, and 1938. The data show that the relative diameters of the vessels in the ring that grew in 1937 and in rings that grew in later years were different from the relative diameters of the vessels in rings that grew before 1937. As illustrated in figure 22, the early wood vessels are smaller and late wood vessels are larger in the 1937-40 rings than the corresponding vessels in the 1934-86 rings. When the difference in the mean diameters of BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION early wood vessels and late wood vessels of 11 selected rings dating from 1930 through 1946 was calculated, and when the ratio of this difference to the mean of the early wood vessels was determined and plotted for each, nls. ~ Cogh FIGURE 20.-Ash tree, showing inclined buried trunk and nearly verti- Buried dead basal sprout is barely visible to the left of White line is horizontal, and shovel is 4% feet long. cal sprout. the shovel. A21 ring (fig. 23), it could be seen that the major change in the difference in mean diameters occurred in 1937. Statistical analysis of these data shows that the vessels formed after 1936 are significantly different in '\ diameter from those formed before 1936. The mean diameters of the late wood vessels of rings formed from 1930 to 1986 were compared with those of late wood vessels formed from 1988 to 1946. Early wood vessel diameters were similarly compared. The means of the two types of vessels formed in 1937 also were compared with the means of the earlier rings and of the later rings. The assumption was made that the vessel diameters are samples of a normal population. The results are summarized on page A22. The t-test, which is a measure of the deviation of the mean of a sample from that of the population, indi- cates that the vessels in rings formed :'rom 1938 through 1946 have less than a 0.25 percentfchance of being similar to vessels in rings formed from 1930 through 1936; in other words, there is 1 chince out of 400 that the vessels of the two groups of yea $8 are sim- ilar. The analysis of the early wood vessels in the 1937 ring further shows that there is about a 90 percent prob- ability that these vessels are similar to those in rings formed later, whereas there is only about z} 5 percent probability that they are similar to those formed earlier. These analyses support the hypothesis that the tree was buried in 1937. (a Wood sample 3 10 |- G / 2 Dead sprout 20 |- ) / Old roots [j I ' [ i Approximate level pre-1936 surface f ly- A -*- ( /_////, tesa o means Tare aa af eatin Cc ip. _____ 30 |- # et. ::: y:" e ool L j atc tag 0 10 50 60 70 8o 90 INCHES FIGURE 21.-Drawing of ash tree, showing basal sprout, location of cores (C) and wood sections, and approximate level of flood plain prior to 1936. A22 VEGETATION AND HYDROLOGIC PHENOMENA 1939 FisurE 22.-Photomicrograph of wood from buried trunk of ash tree, showing that the early wood vessels are smaller and the late wood vessels are larger in 1937-40 rings than in 1934-36 rings. Comparison of vessel diameters-summary Late Wood Vessels Group 1 (21) Group 2 (22) I 1937 1930-36 1938-46 0. 0489 0. 0873 0. 0653 Variance.... . 0000477 0000489 |:. 4 } Probability (F=4) (t-test; t=8.727, 8 degress of freedom) <0.25 percent. Probability 1937 belongs to Group 1<2 percent. Probability 1937 belongs to Group 2<2 percent. Early Wood Vessels Group 1 (21) Group 2 (24) I 1937 1930-36 1938-46 0. 2243 0. 1720 0. 1742 . 000651 000258 1. c_ ;-_____ Probability (Fi=£;)(test; t=3.874, 8 degrees of freedom) <0.25 percent. Probability 1937 belongs to Group 1~%5 percent. Probability 1937 belongs to Group 2=~90 percent. Early wood vessels are the larger white ovals on left side of each ring. Study of the buried sprout that was dead when the tree was dug (figs. 20, 21) supports the thesis that the tree was buried after the growing season of 1936 and not when it was knocked over, prior to this growing season. The sprout, which started to grow when the tree was felled, must have begun life as a stem, rather than as a root, for it has pith at the center-roots do not contain pith ; therefore, the part of the tree from which the sprout arose was not buried at the time the sprout began to grow. The inner ring of the sprout is composed of wood similar to that found in a stem, but wood toward the outside is more like that in roots. This sprout must have started to grow after the tree was knocked over, while the base was still above the ground surface, and must have continued to grow for a time after the tree was buried. By way of summary, then, the tree was knocked over in 1936, and two sprouts grew from the inclined trunk: one from the base and one from the distal part. In April 1937 the tree was buried, and the wood that BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION A23 formed in the buried trunk contains vessels that are different from those formed in 1936 and earlier. The vessels formed in 1937 are like those that formed later, and their size distribution is similar to that of vessels formed in root wood. EVIDENCE OF FLOODS AND DEPOSITION IN TREES ALONG SMALL STREAMS The trees described in the preceding section are growing along the Potomac River, where large floods innundate the flood plain for several days and to depths exceeding 10 feet at the peak. Floods of this duration and magnitude commonly fell large trees. On small streams, on the other hand, evidence of floods in the form of sprouted inclined trunks indeed is rare. A measure of the effective force necessary to abrade bark or to uproot trees has not been devised but seems to be related to the depth and velocity of the water and to the duration of innundation in relation to the size of the tree. Floods on small streams are generally of shorter duration, and depths over the flood plain at the peak are lower than on large rivers As a flood progresses downstream, in other words, the flood wave spreads out (Hoyt and Langbein, 1955, p. 38, 40), and the lag in time between the occurrence of the storm and the passage of the flood crest becomes longer. All other factors being equal, the peak discharge varies almost directly with the size of the drainage area or the size of the stream (Benson, 1962%b, p. B53). Although the relative quantities of sediment transport- ed during floods of different frequencies can be used as a measure of the effectiveness of floods (Wollman and Floods of: 0.9 ,- Mar. 19, 1936 e 0.8 | é U fpr. 28, 1937 a 9.7 |- s 0.6 |- > o 0.5 |- a] £- < &C 9.4 |- =| 0.3 |- &l 02 &l 01} a 8 ssl cp - 3 "3. a- -t e s- 1.1 w co o O 4 0 1 2 3 4 5 6 7 8 9 10 11 12 13 FEET FiGurs 28.-Drawing of buried part of the ash tree in figure 19. Because sprouts 4, 2, and C (fig. 28) have pith in centers of cross sections through their bases, they must have started to grow as stems. The lower part of sprout A4 grew above ground for 2 years, became _- buried, and grew for an indeterminate interval beneath the soil surface; later, it grew above ground for 3 years and then was again buried and continued to grow below the surface until collected. Basal sections through sprouts 2 and C show similar histories but are not correlative in time. Sections through higher levels in the buried sprouts also show varied wood structure, but their sequences of stem wood and rootlike wood cannot be related to sequences in any other sections. Although these sprouts were alive when collected, the rings in the rootlike wood are indistinet and' cannot be dated with certainty; furthermore, it is not known when sprouts 2 and C started to grow. Their records are, therefore, truncated at the beginning and the end and are obscured in the middle. Swollen growths at various levels on the buried sprouts from which other sprouts and roots are grow- ing appear to be analagous to root crowns of trees that have been damaged repeatedly (Lutz, 1934, p. 60, fig. 15). There appear to be three levels of these growths, suggesting that three floods cut off the stems at the respective levels and that later floods deposited allu- vium over them. Again, it is not possible to date their initial growth. F Although it has been impossible to relate the evi- dence of deposition and erosion to specific floods, it is evident that this tree has experienced a varied history. Study of a core from the parent trunk between sprouts B and C indicates that this part of the trunk was buried in 1937 and remained buried until sampled. Another core, taken 1 foot below the surface and to the left of the large vertical sprout in the center of figure 19, suggests a varied history of sedimentation similar to that of the sections of the small buried sprouts. In summary, after the tree was felled in 1986, it could have been partly buried in 1937. Later, some floods could have added additional layers of alluvium on top of the 1937 surface, and other floods could have eroded all or part of these layers. Apparently no flood subsequent to the one in 1937 eroded to the pre-1936 level. The analysis of the form and the wood structure in the trunk of another tree (fig. 29) is presented as another example of the reconstruction of at least a general history of floods and sedimentation. This tree also grows on the Potomac River flood plain, about 2 miles downstream from Great Falls The inclined trunk and vertical sprouts show that the tree was knocked over. The roots growing from the fallen trunk show also that the trunk was buried; a small basal sprout, however, attests that the tree was buried during a flood later than the one that felled the tree. Subsequent erosion is confirmed by the exposed roots. The tree was knocked over after the 1942 growing season, probably during the flood of October 17, which was the second highest flood of record. The year of burial cannot be determined from the cores that were taken because some rings cannot be identified ; however, A26 FiGur® 29.-Ash tree, on flood plain, that was knocked over by one flood, partly buried by another, and exposed by a third. the fact that alluvium was eroded from around the tree between the growing seasons of 1950 and 1951 can be deduced from a change in wood structure in the fallen trunk between rings of these years. The wood formed in the exposed roots also changed in 1951; wood which has grown since then is more like stem wood. Three floods, on November 26, December 6, and December 10, 1950, covered the site and could have exposed the roots. The foregoing detailed description of the tree shown in figure 29, as well as even superficial observations of flood-plain trees, reveals that alluvium is eroded from around roots on flood plains and in channel banks. Wood of ash roots is diffuse-porous, whereas the outer layers of wood in exposed ash roots are ring-porous. The change from diffuse-porous to ring-porous is abrupt and occurs between adjacent rings. This change is attributed to exposure by erosion, and the year of exposure can be determined by counting the rings lying outside the change in wood. Annual rings in the ring-porous wood of exposed roots are distinct. Detailed study by other investigators has shown anatomical differences between wood of buried roots and wood of exposed roots. Morrison (1953) studied the wood anatomy of roots of six species of trees and found that the length, diameter, and concentration of vessels and the width of rays in exposed roots differed from those in buried roots. Others have found that exposure of lateral roots by erosion results in growth of new wood that is more like that in stems (Bannan, 1962, p. 15; Esau, 1953, p. 512-513). VEGETATION AND HYDROLOGIC PHENOMENA In review, the botanical evidence of floods, deposition, and erosion consists of the growth of trees after the flood has subsided. This growth manifests itself in the healing of scars on trunks of trees, in the growth of sprouts from inclined trunks, and in the change in wood structure in buried stems and in exposed roots. The growth and change occur during the first growing season after the hydrologic event and can be dated by counting the annual rings that have formed since the change. BOTANICAL PHENOMENA RELATING TO THE FORMATION OF THE FLOOD PLAIN The relatively level land bordering a stream, called a valley flat ('Twenhofel, 1932, p. 806) or flood plain, is composed of sediments reworked by the river and is subject to flooding (Hoyt and Langbein, 1955, p. 12). The types of deposits that underlie the flood plain have been described by Happ and others (1940, p. 22-25) and by Lattman (1960). Wolman and Leopold (1957 p. 95, 96) have shown that flood plains are formed primarily by the lateral migration of the channel across the valley flat and are thus composed mostly of deposits of lateral accretion. Different definitions of the flood plain exist, but the currently accepted ones seem to agree that a flood plain is the lowland adjoining the channel, subject to flooding, and com- posed of sediments carried and reworked by the river. Similar differences of opinion in the definition of the river bank exist in the literature, and some authors have expressed difficulty in measuring the height of a river bank (Hack, 1957, p. 48; Schumm, 1961, p. 33; \ and Wiitala and others, 1961, p. 53). It has been suggested, furthermore, that bankfull floods, which are of intermediate frequency-that is, floods that occur on the average of about once a year or once every 2 years-are more effective in causing the lateral migra- tion of the channel, thus the formation and modification of flood plains, than the larger, less frequent floods (Wollman and Miller, 1960, p. 66). The sections that follow show that, not only along part of the Potomac River but probably along similar rivers in the East, the channelward limit of flood-plain trees represents the bank. It is a line that can be mapped, and it owes its initial location to the low flow regime of the river. Trees can become established on a flood plain only during extended periods of low flow; yet, once established, they mature and stabilize. the banks. The only hydrologic events that remove the trees are the slow lateral undercutting of banks, which causes the trees to topple into the river, and infrequent catastrophic floods. The presence of mature trees along the channel, then, marks the bank; their age - BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION allows the determination of the frequency, albeit crude, of the reworking of the flood plain deposits by the river. RELATIONSHIP BETWEEN FLOOD-PLAIN TREES AND LOW FLOW A demarcation line readily seen along a stream channel and closely related to the flow regime, as well, is the margin of the perennial vegetation. This line is used to map rivers on topographic maps and, in the humid parts of the United States, coincides with the channelward limit of tree species. The relationship between the flow of rivers and the establishment and growth of trees on the channel banks is only partly understood, because the sequence of events believed necessary for the establishment of trees on banks has not occurred along the main stem of the Potomac River - during the period of study; therefore, the conclusions presented here are only tentative. For trees, or any plants, to become established, three basic elements are necessary: (1) a supply of viable seed, (2) a favorable seed bed, and (3) a period of time during which the environment is favorable for the growth of young plants. Although the yield of tree seed and the time of dissemination are being studied in connection with the larger project, only a few data will be presented here. The time of dissemi- nation, the yield, and a few observations of the fate of silver maple and box elder seed are cited as examples of the relationship of these botanical processes to the flow regime of the river. Behavior of other species- river birch, cottonwood, American elm, and syca- more-could be discussed; however, the pattern is similar. Silver maple trees along the Potomac River near Washington, D.C., drop their seed in late spring, mostly during a 2-week period ending about May 1. The seed are capable of germinating immediately, and hundreds of newly sprouted ones are seen each May. Seed have been caught and counted in traps and in marked plots on the ground. Over a 4-year period, the number of seed per square yard ranged from 55 to 243; and on one day they fell at a rate of 5 per square yard per hour. These data show that an adequate supply of silver maple seed is broadcast on the flood plain. Box elder seed are disseminated from autumn to early spring; and they, like silver maple seed, are capable of germinating when the weather becomes warm in May, when hundreds of newly sprouted seed of this species are also seen. The number of seed that have fallen annually range from 100 to 250 per square yard. Although attempts have been made to collect data on A27 the rate of germination of silver maple and box elder seed on different kinds of soil, all quantitative results have been negative. All newly germinated seed and seedlings of these species have been found only on mineral soil, either recently deposited by a flood or recently exposed by erosion of overlying organic mat- ter, or in thin layers of finely comminuted organic flood debris. Some of the seed traps are on the flood plain at levels that have not been inundated during the period of study ; therefore, the ground is covered with several years' accumulation of organic matter and leaf litter. Although silver maple and box elder trees are not common near these traps on the higher surfaces, some seed of these species are caught annually. No seedlings of silver maple or box elder, or of any flood-plain tree species, for that matter, have been found on surfaces covered with humus and leaf litter in the 6-year period of observation. As examples of the fate of seed and seedlings, a series of observations will be discussed. On April 30, 1958, 155 newly fallen silver maple seed were counted in a plot having an area of 25 square feet. One week later the plot was inundated by a flood, and the seed were either washed away or buried. None on the plot germinated. On May 16, 1962, 1,150 silver maple seed were counted in five 1-square-yard plots underlain by fine-grained alluvium. These plots were examined periodically, and no seed germinated. On June 21, 1962, numerous new silver maple seedlings were ob- served outside the plots, but, as late as August, none appeared in the plots. The surface upon which the new seedlings grew, as well as the plots, however, was inundated by floods on March 7 and March 22, 1963, which destroyed the seedlings and deposited 2-4 inches of alluvium on the plots. Environmental conditions at the five marked plots were not favorable for germina- tion, and, as will be seen subsequently, the 1963 floods probably would have destroyed any seedlings if they had germinated. Seedlings of silver maple and box elder have been found, counted, and observed. Hundreds of silver maple seedlings were found in a small ridge of finely comminuted flood debris on June 8, 1961. In a marked plot extending 6 feet along the ridge and 1 foot across, 228 seedlings were counted. These were destroyed by burial under several inches of sediment on March 23, 1962. Similarly, box elder seedlings were found in two flood-debris ridges in 1958. From late March to late April 1958 the river rose three times, each time to a lower level than before, leaving three debris lines. On May 2, 1958, 64 box elder seedlings were counted in 10 linear feet along the late March line, 13 along the mid-April line, and none along the late April line. A A28 few seedlings were growing on the surface between the upper and lower debris lines, and none below the lower line. Because the count was made just 2 days after the late April rise, it seems reasonable to believe that the late April rise destroyed any seedlings that may have germinated on the surface inundated at that time. All seedlings, including those in the higher debris line, were destroyed by the flood of May 7, 1958, which crested at an elevation higher than the late March flood. In the examples cited, the entire annual crop of seed of silver maple and box elder trees either failed to germinate because the local environmental conditions were not favorable for germination, or the seedlings were destroyed by later floods. For seed of these species to germinate and grow into seedlings and these to become established as a new generation of trees, a new crop of seed must be produced in another year. Because young saplings of all flood-plain tree species are present in the forest along the Potomac River, a sequence of hydrologic events associated with unique climatic conditions must have prevailed in the recent past that has permitted their establishment. This sequence however, did not occur during the period of study. These data suggest that the orderly sequence of botanical, hydrologic, and as yet unknown environ- mental events that must prevail before seedlings will become established is as follows: Streamflow during the winter must remove humus and freshly fallen leaf litter from the surface; seed must fall on mineral soil; microclimatic and edaphic conditions must favor ger- mination and growth of seedlings; and finally, the surface must not be flooded again until the seedlings have grown enough to withstand mechanical injury. The interval necessary to insure the trees a chance of survival between seed germination and the first flood is not known, because no floods have recurred during the period of study in areas where young seedlings grow. Other investigators have noted the orderly sequence of events required for the germination and establish- ment of plants along rivers. Putnam and others (1960, p. 13) found that regeneration of all tree species in southern river valleys will fail if seedlings are repeatedly flooded during the growing season. Dietz (1952, p. 252) observed that, for willows to become established, seed dispersal must occur during the falling stage of a flood, at which time the floating seed are deposited from the receding water in a line on the bank. For seed to germinate, the bank must remain moist; and, for willows, no flood may occur for several months while the seedlings are becoming established. Horton and others (1960) made thorough laboratory, VEGETATION AND HYDROLOGIC PHENOMENA Frcur® 30.-Mature silver maple trees on low bank that was flooded at least 60 times between 1931 and 1960. Flow at time of photograph, February 18, 1963, was about 5,000 cfs. Average annual discharge is 11,000 cfs. The 2-year flood is about 10 feet deep at this section. greenhouse, and field studies of seed germination and seedling establishment of riparian species common in the semiarid southwest. They reported (p. 14-16) that tamarisk and seepwillow seed are spread on river banks during receding streamflows in the autumn and winter. If the bank remains moist in early autumn and in spring, many seed will germinate and become established. Both species can survive submergence for as long as several weeks but will be eroded from the soil if subjected to any current. Gardner (1951, p. 398-399) found that seed of creosote bush germinate on exposed gravel bars in the channel of the Rio Grande in New Mexico and that shrubs become estab- lished during subsequent dry years. Mature trees lining long reaches of river banks are inundated as often as several times a year by high flows and by floods. This fact, plus the close relation- ship between seedling growth and stream hydrology, shows that the establishment and maturation of trees on the bank constitute a botanical process that is adjusted to the low-flow regime of the river. As Leopold and Wolman (1957, p. 63) pointed out, if a river does not use the entire width of the channel, as during periods of low flow, vegetation will quickly occupy the new ground; furthermore, as they stated, growth of vegetation contributes to the deposition of sediment. Shull (1944, p. 776) also noted that several successive years of low water are required for the establishment of trees on banks of the Mississippi River. The channelward limit of flood-plain trees, therefore, represents the high-water mark of the maxi- _- mum stages during periods of low flow (fig. 30). _- The surface that is exposed during low flow, upon which trees become established along rivers that slowly migrate laterally, is comparable to a point bar (Leo- pold, 1962, p. 528; Wolman and Leopold, 1957, p. 91-92). It is initially formed by high flows and floods which also keep it bare, and trees become established across the surface from close to the water's edge only during periods of low flow. The elevation of the surface is raised by deposition during subsequent high flows in a manner similar to that described for point bars in pastures (Wolman and Leopold, 1957, p. ~92-93). These processes are represented diagrammati- cally in figure 31. The rate of change in point-bar formation in forested flood plains is slower than in pastures. --The deposition of sediment around mature flood- - plain trees, which occurs during high flows and which _ was discussed in a previous section, does not adversely affect most trees. The death and destruction of _- flood-plain trees is more complex, involving internal physiological as well as hydrologic processes related to - floodflow ; the effects cf hydrologic processes upon the - development of the forest and formation of flood-plain banks are discussed in the following sections. SIGNIFICANCE OF OLD TREES ON BANKS Detailed mapping of tree species along most of both shores for an approximately 20-mile reach of the _- Potomac River (fig. 1) indicates that for much of their length these banks are characterized by old trees - growing on the vertical face of the bank or, on a few - places, on top of it. These banks are, in fact, for most __of their length, armored with heavy, old roots, tree “ases, and trunks, whose presence indicates that the * \ bank has not changed position for a period equal to at |\least the age of the trees. The flood-plain deposits, at ~ these places at least, have not been reworked for a long period of time. Leopold and Wolman (1957, p. 69) stated that heavy tree roots bind alluvium of flood! {plains and that erosion of the banks is extremely slow. 'They emphasized that the banks of some rivers are not i [feroded during periods as long as 200 years (Wolman and Leopold, 1957, p. 100). Active erosion of banks of the Potomac River is manifest in a few places in exposed tree roots, trees | leaning over the water, and bare cut banks (fig. 32). \ _Old trees grow on top of these banks. The rate of _- erosion has not been determined at these places, and at BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION ~ \ a + A29 only a few of them would repeated measurements be feasible. Frequent floods-those that occur on the average of once in two years-do erode the bank in places, undercutting some of the trees and toppling them into the river. Such trees have been observed from time to time in the course of fieldwork. During this period, 1958 to the present, no floods have exceeded the bank at the places where the trees fell into the water. Else- where, newly exposed roots are seen extending out from eroded banks after recession of floods (fig. 32). The presence of many old trees along the banks of the Potomac River suggests that even the catastrophic floods here are no more effective in the erosion of banks and the destruction of the flood-plain forest than are frequent floods. Leopold and Wolman (1957, p. 64) stated that river banks and the trees that grow on them in the Eastern United States are severely eroded only by the larger floods. In mountain streams of the Eastern United States, Hack and Goodlett (1960, p. 48-51) showed that a single catastrophic flood can determine the character of the flood plain, and they | believe that forested banks can be moved only by floods lof such magnitude. The tree shown in figure 15 is more than 100 years old and has grown on the vertical face of the bank through three major floods which were of sufficient magnitude to be considered cata- strophic and which Wolman and Miller (1960, p. 57) suggest recur once in 50 to 100 years. In the vicinity of Washington, D.C., the March 1936 flood has a recurrence interval of about 70 years, and the Novem- ber 1942 flood, of about 50 years. The third flood to pass over the tree occurred in May and June 1889, prior to the establishment of recording gages on the Potomac River; but it has been estimated as approach- ing the March 1936 flood in size (Grover, 1937, p. 334). In addition to these catastrophic floods, the tree (fig. 15) has been inundated by many other floods of lesser magnitude. The flood of May 10, 1960, reached nearly to the level of the base of the sprout and branch above the knife on the smaller tree in the center of the figure. Such a flood has a recurrence interval of 1.9 years; and 18 floods, including those in 1936 and 1942, have equaled or exceeded it in 33 years. Evidence has been presented which supports the theory that, once the trees become established, they will persist for a long period of time and will coincidentally preserve the location of the bank. The location of the bank, then, is established at a lower elevation close to mean low water and well below the level of floods that recur about once every 2 years. (The old trees and the tops of the eroding banks are gen- erally at about the 2-year-flood level. ¥ X, ( A30 VEGETATION AND HYDROLOGIC PHENOMENA Erosion and accretion No seedlings Approximate level of 2-year flood River level approximately 75 percent of time Accretion h Maximum stage for » years No seedlings; trees here repeatedly damaged by floods Erosion and accretion C Normal climate Approximate level of 2-year flood River level approximately 75 percent of time - at uP Pr 2 a Renewed accretion Fieurn 31.-Diagrams representing establishment of trees in relation to the flow regime of the river and the processes modify- ing the flood plain. BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION 32.-Cut bank of Potomac River showing newly exposed roots and recently fallen trees. Two-year flood just reaches top of the bank. Area is almost 200 yards upstream from area in figue 30. BOTANICAL EVIDENCE OF CURRENT PROCESSES AFFECTING THE FLOOD PLAIN A discussion of the lack of agreement on whether (1) lateral accretion due to. point bar deposition, (2) -deposition on flood plains in backwater during floods, -or (3) erosion and deposition in a sequence of floods = makes the major contribution to the deposited sedi- ment is beyond the scope of this report. This contro- versy, however, fails to note an important aspect shown by the botanical evidence. On some flood plains, certainly on forested ones of rivers that are moving laterally very slowly, local erosion by over- bank flows produces rapid interchange of alluvium only to be followed by deposition in flows of compara- ble magnitude either in the same year or in subsequent years. Flood-plain sediments appear to be constantly reworked to variable depths. This process of trading of flood-plain materials without intervention of channel movement may affect large amounts of material. It is probably enhanced by vegetation, owing to local concentration of flow, where- as it may be nearly absent on pastured or grassy flood plains. This trading process is shown by botanical evidence to be of greater magnitude than had hereto- fore been realized, but it probably occurs at this mag- nitude not only on the Potomac River but also along other eastern rivers of similar character. To the extent that this trading is important the significance A81 of the origin of the first deposited material-lat- eral deposits or overbank deposits-is proportionately diminished. Sediment found on the flood plain is not part of the original point bar or overbank deposit; but it is the result of processes-erosion or deposition-that are much more recent than those associated with the initial flood-plain formation. The surface one sees is of relatively recent origin, even if the average elevation of the flood plain has not changed with the passage of time. The flood plain consists of a mosaic of erosional and depositional surfaces in space, and tree form indicates that this sequence is characteristic of any one place at different times. The net effect of this process is temporary storage of alluvium on the flood plain, similar to temporary storage of alluvium in point bars (Woolman and Leopold, 1957, p. 95). The flood plain, its vegetation, and the complete flow regime of the river are elements in dynamic equilibrium with each other (Hack, 1957, p. 90; 1960, p. 85-87; Hack and Goodlett, 1960, p. 58). The conclusion that banks and flood plains of the Potomac River are eroded only slightly, even by floods having a recurrence interval of 70 years, agrees with the conclusions of Langbein and Schumm (1958). They showed that the annual sediment yield in the United States decreases with an increase in precipita- tion above about 14 inches per year to a minimum quantity in densely forested regions of the humid East and the Pacific Coast States. Much of the sediment carried by the Potomac River during high flows may well come from scour of its bed (Leopold, 1962, p. 520), as well as from erosion throughout the drainage basin (Leopold and Maddock, 1953, p. 21), and, during floods, from erosion of its flood plain. The concept that vertical erosion and deposition are effective in modifying flood plains in the humid East complements the seemingly opposed concept of pre- dominance of lateral corrasion and deposition. Forest- ed river banks are relatively stable because they are composed of cohesive materials bound by heavy roots (Leopold and Wolman, 1957, p- 64). In the semiarid West, however, river banks, they report, are composed of more friable materials, and flood plains support a less dense plant cover; therefore, these banks are susceptible to erosion by floods of lower magnitude and higher frequency. It follows that the dominant proc- esses that modify a flood plain are determined by the flow regime and the vegetation on the flood plain, as well as by the materials composing the bank. One would expect, therefore, other conditions being equal, that different processes will be dominant in valleys supporting different types of vegetation. Differences M A32 in the type of vegetation may result from the use of the land by man or from differences in regional climate. * According to this reasoning, change of the natural vegetation due to change in land use or change in climate will result in a change in dominance of processes that act on the flood plain. Upon destruction of the forest on flood plains in the humid East through expansion of urbanization, "improvement" of streams through channelization, or clearing for agriculture, lateral corrasion and deposition will become the domi- nant processes on the flood plain and will remain so as long as the banks are kept clear of trees. A change in climate to a drier one would result also in an increase in the dominance of lateral corrasion and deposition. This change with change in climate is supported by the conclusions of Langbein and Schumm (1958, p. 1084), who showed that, as conditions change from humid to dry, the sediment load increases, probably as the result of increasing lateral corrasion of the banks. An interpretation of the botanical phenomena against the background of the flow regime of the river defines the flood plain as the frequently flooded surface adjoining the channel and composed of alluvium deposited and reworked by the river. The bank is the channelward limit of perennial vegetation-tree spe- cies in the humid east. The surface is considered to be flooded whenever the level of the river exceeds the bank; and, along the parts of the Potomac River that have been studied, the frequency of these floods ranges from about five times per year to once in 2 years. In summary, the establishment, growth, maturation, and death of flood-plain trees in humid regions are inseparably merged with the complete flow regime of the river and the erosion and deposition of sediment. The bank, marked by the channelward line of trees, represents the maximum high water line during ex- tended periods of low flow or the margin of the laterally eroding channel. Once the flood-plain trees become established, they will persist through several severe floods. Locally, a few trees are torn out by catastrophic floods, but most die when they reach a maximum size or when they topple into the river as the bank is eroded. Growth of the trees is modified by hydrologic processes resulting in tree forms that re- cord the flood history of the surface. ECONOMIC SIGNIFICANCE OF BOTANICAL EVIDENCE OF FLOODS Some knowledge or undersanding of the magnitude and frequency of floods and flood-plain formation is necessary for the design of structures along rivers and the use of flood plains by man. Some of these VEGETATION AND HYDROLOGIC PHENOMENA structures are flood-control reservoirs, levees, and channels, whose design most obviously must be based in a large part upon the characteristics of floods. The demand for knowledge of floods, needed also to design storm-water drainage systems and to prepare ordi- nances controlling the use of flood plains, is especially great as a direct result of the seemingly unabated construction of suburban housing. The decisions made to answer the two basic questions underlying any proposal involving streams-is it needed? and, how large should it be?-are influenced, as Langbein and Hoyt (1959, p. 127-142) pointed out, by uncertainties in the hydrologic data. Some of the uncertainties stem from a complete lack of data from the drainage basin where a project is proposed or from the fact that data have been collect- ed for too short a period of time. About three-fourths of the stream gaging stations in the United States are on streams draining areas larger than 100 square miles, and the total length of small streams greatly exceeds that of larger streams (Langbein and Hoyt, 1959, p. 13-16). Furthermore, about half of the stations have been in operation for less than 20 years. Botanical evidence of floods and flood-plain deposi- tion discussed in this report will aid in reducing uncertainties. Although the methods are crude and much additional research is needed, a group of fallen trees, a number of partly buried tree trunks, or a tangle of exposed tree roots on a flood plain are positive evidence that something has happened; and further study will reveal the cause of the anomalies in the tree growth. In the section that follows, the value and limitations of botanical evidence are treated as a source of data to extend the records of floods backward in time and to provide a record of events at places where none exists. Finally, the value of botanical evidence of sedimentation is discussed. VALUE OF BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION In the absence of flood records, engineers must use indirect methods to determine the frequency of floods of different magnitudes (Jarvis and others, 1936, p. 28-68; Corbett and others, 1945, p. 98-109; Benson, 1962; and Dalrymple, 1960). These methods are estimates of peak flood discharges from which heights of flood crests can be estimated. As Langbein and Hoyt (1959, p. 240) emphasized, " * * * raw hydro- loic data are still strange to many * * *." Many cannot translate the concept of a flood of a given magnitude and frequency to a mental picture of water flowing down a valley in a broad river, covering the entire flood plain. The methods described in this | BOTANICAL EVIDENCE OF FLOODS AND FLOOD-PLAIN DEPOSITION study might provide positive evidence of the occur- rence of floods along reaches where the magnitude and frequency are estimated from a minimum of data. The botanical evidence of floods, consisting of scarred trunks and felled trees, are positive evidence of a catastrophic event. The simple techniques used to analyze this evidence show almost at once when the event occurred. With a little effort a brief history of floods can be developed. At present, however, the evidence is only of the occurrence of a flood. It tells us nothing of the magnitude of the flood except that it exceeded by an appreciable amount the flood that would have just reached the trees. Furthermore, most of the evidence is of the most recent floods and of those that have occurred since the most recent one of catastrophic size. These severe floods, as will be discussed in the following paragraphs, generally re- move evidence of earlier ones of lesser magnitude. All indirect methods of estimating the magnitude and frequency of floods are based on some type of record of hydrologic data, whether it be rainfall or streamflow. Thus, the value of the analysis is depend- ent upon the record. Dalrymple (1960, p. 13-14) stresses the importance of searching for historical evidence of extreme floods and showed that knowledge of only one flood that exceeded the maximum flood of record lengthens the record back to that historical occurrence. The botanical evidence of floods discovered in the course of this study has not shown the occurrence of such a flood in the past. Two reasons, it is felt, are responsible for this failure. The maximum flood of record, from 1895 to 1963, occurred on March 19, 1936. All known historical evidence (Grover, 1937, p. 334; Sanderlin, 1946) indicates that the 1889 flood did not exceed the 1936 flood and the previous maximum flood in 1877 was appreciably smaller than these. Secondly, the floods of 1889 and 1936, as well as the ones in 1937 and 1942, and the ice jam in 1948, probably destroyed evidence of any possible floods prior to 1877 that could have exceeded the 1936 flood. : The fact that one felled tree has been found That suggests evidence of a flood in 1861 (fig. 15) indicates that an intensive study might reveal botanical evidence of a flood that exceeded the maximum of record, thereby extending the record in time. The probability of finding this evidence in any flood-plain forest is - extremely low; and on the Potomac River, where a catastrophic flood occurred 27 years ago, the proba- bility is still lower. - For some rivers and streams, how- _ ever, especially those for which the record is short or for which several kinds of evidence strongly indicate the occurrence of floods many times higher than the A833 highest of record (Stewart and Bodhaine, 1961, p. 25-27), the probability of finding botanical evidence is greater. Erosion and deposition have been intensively studied by engineers, geologists, soil scientists, biologists, and others for more than 30 years, and even a brief summary of these studies is beyond the scope of this report. Much has been written about accelerated erosion, which is believed by some to be induced by man's use of the land, as opposed to natural erosion; however, doubt exists in the distinction between the two processes and of deposits resulting from them (Strahler, 1956, p. 623). The nature of the problems in measuring erosion quantitatively, summarized by Leopold (1956, p. 639-641), is such that the effect of man's use of the land upon erosion and deposition is most difficult to evaluate. The distinction between deposits laid down under the present climate and those laid down under past climates is difficult to make, and mechanical analysis of samples of some sediments of different origin fails to show significant differences (Hack, 1953, p. 185). Langbein and Hoyt (1959, p. 183-184) emphasized that evidence of accelerated ero- sion and deposition in valley bottoms is based chiefly . on the distinction between modern sediments and the buried "original" soil. They reported that physical and cultural characteristics of the deposits-such as bottles, cans and charcoal layers-are used for separat- ing them. They (p. 184) stressed the need for research in the mechanism of the processes and for long-term observations of erosional and depositional phenomena. The methods described here provide a means by which the rates of erosion and deposition at specific sites on banks and flood plains can be determined. Other advantages of the study of botanical evidence of floods and sedimentation phenomena are that, within limits, the trees can be studied at a time selected by the researcher and that the trees can contain a record that would otherwise require many decades of observation. Wolman and Eiler (1958, p. 8) found that after just a few months the sediment deposited by the catastrophic hurricane-Diane floods in August 1955 in New England was difficult if not impossible to distinguish from flood-plain deposits present prior to the floods. As Langbein and Hoyt (1959, p.: 245) stressed, funds for the collection of basic water facts generally are not appropriated until some crisis stresses the need; thus there is a considerable lag between the need for data and their availability. Botanical evidence of floods also can reveal evidence of previously unknown histor- ical floods, and thus provide an incentive for a study of other sources for evidence of these floods and of recent floods in places where intense application of indirect A34 hydrologic methods would provide an estimate of their magnitude and frequency. LIST OF PLANTS Ash 0000. Frazinus pennsylvanica Marshall Baldeypress_________. Tazodium distichum (Linneaus) Richardson Birch, Betula nigra Linneaus Boxelder_-._..._____ Acer negundo Linneaus Populus deltoides Bartram Elm, American----__. Ulmus americana Linneaus Maple, silver________. Acer saccharinum Linneaus Oak, swamp white___. Quercus bicolor Willdenow Syceamore-_._.____.__.. Platanus occidentalis Linneaus Pupelo-_-....____._ Nyssa sylvatica Marshall Walnut, black._______. Juglans nigra Linneaus Wallow Saliz Linneaus REFERENCES CITED Bannan, W. M., 1962, The vascular cambium and tree-ring development, in Kozlowski, T. T., Tree growth: New York, Ronald Press, p. 1-21. Beakbane, A. B., 1941, Anatomical studies of stems and roots of hardy fruit trees, III, The anatomical structure of some clonal and seedling apple root stocks, stem and root grafted with a scion variety: Jour. Pomology and Horticultural Sci., v. 18, p. 344-367. : Benson, M. A., 1962a, Evolution of methods for evaluating the occurrence of floods: U.S. Geol. Survey Water-Supply Paper 1580-A, 30 p. 1962b, Factors influencing the occurrence of floods in a humid region of diverse terrain: U.S. Geol. Survey Water-Supply Paper 1580-B, 64 p. Brown, H. P., Panshin, A. J., and Forsaith, C. C., 1949, Textbook of wood technology: New York, McGraw-Hill, v. 1, 652 p.; v. 2, 783 p. Corbett, D. 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Water Resources Division, 1964, Summary of floods in United States during 1956: U.S. Geol. Survey Water-Supply Paper 1530, 85 p. Wiitala, S. W., Jetter, K. R., and Somerville, A. J., 1961, Hydraulic and hydrologic aspects of flood-plain planning : U.S. Geol. Survey Water-Supply Paper 1526, 69 p. Wistendahl, W. A., 1958, The flood plain of the Raritan River, New Jersey : Ecol. Mon., v. 28, p. 129-153. Wolman, M. G., and EHiler, J. P., 1958, Reconnaissance study of erosion and deposition produced by the flood of August 1955 in Connecticut: Am. Geophys. Union Trans., v. 39, p. 1-14. Wolman, M. G., and Leopold, L. B., 1957, River flood plains: some observations on their formation: U.S. Geol. Survey Prof. Paper 282-C, p. 87-109. Wolman, M. G., and Miller, J. P., 1960, Magnitude and fre- quency of forces in geomorphic processes: Jour. Geology, v. 68, p. 54-74. (Yeager, L. E., 1949, Effect of permanent flooding in a river- bottom timber area: Illinois Nat. History Survey Bull., v. 25, p. 33-65. U. S. GOVERNMENT PRINTING OFFICE : 1964 O - 732-764 7 DAY hroughfall for Summer Thunderstorms in a Juniper and Pinyon Woodland 'Cibecue Ridge, Arizona GEOLOGICAL SURVEY PROFESSIONAL PAPER 485-B f U.A&3D. Throughfall for Summer Thunderstorms in a Juniper and Pinyon Woodland Cibecue Ridge, Arizona By M. R. COLLINGS VEGETATION AND HYDROLOGIC PHENOMENA GEOLOGICAL SURVEY PROFESSIONAL -PAPER +9 5-D The relation between throughfall, precipitation, stemflow, and interception is investigated and analyzed UNITED STATES GOVERNMENT. PRINTING - OFFICE, WASHINGTON :; 1966 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 20 cents (paper cover) CONTENTS Page Page .?. Lusi vet b clean a = =o nite a ale s B1 {- Anflysis...:. ...i cr a B3 2> 22020 eles nce? 2 eel Lo eel n cw ea an aw 1 | Relation of throughfall, stemflow, interception, and ule eras n cade. 2 .s cue neler erence oe a ae 12 Physical aspects of throughfall. 2 | CONClusION@": ce snes 12 Experimental 2] Relected _... 13 Definitions and assumptions........._..L._:_..._.l./. 3 ILLUSTRATIONS Page FrGurs (:/ Map of Cibecue Ridge L0 abel ns tes s ae -n b opie s ue ae 5 nag B1 2-5. Graphs showing precipitation-throughfall relation for- 2. col cus ear =a oak os oon ss dhe bn ma' s anl an a a a s aleals =a e io ie id ale in a anis 4 S .:.: n cee -n on anu alee big bo a aoa - ane aa panes be an bet au en a ob hn inn ante woe 5 d. Juniper And l. c.. cks ann ares tee coleus calne ailes malal a an sa mea an in in 6 5: Oakitrees and manzanita bushes.. . - nue... cul 2. aio ae ae an lies aise ad a a hie a a me a an 11 6. Graph showing relation between precipitation and interception. 12 TABLES Page 1. Location and arrangement of rain gages in the Cibecue Ridge area.. B2 2. Covariance analysis, test of the regressions of precipitation versus throughfall of juniper and of pinyon trees. _... T. 3.*Precipitation and throughfall data for-equal-size storm 8 t.: Three-way analysis Of -- License o ane ae abu aie hoe s a nie aes ao a mins onle a ale aah al tk aim alm o ms a m 9 5. Orthogonal contrasts of. stenificant variables .>. . 2. .- bleue anu ald aes a aeon aa 10 LII VEGETATION AND HYDROLOGIC PHENOMENA THROUGHFALL FOR SUMMER THUNDERSTORMS IN A JUNIPER AND PINYON WOODLAND CIBECUE RIDGE, ARIZONA By M. R. ABSTRACT To determine throughfall for summer thunderstorms in a juniper and pinyon woodland and to gain an understanding of the factors involved, a stratified random sampling experiment was conducted on Cibecue Ridge, Ariz. Forty-eight rain gages were used to measure throughfall. The strata, or variables, investigated were tree type, tree size, and direction and distance of the gage from the tree bole. Equations for curves of pre- cipitation against throughfall were computed for each tree type used. Statistical analyses were used to test the variables investigated, and it was found that: (1) the throughfall for Utah juniper is the same as that for pinyon, (2) the amount of rainfall catch that the gage will receive is a function of the direction in which the gage is located in relation to the tree bole, (3) throughfall is not dependent on tree size (for the sizes tested), (4) the throughfall catch is a function of the distance that the gage is located from the tree bole in threé of the five storm groups tested, (5) the combined effect of direction and distance from the tree bole causes a significant difference in throughfall catch for the storm groups tested, and (6) broad-leaved oaks in the study area have less throughfall than juniper and pinyon if precipitation is more than 0.08 inch. The relation between throughfall (T), precipitation (P), stem- flow (iS), and interception (/) may be expressed as T=P-S-I. From this relation a curve of precipitation against interception was drawn. Interception increases in the initial stages of a storm, reaches a maximum at 0.50 inch of precipitation, and then becomes constant (assuming constant-intensity storms and excluding wind and evaporation effects). INTRODUCTION Cibecue Ridge is on the Fort Apache Indian Reserva- tion in east-central Arizona and is at an altitude of 5,300 to 5,600 feet above mean sea level (fig. 1). The annual precipitation is about 19 inches, of which about 50 percent falls during the major runoff period July through September. In early and middle July, moist airmasses from the Gulf of Mexico are moved into Arizona by the western part of high-pressure systems moving over the southeastern coast of the United States. - The moisture in these airmasses is precipitated mainly during convective-type thunderstorms. The ~. § 2x... oe \,, N . B £ C 4 y % a C € Cibecue Ridge study area \. a € no; / '_l # A : 4 yq mA GK mec o Cedar Creek [L" “a? Trading Post AK, Yy y." "~wal 0 5 MILES Boil 61 £0 _J FIGURE 1.1-Location of Cibecue Ridge, Ariz. cumulonimbus clouds form above the Mogollon Rim, to the north and east of Cibecue Ridge, and then propagate over the area where rainfall occurs. Winter precipitation is received from polar continental and polar Pacific airmasses in the form of frontal-type storms. Winter precipitation is not considered in this report. The most abundant tree types at this altitude on the reservation are Utah juniper Juniperus osteosperma (Torr.) Little and pinyon (Pinus edulis Engelm). The crowns of these trees cover about 50 percent of the Cibecue Ridge site. . Two small drainage basins, 63 and 42 acres in area, were selected on Cibecue Ridge for intensive study of the effects of juniper and pinyon removal on runoff. In general, the purpose of this investigation was (1) B1 B2 to study throughfall in a juniper and pinyon woodland on Cibecue Ridge and (2) to further understanding of the factors affecting the physical aspects of throughfall. ACKNOWLEDGMENTS F. A. Branson provided the basis for choosing tree species and tree sizes by his vegetation transect measure- ments. D. R. Dawdy and N. C. Matalas offered many helpful suggestions in their comprehensive reviews. Data were collected with the help of R. M. Myrick, who also critically reviewed the report. PHYSICAL ASPECTS OF THROUGHFALL The effect of vegetal cover intercepting and thus reducing the amount of precipitation reaching the ground (throughfall) is significant on Cibecue Ridge. Because interception is satisfied mainly from the first part of a rainstorm and because many storms produce less than 0.25 inch of precipitation-less precipitation than is required to reach the retention capacity of the vegetal cover-interception accounts for a sub- stantial amount of the annual rainfall on Cibecue Ridge. Interception may be considered a form of storage: raindrops from a storm are intercepted and stored on the surface of the vegetation until retention capacity is reached. When saturation or filling of the leaves has taken place, subsequent interception is close to nil. Wind and evaporation affect interception. _ Wind tends to keep the vegetation from becoming saturated and because of evaporation more rain is required before the leaves reach their saturation point. The measure- ment of evaporation during a storm is extremely difficult; however, in this study evaporation was considered to be a negligible factor during a storm event, and any errors introduced by ignoring evapora- tion are minor. EXPERIMENTAL PROCEDURE In the spring of 1963 a sampling experiment was devised to measure precipitation throughfall in a juniper and pinyon woodland. The experimental procedure consisted of stratified random sampling (table 1); the strata used were as follows: Tree types: Utah juniper Pinyon Others ! Tree sizes (diameter of bole, in inches): 1-3 3-10 y10 ' Trees other than juniper and pinyon were sampled (table 1) but were not included in the main part of the analysis because of their small percentage of areal cover. VEGETATION AND HYDROLOGIC PHENOMENA Fraction of the distance of gage from tree bole to edge of crown cover: ¥ (distance A) % (distance B) % (distance C) % (distance G; considered within throughfall area because of shadow effect of a tree (Penman, 1963, p. 9)) Direction of gage in relation to tree bole: North East South West The dominant tree type, the dominant size, and the percentage of areal cover occupied by each type were determined from 15 vegetation transects by F. A. Branson for the 63-acre drainage basin on Cibicue Ridge. From the vegetation transects a study was TABLE 1.-Location and arrangement of rain gages used to measure throughfall in the Cibecue Ridge area [Distance: A, 14 the distance from the tree bole to the edge of the crown cover; B, 24 the distance from the tree bole to the edge of the crown cover; C, at the edge of the crown cover; G, %4, or 14, beyond the edge of cover. Direction: N, north; S, south; E, east; W, west] Tree Relation of gage to tree bole Gage Type Size class |Direction| Distance (inches) 1 AZZ ce- ece ber >10 | E C 2 | Arizona white oak .. 1-3 | N A 3 | Juniper...... 1-3 | E A 4 | Pinyon.. 1-3 | W G 5 | Scrub oak ! Large | N G 6 | Juniper.. 1-3 | N G {| B} |g §: |PPIMNON . 1 221 2 CT Gan eva aie - 9 1.c.zs ¥1 I Lee IAL v ate sise bid 1-3 | S8 G 10° | JUNIDET- S.:. con cote ee o nabs aaa as >10 | N B 11 | ere oases 1-3 | 8 A 12 do. 1-3,| 8 B 13 | Scrub oak. ' Large | N A 14 | Juniper 3-10 | E B 15 3-10 | E G 16 <1 | E B 17. | 22. 03. osu ev oo cen 3-10 | N G 18 | 1-3 | E C 10] .s cccer ied cel uns cen em 1-3 | N A 20 (. 01s N0. Crisco. leve as oue 3-10 | W B Pl {.c docs.... 3-10 | S G 39.| MANSAMINR_. .... cl w C 28 | 1-3 | E B 24 i 3-10 | S A 25 | N A 20:1: (10... 1. o Ion ou ee cnt epee c el oss suna soe E B 27 | Juniper... 3-10 | W G :-... do. .. 3-10 | 8 B 20 {-...- do... 1-3 | 8 C 80 | <1 | N A 31 | Arizona white oak.. 1-3 | 8 C 32 >10 | S G 33 3-10 | E A 34 3-10 | S A 35 3-10 | W C 36 3-10 | W A 37 3-10 | N A 38 3-10 | W B 30 1-3 | W A 40 3-10 | N B 41 1-3 | E G 42 1-3 | N B 43 A 3-10 | E C 44 |--... do. s >10 | W A 45 | Scrub oak. ___|! Medium | W C 46 | Juniper...... 1-3 | W B M7! do... Tees 3-10 | S C 48 |- Lc .A Cl 3-10 | N C 1 A large oak is >6 in. in diameter; a medium oak is 1 to 6 in. in diameter. THROUGHFALL IN A JUNIPER AND PINYON WOODLAND, CIBECUE RIDGE, ARIZONA made of tree height, areal extent of crown cover, and tree volume in relation to the bole diameter of given types. The findings show that the bole diameters of the trees studied have nearly the same percentage relation to dominance within a given tree type with respect to the magnitude of tree height and volume and to percentage of areal cover. Therefore, tree diameters were used to place rain gages at localities where the most abundant size class occurred within a type group. On the basis of percentage of areal cover, an allotted number of rain gages was assigned each tree size within that type (table 1). The trees were picked at random within a predetermined 15-acre area of the 63-acre drainage basin. Wedge-type rain gages were used to measure the throughfall. Two 8-inch standard rain gages were used to measure the total precipitation in the open, and a weighing-type recording gage was used to dis- tinguish between the different storms by giving the storm time. Table 1 shows the number and relative location of the rain gages used to measure throughfall. Storm events were recorded from July through September. Many small storm events were not used in the study because of inaccuracies introduced in measuring very small amounts of precipitation. All storms with throughfalls of zero or a trace of precipita- tion were omitted. Immediately after or very soon after a storm, the gages were read and emptied to minimize the error caused by evaporation and to insure that data were related to individual storm events. Olive oil was used in the gages to suppress evaporation. Storm intensities were not measured. The storms analyzed were all high-intensity summer thunderstorms. DEFINITIONS AND ASSUMPTIONS In this investigation all the analyses used to study throughfall are based on the assumption that the data are normally distributed. Common logarithmic trans- formations were used in parts of the analysis to reduce interactions or to more closely approximate the normal distribution and to stabilize the variance (Cramer, 1946, p. 397). The assumption of normality was tested by plotting on normal probability paper the cumulative probability distributions of the (1) log of juniper throughfall, (2) log of pinyon throughfall, and (3) log of total precipitation and the throughfall (not trans- formed) of juniper and pinyon trees combined for one storm group. The plotting position used was (M- 4)/N (Hazen formula) where M is the order of magnitude and N is the number of events. On normal probability paper a normal distribution plots as a straight line. The normal distribution fits the data fairly well in the cases tested. B3 The data for individual storm groups were studied (table 3), and each group, when the data were plotted on probability distribution paper, approximated a normal distribution without the use of transformations. To evaluate interaction between variables, storms of about equal total precipitation (within measurable error) were grouped. Interaction is an estimate of variance used to test the differences between means that cannot be accounted for by shifts in, say for example, the means of tree size, direction, and distance. Zero interaction would be indicative of an additive model- that is, the effect of any one factor, say tree size, on throughfall is not related to magnitude of any other factor, say direction. However, additivity was accepted only because interaction was ruled out by the appro- priate F test, both the F' test and the assumption of additivity are invalid if significant interaction does exist. - Thus, if interaction does exist and is not evalu- ated, it is treated as part of the error (within group) component, in which case the mean square ratios of the variables do not follow the F' distribution used to test the variables (Brownlee, 1960, p. 373; Dixon and Massey, 1957, p. 166; Scheffe, 1961, p. 124). ANALYSIS Throughfall was related to storm precipitation for both juniper and pinyon, and the results are shown in figures 2 and 3. - The equations for the curves in figures 2 and 3 are similar. A regression equation of the rela- tion of juniper throughfall to pinyon throughfall was computed as T,=0,.09 17°. Neither the slope nor the intercept is significantly different from 1.0. Statistical analysis indicates no significant difference between juniper and pinyon throughfalls (table 2); one curve may best be used to describe the precipitation-throughfall relation for both tree types. The plot of total precipitation versus the throughfall for juniper and pinyon is shown in figure 4. The equation of the curve is **, The standard error of estimate is +-12.2 percent and -11.0 percent (0.049 log units) with a coefficient of correlation of 0.994. - For a 1-inch rainfall, this standard error would give a range in throughfall from 0.78 to 0.98 inch. The throughfall data (table 3) for both juniper and pinyon are used in an analysis to determine the effect of : (1) the storm event (the storms were grouped into size classes, each class having several throughfall events with the same total precipitation, as in table 3), (2) di- rection of gage from tree (table 1), (3) tree type (this B4 JUNIPER THROUGHFALL ( T, ), IN INCHES 4.0 3.0 2.0 1.0 o in 0.1 0.05 VEGETATION AND HYDROLOGIC PHENOMENA | | Equation: T, = 0.879 Standard error= 0.0586 log units, + 14.9 percent -13.0 percent Correlation coefficient= 0.991 /./ Standard error | | 0.1 PRECIPITATION (PJ, IN INCHES 0.5 FiGURE 2.-Precipitation-throughfall relation for juniper. 1.0 2.0 3.0 PINYON THROUGHFALL (% ), IN INCHES THROUGHFALL IN A JUNIPER AND PINYON WOODLAND, CIBECUE RIDGE, ARIZONA B5 4.0 f 473 | | | | § 3] 30 // Equation: T. = 0.0867P +47 / / Standard error =0.0398 log units, + 10.0 percent -9.0 percent / Correlation coefficient=0.996 / 2 2.0 /, ok // Bf ft? 1.0 2 _ f / t - fk & s - /’// a Le... a /. /‘ Gel ® 0.5 7 s L. "3 0.1 fe / / AL. 0.05 #14 s Standard error F l _ | | Fst { l 0.1 0.5 1.0 2.0 3.0 PRECIPITATION (P), IN INCHES FIGURE 3.-Precipitation-throughfall relation for pinyon. 791-599 O-66--2 B6 4.0 VEGETATION AND HYDROLOGIC PHENOMENA je | | (33 3.0 2.0 1.0 0.5 THROUGHFALL (T), IN INCHES 0.1 0.05 Equation: T =0.873P 156 Standard error =0.0486 log units, +12.2 Correlation coefficient =0.994 percent -11.0 percent x Juniper ® Pinyon /‘ * f Lofi // A7 a AAA 3 2 / a 4". /// a We 4 P fa Zf a Z ff. Larf. Lf r © y" 7 fa 227. X PA * o= $+ # // = X// x = f 77 Standard ask [l | | Lied 4 0.1 s 0.5 1.0 2.0 30 FiGURE 4.-Precipitation-throughfall relation for juniper and pinyon. PRECIPITATION (P), IN INCHES THROUGHFALL IN A JUNIPER AND PINYON WOODLAND, CIBECUE RIDGE, ARIZONA TaBu® 2.-Covariance analysis, test of the regressions of precipita- tion versus throughfall of juniper trees and of pinyon trees [P, precipitation; T, throughfall] Sum of squares Source of variance ZP ZPT 2T: about regression line Within each group: Juniper... 2.44231 | 2.84778 | 3.37878 0. 05822 Pinyon .... 2.44231 | 2.80069 | 3.23838 . 02672 Among means -|. "0 0 -. 00010 -. 00010 Within ..... 4.88462 | 5.64847 | 6.61716 . 08539 eco i.. cl lens el cecewe cues 4.88462 | 5.64847 | 6.61706 08529 NotE.-Tests: For difference in means, F'=-0.04 (not significant). Whether one regression line can be used for all observations, F=-0.07 (not significant). is another test to see if juniper and pinyon throughfall are different), (4) tree size (trees with boles 1-3 and 3-10 in. in diameter were tested), and (5) the distance that _- the rain gage is located from the tree bole (table 1). Five groups of events (the 0.76-, 0.60-, 0.42-, 0.28-, and 0.12-in. storm groups) with replications were analyzed using a three-way analysis of variance (table 4). The mathematical model underlying the first three-way analysis of variance is Ttflw=fl+Et+D1+t7c+ (ED) 41+ (E15) ik +(Dt)jk+(EDt) inc-+1111“; where T ;;,,-an individual throughfall measure- ment, u=aA fixed value representing the gen- eral mean of the throughfall, E,;=the random effect associated with storm event, D,=the fixed effect due to gage direc- tion, t,=the fixed effect of tree type, (ED) 1;, (Et) is, and (Dt),,=two-way interactions of indicated variables, (EDt);,,=-three-way interaction of indicated variables, and ei;.1-random component or error term. The analyses of the five storm groups are summarized in the upper part of table 4. Because E is a random effect and D and t are fixed effects, the F ratio was obtained by testing E, ED, Et, and ED¢t against the within-group mean square, D and t against ED and Et respectively, and Df against interaction ED¢ (Scheffe, 1961, p. 274). E was found to differ for small-storm groups but not enough to warrant concern. The errors introduced in measuring small storms become rather great percent- agewise; for example, the component of variance B7 (az") was calculated for both the 0.28- and 0.12-inch storm events as 0.0009 and 0.0004 inch, respectively. Because the analysis indicated that the events do not differ within the storm group, it may be assumed that the classification of storms into groups provides replica- tion (more than one throughfall measurement for a given size storm) which may be used to define the sam- pling error for testing the other variables. This analysis showed further that the tree types did not differ more than would be expected by chance, and thus further indicated that the throughfall for juniper and pinyon trees is the same. To investigate other variables and test the direction (D) by a more sensitive method, a second three-way analysis of variance was made on the five storm groups used in the upper part of table 4. The mathematical model used was Tim: Ari-DH“ dek+ (DS)/u+ (Dd) ik . (Sd) jk+ (DSd) 4115+ €ijko where Ty.,=an individual throughfall measure- ment, u=a fixed value representing the general mean of the throughfall, D,=a fixed effect due to gage direction, S,=a fixed effect representing through- fall for different tree-bole diam- eters, d;=a fixed effect due to rain-gage distance from the tree bole, (BS) +D (Dd) ik» and (Sd),,=two-way interaction of variables, (DSd);;,=three-way interaction of the vari- ables, and component or error term. The analyses for the 0.76-, 0.60-, 0.42-, 0.28, and 0.12- inch storm groups-using D, S, and d as variablee- are summarized in the lower part of table 4. The three variables are fixed values and, therefore, were all tested using the error or within-groups mean square. Statistical tests showed that (1) the amount of throughfall a gage catches is a function of the direction of the gage in relation to the tree bole, (2) the size of the tree bole (1-3 and 3-10 in. in diameter) was found not to affect the amount of throughfall from a given size storm, (3) the distance that the gage is located from the tree bole did not vary the throughfall catch more than would be expected by chance for the 0.76-inch storm group but did more strongly affect throughfall for the 0.60-, 0.28-, and 0.12-inch storm groups, and (4) the combined effect of direction and distance was VEGETATION AND HYDROLOGIC PHENOMENA B8 *qn0 poyssA 9885) ; a €1' €1' 08 ® 1C' a 08 ® 80 ° G' | SI * "( 90° :| 10 | PE Su S1 cL ¥". | 1G. 81° | 10° | 20° | II' | 02° go' 98° 08 * 99° F9 ° 1€" 08" 88° | 8¢° ~ -| 06 :] 8C ' | 9C: " Lar" C| OP": | 1€" tg' | - | SE" | 64°: | 96° 99 ° 18° 69° 19° 99 ° 99 ° 09 ° 8€ ° | "< PSC -| TB" 1 06: C. l IF" | CL" -| 60" OL | 98 | w* | 19° | 290° 99 ° 94° 84° CL 0L® 99 ° 08 ' 28° | 6° * ~LAF' -| 00" - 1 £6" * | 98° | 90 'T | 28" &' | 86° | 6r° | 90 'I | 08* 16° A4* 98" 98° 06 ' 16° 98° 19° $6 | 8" * | 6€' | & | IL" * | &' | OCT | go' 96° | 88° | Ol' | 88° | 00 'I €9 'I ILT 61 'T OP 'I 11 '1 8p 'I 84° 90 'I Lass "I | 89° | KEL | 981 "I | €1'T | 08 T | $6 FL | 28 T | 91 CT | aP I | 99°T 90 'C TL 'T 28°C 00 °C OT 'C 10 C OZ 'I FLT 98 I | 00 'C 'I | 60 'I | 80 2 | 982 'c | 09°C | () | 99° 99 'I | 80 °€ | F6°I | | Sr Z (4 10° 80 ° TH €1° SI 60 ° 90 ' ZI* | 80° * | 10° | 60° LOL. *. 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The effect of direction on throughfall in the Cibecue Ridge area may be explained as follows: (1) the summer-thunderstorm clouds have a tendency to form above the Mogollon Rim, to the north and east of Cibecue Ridge, and to propagate over the area where rainfall occurs and (2) the tree foliage may be thicker in one direction than in the others. Local areas of throughfall concentration were attributed by Horton (1919) to the variation in density of the foliage. Having determined that direction, distance, and the combined effect of direction and distance have a significant effect on throughfall, the next step is to compare and test for the elements of direction and of distance that are causing the difference in the catch of throughfall gages. This is accomplished by using appropriate orthogonal (independent) contrasts and statistical tests. All contrasts were tested against the error or the within-group mean square of the three-way analysis of variance used for a particular storm group. The coefficients of each set of contrasts define orthogonal contrasts because the sum of each contrast is equal to zero and the sum of the products of the three contrasts is equal to zero. The sum of squares for each contrast in any storm group added together equals the unpar- titioned sum of squares for the variable used in the three-way analysis of variance (table 4, lower part). Thus, the error in mean square for a given storm group may be used for the F' test. Three contrasts for each of four storm groups using direction as the significant variable and for each of three storm groups using distance as the significant variable were considered. (See table 5.) The direction con- trasts (table 5, upper part) indicate that: (1) the north side of the tree does not have more variance in through- fall than the east side, (2) the south side has significantly less throughfall than the north and east sides of the tree for the 0.42-inch storm group, but not for the 0.76-, 0.60-, and 0.28-inch storm groups, and (3) the west side has throughfall significantly different from that of the north, east, and south sides. The distance contrasts (table 5, lower part) indicate that: (1) the two gages nearest the tree bole do not have significantly different throughfall, (2) the gage at the edge of the tree receives throughfall which is significantly different for the 0.60- inch and 0.28-inch storm groups and not significantly different for the 0.12-inch storm group when compared with the throughfall received by the two gages nearest the tree bole, and (3) the gage at G distance has a greater difference in throughfall than would be expected for the 0.28- and 0.12-inch storm groups when compared with throughfall at the A, B, and C distances. The distance contrasts indicate that the amount of VEGETATION AND HYDROLOGIC PHENOMENA TaBus® 5.-Orthogonal contrasts of significant variables [X indicates significant result] Contrasts for Result of Foss test on Situation indicated direction of gage indicated storm group, in inches describid in t 2. North | East | South | West | 0.76 0. 60 0. 42 0. 28 ) ns. 1 -1 0 og | ae enh c 1 1 -2 0 X X X 1 1 1 -3 X X X X Contrasts for indicated distance from tree bole A B C G 0. 60 0. 28 0.12 1 -1 0 0, Inc dene eleteedent 1 1 -2 0 X H B ce- i 1 1 8 bs xX throughfall received by a gage at distance C is sig- nificantly different from that received by gages at distances A and B for the larger storm groups tested. It may be that during the 0.12-inch storms a gage at distance C received a drip that did not cause a sig- nificant variation in throughfall; however, during the 0.28- and 0.60-inch storms the leaf capacity was filled and drip added a significant amount of throughfall. A gage at G distance would be subjected to greater wind currents; if wind currents increase catch, then the smaller storms, which would logically occur over a shorter time period (assuming that all summer storms have fairly uniform intensities), would have more chance for significantly different throughfall. The same contrasts used to compare the elements of direction and distance were used to compare the ele- ments of the two-way interaction, direction times distance. The 0.76-inch storm group was investigated by partitioning of the sum of squares for the inter-action into orthogonal contrasts for the given storm group. The orthogonal contrasts of the combined effect of direction and distance indicate that the gage nearest to the tree bole on the east side and the gage at distance G on the north side receive throughfall amounts that are significantly different from those received at gages located at other combinations of distance and direction. The effects of direction and distance on throughfall are confirmed by Stout and McMahon (1961) who found that there is a significant difference in through- fall with respect to distance and direction from the tree bole and by Beall (1934) who noted that throughfall is less near the bole than near the edge of the crown cover. Woody plants other than Utah juniper and pinyon were sampled (table 1) for amount of throughfall re- ceived. Curves showing the relation of precipitation to throughfall for oak tree and manzanita bush are shown in figure 5. The equation for the precipitation (P) versus oak-tree throughfall (T,) is T,=0.744P'*" THROUGHFALL (T, ) AND (T.,), IN INCHES THROUGHFALL IN A JUNIPER AND PINYON WOODLAND, CIBECUE RIDGE, ARIZONA 4.0 [ 3.0 2.0 Equations: T.= 0744 p02 Standard error=0.0401 log units, +10.0 percent -9.0 percent T.. = 0.917 p99 Standard error= 0.0386 log units, + 9.7 percent - 8.9 percent * Oaks (T,) x Manzanita (T,,) 1.0 0 in 0.05 PRECIPITATION (P), IN INCHES FIGURE 5.-Precipitation-throughifall relation for oak trees and manzanita bushes. B11 30 B12 with a standard error of estimate of {+10.0 percent and -9.0 percent (0.0401 log units). The broad-leaved oak trees permit less throughfall (0.74 in.) for a 1-inch storm than the needle-leaf juniper and pinyon trees (0.87 in.). Coffay (1962) found the equation for broad- leaved species to be T =0.834P:48 with a standard error of about +19 percent and -16 percent. The equation for the precipitation (P) versus manzanita-bush throughfall (7,,) is °° with a standard error of +9.7 percent and -8.9 percent (0.0386 log units). The curve for precipitation versus manzanita-bush throughfall probably is influenced by precipitation ground splash. All the gages used to measure manzanita-bush throughfall were 18 inches from the ground to enable placement of the gages below the leafy part of the bush. RELATION OF THROUGHFALL, STEMFLOW, INTERCEPTION, AND PRECIPITATION The relation between throughfall (T), stemflow (8), interception (Z), and precipitation (P) may be shown by the equation T=P-S-I. The amount of throughfall is equal to the amount of precipitation minus the quantity of water which reaches the ground by running down the stem of the tree minus the amount of the precipitation stopped by the leaves of the tree. Stemflow was measured on nine trees, six Utah junipers and three pinyons, ranging in diameter from 0.30 feet to 1.3 feet. Stemflow increases slightly with decreasing tree diameter. The stemflow of a tree hav- ing a 4-inch bole diameter is used to show the relation between throughfall, stemflow, and interception, as follows: The relation of precipitation to stemflow was found to be *S. The equation for the precipitation-throughfall relation was found to be T=0. 87 P". By substitution, the relation between precipitation and interception is I., By rearranging terms, the equation becomes Iz=P=-0.09P'**-0.87 P*. VEGETATION AND HYDROLOGIC PHENOMENA Figure 6 graphs th~ preceding equation and shows that interception i. cr-ases rapidly in the first part of a storm and reaches a maximum (0.072-in.) after 0.50- inch of precipitation. The mathematical curve can continue until negative interception is indicated. However, each constant is subject to error, and is defined only over the range of precipitation used. Therefore, the derived equation has a mean-square deviation of sample points from the estimated regres- sion line at least equal to the sum of the mean-square deviations of each of the component equations. None of the curves of these equations may be extrapolated, for each would result in conclusions such as throughfall and stemflow being greater than precipitation or nega- tive interception. Theoretically, after the leaves have become filled and precipitation increases, it is not unreasonable for the curve to approach a constant limiting value of I (Penman, 1963, p. 14) ; interception would be zaro for the remainder of the storm. The dashed line on figure 6 is an estimate of uniform condi- tions. The relation would be expected to vary in the late stages of a storm because of climatic forces such as wind. w Lu al EXPLANATION Z Interception (| )= precipitation ( P )- stemflow - throughfall m 1= P- 0.09P'*5-0.87P ® for P<0.5 inches __ 0.10 y - buss ma me a me me me in me me dakatatatabn - a A o - 0.05 a. a - LJ 6 - ; - - g.. ¢ Arul sig cf SLS cL L _L t eA OL Lick cL cd ~-. c - oen «cars 1 l e an a saan, pa caren § ST Earlywood growth of chestnut oaks CO-58 and 2 co-sy...:._.l. ._ HL LML L Pr. 16 Phostudy .e. 2! Discontinuous cll 19 Phe study ._ 3 | 40 DLL 26 Description Of Lrees -- _ .._ _ ... c 22 len eee wale ans bean 3 | List Ol rink 27. Measurement 5 | References cited_......._. inca 27 ILLUSTRATIONS Page FiGurE 1. Photograph of lower northeast-facing slope C2 2. Photograph of middle southwest-facing slope vegetation. 3 Si ketch showing part of cross-valley transect... .. LLL in. rnam ariens ns sald anl ate ad 4 4. Sketch of tree stem illustrating hypothesized three-dimensional relationships between rings and annual ones uc ont ss anser esses s 6 5-8. Graph showing ring-width sequences of- 5. Red maple RM-18 plotted by year of ring ts 8 6. Red maple RM-61 plotted by year of ring formation. 9 7. Red maple RM-18 plotted by ring number from center of cross section. 10 8. Red maple RM-61 plotted by ring number from center of cross 11 9. Diagram showing stem shape of red maples RM-18 and RM-61 at 10-year intervals. __________________ 12 10-13. Graph showing- 10. Height growth 'of the four sample _L cL LLL OILS 12 11. Ring-area growth of ted maple RM-18:}________._lll.olc B __ 13 12. Ring-area growth of red maple ses 14 13. Diagrams showing vertical distribution of annual ring-area 15 14-19. Graph showing- 14. Ten-year ring-area growth increments of red maples RM-18 and 16 15. Growth rates of a chestnut oak and a red maple, 19059-............_.._..l..l . 17 16. Annual ring-width sequences of chestnut oak 18 17.) Annual ring-width sequences of chestnut oak si uaineesews 19 18. Frequency distribution of earlywood width 20 19. Ring-area growth sequences of earlywood and latewood, and generalized curve of total ring-area growth of. chestnut oak .... coc. Xl LEL. en danken an awan. c s ba m 23 20. Sketch of diagrammatic representation of discontinuity of outer 10 rings at 6-foot level of red maple RM-18. _ 24 21. Diagrams of discontinuous growth of individual rings of red maple RM-18-____________________________ 25 III GLOSSARY Annual increment.-The three-dimensional sheath of xylem added to stems and secondary roots each year. The annual increment has the appearance of a ring (annual ring) when viewed in cross section. Auxins.-Growth regulators, such as hormones, affecting cell enlargement. Basipetal.-Proceeding from the top toward the base. Cambial activity.-The process by which cambial initials divide and form derivatives which differentiate into phloem cells outward from the cambium or xylem cells inward from the cambium. Cambium.-A tissue in many higher plants, including trees, in which cells divide and form new tissues. The cambium is located in stems and woody roots (not in stem tips and root tips) between the wood (xylem) and inner bark (phloem). Canopy.-The uppermost level of tree crowns in a forest. All tree crowns in the canopy level are exposed, at least in part, to direct sunlight. Conifer.-Any cone-bearing tree (most of which trees retain their leaves, or needles, throughout the year) such as pine and hemlock. Crown.-The part of a tree that includes leaf-bearing branches. There may or may not be a distinct branch- free trunk below the crown and a single main stem which may or may not be distinguishable in the crown (of deciduous trees). Dbh.-Diameter at breast height. The approximate height (4% ft above the ground) which is standard for diameter measurements of tree trunks. Deciduous tree.-Tree, such as oak and hickory, which normally produces new leaves every spring, loses them in the fall of the same year, and overwinters in a leafless condition. Dendrograph.-Instrument attached to a tree to obtain continuous records of radial growth (actually, radial change) and to record the measurements on a chart automatically. Dendrometer.-A nonrecording instrument used to obtain periodic measurements of change in a radius of a tree trunk. Diffuse-porous wood.-Wood in which the vessels are of fairly uniform size and distributed throughout each annual increment, as in red maple and birch. Early wood.-Inner part of an annual ring which, in a ring-porous species, contains much larger vessels than are in the outer, or latewood, part of the ring. - Earlywood is recognized in diffuse-porous and nonporous woods by density, cell size, cell-wall thickness, and color variations. Growth.-Increase in size by addition of new cells or cellular material. Growth regulators.-Organic compounds produced by the tree, which increase and (or) decrease growth rates by affecting physiological processes which control cell division, enlargement, and differentiation. Auxins and hormones are examples of growth regulators. Internode.-That part of a stem between nodes. Latewood.-The outer part of an annual ring. See "earlywood." Main stem.-The stem along the main axis of a tree which is or may become part of the tree trunk. Node.-The point on a stem at which leaves and (or) branches arise or have arisen. IV GLOSSARY v Nonporous wood.-Wood of conifers which does not contain vessels, as in pine or hemlock. Phloem.-Food-conducting tissue which constitutes most of the inner bark and is located between the cambium and the outer bark. Radial growth.-Increase in radius at a given height. Total radial-growth increment of a given year (minus bark increment) is ring width of that year. Release.-A change in the external environment of a tree that reduces competition with other trees, as would result if the surrounding trees were removed. Decrease in suppression. Ring.-T'wo-dimensional cross section of an annual increment. Ring-porous wood.-Wood in which the vessels are of two distinct sizes, the larger being only in the inner {early- wood) part of the annual increment, as in oaks and hickories. Stem.-Any of the above-ground parts of a tree which bear or have borne buds and leaves. The trunk and all branches are stems. Subcanopy.-The lower part of the forest canopy. Trees located in the subcanopy are those whose crowns reach the lower level of the forest canopy. Suppression.-A condition of growth retardation usually associated with competition. Terminal growth increment.-An annual increment of longitudinal growth of the main stem. Trunk.-The main stem of a tree; generally the branch-free part below the crown. Xylem.-Water-conducting tissue of most plants and supporting tissue (wood) of trees. Develops inward from the cambium. VEGETATION AND HYDROLOGIC PHENOMENA ANNUAL GROWTH OF SUPPRESSED CHESTNUT OAK AND RED MAPLE, A BASIS FOR HYDROLOGIC INFERENCE By Ricuarp L. PHrers ABSTRACT Three-dimensional shape of individual annual xylem growth increments was ascertained from dissected ring-porous chestnut oak and diffuse-porous red maple trees from a native forest in southeastern Ohio. The increments are near paraboloidal, local deviations from true paraboloid shape being characteristic. The red maple rings (in transverse cross section) are widest near the base of the crown, but display only a slight basipetal increase in cross-sectional area. An entire ring of red maple appears somewhat analogous to the latewood of chestnut oak, the early- wood of chestnut oak being unlike that of red maple. The width of earlywood of chestnut oak does not decrease, or decreases only slightly basipetally, and is thus associated with a pro- nounced basipetal increase in total ring cross-sectional area. Chestnut oak earlywood cells are hypothesized to have origi- nated prior to the current growth season. Earlywood growth thus appears to be affected by an entirely different set of hydro- logic conditions than red maple ring growth and chestnut oak latewood growth, which occur in late spring and early summer. Annual ring growth of red maple and latewood growth of chestnut oak appear to occur at a successively later time in the growth season with distance from the top of the tree. Since water, probably the most limiting factor to growth, is apparently not typically in limiting supply during the early part of the growth season, little or no growth reduction occurs in the upper part of the tree during even extreme drought years. However, growth reduction throughout the tree may occur during the year after a drought, as a result of the physiological damage caused by the drought. Suppression, such as is induced by en- croachment by surrounding trees, results in a similar decrease in growth at all heights which may be erroneously interpreted as resulting from several successive years of drought if rings from only one trunk level are examined. Release from sup- pression by surrounding trees and release from drought may pos- sibly be distinguishable if ring patterns from more than one level in the trunk are examined. - The interrelationships between earlywood and latewood formation in chestnut oak and the causal factors pursuant to variations in size of earlywood are not understood. Discontinuous or missing rings are noted in annual rings of red maple and in the latewood of chestnut oak, primarily in the lower parts of the trunk during years of less than typical amounts of growth. Trees not severely suppressed would be expected to contain few ring discontinuities, and thus would contain rings more suitable for analysis in regard to climatic conditions. -It is botanically impossible for an annual ring to be missing throughout the entire length of the tree, and no evidence was found to indicate discontinuous earlywood growth of chestnut oak. INTRODUCTION A thorough understanding of the relationships be- tween the growth of trees and their hydrologic environ- ment is necessary before tree rings may be utilized with any degree of reliability to infer hydrologic con- ditions. The achievement of such an understanding is far from simple. Dobbs (1951) stated that, in general, botanists and foresters "* * * have shown the least in- terest in the remarkable record which the tree leaves behind it in the wood. This is understandable because it is they who are most likely to realize the complexity of that record." Glock (1955) in a review on the sub- ject, stated that "* * * more and more * * * all workers have become impressed with the multiplicity of factors, the complexity of their interactions, and their detailed areal variability." The purpose of this report is to describe ring growth of two deciduous tree species from measurements at several positions along the trunks. From these descrip- tions, several hypotheses will be presented concerning various influences of the hydrologic environment on ring form and size. This report is of a very limited and generalized study, which serves as the foundation of a more extensive and intensive research program. The ultimate objective of the program is the accurate estimation of hydrologic conditions from tree-growth records (rings). If successful, long-term ring records can be used to extend hydrologic histories in time prior to current records wherever trees of sufficient age still exist. Short-term ring records, which are readily avail- able, may be used to estimate recent environmental con- ditions in areas where no hydrologic or climatologic data are available, such as in most first- and second- order stream valleys. Analysis of tree rings can also C1 C2 be used in studies of changes in environmental condi- tions other than hydrologic, such as are brought about by acid mine drainage and changes in land usage. ACKNOWLEDGMENTS The study was conducted through the facilities of the Neotoma Ecological and Bioclimatic Laboratory of The Ohio State University. During the study, the labora- tory was supported by the U.S. Atomic Energy Com- mission (contract No. AT(11-1)-552) through the Ohio Agricultural Experiment Station. Appreciation is expressed to the director of the laboratory, Dr. Gareth E. Gilbert, for his support and encourage- ment. Appreciation is expressed also to the owner of Neotoma valley, Dr. Edward S. Thomas, for the use of his land and for permission to remove the four trees utilized in these studies. This report is based on parts of a thesis presented in partial fulfillment of the requirements for the degree, Doctor of Philosophy, at The Ohio State University. Several members of the Department of Botany and Plant Pathology of The Ohio State University con- tributed helpful criticisms and suggestions at various stages in the research. Jerry A. Koch, Ronald L. Laughlin, and Victor L. Riemenschneider, of the Neo- toma Laboratory, were particularly helpful in interpre- tations of related studies. Without the special interest and support of Robert S. Sigafoos in all phases of the study, the expeditious completion of the work would not have been possible. THE STUDY AREA These studies were conducted in southeastern Ohio in a small valley named Neotoma, located in NE14 sec. 16, Good Hope Township, Hocking County (long. 82°33'18"" W.; lat. E.). The valley has been the location of ecological studies since the purchase of VEGETATION AND HYDROLOGIC PHENOMENA the land by Edward S. Thomas in 1922. Extensive microclimatic studies were begun by Wolfe and asso- ciates in the late 1980's (Wolfe and others, 1949). More recent ecological and bioenvironmental studies (Wolfe and Gilbert, 1956; Gilbert, 1961, 1964) have been pri- marily concerned with the central part of Neotoma, but have also resulted in detailed descriptions of bedrock, soils, glacial deposits, and vegetation of the entire valley. Neotoma lies just inside the western escarpment of the dissected Appalachian Plateau in southeastern Ohio. Bedrock of the Neotoma area is of two forma- tions of Mississippian age, Logan and Cuyahoga (Wolfe and others, 1962). At Neotoma the sandstone of the Logan caps the underlying Black Hand Sand- stone, but little of the Logan remains. Slight eastward dipping of all strata has affected the soil-moisture dis- tribution (Laughlin, 1964) and the vegetation distri- bution in the valley (Koch, 1964). Vegetation and distribution of soil types illustrate the diversity of habitats on the opposing slopes (figs. 1, 2). Generally, the upper slopes are dryer and con- tain coarser soils than the lower slopes, and the south- west-facing slope is dryer and has a somewhat more shallow soil than the northeast-facing slope (Riemen- schneider, 1964). A forest in which more than a third of the canopy- sized trees are chestnut oak occupies the upper fourth of the southwest-facing slope, the driest site below the rock cliffs. (Nomenclature of trees follows that used by Little (1953).) The soils of the chestnut oak area are a stony phase of DeKalb sandy loam, having inter- nal drainage probably faster than in the DeKalb soils downslope. Below the chestnut oak on the south west-facing slope is a forest of mixed oak trees. American chestnut was an important member of the forest until its death in. FicurE 1.-Lower northeast-facing slope vegetation (looking northward) through which cross-valley transect passes. Alan Heilman, Ohio State University, October 1958. Photograph by ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE FicurE 2.-Middle southwest-facing slope vegetation looking northwest from area through which cross-valley transect passes. Photograph by Alan Heilman, Ohio State University, October 1958. the late 1980's and early 1940's. Dominant canopy members now include scarlet oak, black oak, white oak, chestnut oak, and red maple-trees that were already present in the forest. The upper northeast-facing slope is occupied by a forest consisting mostly of chestnut oak, yellow poplar, and red maple. This forest grows on a Neotoma sandy- loam soil which is typically wetter than the DeKalb soil of the oak forest of the opposite slope and dryer than the Neotoma sandy loam of the lower northeast- facing slope. Neotoma is a name recently proposed as a new soil series for which Neotoma valley is the type location (Finney, 1959). The forest growing on the lower northeast-facing slope is the most luxuriant forest type of the area. Canopy dominants include red oak, red maple, chestnut oak, American beech, white ash, butternut, white oak, sweet birch, black cherry, and yellow poplar. Canopy associates include eastern hem- lock, mockernut hickory, black gum, sassafras, sugar maple, and black walnut. THE STUDY TREES DESCRIPTION OF TREES A 20-meter-wide transect was established across the valley from the southwest-facing cliff to the northeast- facing cliff. The transect was established for several uses in the overall tree-growth research program, a part of which is described in this report. All the trees of 1-inch dbh (diameter at breast height) and larger along a 20-meter segment of the transect near the middle of the southwest-facing slope are represented diagram- matically in figure 3. The figure illustrates the relative 243-554 O-67--2 density of tree stems and layering and overlapping of crowns. - The crown density was greater on the opposite slope. Across the entire transect, chestnut oak and red maple are the most numerous trees. Red maple, in 23 of the 34 plots of the transect, and chestnut oak, in 18 of the 34 plots, were chosen as the species for study. Red maple is a fast-growing deciduous species typi- cally associated with moist habitats, such as flood-plain forests, but capable of reproducing in a wide range of habitats in southeastern Ohio. Chestnut oak is the major tree species in forests on most dry ridges in sand- stone areas of southeastern Ohio. Chestnut oak is not found on flood plains, as red maple is, but grows in many valley-slope forests. Red maple is a diffuse-porous species; chestnut oak is ring porous (see glossary). A red maple and a chestnut oak were felled on each of two opposing slopes of Neotoma valley. Three of the trees were felled in September 1962. The fourth tree, a chestnut oak growing on the northeast-facing slope, was felled in February 1964. The four felled trees were subcanopy size and thus were expected to be characterized by a greater degree of suppression than canopy-sized trees. It was hypothesized that trees sub- jected to a high degree of suppression would be most likely to yield climatically "sensitive" rings, assuming that growth response to change in climatic factors would be magnified under conditions of growth stress. Thus, it was hoped that suppressed trees growing in the center of their range might be somewhat analogous to "sensitive" trees growing near the limits of their range. Red maple RM-18 was in the subcanopy level of the lower northeast-facing slope of the sampling transect. C4 VEGETATION AND HYDROLOGIC PHENOMENA FiGuRE 3.-Part of cross-valley transect on southwest-facing slope which included two of the trees felled for dissection. (The felled trees were a red maple (RM-61) and a chestnut oak (CO-37), shown with a dashed outline. Other trees are indicated as follows: CO, chest- nut oak; RM, red maple; BO, black oak; WO, white oak; BA, bigtooth aspen; SW, sourwood; DW, dogwood; BG, black gum. ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE RM-18 was overtopped by, and leaning slightly away from, a 16-inch dbh white oak canopy tree about 11 feet upslope and to the northwest. Two other canopy trees, a 10-inch mockernut hickory and a 9-inch white oak, partially overtopped RM-18. Removal of RM-18 made no hole in the canopy-evidence that all of the crown was overtopped. The main stem was forked at about 10 feet from the live top. One branch, about 16 feet in length, was dead. Death of the branch may have been attributable to overtopping by surrounding trees. The live branch may not have begun growth until after death of the other branch. Probably at least as ecologically significant in reducing soil moisture as the shading of RM-18 was the indirect effect of the large white oak upslope. Red maple RM-61 was a subcanopy tree near the up- per limit of the mixed oak forest of the southwest-fac- ing slope (fig. 3). Like its counterpart (RM-18) on the opposite slope, RM-61 leaned slightly away from a large 16-inch dbh white oak canopy tree about 15 feet upslope. Also within 15 feet were two canopy-sized black oaks, but most overtopping was by the white oak with a spreading crown more than 30 feet in diameter. Unlike RM-18, it appeared that at least part of the RM-61 crown was exposed to direct sunlight, and no death of major branches was noted. Chestnut oak CO-58 was a subcanopy tree on the up- per northeast-facing slope. It leaned away from, and was overtopped by, a double-trunked canopy-sized chest- nut oak about 20 feet upslope. It leaned into the lower part of the crown of an 8-inch dbh canopy-sized black oak about 8 feet away. Some of the terminal branches of CO-58 that were enmeshed in the black oak crown were dead, and lateral branches had become terminal leaders. The height of the dead branches was just above 30 feet. No samples were taken above this height. Chestnut oak CO-37 was a subcanopy tree on the southwest-facing slope (fig. 3). It leaned slightly away from, and was only partially overtopped by, the same large white oak tree that almost compltely overtopped RM-61. Other than the white oak, the closest tree of any size was an 8-inch canopy-sized black oak about 16 feet upslope. The crown of CO-37 was probably more directly exposed to solar radiation than the crowns of any of the other three sample trees. A brief comparison of the four study trees follows: Red maple Chestnut oak RM-18 | RM-61 CO-58 | CO-37 cs rece choc ene en e inches 4 3 5 4 Branch-free height......__..________ 33 24 33 27 Dota do... & 45 32 51 43 Estimated crown diameter.... ___. do...: 10 10 12 6 ABE IAE Res dC ul years .. 67 49 53 44 C5 Average height growth for the entire life of the trees was about 1 foot per year for chestnut oak on both slopes and about % foot per year for red maple on both slopes. Average yearly cross-sectional area increment at breast height was greater in the northeast-facing-slope study trees than in their southwest-facing-slope counterparts. However, inasmuch as such yearly averages of the trees are based on totals of all past main-stem growth, they are of value only in comparing present size of the trees. If, on the other hand, closeness of other trees, degree of overtopping, and death of major branches give some in- dication of present relative suppression of the trees, then, at the time of cutting, the study trees RM-18 and CO-58 on the moist northeast-facing slope were more suppressed than RM-61 and CO-37 on the opposite slope. MEASUREMENT METHODS The trees were cut as close to ground level as practi- cable, and cross sections 1-2 inches thick were removed at 3-foot intervals from the base to above the lowest major branching of the crown. Each cross section was marked upon removal to show the north side of the standing tree and the top side of the section. The sec- tions were air dried, sanded, and polished. A reference line was inscribed with a knife along each radius to be measured. Recent studies of rings at more than one sample height have been performed with red and loblolly pines (Duff and Nolan, 1953, 1957; Smith and Wilsie, 1961) from which cross sections were taken along the main stem halfway between each set of annual branch whorls. Because annual terminal-growth increments are dis- tinguishable only near the ends of branches on decidu- ous trees such as red maple and chestnut oak, sampling of every annual terminal-growth increment is not prac- ticable. It was believed that sampling at equidistant intervals might provide a means of analyzing growth allegedly induced as a result of nutrient or growth reg- ulator gradients or both. Ring width of RM-18 was measured along the north- and upslope-facing radii (approximately 135° apart). Annual-ring width measurements along the two radii were of sufficient difference that two additional radii were measured. Measurements of sections of the three remaining trees were taken along radii of the four major compass directions. The width of the annual rings in the cross sections was measured to the nearest thousandth of an inch by the use of a mechanical stage equipped with a dial indi- cator. Parts:-of some cross sections were remeasured from time to time and at various positions in the range of the micrometer, and were always within 0.002 inch of the original reading. This slight range indicated VEGETATION AND HYDROLOGIC PHENOMENA suupe - -_ -- Suu vN|| FIGURE 4.-Tree stem illustrating hypothesized three-dimensional relationships between rings and annual increments. ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE that (1) the accuracy of readings was consistent throughout the range of the micrometer, (2) the meas- urement cut provided a sufficiently distinct reference to allow repetition of measurements, and (3) the shrink- ing and swelling of the dried sections during the period of measurements were insignificant. GROWTH FORM Metzger (1893), according to Larson (1963) and Biisgen and Miinch (1929), described tree-stem form as virtually that of a beam of uniform resistance to bending by wind. The beam thus described is a cubic paraboloid whose cubed diameter at any level is pro- portional to the distance from that level to the center of the tree crown. More recently, Gray (1956) sug- gested that the main stem of a tree may be described by a quadratic paraboloid. It should be noted that these workers did not describe individual annual increments as paraboloidal. Duff and Nolan (1953) described the characteristic patterns of annual rings in red pine and demonstrated that the general pattern from center out- ward at any given height progresses from wide rings to gradually narrower rings, and virtually the same pat- tern is found in any given annual increment progressing from the apex of the tree to the base. These findings were confirmed by Smith and Wilsie (1961) in work with loblolly pine. Neither Duff and Nolan nor Smith and Wilsie discussed the possibility of the paraboloid shape of individual annual increments or of the entire trunk, even though their descriptions satisfy the geome- try of paraboloids. If it is assumed (1) that the first few rings near the top of a small tree are the same shape as the first few rings near the top of a canopy-sized tree, that is, that the twigs are the same size and (2) that the annual increments are paraboloid, then it follows that all rings in a tree are of the same paraboloid shape. These as- sumptions, of course, presuppose that environmental conditions, and thus total annual growth, are the same from year to year. Under the above assumptions, the paraboloid patterns of annual increments of a stem grown under constant environmental conditions would be as illustrated in figure 4. Ring width of any given annual increment would be greatest near the apex of the annual increment and would become increasingly nar- row with distance from the apex. Ring width of the centermost annual increment at any height would be the same as the width of the centermost annual increment of any other height at the same vertical distance from the apex of that annual increment, the second ring from the center at any height would be the same width as the second ring from the center at any other height, and so forth. Thus, as illustrated in the two cross sections of CT figure 4, the third ring of the upper cross section is the same width as the third ring of the lower cross section, even though they were not formed during the same year. According to the conditions of the hypothesis, the outer surface of any given annual increment would be the same shape as that of any other annual increment, and growth in length each year, by addition of a new annual increment, would be constant. In longitudinal section, the parabola shape of the outside of an annual increment may be described by the standard parabola equation where 2r=parabola width, y=parabola length, and a=the constant, focal length. It follows that 2 (25) du, which satisfies the conditions of a quadratic paraboloid as applied to tree stems by Gray (1956). The trans- verse cross-sectional area of a paraboloid segment de- fined by the parabola of equations above is obtained by the use of the standard equation for the area of a circle, A= r". In cross section, ring area of a given ring, », becomes the difference in area between the cross section of the base of a paraboloid segment delimiting the outer sur- face of the mth annual increment and the cross section of the base of a paraboloid segment delimiting the outer surface of the preceding annual increment, »-1. Ac- cording to the hypothesis, the two segments are of the same paraboloid. If growth in length is a constant, s, from year to year, then of the paraboloid segment delimiting the outer surface of nth annual in- crement and s(n-1)=length of a paraboloid segment delimiting surface of 1»-1 annual increment, and A,= tr,", where r,"=asn, and Anr-i=1r.-i", where 7r,-1i*=as(n-1). Therefore, the cross-sectional area of the nth ring, R,,, is Rn=An—An~l =1[asn-as(n-1)]= 1(asn-asn-|- as) = Tas. Repeating the procedure for the area of the n»-1 ring yields An -1-Anr's =1[as(n-1)-as(n-2)] == Tas. C8 Thus, the cross-sectional area of any ring, ,, is equal to the cross-sectional area of the preceding ring at the same height, ,.,, providing that the annual increment of growth in length, s, remains constant. The same type of reasoning further indicates that the cross-sec- tional area of any ring at any height in the trunk should be the same as the cross-sectional area at any other height or in any other annual increment. This pattern is in agreement with the general statement of Pressler (1864) as noted by Larson (1963) that "* * * in all parts of the branch-free stem, ring area growth will be the same." Pressler apparently did not suggest a parab- . oloid shape of individual annual increments. Jaccard (1912) assumed that a constant cross-sectional area of a given annual increment at all heights was necessary so water conduction along the stem would not be im- peded. It is doubtful that Jaccard considered a con- stant cross-sectional area between rings at the same VEGETATION AND HYDROLOGIC PHENOMENA ment volume of any segment would be equal to the vol- ume of any other annual increment segment of equal length. If the basic annual increment pattern can be shown to be paraboloidal, then the paraboloid could be a useful tool as a mathematical model in analyses of tree rings and annual increments. ANNUAL INCREMENTS IN RED MAPLES RM-18 AND RM-61 Examination of the ring width sequence of a cross section of any level in the trunk of a tree reveals a time trend in ring width from wider rings near the center to narrower rings with increasing distance from the center (Douglass, 1986). If sequences of trees of various ages are plotted together by year of ring formation, inter- pretation of data of individual years is confounded be- cause the center rings of one tree (inherently wide) may have been formed during the same years that the height. The equations above show that annual incre- | outer rings (inherently narrow) of another tree were a | | | | | 1°0(-- #93 © 100 |- E- . ea x Height, in feet, of sample section { 80) -¥ -o- 30 --I ak (Z) O o -o- 24 F -o- 18 x 6 -p- 12 i- 0 5, 00 [- -o- 6 Es s o O z 0 T 40 L-- o " ted a © ® 20l-- y 3 / \. 6 | 1920 1930 1940 1960 YEAR OF RING FORMATION FiGURE 5.-Ring-width sequences of red maple RM-18 plotted by yéur of ring formation from cross sections at 6-foot intervals. are averages of measurements along four radii: north-facing, 112°, 225° (upslope-facing), and 337°. Data Date of center ring at each measurement: 1914 (6 ft), 1919 (12 ft), 1924 (18 ft), 1927 (24 ft), and 1932 (30 ft). ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE C9 100 § I [ Q (o o Height, in feet, of sample section 80 |- ~g-: 24 weed f =o- 18 O B -O- 12 I S 5 O 0 6 X g AQ L- d ne LJ R- o Z o z O C Q& p 3 Y A o = 40|- O - 3 [e] Z & D i ® 20 - * ® TA o a : 6 /“"{\ i/ f o J * Buf" f | | u J v I is 0 x 1920 1930 1940 1950 1960 YEAR OF RING FORMATION FIGURE 6.-Ring-width sequences of red maple RM-61 plotted by year of ring formation from cross sections at G6-foot intervals. Data are averages of measurements along radii of four major compass points. 1921 (6 ft), 1924 (12 ft), 1934 (19% ft), and 1938 (24 ft). formed. The same confusion is observed if ring se- quences from several heights in a tree are plotted to- gether (figs. 5, 6), because since center rings at an up- per level were formed during the same years as outer rings in the lower levels. Further complications arise if the inner rings at the upper levels are not inherently wide, as is apparently true of trees of the southwestern States (H. C. Fritts, written commun., December 1965). Alinement of sequences from a single tree by ring number from the center of each cross section super- imposes the time-trend curves. Such an alinement for red maple RM-18 is presented in figure 7 from sequences of figure 5. Alinement would permit exam- ination of the shape of the time-trend curve, if the curve is approximately the same shape at all stem heights. Superimposed on the sequence graphs of fig- ure 7 is a smooth curve representing ring widths de- termined from a series of perfect quadratic paraboloids of the shape delimited by the height and basal diameter of red maple RM-18. The smooted curve thus repre- sents the ring width sequence that RM-18 would have had if (1) the annual increment of height and of cross- sectional area from year to year had been constant dur- ing all of the 50 years represented, if (2) annual incre- Date of second ring from center at each measurement height: ment form were perfectly parabolic, and thus if (3) the time-trend curves were the same shape for cross sections at all stem heights. The greatest deviations from the smooth curve are the three peaks at rings 4, 9, and 13, and the apparent absence of growth at rings 28, 31, 36, and 41. - Figure 5 indicates that the three peaks of figure 7 all occurred between 1925 and 1927 when growth at all levels was great. Figure 5 also in- dicates that all four growth minima occurred during 1954. If these instances of extreme growth were re- moved from figure 7, the rest of the data would ap- proximate the smooth curve closely enough to suggest that, notwithstanding environmentally induced yearly variations in height and radial growth, annual growth increment may be somewhat parabolic. Data from red maple RM-61 (fig. 6) were also re- plotted by ring number from the center of each cross- section and are presented in figure 8 along with a smooth curve from data of a series of perfect paraboloids. Again, the ring-width data have some correspondence to the smooth curve. The most striking deviations oc- cur after the 23d ring. After that point, growth is consistently below the smooth curve, but reference to figure 6 indicates that all the rings formed after 1943 C10 VEGETATION AND HYDROLOGIC PHENOMENA 140 l 120 100 c o RING WIDTH, IN INCHES x 10~ a 6 p O 20 Height, in feet, of sample section -- 30 -o- 24 el -o- 18 -O- 12 -o- 6 RING NUMBER, FROM CENTER OF CROSS SECTION FIGURE 7.-Ring-width sequences of red maple RM-18 plotted by ring number from center of cross section. The smooth curve represents a ring width-sequence determined from a series to those of figure 5 plotted by year of ring formation. of paraboloids. were restricted in size. Something happened during or after 1943 which subsequently suppressed growth. An indication of the general stem shape or form of the two red maples is presented in figure 9. Average radius at each sample height is plotted for 10-year in- tervals, and the date of the center ring at each sample height is also included. Horizontal exaggeration of the figure is 36 times and consideration of stem form as anything other than cone-shaped seems unjustifiable. However, other than the 0- and 3-foot levels of RM-61 which are considered as butt swell, width of the 10-year increments is generally greatest at the top-a feature that supports the paraboloid hypothesis. An indication of changes in the rate of yearly height growth was obtained by noting the date of the center ring at each sample height in the study trees (fig. 10). All four trees were apparently growing rapidly in height by the time each was 6 feet tall, but the maples took considerably longer to reach this height than did the oaks. RM-18 appears to have remained in the for- The sequences are identical est understory for at least 20 years before commencing rapid height growth. Rate of height growth of all four trees appears to have declined at about the time the trees reached the lower part of the forest canopy (ap- proximately 25 feet). Death of uppermost branches of RM-18 and CO-58 occurred above the 25-foot height. According to the hypothesis of paraboloid shape, if yearly growth rate of a tree is constant, then the cross- sectional area of all rings (ring-area growth, 2) is a constant, the time trend being a straight line parallel to the abscissa. Early workers who described trunk shape as parabolic agreed that within the crown the form of the main stem probably more closely approximates that of a cone than a paraboloid (Biisgen and Miinch, 1929). Larson (1963), citing Pressler (1864), stated " * * * ring area growth (cross-sectional area of a single annual increment) at any given point on the stem is propor- tional to the quantity of foliage above this point." Thus, the point of maximum ring width would not be at the top of the tree as suggested in figure 4, but near the ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE C11 100 I I l 80 |- - m Height, in feet, of sample section o 24 X o -o- 18 al 5 -P- 12 a a wel | 6 @ > 56 = *= E fe] F & 20|- == o0 10 20 30 40 RING NUMBER, FROM CENTER OF CROSS SECTION FIGURE 8. -Ring-width sequences of red maple RM-61 plotted by ring number from center of cross section. The smooth curve represents a ring width sequence from a series of paraboloids. to those of figure 6 plotted by year of ring formation. base of the crown. Duff and Nolan (1957) found that the point of maximum ring width was in the region of the crown base but that the exact position varied slightly from year to year; it was lower in years of accelerated radial growth and higher in years of restricted radial growth. Ring-area growth, calculated from data of figures 7 and 8, are presented in figures 11 and 12. Ring-area growth from a series of perfect paraboloids defined by the height and basal diameter of the tree is included in each figure as a dotted line. Each dot thus represents ring-area growth of a single ring at any height and is equal to the average yearly ring-area growth at basal diameter height. Ring-area growth of the two red maples is indicated as consistently below hypothetical values for the first 4-6 rings. The combined data of the center six rings of figures 11 and 12 include rings rep- resenting all years from 1914 through 1942. It seems improbable that reduced growth of the first 6 rings at each level is the result of environment only. The first few rings at the center of each section would have been near the top of the tree when they were formed. Thus, in the upper levels of each annual increment, growth apparently is reduced from that of the hypothetical paraboloid shape. It could not be determined if stem 243-554 O-6T--3 The sequences are identical shape in the crown were cone shaped as suggested by earlier workers, but the growth curves indicate crown shapes more conelike than parabolic. The outer rings of the maples (figs. 11, 12) also appear to be reduced somewhat from the hypothetical paraboloid shape. Restricted growth in red maple RM-61 is probably asso- ciated with a change in the immediate environment of the tree during or shortly after 1943. In red maple RM-18, some of the outer rings appear to have been restricted but other outer rings were considerably greater than average size. - In general, though, both the upper (lower ring numbers) and lower (higher ring numbers) parts of the stem appear to be somewhat constricted, relative to a perfect parabolic shape. The constrictions are in the tree crown at and above center of photosynthetic activity, and at the base of the tree, the stem part farthest from the photosynthetic source. Or, in other terms, the upper constriction is in the proximity of only a fraction of the stem tips where growth regulators presumably are formed. The upper central part is at or near the base of the crown (ap- proximately equidistant from all stem tips) where the highest concentration of growth regulators might be expected, and the lower constriction is farthest from all the stem tips. C12 1934 33- RM-61 RM-18 24 1937 1932 30 21 1935 1929 27 19% 1933 1927 24 o 2 1 : 3 15 ;, 1926 -.- 213 0 w C I I G5 CC 5 Z O ooo 0 o r u S93 9 # § PS $ O mem r e uo’ 880 o c & 5g 12 1923 Z 1924 | 18 [- 3 6 to LJ G E ~ 6 rea 1d Z t to E re 1922 & 1923 15 T G O to LJ € T 1 U “ 6 l’lgzo 19191 12 «] \ A & 2 3- -I 1915 1916-} 9 ye Fx o o stags 191 me 6 l _n e 12 n __ f- Too 0 AVERAGE RADIUS, IN INCHES FicurE 9.-Stem shape of red maples RM-18 and RM-61 at 10-year intervals. Area increments of individual rings of the two maples are presented in figure 13 for the years 1927-32. Also included in the figure is a bar graph of evapotranspira- tion deficit for the late spring, early summer, and mid- summer seasons of the same years. The greater the water deficit, as indicated by the evapotranspiration def- icit, the more reduced the growth near the bottom of the tree. Water deficit appears related to the basipetal ring-area trend. This relationship in turn suggests either that growth occurs later in the lower part of the tree than in the upper, or that growth stops first in the lower part. Most of the outer rings (higher ring num- bers) of the two maples (figs. 11, 12) were smaller than the hypothetical situation. VEGETATION AND HYDROLOGIC PHENOMENA 51/- I I I I I I I I I I ~ & =~" yoeq ald _ x 48 |- RM-18 co-58 From northeast-facing slope / RM-61 # 45|- co-37 From southwest-facing slop7/ e o = o x 42;- R I% eee 39|- [ 36|- 33|- 30|- 27|- 24|- 21|- 18|- SAMPLE HEIGHT, IN FEET 15- 12 9|- I l | I I I I 1 1 1 1 | I | 1895 1900 1910 1920 1930 1940 1950 1960 YEAR OF CENTER RING FiGurE 10.-Height growth of the four sample trees, plotted as year of center ring at each sample height. Ring growth is the result of successful cambial-cell divisions and enlargement and differentiation of the cells thus derived. Growth is initiated each spring at or just beneath the actively developing buds at the branch tips, and progresses basipetally throughout the tree. It is generally agreed that the basipetal "wave" of initial cambial divisions progresses slowly in diffuse- porous species (3-4 weeks from buds to base, according to Wilcox, 1962) such as red maple. The bulk of the growth near the base of a tree occurs within about 10 weeks after initiation (Phipps, 1961). If it is assumed that growth at other heights in the tree occurs within about 10 weeks of the time it is initiated, then it can 'be calculated at least half of the growth at any height is occurring at the same time that growth is occurring at all heights. However, regardless of the time during which growth occurs simultaneously at all levels, growth at any given height may be affected by a somewhat dif- ferent set of environmental conditions representing a different part of the growing season from those that affect growth at any other height. Each of the three cell-growth processes-division, enlargement, and dif- ferentiation-is probably controlled by availability of carbohydrates and growth regulators in specific quan- tities. However, as pointed out by Kozlowski (1962), C13 160 } | Height, in feet, of sample section RM-18 140. -o- 30 -> -§- 24 -o- 18 -O- 12 120 |- -o- 6 wed O o lac X 100|- -- w LJ . (€] Z o LJ E ® 3 80|- ~--4 O ® # R O E p o o oi 60|-» o ooooooo—o—a C < [e] Z ® ® Fa 40 [- (. d -- 0 p 20 |- 6 P --I O © 00 10 20 30 40 50 RING NUMBER, FROM CENTER OF CROSS SECTION FIGURE 11.-Ring-area growth by ring number from section center of red maple RM-18 plotted by cross-sectional sequences at 6-foot intervals as was figure 5. Solid dots represent ring-area growth of a single ring at any height. a correlation between carbohydrate and auxin levels complicates a separation of these two as distinct casual factors in growth determinations. For simplification, then, growth is regarded as the result of a complex of interrelated physiological processes, each of which may be varied by any of several environmental conditions. By further simplification, growth at any particular level in the tree is regarded as an expression of surplus photo- synthates of the tree at the time growth at that level occurred, and is in turn conditioned by the environmen- tal conditions of the tree at that time.. Investigations concerning the time and rate of growth at various levels in the tree are being conducted, and are part of the larger tree-growth research program. Ten-year ring-area increments calculated from data of figure 9 are given in figure 14. As suggested above (figs. 11, 12), ring increment is somewhat less at the upper than at the middle trunk heights. A regression fitted to the average annual ring-area-per-year data of RM-18 (fig. 14) appears to be straight line, contrary to the implications of figures 11 and 12, and does not indi- cate a decrease at the lower trunk heights. If it is assumed that growth occurs at different times at differ- ent levels in the tree, then growth of a single ring would not be expected to be constant at all levels because en- vironmental conditions do not remain constant. The data to which the regression line (fig. 14) was fitted represent average annual ring-area growth (X 10) dur- ing a 30-year period. How different the slope of this line would be if-it represented data for more than 30 years is not known. Because the ring-area (abscissa scale) exaggeration of figure 14 is 240 times, it might be assumed that ring area is virtually constant at all levels. However, the increase in ring area with decreas- C14 100 VEGETATION AND HYDROLOGIC PHENOMENA RING AREA /, IN SQUARE INCHES x10 -3 a O Height, in feet, of sample section -O- 24 RM-61 -0- 18 -D- 12 3m =~0- 6 20 0 10 20 30 40 RING NUMBER, FROM CENTER OF CROSS SECTION FrcuUrE 12.-Ring area growth by ring number from section center of red maple RM-61 plotted by cross-sectional sequences at 6-foot intervals as was figure 6. Solid dots represent ring-area growth of a single ring at any height. ing height is significant. For example, average ring- area growth (1930-60) of RM-18 is one-third again as great at the 3-foot level as at the 27-foot level. Thus, though ring-area growth apparently is nearly constant throughout the tree, a linear increase with distance from the top is suggested strongly enough that it can be as- sumed that the shape of the plotted ring-area growth only approaches a paraboloid. Figure 14 indicates a decrease in growth with time in both trees, that is, growth was greatest during the first 10-year interval, 1931-40, and least during the last 10- year interval, 1951-60. This trend seems in agreement with the same general trend of a decreasing rate of height growth during the same period (fig. 10). It might be suspected that as the trees became subjected to increased suppression beneath the forest canopy, growth. in height and growth in diameter would decrease. Be- cause of both the decrease in total incremental growth and the basipetal increase in growth of given increments, the general trend in ring area at any given height de- creases (figs. 11, 12, and 14). Therefore, decreasing size of the total xylem increments was the factor con- trolling the time trend of decreasing ring area at any given height in the two suppressed red maples. - If the trees had not been suppressed, perhaps the total xylem increments would not have decreased in successive years, and the basipetal trend of increasing ring area could have become the controlling influence of the time trend at any given height. In such conditions, the time trend would have indicated increasing ring area. Further, if the trees had been released, the same time trend of increasing ring area would have been expected to follow. The change from narrow to wide rings might be indis- tinguishable from the change resulting when an ex- tended drought is broken, if rings from only one height in the tree were examined. General overall shape of the main stem of each of the red maples indicated stem form to be somewhat para- bolic. Ring-area distribution in individual xylem in- crements of the stem deviates strongly from the para- boloid pattern. In general, the upper part of each in- crement was smaller than that explained as paraboloid, and is believed to have been in the crown of the tree at the time of formation. The lower part of most incre- ments is also somewhat reduced from that of the perfect paraboloid. This reduction is inferred to be the result of the conditions of suppression under which the trees grew ; such a reduction probably would not be apparent in trees not severely suppressed. A basipetal trend of increasing ring area was noted in most increments, but the lower parts of increments formed during marked drought years were greatly reduced in size. Decreas- ing rates of height growth were associated with increas- ing suppression because such decreases apparently did not occur until tree height reached the proximity of the lower part of the forest canopy. Concurrent with de- creasing rates of height growth was a general decrease in total annual increment, also thought to be a result of increasing suppression. ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE C15 15 12 716 9 15 6 44 3 L-Late spring A $4 E-Early summer M- Midsummer RM-61-HEIGHT, IN FEET ABOVE GROUND EVAPOTRANSPIRATION DEFICIT, IN INCHES L J 0 CCE. M C. E "m L E M L E M L E -M C "e_ M 27r 24} e S 21} O CC O 2 18} O co < & E15 | - | E 12F O a md d o} s & 6} 3 1927 1928 1929 1930 1931 1932 RING AREA INCREMENT 0 50 100 £2 e _-_] SQUARE INCHES x 10-3 FIGURE 13.-Vertical distribution of annual ring-area increment in RM-61 and RM-18 for 1927-32, and evapotranspiration deficit of late spring, early summer, and midsummer seasons. C16 27 i l w 24-- a o 0 \ \1951—60 Z) o\ 0 o 0 o 8 1941—5oj / LJ LJ u. Z 15- 0 o o 3 fra 1941-5 i- < A12 lel o Op & Hom! g. | 1991-60 1931-40 t T' g- f o 035 § (\ \\ S-- \\o 0 0 0 Red maple RM-61 Red maple RM-18 0, 0 0.2 0.4 0.6 0.8 1.0 RING AREA/7,IN SQUARE INCHES PER 10-YEAR INTERVAL FIGURE 14.-Ten-year ring-area growth increments of red maples RM-18 and RM-61. A regression line has been fitted to the points representing average yearly ring area (X 10) of RM-18 during the years 131-60. Trends in changes of the total size of xylem incre- ments possibly are descriptive of general conditions of the tree as influenced by slowly changing factors of en- vironment such as would affect suppression. The basi- petal trend of ring areas appears to be an expression of climatic conditions at the time of increment formation. Thus, the radial time trend at any given height appar- ently is an integrated expression of both the total size trend and the basipetal trend of the increment; there- fore, exclusive examination of a radial series of ring areas such as obtained from an increment core prob- ably could not be used to decipher the separate influences of changing suppression by surrounding vegetation and of changing climatic conditions. In theory, a master chronology could be used to remove the effects of age and suppression from a given radial series of ring widths. This procedure presupposes that the series can be cross dated with the master chronology and that the master chronology was synthesized from a sufficiently great number of series to insure that the effects of age and suppression have been completely removed. On VEGETATION AND HYDROLOGIC PHENOMENA the other hand, the effects of age and suppression prob- ably could be removed subsequent to examination of radial ring series from more than one height in the same tree. This method would be contingent only on success- ful cross dating between heights. EARLYWOOD GROWTH OF CHESTNUT OAKS CO-58 AND CO-37 The terms "earlywood" or "spring wood" and "late- wood" or "summer wood" have been extensively used in tree-growth literature and have been applied to non- porous, diffuse-porous, and ring-porous woods. Early- wood and latewood were measured separately in the chestnut oak study trees, but no attempt was made to separate the two in the red maple. Even though early- wood and latewood may be easily distinguishable in diffuse-porous xylem, Chalk (1937) appears to have con- sidered the entire diffuse-porous ring as analagous to the latewood part of the ring-porous ring. The daily radial-growth rate of red maple for a single year may be represented by a single peaked curve characteristic of diffuse-porous species; that of chestnut oak is a double peaked curve characteristic of ring-porous species (fig. 15). Fritts (1962) has demonstrated with dendro- graphs that the first peak of growth of ring-porous white oak corresponds to the growth of the pore zone, or earlywood, of the ring. Dendrometer investigation of Phipps (1961) indicated that the second-growth peak of white oak and chestnut oak roughly corresponds in time with the single peak of red maple and beech (also diffuse porous). Earlywood growth is apparently initiated almost simultaneously at all levels in the trunk in ring-porous species at about the beginning of bud activity in the spring (Priestly and Scott, 1936). It is not known if initiation of latewood growth proceeds in a slow basi- petal fashion in chestnut oak as the increment growth of red maple characteristically does. If this type of growth occurs, then it might take 3-4 weeks for late- wood growth initiation to move down the tree. Thus, if earlywood growth, which starts simultaneously throughout the tree, begins 4-5 weeks earlier at the base than latewood, then latewood growth is initiated in the crown at about the same time that early wood growth is beginning. This relationship, of course, is impossible unless the cells comprising the early wood layer are al- ready present in the cambial layer as derivatives at the beginning of the growth season. If this hypothesis is correct, then the first growth-rate peak indicated by dendrometer measurements at breast height (fig. 15) is not a reflection of cambial-cell divisions, but of cell en- largement. ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE Northeast-facing slope RADIAL CHANGE, IN INCHES x 10-3 D o r- &n a le] *s 1 ae - ~Iza 0 in Ns PRECIPITATION, IN INCHES » \ facing slope RADIAL CHANGE, IN INCHES Late summer Midsummer Late spring Early summer a Chestnut oak - o Red maple FisurE 15.-Growth rates (as radial change) of a chestnut oak and a red maple on each slope, and precipitation during spring and summer, 1959. Growth data from Phipps and Gilbert (1961). Examination of the dissected chestnut oaks revealed no early wood in the centermost ring of any cross section. The centermost ring at any level was, during the year of its formation, part of the terminal leader. When growth in length occurs in spring, the first secondary xylem to develop (as a result of cambial activity) ap- pears to be only latewood. Formation of latewood asso- ciated with growth in length thus occurs before full leaf expansion, which is at the time that earlywood growth occurs at all levels simultaneously. Thus, earlywood growth must be in progress near the top of the tree at the time that cambial activity in the terminal leaders is producing latewood initials. C17 The effects of wounding on growth, as described by Phipps (1961), may be explained on the basis of this hypothesis, if it is assumed that the wound hormone stimulates cell divisions. Dendrometer screws installed in chestnut oaks during the winter dormant period had no apparent effect on earlywood growth of the first year. Excessive radial growth attributable to wound- ing was noted only for the latewood of the first year and the early wood of the second year after installation of the screws. Excessive growth associated with wounding apparently may result from a concentration of growth regulators which induce cell division. Thus, in accordance with the hypothesis outlined above, ex- cessive cell divisions of earlywood initials would affect growth of the second year after wounding, not the first. Wareing (1951) debudded ring-porous and diffuse- porous trees as a check of the contention that growth- initiating substances originate in the buds. He noted no ring formation in debudded diffuse-porous trees ex- cept for a short distance below "strong adventitious buds." In ring-porous species, new annual-ring forma- tion occurred in both control and debudded trees. Wareing (1951) suggested that a reserve of an auxin- precursor was present in the cambium of the ring-por- ous species prior to the growth season and that some environmental condition triggered the conversion of precursor to auxin throughout the tree. This conver- sion, he reasoned, would explain simultaneous growth initiation throughout the tree, even when the tree is debudded. The new annual ring formation in debudded ring-porous species referred to by Wareing probably was only earlywood. Earlywood would be expected to form in debudded ring-porous species if, as hypo- thesized above, undifferentiated earlywood cells are present in the cambial layer before growth initiation in the spring. Latewood growth of rlng-porous species may be simi- lar to the entire growth ring of diffuse-porous spec1es Further, a number of cambial derivatives may remain undeveloped at the end of the growth season. When triggered by some environmental stlmulus in the spring, these derivatives simultaneously begin to develop into early wood tissue throughout the tree. The first cam- bial divisions in the spring thus result in latewood ini- tials. Near the branch tips, just below the current year' 's growth in length, earlywood and latewood growth is occurring simultaneously, and with mereasmg distance down the trunk, latewood growth is occurring increas- ingly later relatlve to the time of early wood growth. The ring-width sequences for both earlywood and latewood of CO-58 and CO-37 are presented in figures 16 and 17. The similarity between the curve for chest- nut oak latewood (figs. 16, 17) and the curve for the VEGETATION AND HYDROLOGIC PHENOMENA C18 yuna} oy} Suofe S[BAIojut 100]-9 1% suopoos ssoJo WoJJ oft '1oju00 U0noos ssolo wor; dogiunu Sut; 4q §G-O; X80 jNUJ}Souo JO pus Jo soouanbas NOLOFJS SSOXI 10 MILN3D WOHJ 'H38WNN ONIH [e] Op O€ OZ OI 0 f | ] | 0 --O01 ==0 =--f08e -| op 9 -O- ® Z1 -O- © & 81 -o- -| o9 ve -o- 0g -o- uonoas ajdues jo jaa; ut 143igH -- -| og O © o - 00 I s-OT X SIHON NI 'HLGIM SNIM ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE C19 100 | Latewood RING WIDTH, IN INCHES x 10-3 I I | Height, in feet, of sample section 40 RING NUMBER, FROM CENTER OF CROSS SECTION FicurE 17.-Annual ring-width sequences of earlywood and latewood of chestnut oak CO-37 by ring number from cross section center. Data are from cross sections at 6-foot intervals along the trunk. total ring width of red maple (fig. 7) is obvious. The major difference between the two is in the first few rings, red maple characteristically beginning with nar- row rings and the first rings of a given sample height of chestnut oak characteristically being the widest. The earlywood data presented in figures 16 and 17 suggest characteristics quite unlike either total ring growth of red maple or latewood growth of chestnut oak. Earlywood growth generally accounts for con- siderably less of the total ring width than does late- wood, but with increasing age (at any given level) the relationship may be occasionally reversed because of the greater variability of latewood growth. Indeed, lack of variability between levels or between adjacent rings of a given level is a pronounced characteristic of early wood growth. This characteristic is enhanced by the fact that early wood growth was always greater than a minimum value (4x 107 in. for oak of fig. 18), while latewood may even be discontinuous. Ring-area growth of chestnut oak latewood (fig. 19) is geometrically similar to the total ring growth of red maple (fig. 11). However, the addition of earlywood (fig. 19) results in a slightly different total ring shape. The generalized curve for total ring area (fig. 19) does not indicate a significant decrease in area with age (of a given level), and the parabolic stem shape thus was not as constricted at the base as was that of the red maples. It might be expected, then, that suppressed subcanopy chestnut oaks could be characterized by a stem with a greater degree of taper than those of suppressed subcanopy red maples. DISCONTINUOUS RINGS Since the advent of ring-chronology work as a tool in recent archeological dating, the occurrence of mul- tiple annual rings (more than one apparent ring per year) and the absence of some rings have been widely known and extensively documented in the literature. C20 VEGETATION AND HYDROLOGIC PHENOMENA 250 o o (e] 200 |- Chestnut oak CO-37 P o 150L_ neal > O = LJ » & 0 ra 0 100 |- \ sex A el \O 50 [- © s o o Pa ° Bwo /O Xo~os o o l O‘O-O-O-O—f‘l—n—n—ndw 0 10 20 30 WIDTH OF EARLYWOOD, IN INCHES x 10-3 FiquUrB 18.-Frequency distribution of earlywood width measurements taken from 1512 locations in chestnut oak CO-37. It is generally agreed that dating errors incurred by the presence of such irregularities may be eliminated by the application of cross-dating techniques to ring sequences of many trees from the general geographic area of study. In theory, these trees represent growth in a wide range of habitats, and not all the trees would be expected to develop irregular rings during the same years. Thus, by examination of enough trees from enough habitats, all ring irregularities could be iden- tified. . However, if even one missing ring of a ring record is not accounted for, the correlation of that ring record with any given climatic parameter is in jeopardy. Because of the inherent serial correlation of rings, fail- ure to recognize the absence of a ring would probably not destroy a correlation between rings and climate, but it would decrease the accuracy of the correlation. In studies involving a limited number of trees in an area for which a master chronology is not available, other methods of identification of ring irregularities must be employed. Larson (1962) has demonstrated that the occurrence of multiple rings in red pine is caused by variation in auxin concentrations associated with terminal-growth activity. - Thus, if terminal growth were stimulated by some environmental condition such as drought break- age after the typical growth peak, tissue would be formed in the annual ring which would resemble that found in the early part of the ring when terminal growth is typically quite active. No distinct examples of false, or multiple, rings were found at any height in the trunks in any of the four study trees from Neotoma. Though variations within the rings of the four study trees were not distinct enough to be considered as mul- tiple rings, subtle variations in cell size, shape, and number were noted. Anatomical variations within a ring might provide growth parameters correlative with environmental conditions based on time intervals much shorter than phenological seasons or calendar months. Circumferentially oriented bands of parenchyma in the latewood of white and chestnut oak may be an example of such an antomical variation. Preliminary examina- tion of parenchyma bands in one of the dissected chest- nut oaks (CO-58) revealed that the number of bands per ring and the distance between bands were quite variable, but tended to decrease toward the outside of the ring, and the number and distribution of bands ap- ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE peared to be unrelated to ring width. If production of these parenchyma bands is environmentally con- trolled, then their occurrence would be expected to cor- relate with environmental conditions of periods of much less than a phenological season, even at a single sample height. The upper part of the xylem increments of the four study trees was never discontinuous. Though environ- mentally induced variation in size from ring to ring was more or less random, there was, as described above, a tendency for all rings to become increasingly nar- row with increasing distance from the apex. Some red maple xylem increments, which were narrow near their apices, tapered down the trunk to the point where they completely disappeared on one or more sides of the trunk. Rarely was a ring missing on all sides of the trunk at any given height, and the ring usually reap- peared on all sides of the trunk near the base in the region of butt swell. Data of discontinuous rings at the 6-foot level of RM-18 for the years 1953-62 are presented diagram- matically in figure 20. The data illustrate only the order in which the rings occurred ; no attempt was made to present ring width to scale. In the actual section, the two radii "a" and "b" were of a single diameter bisecting the angle of the other two radii "north" and "upslope," which were about 135° apart. The four radii in figure 20 were those used for ring measurement with the mechanical stage. -If the four radii only had been used, as would have been done had increment cores instead of cross sections been used, the rings could not have been dated by a simple ring count. If, by chance, the number of rings in each radius had been the same, the rings would have been incorrectly dated. Even with the entire cross section available for in- spection, it is sometimes not possible to ascertain the years represented by all rings. For example, in figure 20, note the discontinuous ring indicated as "unknown" through which radius "b" passes. As illustrated, the "unknown" ring could have been formed during 1954, 1955, or 1956. - Determination of the actual year of for- mation requires examination of the cross sections above and below, and is based not only on the positions of dis- continuous rings in adjacent cross sections, but also on the ring widths. For this example, the year of ring formation was determined as being 1955. By this method, it was possible to date all such "unknown" rings. To illustrate the pattern of discontinuous rings along the trunk, figure 21 was prepared from RM-18 data for the 6-foot height up through the 33-foot height. Pres- ence or absence of rings was determined at 3-foot inter- vals, and determination of pattern between heights was C21 by interpolation. Isolated patches or islands of growth may have been associated with local wounding. If the interpretation of the patterns is correct, several ques- tions are posed. What, for example, is the explanation of the apparent spiralling of the growth layers? - Hori- zontal exaggeration of the illustrations is about 35 times, so it is at least possible that spiralling is not real. If the spiralling does exist, are the tracheae (water tubes) oriented similarly? It is possible that the angle of spiralling is induced by some factor such as water stress, and that the angle may change from ring to ring, or even from level to level in the same ring. The amounts of early and midsummer precipitation, as shown by U.S. Weather Bureau records from Lan- caster, Ohio (9 miles from Neotoma) , were below aver- age during 1954 and 1955; rings for these years were absent in the middle and lower trunk levels (fig. 21). During 1956 when growth was discontinuous in local areas of the lower trunk, precipitation was about aver- age in late spring, above average in early summer, but below average in midsummer. These results suggest correlation between precipitation on a seasonal basis and growth at various levels in the tree. During 1959, precipitation was below average in late spring, greatly above average in early summer, and below average in midsummer. Growth was essentially continuous throughout the tree, and thus did not cor- relate with precipitation in the same manner as growth during 1956. The tree was growing on a silt loam which could act as a partial dam to internal soil drainage from the sandy loam soil immediately upslope. Thus, during 1957, early summer precipitation may have been great enough that a considerable amount of water was stored above the silt loam and continued to drain into it dur- ing midsummer when precipitation was low. If this condition did prevail, growth and precipitation would appear to be correlative only if precipitation and soil moisture are correlative. During 1958, precipitation at Lancaster was about average during late spring, about 214 inches above aver- age in early summer, and about 514 inches above (or twice) average in midsummer. Growth in the lower part of the tree was discontinuous (fig. 21). This re- duced growth was probably the result of physiological drought caused by reduced soil aeration associated with high water content of the soil. Again growth at dif- ferent levels in the tree was indicated as expressions of water conditions of different seasons, but the correlation between growth and precipitation is negative during part of the year. Precipitation during late spring 1962, which was 214 inches below (or less than 40 percent of) average, may have been low enough to affect discontinuous growth in C22 VEGETATION AND HYDROLOGIC PHENOMENA oS NOLOIS SSOHD O€ 10 WOHI 'H3GWNN ONIM OZ 9 eI 8T ve O€ 13 4 44 uonoas jo 79} ut ySigH O @ ® 85-09 420 inupsayy P ® O ® (0~-<-- O 8 Q o Pe- & 1‘s a (PeQ pooma}e7] ~ 0¢ - OOT OET e-OI x SSHONI NI '*/ ANNUAL GROWTH, SUPPRESSED CHESTNUT OAK AND RED MAPLE C23 50 30 20 Earlywood Total ring 10 RING NUMBER, FROM CENTER OF CROSS SECTION FIGURE 19.-Ring-area growth sequences of earlywood and latewood, and generalized curve of total ring-area growth of chestnut oak CO-58. Chup | | | \ | | a o $ § & s Ts 2 § G e-OIX S3HONI 3H¥NOS NI "/ vIHY GOOMATMMY3 s-OI X 3H¥NOS NI '*/ VIMY C24 VEGETATION AND HYDROLOGIC PHENOMENA North ypstop® 1962 1961 1960 1959 1958 1987" "Tose 1955 1954 1 Unknown FisurRE 20.-Diagrammatic representation of discontinuity of outer 10 rings at 6-foot level of red maple RM-18. ANNUAL GROWTH. SUPPRESSED CHESTNUT OAK AND RED MAPLE ©25 G t G DISCONTINUOUS RING 1954 (RM-18) 3 DISCONTINUOUS RING 1955 (RM-18) LGZIZ77 77 I7 --- -our H f////——V//—V o O GIO ////////// A GG ///,é///,"'7 /// GGGGGGGG rt _\////él»/ - fV/// #99 // If! & O Do N N ~ HEIGHT, IN FEET ABOVE GROUND o HEIGHT, IN FEET ABOVE GROUND D & T § § § v vl ho p u co fs i co r on s on - No - ho a-~ wk y". oes GGP h A S 4 -LOP ,///L/ 2 /—~«///) a North b Upslope a North b Upslope w w & & DISCONTINUOUS RING 1956 (RM-18) DISCONTINUOUS RING 1957 (RM-18) Br GG T TGG 7 so OZ GOO JIL //%/// G GIG /////////////—W GOO ~ HLL GO /////////////,A———«7//—"a7// G7 W/J/kfifigvy/ -O //H//—V/f~//// sit -Y VCL & t Fo [«] GIGOLO L L 2 GIO OIL IIIC III f—JW/N/ G ///////////////////////////////////La§/////// GHI //////////M////M WII IIIC mr =- -_ . 1 h io ~ -> ALG North b Upslope North b Upslope D N D N to J; ho J:- he H v- co a co r U1 w- on r ho HEIGHT, IN FEET ABOVE GROUND h HEIGHT, IN FEET ABOVE GROUND ro RD w \ G G o t DISCONTINUOUS RING 1958 (RM-18) DISCONTINUOUS RING 1962 (RM-18) 77 7 p- GF > ria / so - /////// ROO s- (e-- -At HO // ///A //// 7 GI L IIL GIGI III /////////////////////////’///;V/// G G o G o D ~ D N ho $ ho p OU UII O OOO sO ////”—4\ W/M 1s 944 /////////////////A—V// L 1s GZ Wfl—W/ 8299 WWR OO WO ///;‘(/////////// Le ////////////— Feb. 14, 1965 / s / co /f. E / u. Feb. 25, 1965 / © # fas £ / T f. & org u 05/9 o > ,; & 1969 ~¢?./<'PA wer }: 0/5 «6 -§/§7 &/8 isd & / -| / f f f ppr. 8 1965 f. f $ | ol 1 1 / | 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 DISTANCE DOWNSTREAM, IN MILES FIGURE 4.-Ground-water depths in the alluvium of Ash Creek. (pl. 1). In the lower reach of Ash Creek, a perched aquifer formed on a lens of compacted clay in the sec. 1, T. 16 S., R. 19 E., was maintaining a base flow as late as January 4, 1966. On January 7, 1966, the flow in the lower reach of Soza Canyon ended at a point about 1 mile downstream from the canyon mouth. However, in the extreme lower reach entrenched in bedrock, the underflow, which usually emerges a few feet from the San Pedro River (fig. 3), came to the surface at a point about 0.5 mile from the river (fig. 5). This type of interrupted flow was not observed in the lower reaches of the other tribu- taries in the study area. On the other hand, on January 7, 1966, Buehman Canyon (p. D7) was the only tribu- tary still flowing as near as about 0.25 mile to the San Pedro River. The unusual flow events ? of December 1965-January 1966 partly invalidate the flow regimens based on ob- servations made the previous fall, winter, and early spring. In December 1965-January 1966, many reaches of streams previously described as having ephemeral flow regimen qualified for the next higher category of flow duration, or intermittent regimen. Events such as those of December 1965-January 1966 indicate the need for caution in categorizing processes on the landscape. @ Sustained flow in, for example, the lower reach of Ash Creek was apparently last seen in the 1940's (Mr. George Sherman, foreman, Tres Alamos Ranch, oral commun., 1966). PLANT ECOLOGY OF AN ARID BASIN, SOUTHEASTERN ARIZONA D11 10°25" Base from U.S. Geological Survey Redington, 1957 1 o CONTOUR INTERVAL 50 FEET DATUM IS MEAN SEA LEVEL EXPLANATION 2) Bedrock isa tage Flows Contact Dashed where approximately located 1 MILE FIGURE 5.-Flows in the lower reach of Soza Canyon on January 7, 1966. The classification of streams based on the field checks of October 1964-April 1965 (pl. 1) was nevertheless used because it seems to provide a convenient indirect measure of relative moisture conditions during at least the cool part of 1 year. VEGETATION GENERAL DESCRIPTION Most of the Tres Alamos-Redington area supports a vegetation composed of shrubs, small trees, and con- spicuous cactuses, including the columnar giant cactus. (Scientific names of plants are given in the list on p. vy-vI.) When this vegetation is in full foliage, as in sum- mer and early fall, the San Pedro Valley appears from a distance to have a continuous plant cover, especially in years of unusually extensive grass and ephemeral growth. The vegetation of the valley consists, however, primarily of stands of shrubs or of small-tree savannas 307-106 O - 68 - 3 sufficiently open to allow easy movement. Shrubs are woody plants with several stems of approximately equal size emerging from the ground. A savanna is a stand of trees, or plants with a single stem and branches off the ground, not forming a closed canopy and generally floored by grasses. Most of the common and conspicu- ous plants belong to the families Leguminosae and Cac- taceae. Others are creosotebush (Zygophyllacéae), oco- tillo (Fouquieriaces), yucca and beargrass (Liliacem), honeysage (Verbenaceae) , and agave (Amaryllida- ceae). The valley floors of the study area commonly support bottom-land forests consisting of trees of such familiar North American-Eurasian genera as ash, alder, cottonwood, hackberry, mulberry, sycamore, sumac, walnut, and willow. In contrast, the vegetation growing outside the valley floors consists largely of species and genera not found outside the southwestern United States and nothern Mexico, or even outside the bound- aries of the Sonoran Desert (Shreve, 1951). D12 Above an altitude of 4,500-5,000 feet, the main vege- tation form is an open oak woodland, usually contain- ing juniper, manzanita, and cypress. Above the oak woodland, at altitudes of more than 6,000 feet, the mountains support a coniferous forest composed mainly of pines. Above the pine forest is a forest of spruce and fir. FLORISTIC REGIONS AND PREVIOUS WORK The flora in the Tres Alamos-Redington reach of the San Pedro Valley growing below 4,500 feet belongs to three regions long recognized (Harshberger, 1911; Shreve, 1951; Benson and Darrow, 1954; Shreve and Wiggins, 1964). They are: The Sonoran Desert, the Desert Grassland, and the Chihuahuan Desert. Above 4,500 feet, the oak woodland, the pine forests, and the spruce-fir forests have been assigned to "Arizona chap- arral," "western xeric evergreen forests," and "northern mesic evergreen forests" (Kearney and Peebles, 1960, p. 13-14). The plant life of most of the study area below 3,200 feet belongs to the Arizona Upland subdivision of the Sonoran Desert floristic region, which is marked by the abundance of paloverde, mesquite, ocotillo, saguaro, barrel cactus, brittlebush, and many species of cylindro- puntias (chollas) and platyopuntias (pricklypear) (Shreve and Wiggins, 1964, v. 1, p. 50). The southern, or upper, boundary of the Sonoran Desert in the study area varies, depending upon whether the range of the saguaro or that the green and blue paloverde is used to delimit this floristic region (fig. 6). The ranges of these two species have their southernmost, or upper- most, point on the west valley flank. The southernmost part of the study area and Allen Flat are in the Desert Grassland, which is character- ized by open stands of mesquite, acacias, yucca, and beargrass, which are usually floored by grasses such as grama, three-awn, and muhly (Benson and Darrow, 1954, p. 18). The term "savanna" is perhaps a more apt description of the vegetation form in the Desert Grassland. The San Pedro Valley contains what are probably the westernmost areas of occurrence of Chihuahuan Desert plants (Benson and Darrow, 1954, p. 16). The Chihuahuan species (Chihuahuan whitethorn acacia, sandpaperbush, allthorn, and tarbush) are confined largely to calcareous subtrates of the San Pedro Valley (Benson and Darrow, 1954, p. 16). Sandpaperbush, for example, grows in large stands on the limestone out- crop in T. 12 S., R. 18 E., along the Tueson-Redington (Redington Pass) road. The ranges of three of the Chi- huahuan species present in the study area were mapped (fig. 6). VEGETATION AND HYDROLOGIC PHENOMENA No published ecological or botanical work dealing specifically with the Tres Alamos-Redington area ex- ists. General references to the floristics and life forms of the study area are contained in standard works on the flora and vegetation of Arizona (Kearney and Pee- bles, 1960) , on the Sonoran Desert (Shreve, 1951 ; Shreve and Wiggins, 1964), and on the Southwestern desert woody flora (Benson and Darrow, 1954). These works also include information and the presence of individual species in the San Pedro Valley. METHODS OF STUDY The description of the vegetation of the T'res Alamos, Redington area is based on spot sampling and on con- tinuous mapping of the ranges of selected species (pl. 1). The vegetation described consists mainly of woody plants at least 2 feet tall when full grown. Some non- woody plants (cactuses, agaves, yuccas, and beargrass) were included along with small woody species (for example, desert zinnia), because of their abundance or conspicuousness, or both. Spot sampling consisted of noting the presence of species, the basic units of vegeta- tion, in sight at a point. The importance, or abundance, of a particular species was indirectly determined by noting the percentage of sampling points at which the species was tallied in relation to the total number of sampling points ("frequency of occurrence"). The vegetation was also sampled by means of 21 basal area plots located in 20 selected reaches of tributary streams and on one interfluve (pl. 1). "Basal area" is a forestry term that denotes the sum of the cross-sec- tional area of tree boles, expressed in square feet, in a given area. It is a measure of woody vegetation, and, as used in the study, of the relative local abundance of species. The basal area plots consisted of strips 50 feet wide and 1,056 feet (0.2 mile) long, designed to include representative reaches of valley floors while excluding overlap onto side slopes. Area of the plots is 52,800 square feet, or 1.2 acres. Within the plots, all plants with a circumference of at least 6 inches, at breast height (4.5 feet) for trees and at ground level for shrubs, were tallied. VARIATION IN THE VEGETATION OF THE UPLANDS In the study area, large differences in the vegetation of the uplands, or habitats other than valley floors, oc- cur primarily with altitudinal differences. Thus, for example, the paloverde woodland and the succulents characteristic of the Sonoran Desert (Shreve, 1951, pls. 9, 11) present near Redington are 5,000 feet lower than the spruce-fir forest growing on the summit of the Rin- con Mountains. Smaller variations in the vegetation, PLANT ECOLOGY OF AN ARID BASIN, SOUTHEASTERN ARIZONA 110°40" D13 110°00' 3230" "> PIMA COUNTY | GRAHAM COUNTY T 82°50: Hookers Hot, pq Springs S 3 G ye my. e C is . b e . a f t % Fe \ 19h. «* 5 n z C- e 4 § ~ f X. &\~>> fn EXPLANATION O }, agN he) O s HAPPY f i 2 __\ VALLEY] eac! aes Saguaro & -C , ‘A’il‘n‘fir } * 7% Marsa / acacla Lal ) $ , ip Green paloverde > 4 ¢* 8 ? A 4 1 (j syc" - ik f pamela Allthorn ~~ Afey % INA a ! § de ay Sh bs at fi/ ’//LIJ\\ = 2 6 4 Tarbush x4 y If p‘k git 92 <3 - 7- 3 ~Z o4 ; a LELTITT felt \ SA é andpaperbush san af "o nere aes e AJ rt > 8 Basin boundary Rtanch® cX A] .g. 5 74 Tres Alamos, Subbasin boundary ims? r s p 5 SMILES 2 f # 0 © rei nn td 1 toed .~/ x 32° 00° f 110°40' Base from U.S. Geological Survey topographic quadrangles, 1:62, 500 \ _ Pomerene \o 1 32°00° 15" 110°00' FicurE 6.-Ranges of selected species. for example, the difference between the Sonoran Desert vegetation growing near Redington and the Desert Grassland found on Allen Flat, are probably also due to temperature and moisture differences caused by differ- ences in altitude. Allen Flat is 1,500-2,000 feet higher than Redington. Variations in the vegetation coincident with climatic differences at various altitudes were de- scribed for the Santa Catalina Mountains (Shreve 1915). In the study area, however, variations in the veg- etation of the uplands occur at the same altitudes. These variations are probably due mainly to moisture differ- ences caused by different substrates and topography. Variations in the plant cover coincident with differ- ences in topograpky are conspicuous on the eastern flank of the San Pedro Valley in the Happy Valley quadrangle (fig. 7). There, the relatively undissected part of the valley flank, shown on the topographic sheet by regular, widely spaced contour lines, supports a savanna composed of trees about 10-15 feet tall and largely floored by a continuous grass cover (fig. 8). When in full foliage, this savanna appears dark green from a distance. It is composed primarily of mesquite, catclaw acacia, and yucca, and is most extensive in T. 14 S., where the largest relatively undissected valley flank is located. The dissected parts of the valley flank are, in contrast, mantled by shrubs generally above 5 feet tall (fig. 9). The vegetation growing on the dissected valley flanks D14 VEGETATION AND HYDROLOGIC PHENOMENA 110°20' R.20 E. 110°15¢ T. 14 s. #2 % o T.15 S. & ? LILY E LAF Base from U.S. Geological Survey Happy Valley, 1958 and Dragoon, 1958 1 Va 0 1 2 MILES L I | M I CONTOUR INTERVAL 50 FEET DATUM IS MEAN SEA LEVEL FiGuRrE 7.-Vegetation of the uplands in Tps. 14 and 15 S., R. 20 E. EXPLANATION Savanna --- Creosotebush Primarily honeysage, mesquite, and ocotillo PLANT ECOLOGY OF AN ARID BASIN, SOUTHEASTERN ARIZONA FicurE 8.-Savanna composed primarily of mesquite, yucca, and cat- claw acacia growing in T. 14 S., R. 20 E. Note the grass cover and the smoothness of the slope. The substrate is sandy to gravelly loams overlying gravelly to cobbly terrace alluvium. View toward north- east; south end of the Galiuro Mountains in distance. August 1965. FicurE 9.-Shrubs growing on dissected valley flank in Tps. 15 and 16 S., R. 20 E. Shrubs are mainly creosotebushes. The substrate is basin fill (table 2). View toward southeast and Dragoon Mountains. August 1965. is distinctly olive green all year and is usually not floored by grasses. This vegetation owes its appearance primarily to the abundance of creosotebush, an ever- green shrub that was not observed in the savanna (fig.: 7). The savanna and the creosotebush also grow on rela- tively undissected valley flanks-hereafter referred to as smooth slopes-and on dissected flanks west of the San Pedro River (fig. 7). They were not observed on the bedrock cropping out near The Narrows or on the bedrock of the lower mountain fronts in T. 15 S. These bedrock outcrops are mantled primarily by shrubs such as honeysage, false-mesquite, and mimosa, and by cac- tuses such as saguaro, cholla and pricklypear. The differences in species composition between the vegetation growing on the smooth slopes and that grow- D15 ing on the dissected flanks are shown in table 7 and figure 10. On the smooth slopes, mesquite, catclaw acacia, graythorn, and lycium-plants that are common along streams (p. D20-D27)-are more common than on the dissected valley flanks. Mesquite and catclaw acacia also grow as small trees on the smooth slopes, but on the dissected slopes they are generally shrubs less than 6 feet tall. The smooth slopes also support desert-honey- suckle and desertbroom (table 7), species common along streams (Kearney and Peebles, 1960, p. 801, 883) and apparently absent on the dissected slopes. In general, the form and species composition of the vegetation growing on the smooth slopes suggests higher moisture levels than on the dissected slopes. This hypothesis is supported by the differences in surficial substrates of these two topographic forms. The smooth slopes mantled by the savanna are under- lain by brown coarse terrace alluvium which has buried fine-grained reddish-brown (pink when dry) basin fill TaBu® 7.-Species present on smooth slopes and on dissected flanks of the San Pedro Valley in Tps. 14 and 15 S., R. 20 E. Species Smooth - Dissected Slopes flanks aan se Cl ELC Desert-honeysuckl6... oB CabCIAW ACRCIRA Leol celle c eb Whitethorh acacia 'l Palmer REAVE. -c Mountain gave.. Four-wing SARUATO-.. tech Plue uce, CrayLhorn - .. 2. 2 ius aon oes oe iman alant aas IOIMUT -:. nene ne Darrel cn aat den aaeges White bur-S8Gge-......:.0cll ucr e on alble aln nda L cs ece noice ele anes a aes on Lycium (Lycium berlandieri?) ______________ Lycium (L. ersertum?)}=22 222... Pricklypear (Opuntia engelmannit) __________ Pricklypear (O. phaeacantha)-______________ Cholla (0. fulgida var. mammillata) -_____._.__ Cholla (0. versicolor) Christmas cactus cus cen n cans Mesquite. 002. caren ICU Lec- iu anu ie ans Yellow White cece ued. o Brickellia (RBrickellia californica). False-mesquites . eral cer aul Cassia (Cassia COVESIN) --. abe anes Mexican .._. LLCO 0 J. CE .nl. .ll cel. Encelia.: ~ lsc lls I0. Uk aa nr Tarbushc. . _c: lun cels NE Er ai s a en One-seed JUnNIPEr-- >...... ice nlc ns aas _ enc sen tia a ss comon onlt c Lun Lu Russian-thistle. . . sl eon a naaa eas PA bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bdibd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd bd 1 Chihuahuan whitethorn acacia may also be present. Fieldwork was carried out during the "leafless stage," when positive identification of these two closely related species is difficult. D16 DISSECTED VALLEY FLANKS VEGETATION AND HYDROLOGIC PHENOMENA SMOOTH SLOPES Percentage 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 Percentage __| { ol T AL f ool of ofa frc d -L-] Creosotebush Whitethorn aca Percentage 100 90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 100 Percentage FicurE 10.-Frequency of occurrence of species with more than 25 percent frequency on dissected valley flanks and smooth slopes in the Happy Valley quadrangle. Total number of plots on smooth slopes and on dissected valley flanks is 53 and 50, respectively. * Owing to difficulties in identification, especially of young plants, the percentage indicated should be considered tentative. (table 2). These deposits are well exposed along the escarpment in the NE14, sec. 30, T. 15 S., R. 20 E., reached by the Keith Ranch road. Deep dark-brown sandy to gravelly loams have developed on this allu- vium. These loams, which are in places at least 6 feet thick, belong to the White House series (S. W. Buo!l, Dept. Agricultural Chemistry and Soils, Arizona Univ., oral commun., 1965). (See Nat. Coop. Soil Survey, USA, 1964). Deep dark-brown loams were not seen in the dissected portion of the valley fill, where the stands of creosotebush and other species occur. The pres- ence of thick dark soils on terrace alluvium or other more recent coarse material and the absence of these soils on other deposits, primarily fine-grained older valley-fill units, is apparently characteristic of the San Pedro Valley. This relationship has been observed in the Curtis-San Juan area, about 10 miles south of Tres Alamos (Smith, 1963, p. 44-47), near Tombstone (fig. 1; Renard and others, 1964, p. 472), and near Mammoth, about 15 miles north of Redington (Creasey, 1965, p. 24). In the Happy Valley quadrangle, smooth slopes, un- derlain by terrace alluvium at least 20 feet thick and by deep, friable loams, occur primarily downslope from granitic-granodioritic mountain fronts (Arizona Bu- reau of Mines, 1959). The largest of these smooth areas, in T. 14 S., R. 20 E., is downslope from an outcrop of granodiorite that has been eroded into a mesa (Cooper and Silver, 1964, p. 26). This granodiorite "disintegrates readily into fragments 2 to 10 mm in diameter" and is only locally resistant to weathering where it is either "altered and silicified" or apparently "more resistant as a result of structural complications" (Cooper and Silver, 1964, p. 26-27). The depth of weathering of the gran- odiorite underlying the upper part of the slope in T. 14 S. is indicated by the driller's log of well (D-14-21) 19 cad (U.S. Geol. Survey, Tucson, unpub. well rec- ords). This log shows "decomposed granite" to a depth of 20 feet, "medium hard granite" between 20 and 200 feet, and "hard granite" below 200 feet. The availability of large amounts of noncohesive-weathering material downslope from granite or granodiorite probably causes washes to braid or shift channels frequently (See Leo- pold and others, 1964, p. 284-295.) On the smooth slopes of the Happy Valley quad- rangle it is commonly difficult to distinguish between wash bed and interfluve. (See Tuan, 1959, p. 88.) Thus, braiding and channel shifting in noncohesive material may produce and maintain the smooth slopes by dis- tributing material evenly on a surface. These processes probably also tend to disperse moisture throughout a slope. In contrast, on a dissected slope, runoff is con- centrated in a more fixed channel network, and a greater proportion of this runoff is probably shed from the PLANT ECOLOGY OF AN ARID BASIN, SOUTHEASTERN ARIZONA slope. In summary, the interrelationship between rapid weathering of crystalline rocks, deposition of coarse or relatively coarse material, and formation of deep loams seems to have resulted in a relatively moist upland habi- tat. This habitat is sufficiently moist to support small trees in an area where, in an average year, only 12 inches of rain falls. The dissected valley flanks in the Happy Valley quadrangle are underlain mainly by basin fill and by cemented or partly cemented deformed gravels (table 2). Soils are almost completely lacking on these de- posits. The basin fill is a predominantly fine grained de- posit high in clays and silts that commonly forms nearly vertical banks tens of feet high along entrenched washes. The basin fill is marked by low surface and subsurface permeability. After summer storms, water was seen standing on surfaces underlain by basin fill for at least 2 hours after the end of precipitation. A similar puddling of water was not observed on the White House loams. In The Narrows-T'res Alamos area, the basin fill has such low subsurface permeability that it is not considered to be an aquifer (Montgomery, 1963, p. 25). At St. David and Benson, immediately south of the study area (fig. 1), artesian ground water results from the confining effect of basin fill overlying more porous aquiferous de- posits (Halpenny and others, 1952, fig. 8). The low permeability of the basin fill is also shown by the re- sults of a field test of infiltration. The test consisted of measuring the length of time water remained at the surface after 12 ounces of water was poured from a constant height of 15 inches. The mean and median times for 93 observations made in see. 33, T. 14 S., R. 20 E., see. 25, T. 15 S., R. 19 E., and sees. 4, 28, and 31, T. 15 S., R. 20 E., were 43.5 and 40 seconds. Correspond- ing values for 100 tests made on the White House loams in sees. 23, 25, 28, 88, and 35, T. 14 S.. R. 20 E., and sees. 17, 18, 19, 22, and 80, T. 15 S., R. 20 E. were 20.8 and 20 seconds. The deformed gravels are either cliff forming or have been eroded into badlands, depending upon the degree of cementation. They are commonly trenched by can- yons tens of feet deep and less than 10 feet wide (p. D4). Areas underlain by the deformed gravels are probably also marked by low infiltration and rapid runoff. Vegetation growing on the dissected valley flanks is adjusted to low moisture levels, perhaps the lowest in the study area. However, the abundance of certain species growing on the dissected valley flank may or may not be directly related to moisture regimen. For example, the creosotebush is abundant on these val- ley flanks, but it also grows in the channel of the San Pedro River. On valley floors or where the land is ir- D17 rigated, the creosotebush is commonly more than 10 feet tall (Dalton, 1961, fig. 2). Creosotebush is commonly on calcareous substrates (Benson and Darrow, 1954, p. 219) but transplanted creosotebushes "continued to grow and thrive" in washed silica sand (Dalton, 1961, p. 92). No satisfactory explanation can be offered for the distribution of this plant in the study area. Perhaps the distribution of this shrub is controlled at the ger- mination-seedling stage of growth, particularly by the pH of the substrate. (See Dalton, 1961, p. 51.) The high frequency of occurrence (52 percent) of honeysage on dissected valley flanks reflects the common occurrence of this plant on slopes with an angle of more than about 15°. On side slopes, this shrub is commonly so abundant as to impart a distinctive grayish-green (gray in winter, grayish white when the shrubs are in bloom) color and fluffy aspect to the vegetation as seen from a distance. The occurrence of stands of honeysage on side slopes and the absence of these stands on level surface is particularly striking at the edge of terraces underlain by basin fill (fig. 11). Honeysage is also com- mon on bedrock side slopes (p. D15) and on sandy wash floors. It is rare on the gentle, smooth slopes underlain by loams. The field relations of honeysage suggest that this shrub requires well-drained substrates for survival. Ocotillo, a striking plant commonly more than 20 feet tall with showy red flowers in spring and early summer, is common on outcrops of deformed gravels and ce- mented terrace gravels (fig. 12) and in areas of surficial caliche or caliche at depths probably not exceeding 5 feet. Caliche is fairly common within the outcrop area of the basin fill (table 2). Ocotillo is rare on the deep loams that underlie the smooth slopes. As the ocotillo is also common on bedrock outcrops regardless of bedrock type, it is suggested that this species grows abundantly only in areas where consoli- dated material provides an anchorage. Thus, ocotillo seedlings grow in areas underlain by fine-grained de- posits where adult ocotillos do not grow. Toppled adult ocotillos and saguaros are a common sight in the study area, regardless of substrate; apparently both of these species topple easily because they are top heavy. The relationship between ocotillo and consolidated substrate may explain the presence of vast-in places, square miles-stands of this plant in the north half of the Tres Alamos-Redington area, where the largest outcrops of the Pliocene cemented gravels occur (pl. 1). VARIATION IN THE VEGETATION OF VALLEY FLOORS The vegetation growing on the valley floors of tribu- tary washes, creeks, and canyons, and of the San Pedro River ranges from stands of shrubs with the same spe- cies composition as those growing on the adjacent D18 Terrace taue north approximate. mEAN oeciination, 1968 AC 0 5 10 FEET ® 22 0" 2000 FC CONTOUR INTERVAL 5 FEET hg DATUM IS TERRACE TOP, 3750 FEET ABOVE MEAN SEA LEVEL Planetable survey by Robert C. Zimmermann, March, 1965 EXPLANATION .¢. Honeysage & PR Mesquite AC Whitethorn acacia FC Barrel cactus FD White bur-sage LT Creosotebush YU Yucca FicurE 11.-Distribution of honeysage at the edge of a terrace in the NEW sec. 10, T. 16 S., R. 20 E. uplands (fig. 13) to a closed-canopy forest as much as 80 feet tall, composed mainly of trees that grow only on valley bottoms (fig. 14). Many intermediate types of valley-bottom vegetation differ from these two extremes both in species composition and in height and density of the plants. The valley-floor vegetation includes many species that were observed only on valley bottoms or, rarely, on side slopes marked by springs or seeps. These plants (table 8) are referred to as "valley-floor species," to distin- guish them from those plants that grow on both uplands VEGETATION AND HYDROLOGIC PHENOMENA FicurB 12.-Ocotillo (tall plants) growing on partly cemented gravels in sec. 24, T. 15 S., R. 20 E. Other shrubs are creosotebush, cholla, and honeysage. FIGURE 13.-Wash with ephemeral flow regimen, located on basin fill in the SB%, sec. 18, T. 12 S., R. 19 E. Both side slopes and wash floor support saguaro, foothill paloverde, creosotebush, mesquite, catclaw acacia, barrel cactus, and yellow desertzinnia. FiGurE 14.-Bottom-land forest along the San Pedro River near the mouth of Soza Wash. Most of the trees are cottonwoods. PLANT ECOLOGY OF AN ARID BASIN, SOUTHEASTERN ARIZONA and valley floors. Many valley bottoms of the study area do not support any valley-floor species. VALLEY-FLOOR VEGETATION UNDIFFERENTIATED FROM THAT OF ADJACENT UPLANDS The vegetation growing along an ephemeral wash tributary to Tres Alamos Wash may serve as an ex- ample of valley-floor vegetation composed of the species that grow on the surrounding uplands. The wash drains about 1 square mile underlain by dissected basin fill (table 2), located mostly in sees. 1 and 2, T. 16 S., R. 20 E. The species growing on the wash floor and on the side slopes at three sampling points (202, 203, and 204, pl. 1) are listed in table 9. Dimensions of the channel and valley bottom at the three sample locations respec- tively, are: Width of channel, 10, 12, and 3 feet; total width of valley bottom, 70, 12, and 3 feet. None of the plants tallied along this wash is a valley-floor species (table 8). TABLE 8. -List of valley-floor species Alder, Arizona Oak, Mexican blue ® Arrowweed scrub ® Ash, Arizona or velvet Poison-ivy Brickellia * Rabbitbrush * Buckthorn Ragweed, canyon Bumelia Saltcedar, five-stamen Burrobrush Seepwillow, batamote Buttonbush Soapberry ° Cassia (Cassia leptocarpa) Squawbush Cottonwood, Fremont Sumac Cypress, Arizona ' Desert-willow Elderberry, Mexican Grape, Arizona Hackberry, paloblanco Sumac, littleleaf ® Sycamore, Arizona Tree tobacco Trumpetbush Walnut, Arizona Hopbush Willow, black or Goodding Indigobush Bonpland Mulberry, Texas yew-leaf Oak, Arizona white ® Emory ® * Possibly Brickellia floribunda. 2 Above 4,200 feet ; also on uplands underlain by bedrock. 3 Above 4,000 feet ; also on uplands underlain by bedrock. * Above 4,500 feet ; also on uplands. 5 On talus slopes above 5,000 feet. BOTTOM-LAND CLOSED-CANOPY FOREST The reaches of Paige Canyon and Turkey Creek lo- cated in Happy Valley, a high basin underlain by un- consolidated fill, pl. 1), support a closed-canopy forest composed primarily of sycamore and cottonwood mixed with ash, walnut, hackberry, and mesquite (table 10). This bottom-land forest has a basal area (tables 11 and 12) comparable to that of forests in the humid Eastern United States. (See Hack and Goodlett, 1960, p. 21.) The reaches of Paige Canyon and Turkey Creek in Happy Valley have fairly gentle slopes (50-100 ft. per mile), are wide (more than 100 ft.), and have semi- perennial and intermittent flow regimens (fig. 4). 307-160 O - 68 - 4 D19 TaBur 9.-Valley-floor (VF) and side-slope (SS) vegetation of a t(rilbut31ry of Tres Alamos Wash at locations 202, 203, and 204 pl. 1 Location Species r 202 203 204 VF SS VF SS VF S Whitethorn X X x: X X. x Catclaw X AX X .X. xX _ X Mexican bue aC K Barrel X LLC C eb- ia Oclotillo_..l..el.llllenlall.ger... K Ne White X_ X' XX -x /x 222 , co 2 be Leow alan a nena indie en T Nise ta ices xX X X X XxX -x Lycium (Lycium berlandieri?) __ ___. X or Pt eatin. Cholla (Opuntia versicolor) _ ______._. X C X "X XxX xX... Yucca: _s. 2201 X X iX t_. Yellow Cer X White =_... ull TABLE 10.-Species composition of valley-bottom vegetation of Paige Canyon near Watkins Ranch Cassia ' Pricklypear (Opuntia Hackberry ' engelmalnnii) j 1 Sycamore ARE}? lintbrush Cottonwood * { r Mesqul'og v a Walnut Black willow One-seed juniper Arizona grape ' 1 Denotes valley-floor species as defined on page D18. 11.-Basal area in plot located along Paige Canyon at locality 6 (pl. 1) h Basal area Species a am] o Sycamore.:>....._1. LL LIL LCI. LIC IOS 132. 66 Walnut.... ran a Eneas ah a mean bis a a (nlp 9. 70 AShL LEL. Al 2:2 enn alama snares sn as bid e ba ee ba aa ames 8. 65 Cottonwood... : osi EMEA Leer aaa a ae ales 5. 31 ls mane ens . 29 MeSQUILGe. .z. ans . 90 Total basal ATRL - O02 2022 .s d ne nad aie ane ain 156. 70 TaBLE 12.-Basal area in plot located along Turkey Creek at locality 5 (pl. 1) Species Busaés 31-ch .co ssa amkakacks sn 64. 70 l nso s eil 1 57. 09 Ash: n ele nl es n- U an a has- lan a e a en 2. 41 Walnut..22 2122000212. Advest due aas al an a e wie a a aint am 2. 17 Mesquite; -::" C: cll on . 49 'Total basal aren c 126. 86 1 Contributed by four trees. D20 VARIATION IN THE VEGETATION OF EPHEMERAL STREAMS The two foregoing examples have shown the striking difference in valley-floor vegetation between a small ephemeral wash and two streams with longer lasting flows. Variations in the valley-floor vegetation occur, however, between streams that have ephemeral flow regimen but different drainage areas. These variations also serve as examples of vegetation types intermediate between the two extremes described above. The valley-floor vegetation of Great Bajada Wash at the location of basal-area plot 10 (pl. 1), where this ephemeral stream has a drainage area of about 2.8 square miles, has the same species composition as that growing on the adjacent uplands. Compared to the vegetation on the uplands, that along the wash has seven times as much basal area, is taller, and has a greater proportion of catclaw acacia (table 13). The vegetation in plot 10 is representative of the valley- floor vegetation growing along Great Bajada Wash between this plot and the San Pedro River. Total drain- age area of Great Bajada Wash is 3.8 square miles. 13.-Basal area of valley-floor and upland vegetation along Great Bajada Wash at locations 10 and 11 (pl. 1) [Drainage area at location 10 is 2.8 square miles] VEGETATION AND HYDROLOGIC PHENOMENA sists primarily of thickets of mesquite and catclaw acacia about 20-30 feet tall, mixed with burrobrush, graythorn, and desert-willow. This vegetation is char- acteristic of ephemeral streams with more than about 10 square miles of drainage area. Such streams also commonly support hackberry (pl. 2), a tree present along Roble Canyon and Teran Wash but not in plots 18 and 19. TaBus 14.-Basal area of valley-floor vegetation of Roble Canyon at location 19 (pl. 2). Drainage area is about 12.3 square miles [Maximum height of vegetation about 30 feet] Species Basal area (sq 1t) 30. 38 27. 43 3. 02 Whitehorn c l.} 9. 91 Graythorns 2. .to lcd Loose CLL - . 18 blue =-. nmn Of Burrobruash c l- ccc . . 03 Total basal cels ICAU 71. 02 TaBL® 15.-Basal area of valley-floor vegetation of Teran Wash at location 18 (pl. 2). Drainage area is about 14 square miles [Maximum height of vegetation about 30 feet] Species Basal area Basal area (sq ft) (sq ft) Valley floor _ Upland Mesquite: t:: c senor. n ree enas. 52. 84 $ 82 CatclaWw ACACIA: .. 2. 2. La ned Eel leuke bons an onn 5. 63 eto lll nlc. iX - 1h Pole area eee ieee etre ci poing 58. ar 2. 18 . 36 Total basal 14. 84 2 09 The botanical data for Great Bajada Wash, Roble anyon, and Teran Wash show that the larger the Maximum height of vegetation (ft) ___.. 12. 00 8. 0 C TOs S In contrast, the vegetation growing along the ephem- eral lower reach of Roble Canyon, at a point where the drainage area is about 12.25 square miles (loc. 74, pl. 1), includes two species-desert-willow, a tree, and burro- brush-that were seen only on valley floors. Other species at location 74 (pl. 1) are: catclaw acacia, white- thorn acacia, blue paloverde, graythorn, pricklypear (Opuntia engelmannit), and mesquite. In plot 19, near location 74, the basal area is also almost four times that measured along Great Bajada Wash at location 10. (Compare tables 13 and 14.) The data for plot 19 also show that the basal area of vegetation growing along an ephemeral stream can be as much as half that of the bottom-land forest of Turkey Creek (table 12). A basal area exceeding 50 square feet was also measured in the middle reach (location 18) of Teran Wash, where this ephemeral stream has a drainage area of about 14 square miles (table 15). The vegetation of Roble Canyon and Teran Wash at locations 18 and 19 con- drainage area, the denser and taller the valley-floor vegetation of ephemeral streams. Streams with drainage areas the size of those of Roble Canyon (total drainage area 13.5 sq mi) and of Teran Wash (total drainage area 16.3 sq mi) also support species that were observed only on valley floors. Comparison of the vegetation of Roble Canyon and Teran Wash with that of Turkey Creek (drainage area about 8 sq mi) shows, on the other hand, the importance of flow regimen in determining the aspect and species composition of valley-floor vege- tation irrespective of drainage area. Plate 2 also shows that the upper reach of Great Bajada Wash, at a point where the drainage area is about 1 square mile, supports hackberry, desert-willow, and soapberry, three valley- floor trees that do not grow at location 10 (drainage area 2.8 sq mi), farther downstream. The upper reach of Great Bajada Wash is located on bedrock. Thus, drainage area, flow regimen, and geology affect the dis- tribution of species on the valley floors. The effect of drainage area and geology on the distri- bution of plants, whatever the ultimate causal relation, PLANT ECOLOGY OF AN ARID BASIN, SOUTHEASTERN ARIZONA is eliminated by sustained flows. This is illustrated by the vegetation growing near Kiper Spring, SW!4, see. 10, T. 16 S., R. 19 E., on a slope underlain by basin fill and marked by seepage. This vegetation consists of cottonwood, ash, black willow, walnut, hackberry, buck- thorn, Texas mulberry, mesquite (about 35 ft tall), Arizona white oak, and Emory oak. The seepage area also supports fig and osage-orange, two exotic species that were probably dispersed from a nearby abandoned ranch. VALLEY-FLOOR VEGETATION OF TRES ALAMOS WASH AND ASH CREEK The valley-floor vegetation of Tres Alamos Wash and Ash Creek, the two streams that form the south bound- ary of the study area, was sampled from the headwaters of the mainstem to the confluence with the San Pedro River. The data for these two streams show the entire range of variation in the valley-floor vegetation along two streams, as well as the botanical contrast between two tributaries with similar mainstem elevations (table 1) but greatly dissimilar basin topography, geology, and flow regimens (pl. 1). Tres Alamos Wash is located on gently sloping valley fill and has ephemeral flow regimen throughout its course. Ash Creek, with steep headwaters located on bedrock, has flow regimens rang- ing from semiperennial to ephemeral. Although Ash Creek has a drainage area (51.75 sq mi) less than one- half that of Tres Alamos Wash (134.75 sq mi), its valley-floor vegetation includes more valley-floor spe- cies and is generally taller and denser than that of the larger tributary across the San Pedro River. The valley-floor vegetation of the headwaters of Tres Alamos Wash on Allen Flat is composed mostly of mesquite, yucca, and beargrass, plants which are com- mon in the Desert Grassland (p. D12) that occupies that high basin. Valley-floor species such as hackberry, des- ert-willow, and rabbitbrush were seen only at and down- stream from a point where the drainage area is about 12 square miles (pl. 2; table 16). The largest number of valley-floor species grow in the middle reach flanked by the bedrock of the Johnny Lyon Hills. In the lower reach located on valley fill, the number of valley-floor species is smaller (table 16; pl. 2). The density and maximum height of the vegetation are least on Allen Flat, greatest in the middle reach flanked by bedrock, and relatively low in the lower reach (table 17). The vegetation of the lower reach consists primarily of the mesquite and catclaw acacia thickets characteristic of large ephemeral streams. The valley-floor vegetation of Tres Alamos Wash is another example of vegetation increasingly differen- tiated from that of the uplands with increasing drain- age area. However, in a basin underlain by unconsoli- dated deposits and with low relief such as Allen Flat, ©Desert-willow *. D21 TABLE 16.-Species present on the valley floor of Tres Alamos Wash at selected locations (pl. 1) [Figures in parentheses are approximate drainage areas (sq mi) at sampling points] Locations ! 19(15) 45(110) Species 22(4.5) 16(134) PBeargrags: 2 IC! ae -. Ll. abe st X X Mesquite... Rabbitbrush *. . Hackberry °____ ASR 6s Littleleaf sumad °.. .-.. IC Xl rece s Soapbetty 5 cna X Whitethorn on X -=. arie sales at X WaInUL se an xX X Burrobrush LOLOL X X CatelaWw ACACIA cel nc cl x X Cholla (Opuntia UErstCOlOr) .._ <=... X Pricklypear (0. X Lycium (Lyctum berlandiera?) __ § X sn Descrtbroom.. .:. n LT AL LLU e ana eaua= ens ! Sampling points listed in order from headwaters to confluence with San Pedro River. 2 Valley-floor species (p. D18-D19). Rabbitbrush was observed only on valley floors on Allen Flat. TaBus 17.-Basal area of valley-floor vegetation of Tres Alamos Wash in upper (plot 17), middle (plot 16), and lower (plot 12) reaches (pl. 1) [Figures in parentheses are approximate drainage areas (sq mi) at the site of the basal-area plots] Basal area (sq ft) Species 17(60) 16(110) 12(132) 0. 07 - 34. 19 26. 39 Walnut 12. : oc o_ LELA LI Aai cates 20:07 : c:lc.. Mackbetfy } 16. 14 CaVCelAW ACACIALL -l... 9. 49 8. 35 Ack e saw 1814 ° 0.0.0. Desert- Willow !. _ - . nl cn onne ea ene neenee ens +4TB Whitethorn acacia. 47 . 97 Littleleaf sumae s O00 AAT b ARC Burrobrush 1. isles eins . O7 . 39 Total basal area...... 0. 07 _ 82. 81 36. 10 Maximum height of vegetation (ft) 8 40 20 1 Valley-floor species (p. D18-D19). this differentiation occurs gradually, as large drainage areas are indirectly required to support valley-floor spe- cies. Tables 14, 15, and 17 also show that the basal area of the vegetation of Tres Alamos Wash at a point where the drainage area is about 60 square miles (plot 17) is a fraction of the basal area measured along Roble Can- yon and Teran Wash at points where the drainage area is less than 15 square miles. In contrast to Tres Alamos Wash, Roble Canyon and Teran Wash have steeper headwaters located on bedrock. The presence of dense tree vegetation in the middle reach of Tres Alamos Wash flanked by bedrock suggests that geology affects the distribution of plants without causing a visible dif- ference in flow regimen. D22 The vegetation of the lower reach of Tres Alamos Wash indicates that, beyond a point where the drain- age area is a certain size, the size of the catchment basin does not affect the composition and form of the vege- tation. Comparison of the basal area data for Tres Ala- mos Wash in plot 12 with those for Great Bajada Wash, Roble Canyon, and Teran Wash (tables 13, 14, 15, and 17) reveals that the density of thickets along ephem- eral streams does not increase indefinitely with increas- ing drainage area. The basal area measured at a point where the drainage area is more than 100 square miles (Tres Alamos Wash, plot 12; table 17) may even be less than that measured at points where the drainage area is less than 15 square miles (Roble Canyon and Teran Wash; tables 14, 15). In general, there is consid- erable botanical variation between a stream with a drainage area of less than 3 square miles (Great Ba- jada Wash, table 13) and streams draining more than 10 square miles (Roble Canyon, Teran Wash; tables 14, 15). However, the vegetation of streams with drain- age areas of more than 10 or more than 100 square miles may have about the same density and species composition. The valley-floor vegetation of Ash Creek includes valley-floor species at points where the drainage area is between 2 and 3 square miles (pl. 2) and, at most loca- tions farther downstream, a greater number of these species than the vegetation of Tres Alamos Wash (tables 16, 18). The contrast between the valley-floor vegetation of Ash Creek and that of Tres Alamos Wash is also shown by the basal-area data given in table 19. At comparable distances from the San Pedro River, the valley-floor vegetation of Ash Creek is consistently taller and denser than that of Tres Alamos Wash, de- spite smaller drainage areas. In the ephemeral lower reaches, at distances from 3 to 4 miles from the river, the botanical differences between the two tributaries are not as pronounced, although the dense stands of hack- berry and walnut present along Ash Creek are not found in the corresponding reach of Tres Alamos Wash. The lower reach of Ash Creek also supports ash, seepwillow, and large individual walnut trees (fig. 15). Ash and seepwillow were not seen along the lower Tres Alamos Wash, and the walnut along the lower 8 miles of this stream is generally a shrub less than 15 feet tall. In common with the vegetation of other tributaries, the vegetation of the lower reach of Ash Creek has, how- ever, a progressively smaller number of valley-floor species in a direction approaching the San Pedro River (fig. 20). The valley-floor vegetation of Ash Creek, especially when compared with that of Tres Alamos Wash, in- dicates that geology, by either concentrating or dispers- VEGETATION AND HYDROLOGIC PHENOMENA 18.-Species present on the valley floor of Ash Creek at selected locations Location (pl: 1)... 1 1 12.1 ARCT EATER. 67 _ 64 59 66 9 Flow regimen 1. .. c,. oll dare erg alg Pr .fr :I SP E Approximate drainage area......._....... (Gqmi):.:. 2 4 21 31 50 il oblast Coral beans. 22 olur eela cee oak as eno X Emory oak sL z lice. cl X Serub cgay X Manzanita. s- csc l cel X Feepwillow . gol X NX c xX :X Ash fo tn een lanl PL in xX -X Hackberry 22. 202 oe AISLE EL a vaan o elie a alaaile e X Sycamore 2: r Ecg C lib. X Cottonwood *s : oe uae neler dae te naa e X Yew-leat willow 0000000 a nausea . K black willow L cl} xX: Kis 2. X X X Desert-willow cc Wamub il eee ade cael ae eas baa as a Catclaw acaba - lll lud elin ase 2 ree rect -rueues IndigobuUush f= s «corals lene eer e nas ee =a e we XC Texas mulberry X {._ Buckthorn 220230200 09400200. gall Les oven oes X POISON-IVY feeler n ::- ians 5 Apo Arizona srape $2.2. 00.0 calcein co cAI LUI Desert clu ce dln oue ult bem. One-sced ss X se.. Lycium (Lycium berlandigeri?)y ._. Te Cel. Arizona white OAK X ai.. Rabbitbrush X Burrobrush 22000. 02 Lent ILL a Re Uae a ne rae nes es X M44 ! PP, persistent pools; I, intermittent; SP, semiperennial; E, ephemeral. 2 Valley-fioor species (p. D18-D19). FicurB 15.-Valley-floor vegetation of Ash Creek near location 77 (pl. 1). Trees are mainly walnut, mesquite, and desert-willow. Large walnut in the center of the picture has a diameter at breast height (4.5 ft) of 5 feet. The water table in this reach of Ash Creek is about 60 feet deep. ing moisture, strongly affects the distribution of plants. Bedrock, for example, seems to compensate for small drainage areas. On bedrock, valley-floor species occur at points where the drainage area is smaller than in basins underlain by unconsolidated deposits. On bed- rock, streams may also have sustained flows. Reaches PLANT ECOLOGY OF AN ARID BASIN, SOUTHEASTERN ARIZONA D23 TaBur® 19.-Basal area (sq ft) of valley-floor vegetation of Tres Alamos Wash (TA) and Ash Creek (A) at selected locations Distance from river 22. 00, UCL 6-7 3-4 ! Se ALT LeU arc ce ao dh sa ave the d on Tlob NO.: TLIN EAI ATTN Yee ece basa a ecause bk Flow regimen 1. 2. ... 20 2.1 L .oo ee desire doen a Perea ls TA TA TA 12 E 7 E Heo Gatelaw Acacia. .... 1... 00 resourses iio ce Mesquite: enc un aie ue o 2a eus V ..... ...... l doco eae uy Currobrush L0 rond toc vould ad: Desert-willow l 3 26 _.... 20020000 0s in eon ea ain . +49 cee:e enn a Emory 5. Arizona white oak. 1... oso aln oen 2. Mexican blue nl cll vada 2. Serub core rel ns avea an uas 1. iNrizona cleats eti Mimosa. +2... :o cl nee tein n e eee eed s ASN AEC e ori oi inin bri rein arian aoe nae no : Sycamore 8. Hackberry 2. ... :.. 1.2 nl n en da a o ie 5. Plack willow °°... .nl el ILC ir aren yeas pena a aaa Cobton wood 2. . 2 2 o 2 22 se ues 2 t oa ot Ha e p e mea one a ae e ae 16. 0. 89 . 22 §: 0D 26. 39 6. 08 """" o "ao :-[ [° _C 1. 12 AS:. yr a mlm t moc 1 t Ott... ate 59. 03 10 mer- Ln col SO elec . 61 B M L.-. .I.. . disk nle thid Total basal 2. 13. 38 - 42. 54 20.71 4.93 61.64 52.20 36.10 37. 21 47. 68 E, ephemeral; I, intermittent; SP, semiperennial. 2Valley-floor specles (p. DIS—D 9). with these flows support many species that do not grow along streams with ephemeral regimen. The geology and topography of upper basins also seem to indirectly affect moisture levels in lower reaches. This is suggested by the botanical differences between the lower reaches of Ash Creek and Tres Alamos Wash. These lower reaches are both located on gently sloping valley fill. The lower reach of Ash Creek, a stream with headwaters in steep mountains, supports more valley-floor species and denser vegetation than the corresponding reach of T'res Alamos Wash. Tres Alamos Wash rises in a relatively level basin underlain by valley fill. The effect of the geology and topography of the upper basins on the flow in the lower reaches was observed in December 1965, when concentration of runoff in the headwaters of Ash Creek resulted in sustained flows in the lower reach of this stream (pl. 1) ; in contrast, the mainstem of Tres Alamos Wash did not flow at all. KELSEY CANYON In Kelsey Canyon, as in Tres Alamos Wash, the num- ber of valley-floor species increases with increasing drainage area of the upper reach, reaches a maximum in the middle reach located on bedrock, and then de- creases in the lower reach located on valley fill (table 20). In the lowest reach, near the confluence with the San Pedro River, burrobrush is apparently the only val- ley-floor species growing in the channel and flood plain TaBur 20.-Species present at selected locations along Kelsey Canyon LoCAHORADL 1). .19, 047 (cl 13 10 40 57 Flow regimen 1.2. -l ac. cs /l clu des erase E E SP E Cholla (Opuntia versicolor) _____--_. TC L UL Lc een 2a n -_ 2-D noc ) Core pada oops Rabbitbrush 2. .._.__._. C rei BDesert-willow l X Ree e.. Litticleaf sumac X S ! :- 2 un ee ewes ole an X X X Catclaw L X Seepwillow 2.1.2... lace en luli est ud XU Hackberry 1... ::= .n icle ere cen abit s X : ANAL Lr e ae cn X Cottonwood #. 212 LILO eL XC Saltcedar 2s cine eri r cle cea an ne- XC settle caren alence. Cm Blue paloverde. <: se sold cL ICC. ex- Barrobrush 0090 Loie ie nen denen ee a at's X Whitethorn Acacia. ~.. 1 Lull ule een ece. X Pricklypear (Opuntia engelmannit) ________L_LLLLL_____ X ! E, ephemeral; SP, semiperennial. 2 Valley-floor species (p. D18-D19). of Kelsey Canyon. Kelsey Canyon and Tres Alamos Wash both rise on Allen Flat. In contrast to the middle reach of Tres Alamos Wash, that of Kelsey Canyon has semi-perennial flow regimen. This reach supports cot- tonwood, seepwillow, and saltcedar, species that were not seen in the middle reach of Tres Alamos Wash (table 16, loc. 45). The middle reach of Kelsey Canyon is also the only known station of saltcedar away from the San Pedro River channel in the study area. D24 LOWER REACH OF HOT SPRINGS CANYON The preceding examples have shown that streams lo- cated on bedrock commonly have sustained flows, or flows other than ephemeral, and that these streams generally support many valley-floor species and dense and tall woody vegetation. However, not all reaches located on bedrock and having sustained flows support dense vegetation sharply differentiated from that grow- ing on the adjacent uplands. For example, reaches of Hot Springs Canyon that have perennial flow support only low thickets of mesquite and burrobrush (fig. 16). In the lower reach of Hot Springs Canyon, tall vege- tation containing many valley-floor species and having a basal area comparable to that measured along Paige Canyon or Turkey Creek (tables 11 and 12) grows near the canyon mouth, where the valley floor widens and perennial flow ends (table 21). Thus the width of the valley floor also seems to control the distribution of valley-floor vegetation. FiqurE 16.-Reach of Hot Springs Canyon with perennial flow at location 51 (pl. 1). Valley-floor vegetation consists of mesquite and burrobrush. Farther downstream from the canyon mouth, the vegetation along Hot Springs Canyon consists mainly of the mesquite and catelaw acacia thickets character- istic of reaches with ephemeral flow regimen (table 22). The changes in the vegetation of the lower Hot Springs Canyon, at the transition from bedrock canyon having sustained flows to a wide reach located on valley fill and having ephemeral flow regimen, occur with some variations along all tributaries at the point where the streams leave the mountain front. The changes in val- ley-floor vegetation at or downstream from the moun- VEGETATION AND HYDROLOGIC PHENOMENA tain front-valley fill contact are probably the most strik- ing examples in the study area of the effect caused by differences in geology and flow regimen on vegetation. TaBur 21.-Basal area of valley-floor vegetation of Hot Springs Canyon at location 21 (pl. 1) [Approximate maximum height of vegetation, 60 feet] Basal Species area (sq f0 Black willOw 122 .o cl eni kanssa ana aoa nake 33. 30 ans ka aand nae as 25. 46 Ath AZ Pri a eil essai na ao a aan bo aka an an ans aidan 21; 87 SyCAmore in cell n ane a ame a nees ] . \ \ 1 \\ A1 a A #7 | ge uf \\ [Z. a \ \\ / / & 60 \ AZ LA \ [/ S 50 t // p SXU Al_fl. uJ J I TY Kal f-|_z $ 30 X s \\ / ¥ \\// / I 20 \\- M 7% \\ f % 7 £0 S 7. \ \ // \x\\\ /. 1941 1942 1943 1944 1945 WATER YEARS Ficurs 22.-Number of days of flow in Rillito Creek near Wrights- town (1) and at the Oracle Road gaging station (2) in 1941-45. The two stations are about 8 miles apart; Wrightstown is the up- stream station. Solid lines indicate total annual number of days of flow, dashed lines total number of days of flow in winter and spring, December 21 through June 21. Data from U.S. Geol. Survey, issued annually. regions. Where the rainfall is more frequent and abun- dant, the differences in plant life between habitats at different topographic locations or with different geology are considerably reduced. Hence, in humid regions the contrasts in vegetation between, for example, valley floors and uplands or valley floors with different flow regimens are less conspicuous. On the valley floors of the study area, the vegetation varies primarily with flow conditions that are prob- ably present most of the time. These are the perennial flows, the semiperennial flows that can be recognized as such mainly in the dry early summer, and the absence of flow save during a few hours following convective storms in the summer in those streams that have ephem- eral flow regimen. However, variations in the vegeta- D45 tion also coincide with flows that are average, in the sense that they probably occur annually, but that are not as readily apparent from field inspection as the flow regimens described above. Such flows have been called intermittent because they are intermediate in duration between ephemeral and semiperennial flows. These flows seem to occur mainly as a result of prolonged frontal precipitation in the winter and early spring. The distri- bution of some plants in the San Pedro Valley also seems to reflect flow events that are not normal; they may have a recurrence interval of perhaps as much as 20 years. An example of such a distribution is the pres- ence of ash, a tree generally associated with sustained flows, in streams with ephemeral flow regimen. Ash may become established in these streams as a result of un- usually heavy and sustained runoff, as occurred in De- cember 1965 and January 1966. Some of the relationships between plants and environ- ment observed in the San Pedro Valley were described in earlier studies of desert vegetation. In the Sonoran Desert, the occurrence of distinctive types of vegetation in streams with different flow regimens, volumes of al- luvium, or altitudes of headwaters was recognized by Shreve (1951, p. 69-72). Shreve (1915, p. 19-21) also noted that the differential extension of canyon vegeta- tion away from a desert mountain range such as the Santa Catalina Mountains depends indirectly on the size of the stream, the volume of its flow, and on how far this flow is maintained away from the mountain front. In the Egyptian desert, the presence of certain species on valley floors is apparently related to the size of the catch- ment basin (Kassas and Girgis, 1964, p. 117). A sorting of distinctive assemblages of species in different valley- floor habitats with different moisture regimens was de- scribed in studies of the Hoggar and Tibesti massifs of the Sahara desert (Quézel, 1954; 1958). In the Hoggar massif, abundant regeneration of tree species occurred in wadis following unusually heavy rains and sustained runoff (Quézel, 1954, p. 8-9, 47, 109). Such trees sur- vive subsequent years of drought (Quézel, 1954, p. 47). The establishment of trees on the valley bottoms of the Hoggar massif is apparently related mainly to infre- quent flow events. The study of the vegetation of the San Pedro Valley supports the view that the plants are constantly adjust- ing to a dynamic environment. (See Hack and Goodlett, 1960, and Heinselman, 1963, for statements on humid regions.) In a desert, as elsewhere, plants are adjusted to the environment at any given time, for growth cannot occur under any other circumstances. On the other hand, in a desert the establishment, and, hence, the distribu- tion, of plants may be related to processes of widely different frequency of occurrence. Some distributions D46 may be related to processes that favor the establishment of plants but may not recur during the lifespan of the same plants. REFERENCES Arizona Bureau of Mines, 1959, Geologic map of Cochise County, Arizona : Tucson, Arizona Univ. Arizona State Land Dept., 1963, Annual report on ground wa- ter in Arizona spring 1962 to spring 1963: Water Resources Rept. 15, 136 p. Arizona Univ., Inst. Atmospheric Physics, 1959, Report on the meteorology and climatology of arid regions, no. 7, Arizona statewide rainfall. Benson, L., and Darrow, R. A., 1954, The trees and shrubs of the southwestern deserts: Arizona Univ. Press and New Mexico Univ. Press, 437 p. Bryan, Kirk, 1925, Date of channel trenching (arroyo cutting) in the arid Southwest: Science, v. 62, p. 338-344. 1926, San Pedro Valley, Arizona, and the geographic cycle (abs.) : Geol. Soc. America Bull., v. 37, p. 169-170. Cannon, W. A., 1911, Root habits of desert plants: Carnegie Inst. Washington Pub. 131, 96 p. 1913, Some relations between root characters, ground water alnd species distribution : Science, v. 37, p. 420-423. Carpenter, E. J., and Bransford, W. S., 1924, Soil survey of the Benson area, Arizona : U.S. Dept. Agriculture Bur. of Soils, advance sheets, field operations of the Bur. of Soils, 1921, p. 247-280. Chew, R. T., III, 1952, The geology of the Mineta Ridge area, Pima and Cochise Counties, Arizona: Arizona Univ., M.S. thesis, 53 p. Cooper, J. R., and Silver, L. T., 1964, Geology and ore deposits of the Dragoon quadrangle, Cochise County, Arizona : U.S. Geol. Survey Prof. Paper 416, 196 p. Creasey, S. C., 1965, Geology of the San Manual area, Pinal County, Arizona: U.S. Geol. Survey Prof. Paper 471, 64 p. Creasey, S. C., Jackson, E. D., and Gulbrandsen, R. A., 1961, Reconnaissance geologic map of parts of the San Pedro and Aravaipa Valleys, south-central Arizona : U.S. Geol. Survey Mineral Inv. Map MF-238. Dalton, P. D., 1961, Ecology of the creosote-bush Larrea triden- tata (DC) Cov.: Arizona Univ., unpub. Ph. D. dissert., 162 p. De Wiest, R. J. M., 1965, Geohydrology : New York, John Wiley & Sons, Inc., 366 p. Fenneman, N. M., 1931, Physiography of western United States : New York, McGraw-Hill Book Co., 534 p. Fernald, M. L., 1950, Gray's manual of botany [8th ed.] : New York, Am. Book Co., 1632 p. Gardner, W. R., 1960, Soil water relationships in arid and semi- arid conditions, in UNESCO, Plant-water relationships in arid and semi-arid conditions, reviews of research: Paris, p. 37-61. Gary, H. L., 1963, Root distribution of five-stamen tamarisk, seep-willow, and arrow-weed: Forest Science, v. 9, p. 311- 314. Gatewood, J. S., Robinson, T. W., Colby, B. R., Hem, J. D., and Halpenny, L. C., 1950, Use of water by bottom-land vegeta- tion in lower Safford Valley, Arizona: U.S. Geol. Survey Water-Supply Paper 1103, 210 p. Gazin, C. L., 1942, The late Cenozoic vertebrate faunas from the San Pedro Valley, Arizona: U.S. Natl. Mus. Proc., v. 92, no. 3155, p. 457-518. VEGETATION AND HYDROLOGIC PHENOMENA Gidley, J. W., 1923, Preliminary report on fossil vertebrates of the San Pedro Valley Arizona, with descriptions of new species of Rodentia and Lagomorpha: U.S. Geol. Survey (Prof. Paper 131-B, p. 119-131. Gilbert, G. K., 1875, Report on the geology of portions of Nevada, Utah, California, and Arizona : U.S. Geog. and Geol. Surveys West of 100th Meridian Rept. (Wheeler), v. 3, p. 501-567. Gilluly, James, 1956, General geology of central Cochise County, Arizona: U.S. Geol. Survey Prof. Paper 281, 169 p. Hack, J. T., and Goodlett J. C. 1960 Geomorphology and forest ecology of a mountain region in the central Appalachians: U.S. Geol. Survey Prof. Paper 347 66 p. Halpenny, L. C., and others, 1952, Ground water in the Gila River basin and adjacent areas Arizona-a summary : U.S. Geol. Survey open-file report, 224 p. Harshberger, J. W., 1911, Phytogeographic survey of North America: New York, G. E. Stechert, 790 p. Heindl, L. A., 1963, Cenozoic geology in the Mammoth area Pinal County, Arizona: U.S. Geol. Survey Bull 1141-BE, 41 p. Heinselman, M. L., 1963, Forest sites, bog processes, and peat- land types in the glacial Lake Agassiz region, Minnesota: Ecolog. Monographs, v. 33, p. 327-374. Horton, J. S., Mounts, F. C., and Kraft, J. M., 1960, Seed ger- mination and seedling establishment of phreatophyte spe- cies: U.S. Dept. Agriculture, Forest Service, Rocky Moun- tain Forest and Range Expt. Sta. Paper 48, 26 p. Kassas, M., and Girgis, W. A., 1964, Habitat and plant communi- ties in the Egyptian Desert. V. The limestone plateau: Jour. Ecology, v. 52, p. 107-119. Kearney, T. H., and Peebles, R. H., 1960, Arizona flora : Berkeley and Los Angeles, California Univ. Press, 1085 p. Kennon, F. W., 1954, Magnitude and frequency of summer floods in western New Mexico and eastern Arizona: U.S. Geol. Survey open-file report, 15 p. Kennon, F. W., and Peterson, H. V., 1960, Hydrology of Cornfield Wash, Sandoval County, New Mexico, 1951-55: U.S. Geol. Survey Water-Supply Paper 1475-B, 108 p. Keppel, R. V., and Renard, K. G., 1962, Transmission losses in ephemeral stream beds: Am. Soc. Civil Engineers Proc., Jour. Hydraulics Div., v. 88 (HY3), p. 59-68. Kincaid, D. R., Osborn, H. B., and Gardner, J. L., 1966, Use of unit-source watersheds for hydrologic investigations in the semi-arid Southwest: Water Resources Research, v. 2, p. 381-392. Knechtel, M. M., 19836, Geologic relations of the Gila conglomer- ate in southeastern Arizona: Am. Jour. Sci., 5th ser. v. 31, no. 182, p. 81-92. Kottlowski, F. E., Cooley, M. E., and Ruhe, R. V., 1965, Quater- nary geology of the Southwest, in Wright, H. E., Jr., and Frey, D. G., eds., The Quaternary of the United States: Princeton Univ. Press, p. 287-298. Kramer, P. J., 1949, Plant and soil water relationships: New York, McGraw-Hill Book Co., 347 p. Lambe, T. W., 1951, Capillary phenomena in cohesionless soils: Am. Soc. Civil Engineers Trans., v. 116, p. 401-482. Lance, J. F., 1959, Geologic framework of arid basins in Arizona : Geol. Soc. America Bull., v. 70, p. 1729-1780. 1960, Stratigraphic and structural position of Cenozoic fossil localities in Arizona: Arizona Geol. Soc. Digest, v. 3, p. 155-160. Leopold, L. B., Wolman, M. G., and Miller, J. P., 1964, Fluvial processes in geomorphology: San Francisco and London, W. H. Freeman and Co., 522 p. PLANT ECOLOGY OF AN ARID BASIN, SOUTHEASTERN ARIZONA Meinzer, O. E., 1927, Plants as indicators of ground water: U.S. Geol. Survey Water-Supply Paper 577, 95 p. Melton, M. A., 1959-1960, Origin of the drainage and geomorphic history of southeastern Arizona: Arizona Univ., Arid Lands Colloquia, p. 8-16. 1965, The geomorphic and paleoclimatic significance of alluvial deposits in southern Arizona: Jour. Geology, v. 73, p. 1-88. Meyer, B. S., Anderson, D. B., and Bohning, R. H., 1960, Intro- duction to plant physiology : Princeton, N. J., Van Nostrand, 541 p. Montgomery, E. L., 1963, The geology and ground water investi- gation of the Tres Alamos dam site of the San Pedro River, Cochise County, Arizona: Arizona Univ., M.S. thesis, 61 p. National Cooperative Soil Survey, USA, 1964, White House Series: U.S. Soil Conserv. Service revised soil series description. Oppenheimer, H. R., 1960, Adaptation to drought: xerophytism, in UNESCO, Plant-water relationships in arid and semi- arid conditions-reviews of research : Paris, p. 105-1838. Phillips, W. S., 1963, Depth of roots in soil : Ecology, v. 44, p. 424. Quézel, Pierre, 1954, Contribution a l'étude de la flore et de la végétation du Hoggar : Algiers Univ. Inst. Recherches Saha- riennes, Monographies Régionales 2, 164 p. 1958, Mission botanique au Tibesti: Algiers Univ., Inst. Recherches Sahariennes, Mem. 4, 857 p. Renard, K. G., Keppel, R. V., Hickey, J. J., and Wallace, D. E., 1964, Performance of local aquifers as influenced by stream transmission losses and riparian vegetation: Am. Soc. Agr. Engineers Trans., v. 7, p. 471-474. Robinson, T. W., 1958, Phreatophytes : U.S. Geol. Survey Water- Supply Paper 1423, 84 p. Russell, E. W., 1961, Soil conditions and plant growth : London, Longmans, 688 p. Sellers, W. D., ed., 1960, Arizona climate: Arizona Univ., Inst. Atmospheric Physics, 60 p. Shreve, Forrest, 1915, The vegetation of a desert mountain range as conditioned by climatic factors: Carnegie Inst. Washing- ton Pub. 217, 112 p. D47 Shreve, Forrest, 1951, Vegetation of the Sonoran Desert: Car- negie Inst. Washington Pub. 591, 192 p. Shreve, Forrest, and Wiggins, I. L., 1964, Vegetation and flora of the Sonoran Desert: Stanford Univ. Press, 2 vols., 1740 p. Smith, D. G., 1963, Pleistocene geology and geomorphology of the San Pedro Valley, Cochise County, Arizona: Arizona Univ., M.S. thesis, 73 p. Smith, Winchell, and Heckler, W. L., 1955, Compilation of flood data in Arizona 1862-1953: U. S. Geol. Survey open-file report, 113 p. Todd, D. K., 1959, Ground water hydrology: New York, John Wiley & Sons, Inc., 336 p. Tuan, Yi-Fu, 1959, Pediments in southeastern Arizona: Cali- fornia Univ. Pub. Geog., v. 13, p. 1-163. 1962, Structure, climate, and basin land forms: Assoc. Am. Geographers Annals, v. 52, p. 51-68. U.S. Agricultural Research Service, 1963, Hydrologic data for experimental watersheds in the United States 1956-59: U.S. Dept. Agriculture Misc. Pub. 945. U.S. Dept. of Agriculture, 1938, Soils and men: Yearbook of Agriculture, 1232 p. U.S. Forest Service, 1948, Woody-plant seed manual: U.S. Dept. Agriculture Misc. Pub. no. 654, 416 p. U.S. Geological Survey, issued annually, Surface-water supply of the United States, Part 9, Colorado River basin: U.S. Geol. Survey Water-Supply Papers. U.S. Geological Survey, issued annually after water year 1960, Surface-water records of Arizona: U.S. Geol. Survey open- file reports. Wadleigh, C. H., 1955, Soil moisture in relation to plant growth, in U.S. Dept. Agriculture, Water: Yearbook of Agriculture, p. 358-361. Wilson, E. D., Moore, R. T., and O'Haire, R. T., 1960, Geologic map of Pima and Santa Cruz Counties, Arizona: Arizona Univ., Arizona Bur. Mines. Zohary, Michael, 1961, On hydro-ecological relations of the Near East desert vegetation, in UNESCO, Plant-water relation- ships in arid and semi-arid conditions (Proc. Madrid Sym- posium) : Paris, p. 199-212. A Page Di2 catclaw. See Catclaw acacia. Chihuahuan whitethorn.................. v whitethorn. See Whitethorn acacia. MERCIAN AEC Len se ae reve ed a 40 constricta . ...... v qreggii.......... v Fraddiana 2s eil nn r A edi 40 » - L200 2 n oen bene ae wane ben's v Adiantum sp.. 000. IET e c L0. LI Icl er enn ea e a ute v Agave 00000 NN LIC Lacie i. v -I es elle IAAL T us deus Aks are 22 rP en GLAST ede o 11, 25, 27, 42 AMIEONHA SL ULT IL Yos in shun de | Lv erea an v, 19 Alfalfa, maximum rooting depth.............. 40 MIKA MAbs. 2 22200200 ee rer l Hive ean ni 6 Allen Flat.. - 4,12, 13, 21, 23, 34, 42 Alligator ...0:0. 02s lcci NL AMthOrn.. 2s eee t enne een ood v, 12, 15, 19, 28 Almus oblongifolia: 2.2.21 200 ee ec bs v Aloysia +222. 2-0-1 000 Irv v Altitude, effect on vegetation................. 12 11 Amorph@ 1.12000. 220. Phas v Amisacanthus v Anisacanthus thurberi...... ... v Apple, maximum rooting depth .............- 40 Arctostaphylos pungens... _.... v :X AXL :s ion coeds dne en vi ATIZONS .- 20.00 v, 19 Arizon® agh .. 122.3 020-0. 1 08 Porc sn oen v, 19 Arizona cypress. ...... ... ... 19, 23, 27, 48 Arizona grape....-......_..... v, 19, 22, 25, 26, 27, 43 Arizona sycamore. See Sycamore. Arizona 12 Arizona walnut. See Walnut. Arizona white oak..........__........ v, 19, 21, 22, 23 Arrowweed................. L.. ¥,19, 27,40 Sh mole S s neue sey aus 11, 19, 21, 34, 36, 41, 43 Arisona, or v, 19 Ash Creck.............. germination............ Hot Springs Canyon ... iC€elsey Canyon.... maximum rooting depth.................. 40 Paige Canyon.......:.... 19, 20 Redfcld 25 San Pedro 27, 28 Sora Canyon: 26, 37 Tres Alamog Wash.: ....:._.;..c...... 21, 23, 35 Turkey Creek......._... 19 Wsh Creok on. eri 20, 34, 35, 36, 41, 42 streamflow data_........_._.. 8 valley-floor vegetation............_....... 21 Affiple® CORESEERE L : 2200.0 cecil ec re. v L-. c cca rons cake ea sil 40 B Baccharis .. . . vi sarothroides. . Batrelcactus....:.............. Basal area, bottom-land forest............._.. 19 Gefinitionts ~s 2000 cee 12 valley-floor vegetation.............. 20, 21, 28, 24 INDEX [Italic page numbers indicate major references] Page BASIMAUATAIL -s 0300000 aaa een cc bleed Ds Batamote seepwillow. See Seepwillow. Bear Creek, streamflow characteristics. .._... 9 valley-floor vegetation........_.__.__..__._. 43 D .. ccc 00 on celina ais v, 11, 12, 21, 22 Black willow. _...1. £ ..... ae 19, 21, 36, 42, 43 ASH CFeGK : 2 Uo 2.4 10 02nd einen oa cua ae 22, 23 germination.... ..... 39 Hot Springs 24 maximum rooting depth.................. 40 Paige Canyons ...see aa eva 19 San Pedro River. 27, 28 Sora Canyon. Q2 tolic ioe. 26, 28 Tres Alainos Wash. . 21 Blue paloverde.........:.:.:...-.s v, 15, 20, 23, 31, 43 Bolsa Quartzife : :.... .2 loool Clee. dias s 5 Bonpland willow.... .. .... vi, 19, 27, 48 2.0. 211 9000, na evan ae t reena aa ee air 28 p 2. ..... 00. lo shave a v Brfickellia. .l}... 0000] 1. e. rec v, 15, 19, 26, 27 Bricketlic californica >. u eons ous v, 15 floribunda. . .. ... sok A19 Brittlebush . u ¥, 1215 Buckthorn........ , 19, 21, 22, 27, 48 Buchman ..; .- 29, 35, 87 streainflow data:. 7,8 variations in valley-floor vegetation . . .... 26 1. v, 19, 27 Bumelia lanuginosa. . .. Res. v Bur-gage, white... 00. OT v, 15, 19 0st v, 19, 31, 36, 43 Ash Crock '-........ 22 Buehman Canyon... 26 Kelsey Canyon...... 28 Paige Canyon:: ...A: ON 26 Redfcid Canyon.... 22.0; c lc cect 25 Hot Springs Canyon.. 24 Roble Canyon......... 20 San Pedro River...... 27 Sora Canyon. . .. . .url eee eect n els 26 Tres Alamos 21, 23 v, 19, 22, 26, 27, 43 C CachaGene i% ooo .n ol ote ee bese che uue 11 Cactus, barrel. :..... v, 12, 15, 19, 26 Christmas...... .. ro resent elo ik v, 15 giant, or saguaro........._. 7 v 2. 5 6 Calliandra eriophyMa........._........ ele Canyon ragweed .co... ecu cari v, 19, 26, 27 Carlowrightia . . 2500 s. .s. 2.2.3 a hn v Carneglea gigantea . v .e ecus dics v, 15, 19, 26, 27, 43 CONeSif . 3 an once oun oe ende anv aaa v, 15 - v, 36, 41 maximum rooting depth....... A 40 San Pedro River channel................. 27 upland IOO UIL 20 valley flanks. .. 13, 15,19 valley floors.. .... _ 19, 20, 21, 22, 23, 24, 25, 26, 28, 48 Celtis reticulata v Cephalanthus occidentalis....._._._._..__.___._._ v Corcidiuwm . .x... 220.00 ene li- v microphyllum . v 37 Page Chihuahuan Desert plants................... D12 Chihuahuan whitethorn acacia............. v,12, 15 Ohifopsis linearis. 11.200. ce n iving v ... . v,12,43 Kelsoy Canyon.... 120.0000 28 Redficld Canyon.. 25 San Pedro 27, 28 Tres Alatuos 21 valley flattks .... )... .. coucouller ed n 15,19 valley floofs.2. : TGE sL ra oes 19 Christmas cactus; 000000 ec Ld. iiss v, 15 Chrysothamnus mauseosus........._._.___....... v Cochise County: -__. LE. 2 Oondalia -Lycivides.. ... de aisi cece v L2): 2.0.2 oxen nat s ene v Opral L.-. 1000 ec eee ere v, 22 v, 11, 19, 21, 34, 36, 42, 43 Ash o Ler cnn ic 22, 28 germinabHon i rer dense 30 Hot Springs 24 Kelsey CANYORLL__. . 28 maximum rooting depth.................- 40 Paige Caftiyo. -.-.. 19, 26 Redfield Canyon. San Pedro River.... Soza Canyon....... Turkey. c, 19 Oreosofebligh.. ~: >- cs.. 0cl Ld.. cE Ice v, 11, 43 maximum rooting depth.. 40 San Podifo RIveL.L ... ..... 27 Tres Alamos Wash. 21 valley Alaniks.......... s 20. co ane 15, 19 valley floors ©: 7:0. enc loco ute 17, 19 Orucifio, Mexican... .\: uce leis icc 15, 19 OylndropHnbla.2. />-- -. s v . .n rol cl r 4 o_ es ens bone 12 ATiGGNa. . |. O00... 19, 23, 27, 48 D Dasylirlon ifhesleri.2 ..... cllco cu vi Datura meteloides............. v Davis Canyon...c...........: 34 Deformed gravels... .s 5 Desert Grassland, floristic region............. 12 Desert hackberry........._...... v, 15, 22, 24, 25 Desert-honeysuckle....................c...... v, 15 Desert-willow............. v, 19, 31, 32, 34, 36, 41, 43 Ach (Oreok .... :. .o lle ene nea be seve ee 22, 23 Buchman 26 distribution and ecology.... 42 fe Hot Springs 24 Kelsey Canyon. ...or... 0200 ven 23 maximum rooting depth........ R 40 Paige Canyon.........:_....... * 26 Redfield Canyon. £ 25 Buble 20 San Pedro River. 27 Soza Canyon....... & 26 Tres Alamos Wash.............~ .. 21, 28 Desertbroom........ v, 15, 21, 23, 27, 36, 43 DodOnGeét v DoUglat-ir.\ 1 -. orci cll el ae v Drainage area, relation to valley-floor vege- c-. ooc! coool 20, 22 E Ecology, valley-floor vegetation............... 81 Edgar Canyon. .. _- 28 D49 D50 Page Elderberry, Mexican..................... v, D19, 27 Emory oak......___.. v. ¥7 19, 21, 23, 28/48 Enéelia 22 2000, 00000 .s bs aie teu v, 15 farinos . . 2s s uou di. ea es ie v rUbeRCEN® .o... cous viel nomas rt ete v Engelmann spruce . . . vi Ephedra drifuren c 28200. ce IIE v Ephemeral flow regimen, definition. . ..___._._ 7 Erythrina flabelliformis.............22.22220002 v Escabrosa Limestone..:............_...._.... 5 False-mesquite . . ...... Perocactus . oer v fone doe n cL en bea core nath a v, 21 MHM Heol ri eas 12 Douglas.......... v white:......... v Pious carien su 22000012. 0. Codi reveals v Five-stamen saltcedar.........._...__.__.____._. v, 19 FIOUFERSIOCETRHALE:L 22:02. 0.20. 94 vi Flow regimen, relation to germination........ 31 relation to valley-floor vegetation.... y 20 Foothill paloverde:.. ...l... v Pouguieria v Fougqulerincene.. ...l s. 11 Four-wing saltbush . . o/c. ¥, 15, 24, 20, 27, 40 Franseria ambrosioides . ...._..._._.....__.__._._.__ v He As s en eon eve neden s v PFraXINUE :. 1. 2 2.0. Joos sole eve . v Fremont cottonwood. See Cottonwood. G Galitito Mountaing }.. 3. lus l 4, 5 tertiary vologhies........ ...l. 5 Geology, relation to valley-floor vegetation . .. 22 Gila Conglomerate. ...._.__._.___..___ y 5 Gila loam soil series . . 6 Gila River. :..... .l. lll. s Pl cae ani 4 flops -s". :.. cu roo oes crea eon areata 9 Goodding willow. See Black willow. (COUnEY - :: culls es ier iate 2 os 1.20210. o oo oo a vale aad v, 12 Gramiflege.. ... occ. : oll er coll cecal aca 28 Granodiorite, Happy Valley quadrangle...... 16 Grape, v, 19, 22, 25, 26, 27, 43 Gravels, deformed.... .-..}... ..... 5 (CraythOM L 2222201 Lv .on c onne inon avea ad v, 36 ASH c} aoe 28 Buchman Canyon.... 26 Paige Canyon.... s 26 Redfield Canyon.................. Bevaeys 25 Roble CSNYONLL.L :. ous 0.2 ience act 20 San Pedro River.. :. 27,08 Tres Alamos Wash............. 21 valley flanks..........__._... wo 15 Great Bajada Wash.... 32, 34 valley-floor vegetation........_.______.___.. 20 Green & v Growth of plants and ground-water depths... 41 ---: -o cori ben 40 H Hackberry. .. .... 11, 19, 21, 27, 28, 31, 34, 41, 43 Ash Creek Aig, 28 Buchman 26 CeSert LALA A I Neca n seran v, 15, 22, 24, 25 @erminations 2. .- 00,2. 00.2 oul ored neend 29 Hot Springs Canyon. ..... ale: 24 Kelsey Canyon.......... vee 28 maximum rooting depth................~. 40 Paige Canyon ..2202... ovo Ls ione 19, 26 Redfield Canyon...... read 25 20: en LLCT 26 Tres Alamos 202... 21 Flappy Valley Happy Valley quadrangle, basin fill........-. 17 @ranodipfite . . :. . ; .so c o. ot coh rian. 16 INDEX Page Moneysage..............;... v, D11, 15, 17, 19, 26 crs v, 19, 25, 27, 43 Hot Springs Canyon.. 00000002 34, 42 streamflow data... S1 C7,8 valley-floor vegetation. 24 Hymenoelea . -cell v I Indigohiish: : .: .s Duel cours lene v, 19, 22, 27 Intermittent flow regimen, definition......... 7 J Hin§otweed : . . . : .- 1. 222 ee ars l dti tt v, 28 Johnny Lyon Granodiorite. 5 Johnny Lyon Hills. :.... }. ..); 4, 5, 34, 85 JolfHit : £020. 00200. 00, (oot pdt ay v, 15, 26 o. 1s 002 oren dud sad blade ace ae ee 12 . :r ssl ENO och - niet crews laa v sL v, 15, 19, 22, 25 Juniperus deppeana . v a ) . . 2 v2 ooo oe aie errata v K Keith Ranch Creok 00000 :L eate 34 Kelsey. Canyon =.... valley-floor vegetation.......... spinosa . ...... ..... 0.000. L Lake beds....... s 5 Larrea tridentata. & v Leguminogne. ... ro Losi LL onle 11 O90. 000 .e ere cece cnd Ack 1 Lippig.......:/-o.lss 4 v Little Dragoon Mountains.......... .. 4,85 Little Rincon Mountains...._............._.. 4, 34 Littleleaf sumac................ vi, A9, 21,28, 27 Location of report area. .. 12s 2 LyeluM-..~.. ...se cous arse v, 28, 43 Ash Creek... * 22 Paige CANYON. .:.: 2.0.0.0 2. ore g 26 Redficld 25 San 27 Tres Alamos Wash # 21 valley flanks. A 15 valley floors . he 19 Lycium berlandieri.... v, 15, 19, 21, 22, 25, 26, 27, 43 2% . 1220 00 ren oo e o oeil anna ese v, 15 M Mablura Pomifera-.. 21022; 02. oul one vised v Maidenthair fern: . .0. 2020.20 1112 lo 37 Mali®. 2221.1 isl ol cous S meade at ania died 40 -.. cece ollo an v, 12, 22 2.21000. v, 15 Menodora scrabra v v, 12, 13, 21, 36, 39, 41, 43 Ash (Oreok: ...s. n lle rre 3+. 49,83 Buchman Canyon.............. % 26 Great Bajada Wash........... Hot Springs Canyon....... C 24 maximum rooting 40 Paige Canyon.. . no rooster an been 19, 26 Redfield Canyon........... Roble Canyon......._...... San Pedro River........... . (Peran Wash. gc 20 Tres Alamos Wash.)... 21, 23 Turkey Creek.........._... cx 19 valley . 15,19 valley floors. ; ... .. s on er reac 19 Mexican blue oak. ~...). ..sl2l2l . v, 19, 23, 43 Mexican erueillo-. ..>. ... 0.0... cul ata cane 15, 19 Mexican elderberry............... 27 Mimosa.... v, 15, 23, 43 Mimosa ... 20.0 oar ane v Mineralization of water. 28 Moisture sources clyde. beide 41 Mortonta seabreliass ..". 2.3... ducer edie v Page Morne microphyll¢.. . . /. 2; lll ono el aaa wi v -L -L I0. concer. contevesces -.. ¥, D15 . ...!]. 0.0 .be -e ece es 11 . ool ree LCA Le col wan v, 19, 21, 22, 37 N Natfows, The-. 0. 20 .n Golo an deena ues 5 Nicotiana glauca. . vi Nolina microcarpa. . v 0 OAK ooc: skal sance - went 12, 27 Arizona v, 19, 21, 22, 23 EMOFY ..: coccus ree ele ave dice v, 19, 21, 22, 23, 43 Mexican .. 8200's v, 19, 23, 43 1 .. la- {Lviv haver v, 19, 22, 23 OgofiMo...1 :.: (conn cedars v, 11, 12, 15, 17, 19 One-seed juniper................_. v, 15, 19, 22, 25, 26 Opuntia engelmannii_... v, 15, 19, 20, 21, 23, 26, 27, 43 fulgide manmiliatt -.. .c 920. 02002 v, 15 de pine@ulis : s SLI eve Al ue sev ae ans v DRACGEMRIEREL 22 .A ive ere ae neal ened v, 15 versicolor -l.: v, 15, 19, 21, 23, 25, 27, 43 Spe avea nee doan d deus no delos v .L cf enol oona n n ¥, 21 P Paige 19, 26, 34, 35, 36, 37, 41 streamflow data......._..._......!... 7 variations in valley-floor vegetation... .... 25 Palmer Aga¥Vé. lou... ovi no Peca seen en ioe v, 15 Palmilla...... i Paloblanco. .. Paloverde. ... Diges. LODI o id v, 15, 20, 23, 31 foothill, of green.... .... v Pantano .. 29, 43 Parthenium argentatum.... . C 40 Perennial flow regimen, definition...........-. 8 Persistent pools, definition.............-...-- 7 Physiography of report area. ......._._.__...-- 2 Picea engelmanni.................. < vi Pima County.... 2 12 ponderosa. ..... v Southwestern white. ............__....... v Pinus pOndéT08q................. v PeRteRH . :~ 1. nine L e cue eee edad v Plafnus lede cash eels vi -.. > .s... .oo lL O00. recu ceenine v Pii . S. L .c coden eevee a v Poison-ivy...... v, 19, 22, 27 Ponderosa PING... Liz.. ...ll. fou e v Populus 1... cic v Precipitation: a:. coon 9 average ANMGALL 1... 222.010 20d resend 6 Pricklypear. ...... v, 12, 43 Kelsey Canyon... ...:}. 23 Psige Canyon. ce iene 19, 26 San Pedro River: -L.. 27, 28 Tres Alamos 21 valley flanks..............- 15 Prosopte deus 40 juliflora velutina . . v Pseudotsuga v Q arigon ign 31 .. 2 uuu Los eae eds v €MONYi- 121. en fete. v oblorgifolia........... .. MR ille ay a v 20000000 Meu eases nee s i> v R Rabbitbrush. .= v, 19, 21, 22, 28, 27 Ragweed, canyon. : .s cl" v, 19, 26, 27 Red Silt Wash:... .s /. cool el ue che aed 32, 33 Page Redfcla D4, 25, 20 streamflow 7,8 variations in valley-floor vegetation.... ... 24 Bedington ores 4 Redrock sacs ..... oie. vino eer nere 42 Rel@Ma alts 22 cr Pin Ivie cee n 40 Rhamuwus betwlaefolia.. v 3.21. 0022 AICI cel vi microphyliq ss. 3. 22 alel lle eed e cease vi r@dieans 2.002. v trilobata. .. vi Rillito Creek. 44 .ro duno es n 2 Y s be anl le eon ae 9 (Rincon Creck 22. 20000 SILU. 20, 44 streamflow characteristics. ........_....-. 9 valley-floor vegetation.................... 44 Rincon Mountains...... i000. cs 4,12 Roble Canyon, valley-floor vegetation........ 20 Runoff characteristics on smooth and dis- Sected o .O 0.0 council collin 16 Bussian-thistle. v, 15 S Sabino Creek.. 1.2.00 00A TI- 29, 82 streamflow characteristics. .._......._.... 9 valley-floor vegetation........_.__........ 44 Sacaton 5 Saghiatos cL 2 EA Ido crece rec lune v,12, 15 iSulia vi accesss ien l ols bine Pobal a To be bd vi tazifolia . . vi Sateola .....) v Salt 27 Salt River, floods. ala ee 9 Saltbush, four-wing......._.__... v, 15, 24, 26, 27, 40 Saltcedar. Err L e ei ed eli ceva baie as 28, 27, 28 cel, v, 19 @ofmiNaMONE 7-21.12. veces 30 Bambucis mevicana...............000....0000. v San Fedro 2, 41, 42 basin dimensions of tributaries. ......... 4 drainage cll clue 4 floodss s eye Lopes uo in ioe neden coc 9 relation of water quality to vegetation . . . .. 27 vegetation of bottom lands.........__._.. 27 San Fedro Naley... 37 Cenozoic geomorphic history..........._. 6 effect of topography on plant cover...... 13 ground water. .-. 2020.22 uce 9 precipitation.. --. 7 ELL Te Baik es aus 16 100. will 4 SUUCIMTCIEIT ... 000 en nL Ace teers 2 valley fill; .: 00} o eno eee eol 4 variations in vegetation. 2 SandpaperDUsh2... :- e v, 12 Santa Catalina Mountains.................... 4 Santa Cruz River, floods..........._......... 9 SEpIndUS .L. .1 . 00.10 ec ci le ll vi Scrubloak.-c 2006 001 200000. v, 19, 22, 23 Seepwillow .i vi, 19, 34, 36, 37, 43 ASMOTECE: ECI IU: co tecr e erect nisin nie 22 Buehman Canyon.»........2...0c.000.0.0l 26 @ermingtone. .>. -U... - nll. e nee 20 Miot Springs Canyon...................}. 24 Kelsey cs 23 maximum rooting depth.................. 40 Paige 26 .ll 25 San Pedro River: 27 .LA. AIL 26 INDEX Page vi, D19, 27, 32, 41, 43 Buchman Canyon... 26 Great Bajada Wash . 0.00000, 20 Hot Springs 24 Faige Canyon.. 22. LIL s 26 Sore Canyon. : 2-22 ceci eel Haren cols o 26 Tres Alamos Wash . . 21 Soil, San Pedro 16 Soll groups.: 2... ...o ek p cae rive 6 Sonora; MexiGo. -- _c selec cel sin coun s 2 Sonoran Desert floristic region................ 12 is ocal ca Loe deans ... V1, 22,43 Southwestern white pine. ....._._.__.._.____.. v Sora Canyon.>...:.000 ree eagle lls 29, 37, 38, 41 effect of bedrock on flow.................. 8 ground-water depths. ......._...___._._.____. 9 streamflow dats .s. .or ece limn cs cl 7,8 variations in valley-floor vegetation.... ... 26 SpHMIGG a+ 5, ool o.. o clued avena ae awe nne - oue s 12 ...o ci ces vi Squaw bush.... ...so. loo nen. vi, 19, 27 Stream terrace, San Pedro Valley 4 Streamflow, seasonal changes...........-.-.-- 9 Streamflow data -~. l oI 00. r icc 7 Sumac .o l. .cc oer } vi, 11, 19, 27 HfHcleaf.. ..}; eca too vi, 19, 21, 28, 27 Sustained flows, definition. 7 cle fuentes vi, 19, 34, 36, 42, 43 Ath Crock 2s. leona iio canne 22, 28 Buchman 26 germination.. .s aree 30 Hot Springs Canyon.. 24 Paige Canyon. 19, 26 Redfield Canvyon.:.l.lcss louie. rill ilt 25 San Pedro le oils 27, 28 Tres Alamos 28 Turkey ..} con. elie ues 19 T un cs. on eevee Pdr En nece c nea d's o 40 .. 291.3. 20 eu seee eens nese an nne 40 2: 2290. .oo oona re enas boca ce aces 40 0s. ions aud aa noon aoa ey oe v, 40 Tanque Verde Creek, streamflow character- oo oon norn eared een nea nL 9 . 01 moe teat uce vi, 12, 15, 19 Tecoma <. ..- .oo. Pee -l nevi tein r ae hes vi Temperatures, seasonal mean... . 6 Teran Wash, valley-floor vegetation.........-- 20 'DetTace AllyIMM .- 2. ooo NCSC T sec c.. 4 5 Tertiary volcanics, Galiuro and Winchester Mountains. .c. s. cul . 5 Texas mulberry....... v, 19, 21, 22, 37 THrCGAWNA. .- sL .... eon cie caves ne vi, 12 Tobacto, Mob... .:... l xe ea beile n eties vi, 19, 27 Tres Alamos formation.......-......._........ 5 Tres Alamos 32, 33, 34, 35, 41, 42 valley-floor vegetation . 21 TrumpetDAsh. 2. . 1. . seu ugh a. e vi, 19, 26, 27 TAICEON ATTOYO. - 2-2 nel eden de een ee be wells 32 Tucson basin, hydrologic characteristics of gaged 44 species present......... 48 Turkey Oreck: I... c 19, 35, 36, 42 U Upland species ... . s-»... ln. rie ree 15, 20 Upland vegetation.. .. ME. .s 12 v Valley fill, San Pedro Valley.................. 4 Valley All rile 5 Valley flanks, variations in vegetation ...... .. 2 $ D51 Page Valley-floor vegetation............_...___.__.._. Di? capillary rise. .... 40 ecology........'.. 81 effect of bedrock canyon in middle to lower TEAUH. -. onl Clr. cena dn att 36 effect of extreme lower reach located on 132.020. cuse. ol Lete 87 effect of headwaters located on bedrock... _ $3 effect of headwaters located on valley fill. 81 effect of lower reach located on valley fill. 86 effect of middle reach located on bedrock . 85 effect of middle reach located on valley fill. 35 effect of perched aquifer......_....._..._. 35 effect of volume of alluvium... ............ 34 germination - .s .. ... enn nn oy 29 relation to width of valley floor........... 24 roofing depths.. .y. loc 1. onto sere 39 Tucson basin-.......... 48 Vegetation sampled, description.............. 12 Velvet aghiz, 22. 000.00 LOT L cedar ad ive nich v, 19 Verbenacéag.. 122. oye noone ali tears 11 Vitis arizonica.............. A v w vi, 11, 19, 31, 32, 33, 34, 36, 41, 43 O. 22 O. noice or ne red bee b cece 22, 28 Buchman Canyon... 900. crece 26 Hot bprings 24 maximum rooting depth.................- 40 Paige Canyon.. ... olen olen dation. 19, 26 Redficld Canyon. cdi cic 25 San Pedro River.. 27, 28 Soza Canyon....... 26 Tres Alamos Wash.. - 21, 28 Turkey Creek.... 19 Walnut z-. .so toc ece nece s eela bev ens 33, 35 Walnut Gulch basin... .-.. Circe. ces 37 WelwMechin mirabilis. . - . .. Te 40 White DHr-sage. .. educa v, 15, 19 White desert ziniiac:..........._.._...l.., vi, 15, 19 ..- else ers seran boss bows v White House soll geries....._...._...__.._._L.. 6, 16 Whitethorn acacia... .. v Great Bajada Wash. 20 Hot Springs Canyon. 24 Kelsey Canyon. :L n. .o. nld 23 PAIGG UANYONIL: tlir sori ces cals 26 Redfield Canyon. 25 Rouble CANYON, - LL. eda te ci 20 San Pedro RIVer . 27 Tres Alamog.Wash.. 2.../. l. 21, 28 valley flanks. . . .... lsc lela lune 15 valley floors.. .... 19 WilloW - cero n crcl Aare rope cee oben Pemac anale 11,34 black. See Black willow. .s... vi, 19, 27 Goodding. See Black willow. yew-leal: cl L cuca cee vi, 19, 22, 26, 27, 37, 43 Winchester Mountaing..........__..._.....-- 4, 5, 34 Pertlary voleatifes. 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Sf Past r/ 8 3 R I/flrffi/Afilfwu Shere fo ect %p 4 oss &/I’4/ / s | 30° [AZ/e”: f A | tec oct, ARY t S y Oy ~ Re ; '. ts & tof s gs ps com tno 32 -z So N \ // lfly/y/ S [Muffin/£24.12 x, 3 M\7m siemsseeceé sss ees] o-" wzzfizaozfi ° "s Roonis S x yoyo o > SNIYVLNNOW fi/wvm 7am e a boo/4 & Stuar i/V. & p grommet {awn/l ”Ly/WWW”! & S S § & $ ® ”7//%///// . § a /y.w//////. 3 , § & g/f/A/zul/flq I \ ouav fig.” gm!” ‘I. W M, € awe. § 3 8 io it m 8 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY (J/ "9 nave aper Historic Flood Information for Northern California Streams From Geological and Botanical Evidence GEOLOGICAL SURVEY PROFESSIONAL PAPER 485-E Prepared in cooperation with the California Department of Water Resources Historic Flood Information for Northern California Streams From Geological and Botanical Evidence By EDWARD J. HELLEY and VALMORE C. La MARCHE, Jr. VEGETATION AND HYDROLOGIC PHENOMENA GEOLOGICAL SURVEY PROFESSIONAL PAPER 48 5-E Prepared in cooperation with the California Department of Water Resources UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress Catalog-card No. 73-600234 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price _ $1.45 (paper cover) Stock Number 22401-02414 CONTENTS Page Page AET: T.... s) le iLL eis evere ie cue vee aa dha re eep 24000 reba vee bee E1 | Extension of flood records in northern California ................ ET !!.... nr ine le ech avenin nea ns 1 Methods cies. 7 Standard meLlHOGS -. eller reverses 1 Tree-ring dating of flood deposits ................................... T Extension of flood records by geological and Radiocarbon AALINE 8 DOoLaniCal-EvIGENCE re nen 2 | Description of sites with good evidence for past floods.... 9 Description of the area studied ..............:............................... 2 Blue Creek near 9 Climate [. "ok Scott River at Indian Scotty Campground .. a. 49 Surface-water hydrology .; 4 Trinity River at Eagle Creek Campground ................... 12 The floods of December 1964 ......................................._.._...l.. 6 Bast Fork Willow Creek 15 IMELEOTOIOSY -... ...... .. 7.2 1 vies. eer ies in depo 6 | Summary and conclusions ....... ~ I5 RAMONA: 00.2: :...... ei V ree Lele or ne d d ea hvae 6] »Ref@renCeS CIEOQ ... ....::-... :. :-/... 15 ILLUSTRATIONS Page PLATE 1. Maps showing geology and graphs relating to cross-dating of redwood, northern California ............................ In pocket FIGURE 1. Geomorphic provinces and major drainages of a part of northern California ...... E3 2. Isohyetal map of a part of northern California Reede 5 3-4. Photographs showing- 3. Ring-counted and radiocarbon-dated stumps used to date flood deposits along Blue Creek near Klamath; Calif. ne ss eheue bray ric bacha aes dove 8 4. Douglas-fir tree killed by burial in flood debris during 1964 flooding as a result of backwater effects caused by a culvert on Ti Creek at the KI@MAth RiveP eee 9 5. Map showing sites where evidence of prehistoric flooding has been found in northern California . :... 30 6. Photograph of prehistoric flood channel between older gravel 3 and older gravel 2 18 7. Photographs showing Surface NMOFDPhOIOGY neenee elle 14 TABLES Page TABLE 1. Radiocarbon and dendrochronologic data for trees sampled at Blue Creek ... E1l 2. Corrected radiocarbon-based dates for trees sampled at BIUG CI@@K 11 III VEGETATION AND HYDROLOGIC PHENOMENA HISTORIC FLOOD INFORMATION FOR NORTHERN CALIFORNIA STREAMS FROM GEOLOGICAL AND BOTANICAL EVIDENCE By EnwaArp J. HELLEY and VALMORE C. LaAMARCHE, JR. ABSTRACT Severe flooding in the mountainous region of northern Cali- fornia has produced texturally and morphologically distinct gravel deposits. Observations of the erosion and deposition pro- duced by the devastating floods of December 1964 allowed comparison and identification of ancient flood deposits, Age limitations have been assigned to these ancient floods at four widely scattered detailed study sites in northern California. Long-lived coniferous trees, both living and those killed by the 1964 floods, have been used to assign minimum ages to these deposits. Maximum ages have been determined on the basis of radiocarbon dating of material entrained in the same deposits. Regional extension of standard flood frequencies is not at- tempted. Comparison with historic records at the four detailed study sites suggests that severe floods of magnitude similar to that of December 1964 have occurred several times in the last few hundred years. INTRODUCTION Floods are those flows which overtop the banks of a channel and spread out across the flood plain, often causing damage and loss of life. Flood-frequency studies attempt to predict the frequency of recurrence of flood- flows. Determination of the statistical distribution of peak-discharge data is called flood-frequency analysis; the analysis attempts to determine the average interval between floods that exceed a given magnitude. The general purpose of flood-frequency analysis then, is the prediction of what is likely to happen in the future. A knowledge of the magnitude and frequency of recurrence of floods has obvious practical applications to the proper design and location of structures such as dams, bridges, and roads. Moreover, the frequency with which certain flood plains are inundated must be con- sidered in determining the size and strength of engi- neering structures or the feasibility of planning con- struction at all. Flood insurance and flood-plain zoning are obvious economic problems which are dependent on some knowledge of flood frequencies. Therefore, it is imperative that methods of flood-frequency analysis be sound. f STANDARD METHODS The frequency with which floods occur and their relative magnitude are inversely related; that is, very large floods are infrequent. Smaller floods, on the other hand, usually go unnoticed and may recur as often as once every year. Severe floods usually are noticed because they affect human activities. Such floods may occur only once in 15 or even 100 years. Several methods have been used to analyze flood events. Complete descriptions of the different methods may be found in Dalrymple (1960), Benson (19622), and Cruff and Rantz (1965). Methods used by the U.S. Geological Survey are based on the annual peak dis- charge. This annual flood is the highest momentary peak discharge during any given water year (October 1-September 30) and when listed for the period of record, the resulting array is referred to as the annual flood series. Another series called the partial-duration series is sometimes used and is based upon a list of floods above a given base discharge. From either of these two series a recurrence interval may be calculated. Accordingly, it should be noted that a flood having a recurrence interval of 2 years, when computed from the annual series, has one chance in two or a 50-percent chance of occurring in any given year. A 100-year flood on the other hand has only a 1-percent chance of occur- ring in any one year. Naturally it follows that the size of the flood population (number of years of record) becomes very important in calculating the recurrence interval. Because most flood records are for a period of less than 40 years (Cruff and Rantz, 1965, p. 2), the chance for the available sample to be skewed or affected by an extreme event is very great. In an attempt to offset this bias, Federal agencies adopted a uniform technique for determining floodflow frequencies (Water Resources Council, 1967). In December 1967 the coun- cil agreed that the state of the art had not developed to the point where complete standardization was feas- E1 E2 ible. They did, however, recommend the log-Pearson type III distribution (Water Resources Council, 1967, p. 6). Detailed descriptions of this method were given by Foster (1924) and by the Inter-Agency Committee on Water Resources (1966). Basically the Pearson method is more flexible and definitive than other methods because the distribution of the array of flood peaks is defined not only by the mean and standard deviation but also by the coefficient of skew of the array. An excellent example of the case of the log- Pearson type III method as applied to north coastal basins in California is given by Cruff and Rantz (1965, p. 13). However, as useful as the skewness might be in improving the statistical analysis, it may be mis- leading unless the sample from which the skew is com- puted is large. It would appear then that we can do little about sampling error, unless as suggested by Cruff and Rantz (1965, p. 47), we can use historical data to extend the base period for which a given flood frequency is attempted. The application of historical data is aptly demon- strated by Benson (1962b) with reference to long his- tories from colonial New England. Research of personal diaries, church records, will records, newspapers, and town histories allowed extension of an existing base period of flooding from 50 to 300 years (Benson, 1962b, p. 6). Unfortunately many regions of the United States do not have long historical records, and this is particu- larly true of the region with which this report is con- cerned. North coastal California does, however, contain some extremely long-lived nonhuman inhabitants. These are its coniferous trees, especially the coastal redwoods, which have been witness to natural processes for many centuries. EXTENSION OF FLOOD RECORDS BY GEOLOGICAL AND BOTANICAL EVIDENCE Several kinds of observations may be useful in mak- ing inferences about the magnitude and recurrence interval of floods that can be used to supplement or extend existing gaging-station or historical data. These observations can be divided into two general classes. First, it may be possible to state the minimum time interval that must have elapsed since the last occur- rence of a flood of a certain large magnitude. Second, in certain cases, physical evidence of specific flood events can be identified and dated and may permit estimates of peak stage or discharge. A number of studies have been carried out in which estimates were made of the probable recurrence interval of recent large and devastating floods. Jahns (1947) studied the distribution and texture of flood deposits on terraces above the Connecticut River in Massachu- setts. He concluded that there was no evidence of the VEGETATION AND HYDROLOGIC PHENOMENA occurrence of a flood equaling or exceeding that of 1936 during at least the previous several hundred years. Mansfield (1938) found that older flood deposits along the Ohio River could be readily identified, and he tentatively concluded that the flood of 1937 exceeded any in the recent geologic record. The recurrence inter- val of cloudburst floods in the Appalachians (Hack and Goodlett, 1960) was estimated as more than 100 years, on the basis of the maximum age of trees growing on alluvial fans that typically formed at the mouths of small tributary streams during past floods. The rare occurrence of such events was also shown by the total destruction during a major flood of older trees that had grown to maturity on the flood plains of larger streams. Stewart and LaMarche (1967) concluded that floods as large as that of December 1964 were infrequent on Coffee Creek in northern California, because this event destroyed flood-plain forests containing many trees over 200 years old, and caused deep erosion of previ- ously undisturbed deposits as old as 1,700 years. Past floods can be identified and dated only if some interpretable record has been left. Sigafoos (1964) showed how botanical evidence could be used to date floods in the Potomac River valley. The burial, over- turning, breakage, and scarring of deciduous trees located on the flood plain provided a record of major floods that could be deciphered by careful study. Dates of flood scars on trees provided the basis for an estima- tion of flood frequency in another study (Harrison and Reid, 1967). Geologic and botanical methods thus may be applic- able to flood-frequency problems where local circum- stances permit. The present study was undertaken in an attempt to apply such methods in northern Cali- fornia, an area with relatively sparse and short runoff records. Circumstances were felt to be favorable be- cause of the recent occurrence of widespread, destruc- tive flooding (1964) that could be used for comparison with the relative magnitude of past floods, and because the flood deposits of the smaller streams (draining less than a few hundred square miles) are morphologically and texturally distinctive. In addition, trees of several coniferous species that attain great ages are widely distributed on the flood plains of major streams, and many of the trees have not yet been completely elimi- nated by logging, fire, or construction activity. DESCRIPTION OF THE AREA STUDIED The area studied extends 300 miles north along the California coast from San Francisco Bay to the Oregon border and inland as much as 100 miles. Most of our emphasis was placed on the watersheds of the Smith, Klamath, Trinity, Mad, Van Duzen, and Eel Rivers. HISTORIC FLOOD INFORMATION FOR NORTHERN CALIFORNIA STREAMS The study area includes the Northern Coast Ranges, Klamath Mountains, and Southern Cascades physio- E3 exception of those of the Smith and Klamath Rivers and their tributaries lie wholly within the Northern graphic provinces (fig. 1). All watersheds with the | Coast Ranges province. The Northern Coast Ranges 25 124° e SLC t -[ lr _u lr?" ___ _ oregon -__- uaf TX C bas "ao E - rod ~ # \\ gmill K Pt St George / \ M g a o XL \ X Indian/8m i M & West § amp@round \ Ne YJ 4 3‘ Fork Q}; jiquldehCr z ".~ (6a 620 Klamath \\ "C s "‘~ Mount ‘-‘ gue CJ x > \ Shasta \ I x ‘ § j * Eagle Creek I F x“ KLfiMATH MTS _ ¢ ag|e\Creek Campground EZ \ 7>\ Ramshorn Cr 51 \ *In a o LG A ‘\‘ t" 4 / 41 w o" i OS @. x >, kast Fork $6 '( Willow Creek E. Q OREGON GZ INDEX MAP 39° ~ Pt Arena 20 40 MILES La 1 t fut on a FIGURE 1.-Geomorphic provinces and major drainages of a part of northern California. E4 are underlain by thick sequences of sandstone and shale which have been intruded by large masses of ultramafic rocks, now largely altered to serpentine. The geologic structure is characterized by northwest- trending folds and faults which control much of the surface drainage. Stream valleys are developed along shear zones associated with major faults, producing a crude trellis drainage pattern. The combination of sheared rocks, shallow soil profile development, steep slopes, and heavy seasonal precipitation produce land- slides and soil slips so common to the area. The Klamath Mountains are rugged and somewhat inaccessible. They lie between the Northern Coast Ranges and the Southern Cascades physiographic provinces. The Klamath Mountains are underlain by highly metamorphosed volcanic and sedimentary rocks that have been intruded by granitic and ultramafic rocks. Structurally these mountains are more complex than the Northern Coast Ranges but display very well defined arcuate regional trends. The Coast Ranges province joins the Klamath Mountains province along the distinct 6,000-foot high ridgelike South Fork Moun- tains, which have the topographic expression of the coast ranges but are underlain by rocks similar to the Klamath Mountains. Accordant summits and highly dissected old land surfaces are common along major watercourses in the Klamath Mountains. The modern drainage, unlike that of the coast ranges is transverse to both lithic and structural trends and is deeply incised, thus suggesting superposition. The Cascade Range lies east of the Klamath Moun- tains and north of the Sierra Nevada. The Klamath River drainage heads in this plateau of effusive volcanic and pyroclastic rocks. From near the California-Oregon border the Klamath River flows in a well-defined can- yon cut deeply in the volcanic rocks. Upstream from the border, however, surface drainage is poorly devel- oped, perhaps because the highly permeable rocks allow ready infiltration of snowmelt and precipitation. CLIMATE The climate along the immediate coast of northern California is marked by moderate and uniform annual temperature, heavy and sometimes recurrent fog, and prevailing west to northwest winds. Inland tempera- tures increase and become more variable, while precipi- tation decreases. Temperatures inland have ranged from 0° to 110°F; however, winds become only moderate. Both temperature and precipitation are influenced greatly by elevation and local topography. Precipitation is of greater frequency and annual mag- nitude than anywhere else in California. Nonetheless, it is distinctly seasonal with little occurring from April VEGETATION AND HYDROLOGIC PHENOMENA through October. The seasonal distribution of pre- cipitation is largely controlled by the presence of an anticyclonic cell (high pressure area) normally found off the California coast, especially during dry periods. The frequent and heavy winter precipitation usually occurs when this anticyclone is far south of its usual position. When this occurs warm moist tropical air masses are free to migrate eastward to the Pacific Coast. Snow falls in moderate amounts at elevations above 2,000 ft, but only at elevations above 4,000 ft does snow remain on the ground for any appreciable length of time. With many mountain peaks at 6,000-7,000 ft above sea level and a few about 9,000 ft, features of past glaciation exist, but the glaciers themselves are virtu- ally extinct. SURFACE-WATER HYDROLOGY Precipitation and runoff phenomena have been described in detail by Rantz (1968), Cruff and Rantz (1965), and Rantz and Thompson (1967). The descrip- tions given here are brief and intended only as a general outline. The reader is referred to the earlier work for more specific information. About 75 percent of the total annual precipitation falls in the 5-month period, November-March. Most of this precipitation occurs during general storms of sev- eral days duration and relative moderate intensity. The isohyetal map (fig. 2), slightly modified from Rantz (1968) shows marked orographic control. This map was constructed from data for a 60-year base period from 1900-1959. It shows that average annual precipitation is influenced by distance from the ocean, elevation, and shape and steepness of mountain slopes in addition to the direction of slopes in relation to moisture-bearing winds. In general, precipitation increases from south to north and is much heavier on southern and western than on northern and eastern mountain slopes. The wide range in average annual precipitation is striking, decreasing from 120 in. in the northwest to a low of only 10 in. in the northeast. Precipitation has varied widely in time as well as space. For example, the precipitation station at Dos Rios in the Eel River basin (fig. 2) has a 60-year mean annual rainfall of 46.4 in. but ranged from 15.3 in. in 1924 to 85 in. in both 1956 and 1958. Obviously rainfall variability can be expected to pro- duce variable unit runoff throughout the region. The present topography, geology, and climate are major factors that combine to influence the dynamic runoff phenomena characteristic of the north coast. Consider the Eel River basin as a typical example. With only 2 percent of the State's land area it yields 9 per- cent of the State's runoff (over 5 million acre-feet an- nually). Average annual rainfall for this 3,000-square mile drainage basin is about 59 in.; some 35 in. or about HISTORIC FLOOD INFORMATION FOR NORTHERN CALIFORNIA STREAMS E5 60 percent runs off. Most of this runoff occurs during and shortly after the late fall and winter storms. Because of the low permeability of surficial materials, base flow is poorly sustained, thus adding to the large variations in streamflow. Although suspended sediment loads have been measured in the north coastal basins 122° OREGON 121° | T CALIFORNIA SST -~" \30 6 10 30 Mount Shasta 42° Pt St George EXPLANATION 50 Isohyets of mean annual precipitation, in inches (modified from Rantz, 1968) OREGON INDEX MAP 0 20 40 MILES heron sd 2 22s L oce. FIGURE 2.-Isohyetal map of a part of northern California. E6 for only slightly more than 14 years, a recent summary of the first decade of data revealed some dramatic information. Using data collected from 1957-67, a per- iod that spanned the State's largest flood, that of December 1964, Brown and Ritter (1971) show that the Eel River discharged an average of 31,000,000 tons per year of suspended sediment. Converted to a sedi- ment yield of 10,000 tons per square mile annually, this rate is larger than any basin for its size in North America. For example, this rate is 4 times that of the Colorado and 15 times that of the Mississippi. Most significant is the fact that most of this load was moved by high flows, which occurred on the average 10 percent of the time or less. With very few exceptions, through- out the entire Eel River basin, 50 percent or more of the total annual suspended load was carried on fewer than 6 days during the water year. It is also noteworthy that the high sediment yield of 10,000 tons per square mile per year does not include bedload or dissolved load. A minimum erosion rate extrapolated from these data is 4 feet per 1,000 years for the entire Eel River basin with various subbasins having erosion rates of up to 10 feet per 1,000 years (Brown and Ritter, 1971). The data suggest that most material is transported and hence the geomorphic work is done in a very short time. In other words, the infrequent hydrologic event is most significant in the mountainous areas of northern Cali- fornia. A brief description of the largest hydrologic event ever recorded in northern California follows. THE FLOODS OF DECEMBER 1964 METEOROLOGY The following description of the meteorology respon- sible for the floods of December 1964 is a condensation of the work of Rantz and Moore (1965). Heavy rainfall began on December 18, 1964, caused by a storm sys- tem which approached the California coast at more northerly latitudes than usual. The storm of December 18-20 brought snow and lower temperatures to higher altitudes and latitudes of the region. This early cold storm set dangerous antecedent conditions by freezing soil moisture and storing additional storm runoff in snowpack. After December 20 succeeding storm tracks moved progressively southward in response to a deteri- orating high pressure system over the Pacific. Concur- rently, an outbreak of cold arctic air moved farther south out of the Gulf of Alaska and only intensified the tropical storm systems as they approached the coastal areas of northern California. These new storms (after Dec. 20) struck the coast at nearly right angles to the orientation of the mountain ranges thus producing high rainfalls. Higher temperatures associated with the new tropical storms raised the freezing level to altitudes as high as 10,000 ft and caused high precipitation, all in VEGETATION AND HYDROLOGIC PHENOMENA the form of rain even at the highest altitudes. Rates in excess of 8 in. in 24 hours were common throughout the north coast although there was wide regional variation. Precipitation totals for the 5-day period December 19- 24 exceeded 20 in. in many places but ranged from a low of 10 to a high of more than 30 in., with the highest values recorded in the mountainous regions of northern California. During the period after December 24 a surge of rising pressure effectively blocked the storm track by moving into the area northeast of Hawaii. The pressure cut off the flow of warm moist air to the west coast but allowed colder arctic air to move southward and cause heavy snow and hail down to very low altitudes. This very effectively reduced further flooding hazards but seriously hampered rescue work in the area. RUNOFF With favorable antecedent conditions, high soil mois- ture, and a thick snowpack, the warm torrential rain of December 19-23 quickly brought north coast streams to the bankfull stage. Exactly 9 years earlier, most of these same streams had flooded to cause a then unprec- edented disaster. However, the floods of December 1964 were generally more intense; in many areas of both northern California and Oregon peak stages not only exceeded those of 1955 but were equal to or greater than those that occurred during the almost-legendary floods of 1861-62 (Rantz, 1968). The floods of Decem- ber 1964 were directly resonsible for the loss of 47 lives and caused damage that totaled almost one-half billion dollars. The Eel River is a prime example of the response of north coastal streams to the heavy precipitation and consequent runoff. On December 18, 1964, the Eel River at Scotia was discharging a meager 4,600 cfs (cubic feet per second) but peaked only 5 days later at a record 752,000 cfs. The Klamath, Trinity, and Smith Rivers, and other streams also peaked at record-setting stages and rates of flows. At Alderpoint, on the main stem of the Eel, the river rose 90 feet above its normal low-water level. For a 3-day period beginning Decem- ber 22, 1964, the Eel River discharged 116 million tons of suspended sediment. Only 94 million tons were dis- charged in the previous 8 years (Brown and Ritter, 1971). Unit runoff for the storm of December 19-23 was as variable as the widespread heavy precipitation. Runoff ranged from a low of about 20 cfs/sq mi (cubic feet per second per square mile) on the Shasta River near Yreka to over 580 cfs/sq mi in parts of the Eel River basin. Although the storm of December 19-23, 1964, was intense over large areas of the Western States, the runoff was not uniform owing to many fac- tors. Erosion was most severe in the eastern sections of the Eel River basin where North and Middle Forks HISTORIC FLOOD INFORMATION FOR NORTHERN CALIFORNIA STREAMS were fed by high unit runoff from steep west-facing slopes. These slopes, saturated by antecedent precipi- tation and somewhat unstable even under normal rainy conditions, were badly eroded by landslides, slumps, and gullying, especially in areas of sparse vegetal cover. Over reaches several miles long streambed elevations rose 6-8 feet (Hickey, 1969). These streambed changes reflect large quantities of sediment placed in the stream from bank erosion and landslides. At most sites studied by Hickey (1969) the changes were positive; that is, streambed elevations rose. This effect will probably continue in a downstream direction in succeeding years. Although only qualitative information can be inferred from Hickey's (1969) study it is certain that large quantities of bed material were moved. The quantita- tive information regarding sediment transported is that of Brown and Ritter (1971) and refers only to sus- pended load. Their study showed that 51 percent of the total suspended sediment discharged by the Eel River in the 10 years from 1957 to 1967 was transported dur- ing a scant 30-day period. Studies in progress on the Middle Fork of the Eel River suggest that the bedload component of the total sediment transported varies between 10 and 40 percent. Obviously the effect of a rare hydrologic event such as the floods of December 1964 have long-term implications beyond the immedi- ate loss of life and property. Channels have changed geometry and location within valleys, and the capacity to transport both water and sediment are altered per- haps for many years to come. Flood records must be extended to give man a better perspective of floods and flood-plain use. EXTENSION OF FLOOD RECORDS IN NORTHERN CALIFORNIA METHODS Some of the geological and botanical methods used elsewhere were found to be of limited applicability in this study. The stratigraphic approach of Jahns (1947) and Mansfield (1938) is more appropriate for large streams with broad flood plains, where thin layers of relatively fine-grained flood deposits may be laid down over large areas. In the steep, narrow canyons of moun- tain streams in northern California the flood deposits tend to be coarse, thick, and local in distribution. Deep lateral and vertical erosion during major floods fre- quently destroys older flood deposits, so that a regular succession of beds representing a sequence of past floods is rarely found. However, such depositional records do exist locally in the study region. For example, at the mouth of Bull Creek, above the junction of the South Fork and the main stem of the Eel river, backwater conditions exist during major floods that result in the deposition of thin silt-clay beds. Fifteen such flood- E7 deposited layers totaling 30 feet in thickness have been recognized (Zinke, 1968). Detailed investigation of flood damage to individual trees, as described by Sigafoos (1964), was not at- tempted in this study. We observed few examples of scarring or breakage as the result of the 1964 or earlier flooding, and saw no instances of survival of overturned or buried trees. The coniferous trees in the study regime seem less suitable for this kind of investigation than are the deciduous flood-plain species of other regions. TREE-RING DATING OF FLOOD DEPOSITS The minimum age of a flood-plain deposit can be estimated from the age of the oldest tree that is grow- ing on the deposit. The age of a living tree is determined by counting the annual rings in a sample taken with an increment borer. The main source of uncertainty is the need to estimate the number of years that were required for height growth of the tree to the level at which the sample was taken, normally about 3 ft. We have allowed 5 years for height growth in all such age determinations in this work. The actual age of the deposit is necessarily at least somewhat greater than the date of establish- ment of the oldest tree, because considerable time may have elapsed between deposition and the establishment of tree seedlings on the new surface. In all of our study localities, we found that seedlings of at least some local coniferous species were abundantly established on 1964 flood deposits by the summer of 1969-a lapse of no more than 5 years. In a more detailed investigation, Sigafos and Hendricks (1969) also found an average time interval of 5 years between surface stabilization and tree-seedling establishment on glacial moraines and outwash deposits on Mount Rainier, in the State of Washington. Therefore, in estimating the minimum age of a flood deposit, at least 5 years should be added to the age of the oldest tree on the deposit. However, a deposit may be much older than age data from trees would indicate, because many generations of trees may have lived and died on the surface in the time interval between the date of deposition and the present. In some of our study localities, stumps of recently cut trees were also used to obtain minimum age esti- mates for flood deposits (fig. 3). In some cases, cutting followed the 1964 flood and was designed to salvage trees that had been damaged or killed by flood deposi- tion. Although the condition of the cut surface gives a clue as to time elapsed since cutting, we relied pri- marily on local information for general or specific dates of cutting activity. The use of stumps introduced an additional uncertainty into the age estimates-that is, the uncertainty in the time that has elapsed since cutting. E8 VEGETATION AND HYDROLOGIC PHENOMENA FIGURE 3.-Ring-counted and radiocarbon-dated stumps used to date flood deposits along Blue Creek near Klamath, Calif. RADIOCARBON DATING The radiocarbon method was used to estimate ages in the few cases in which datable material could be found in flood deposits. There are a number of possible sources of uncertainty in radiocarbon age determina- tions. However, there are only two major sources in the dating of wood used in this study. The first is the counting error, or statistical uncertainty in the meas- urement of the carbon-14 content of the sample. This uncertainty is conventionally expressed as a range of plus and minus one standard deviation (one sigma) of the stated age. On the average, two-thirds of a large number of repeated observations on the same sample would be expected to give dates in the range from the stated age minus one sigma to the stated age plus one sigma. Sigma ranges from 60 to 100 years in the deter- minations that we obtained from a commercial radio- carbon laboratory. A second source of error or uncertainty may be more important than the counting error in radiocarbon dates from certain time periods. This is the discrepancy between radiocarbon (C*) age and true age that is due to past fluctuations of the concentration of C" in the atmosphere (Stuiver and Suess, 1966). For example, wood that was formed during a period when atmos- pheric C** concentration was much higher than normal will yield an anomalously "young" date. Conversely, a date that is too "old" will be obtained from wood formed during a period of relatively low atmospheric C'" content. During intervals of rapid atmospheric C* fluctuation such as the past 500 years, a sample with a given C* content may represent any of several possible time periods. It is possible to correct an apparent C* age to get a better estimate of the true sample age. A large number of selected comparative C* and "true" dates have recently been published, based on radiocarbon analysis of wood samples that have been accurately dated by dendrochronological methods (Damon and others, 1970; Ralph and Michael, 1970). In our work, an esti- mate of the true sample age was made by comparing the one-sigma radiocarbon age range of our sample with the one-sigma range of wood samples of true known age (calibration sample). The most probable true age of our sample is assumed to be the true age of the calibra- tion sample with an overlapping one-sigma radiocarbon age range. In most cases, more than one calibration sample has a radiocarbon age range that overlaps our HISTORIC FLOOD INFORMATION FOR NORTHERN CALIFORNIA STREAMS sample age. This results in a large uncertainty in the true age of our samples. Despite the abundance of logs and organic debris in the 1964 flood deposits, such material was rarely seen in exposures of older flood deposits. We were able to find and sample buried logs and natural stumps in only a few of our study localities. DESCRIPTION OF SITES WITH GOOD EVIDENCE FOR PAST FLOODS Field studies began during the summer of 1968 with reconnaissance automobile trips along all major drain- ages of the north coast. The necessity of covering large land areas in a short time precluded foot traverses, and boat traverses were impossible during low water dis- charges. Therefore, it is possible that many potential sites with good prehistoric flood evidence may have been overlooked. Although we observed many dead trees and buried stumps, all of which could be related to the flood of December 1964, not all were long-lived species and many more were killed because of human activities. For example, backwater conditions gener- ated by narrow culverts caused severe upstream aggra- dation that normally would not have occurred. This aggradation buried many trees in as much as 30 feet of alluvium; although spectacular, these sites were dis- counted as being unnatural (fig. 4). The location of sites are shown in figure 5 where evi- dence of prehistoric flooding has been found. Unfortun- ately not all sites provide evidence for both maximum and minimum recurrence interval. Any one site rarely offered both types of age-control data. Figure 5 shows that widespread botanical evidence does exist and this evidence is a potentially useful tool in placing age con- straints on the potential frequency of occurrence of modern natural processes. Only four sites will be dis- cussed in detail to show the techniques utilized in plac- ing some time limitations on ancient floods. These four sites are Blue Creek near Klamath (pl. 14, B, C), Scott River at Indian Scotty Campground (pl. 1D), Trinity River at Eagle Creek Campground (pl. 1E), and the East Fork of Willow Creek (pl. 1F). Large- scale topographic maps were especially made of these four sites from low altitude aerial photographs. The detailed maps allowed contact geologic mapping at a scale of 1 inch equals 100 feet. Contour intervals are 5 ft on the Blue Creek, Scott River, and Trinity River maps and 2 ft on the Willow Creek map. BLUE CREEK NEAR KLAMATH DESCRIPTION The valley of Blue Creek contains at least three gravel units older than the flood deposits of 1964. The highest level deposit, older gravel 3, is a deeply E9 FIGURE 4.-Douglas-fir tree killed by burial in flood debris during 1964 flooding as a result of backwater effects caused by a culvert on Ti Creek at the Klamath River. weathered gravel located east of the creek near the southern end of the study area (pl. 14). The gravel rests on bedrock about 25 feet above the present channel and is about 65 ft thick. A much lower gravel deposit, older gravel 2, underlies extensive terraces bordering the stream. The terrace surface is about 20 ft above the channel, and the coarse, obscurely bedded and poorly sorted gravel is about 20 ft thick. A small gravel deposit with a surface at about the same relative height is located in the West Fork of Blue Creek, 1,000 ft upstream from the confluence with Blue Creek (pl. 1B). The lowest pre-1964 deposit, older gravel 1, that could be identified is a gravel bar that was overtopped by the 1964 flood and is partly buried in 1964 deposits (pl. 14). AGE DATA The oldest fluvial deposit along Blue Creek is the small patch of older gravel 3 resting on bedrock east of the stream. Based on its topographic position, small E10 VEGETATION AND HYDROLOGIC PHENOMENA extent, and degree of weathering, it probably is of Ter- The extensive terrace gravel, older gravel 2, can be tiary or Pleistocene age. It is probably unrelated to | assigned a minimum age of 100 years, based on esti- more recent flood events. mated dates of establishment of the largest trees grow- 124° 123° 127° 5 C OREGON 12r # J /- < W” a Sm“ Pt St George '\ i a s N- \, x Ind|an Scotty ' West? &. Campgro *s ) F ork «e Boulden C; ta Klam tat 4 7 2} E ath \ ® Q 3 ve © yal. 3 \ pul G A bui 9 * G Eagle Creek ) g x KLiMATH MTS _ ¢ agle Creek Campground G/ \ \ /> 4 3) Ramshorn Cr 51 “. Ill/U, { | \ y ai" }= is 948 Ag G. K1, Kast Fork EXPLANATION Blue Creek Scott River Trinity River East Fork Willow Creek $f - Botanical sample X b Radiocarbon sample INDEX MAP 390 Pt Arena 0 20 40 MILES 12 s 2 ree bcs nn P0 d FIGURE 5.-Sites where evidence of prehistoric flooding has been found in northern California. HISTORIC FLOOD INFORMATION FOR NORTHERN CALIFORNIA STREAMS ing on the terrace surface (pl. 14, B). A maximum age for this deposit can be assigned on the basis of radio- carbon and dendrochronological dating of included logs and buried trees. The approximate date of death of the buried trees can also be estimated from study of growth fluctuations in a nearby living tree. Radiocarbon age determinations were obtained for wood samples from the stumps of a buried tree (BC 11) and from two logs (69-146 and BC 1) included in the terrace gravel along Blue Creek (pl. 14, B). The result- ing ages were between the mid-1500's and the present. (Years given are A.D.) The older gravel 2, therefore, probably was deposited between 1545 and 1870. The radiocarbon date of the stump (69-145) in the gravel deposit on West Fork, Blue Creek gives a date of death between 1600 and the present. Thus, this deposit seems to be correlative with the terrace gravel along the main stream. Tree-ring dating methods were also used to obtain an age estimate for the terrace gravel. Four of the buried redwood stumps (BC 9, 10, 11, 13) were sampled using a power increment borer. A large living redwood (BC 21) on the hillslope immediately adja- cent to the buried stand of trees was also cored. Study of the annual ring patterns showed that the growth records of three of the stumps could be matched by cross-dating techniques (pl. 1C). The same ring pat- terns appear near the inside of the core from the living tree. Therefore, it is possible to assign approximate calendar dates to the annual growth rings in the stumps. These dates are approximate because certain annual rings may not be present along the sampled radius of the living tree. Such locally absent rings pre- sent a well-known dendrochronologic problem in old coastal redwoods (Fritz, 1940). Despite the uncertainty in the tree-ring dates, the time of death of the buried redwood stand probably can be estimated more accurately from this evidence than is possible using the radiocarbon method. The tree- ring dates for the outermost annual ring in each of the three dated stumps ranges from about 1660 to about 1705. These are only minimum estimates of the dates of death of the trees, because fire and decay have removed three or more inches of wood (primarily sap- wood) from the outside of the stumps. This estimate is based on the thickness of the zone of decayed wood that lies between the bark and the sound wood at the base of the stumps. Three inches of wood corresponds to 100 to 150 years of growth in these stumps. There- fore, this must be added to the dates of the outermost rings in the sound wood, giving estimated dates of death sometime after 1800. Another line of tree-ring evidence suggests that the trees in the redwood stand in the valley of Blue Creek E11 died between 1860 and 1870. The annual rings in the living redwood (BC 21) show an abrupt tenfold increase in average thickness beginning about 1870. This growth "release" is similar to that observed in trees when neighboring trees are removed by fire, wind- storm, logging operations, or other causes. This growth release probably followed the death of the trees in the buried stand in the valley of Blue Creek. Thus, the buried trees probably died in the 1860's as a result of burial to a depth of 20 feet by the terrace-gravel deposits. Three separate lines of evidence suggest that the deposition of older gravel 2 occurred probably between 1860 and 1870. Major flooding on north coast streams is known to have occurred during the winter of 1861- 62. Deposition of the gravel probably took place during one or more floods on Blue Creek during the 1861-62 season. Our previously published estimate (Helley and LaMarche, 1968) of the date of the gravel as 1,500+100 years is thus considerably in error. One source of this error was our use of an uncorrected radiocarbon date of 1,100+100 years that actually corresponds to a tree date between 1200 and 1300. The second source of error was our failure to take into consideration the 100 to 150 years of annual growth that is missing from the outside of the buried stump. The dendrochronologic and radiocarbon data are summarized in tables 1 and 2. TABLE 1.-Radiocarbon and dendrochronologic data for trees sampled at Blue Creek 8 + ¢ bo! a a“? £55 8 SR pil. bigs $ § g 8 S02 Slip ee & RpBbg BHT" 33 ogi ig 3 Buried stumps BC 11 ::..... I-2572 Redwood 1100+100 460 1560+100 69-145 ........ I-4728 - Douglas-fir - >1765 95 >1860 Logs included in deposit ...... I-4151 - White fir 1680+60 141 1821+60 BC 1B2 ......I-4341 - White fir >1765 30 >1795 69-146 ...... I-4729 Douglas-fir 1655+90 195 1850+90 TABLE 2.-Corrected radiocarbon-based dates for trees sampled at Blue Creek Specimen Probable Condition of number outside date, A.D. specimen Buried stumps BC 11.......... 15060-1710 ............ Sapwood missing. 69-145 ...... 1610-present ........ Sapwod partly preserved. Logs BC SA... rsn event Sapwod partly preserved. 1¥ .:... 1591-present 1B2 ..... .:;....;...... ...o... eeu 69-146 ........ 1645-present ........ Sapwood and bark preserved. E12 SCOTT RIVER AT INDIAN SCOTTY CAMPGROUND DESCRIPTION Two well-preserved gravel deposits are exposed along the left bank of the Scott River in the northeast quarter of the Scott Bar 15-minute quadrangle just east of its confluence with Boulder Creek. Few older gravel deposits are preserved along the Scott River and those described here are in a protected bend in an otherwise steep canyon. The left bank of the Scott River at this site is under- lain by two gravel units older than the 1964 flood deposits (pl. 1D). The highest deposit, older gravel 2, up to 40 feet above the present river bed, is the thickest and most extensive. It extends 600 feet along the river and is as much as 250 feet wide. This deposit is about 25 feet thick, very coarse, poorly sorted, and covers a bedrock surface. Its flat to slightly undulating surface has only traces of old channels preserved. Another gravel deposit, older gravel 1, is found lower and closer to the channel. It, too, underlies the left bank, but is thinner and less extensively preserved as a thin layer about 10 ft above the river bed. This deposit is only slightly more than 5 ft thick. One small patch of this gravel is found as an island in the channel about 500 ft downstream. The gravel deposited by the floods of 1964 covers older gravel 1, and has, in part, eroded the lower section of older gravel 1. Streamflow measurements at the U.S. Geological Survey's gaging station located approximately 5 miles upstream indi- cated peak stages of a little more than 25 ft during the December 1964 floods. Although no stage information was available at Indian Scotty Campground, valley shape considerations would necessitate that the older gravel 1 was inundated by the 1964 floods. % AGE DATA The oldest gravel (older gravel 2) can be assigned a minimum age of 445 years based on ring counts on the largest stump preserved on the surface. "Release" effects shown in living trees adjacent to the stump were used to establish the date of cutting. These counts suggest a depositional date before 1525. Both stump counts and increment cores were taken on older gravel 1. The oldest core taken was from a tree on the island in the channel downstream, and it appears to be 80 years older than stump and increment core counts upstream. Although no textural or morphologi- cal difference was detected between upstream and downstream deposits of older gravel 1, a chance does exist that two events may be recorded in the younger of the gravels. The date of deposition of the younger gravel at the downstream site is earlier than 1610. At the upstream site the oldest date appears to be 1690. Since the upstream site is in a narrower channel, where both water velocities and stages would be higher during VEGETATION AND HYDROLOGIC PHENOMENA floodflows, it may simply have been more difficult to establish growth at the upstream site. No samples suitable for radiocarbon dates could be found in the two older gravel deposits. From existing gaging-station records it would appear that the historic floods of 1861 and 1955 were equal in magnitude, and both were probably less severe than the December 1964 floods. The December 1964 floods would be equal to or slightly less severe than those responsible for the depo- sition of older gravel 1. No estimate can be made for the flood responsible for older gravel 2; however, owing to the very coarse texture, thickness, and extent of the deposit, it is highly probable that the flood was of greater magnitude than the floods of older gravel 1. TRINITY RIVER AT EAGLE CREEK CAMPGROUND DESCRIPTION Trinity River at Eagle Creek Campground (pl. along the eastern edge of the Trinity Alps part of the Klamath Mountains Province, has been the location of repeated gravel deposition. Here the valley of the Trinity River is wide, flat, and situated just down- stream from a very narrow, steep-walled, straight, and hence, highly competent channel. In addition to the abrupt change in channel geometry, two tributaries enter the Trinity River in this wide valley, enhancing the potential for sediment deposition and preservation. At least three older gravel units are easily recognized here (pl. 16). The oldest of these units, older gravel 3, covers the largest area. It extends from the head of the valley, where it forms the banks of the Trinity River, downstream for approximately 1,200 ft. It is as much as 15 ft thick and consists of poorly sorted boulder gravel with most clasts displaying thin weathering rinds. The surface is subdued but broad swalelike chan- nels and low levees are discernible. The next-youngest gravel, older gravel 2, is incised and lies nested with older gravel 3 (fig. 6). It is not as extensive and only slightly more than 5 ft thick. The younger gravel has been slightly modified by both erosion and deposition caused by the floods of 1964. Debris from the 1964 flood covers much of the surface of older gravel 2, especially at the confluence of the Trinity River with Eagle Creek (pl. 1E). The surface morphology is distinct, showing well-preserved flood channels and levees which are especially analogous to those seen on deposits of the 1964 flood on the East Fork of Willow Creek (fig. 7) and those described on Coffee Creek by Stewart and LaMarche (1967). A small, but distinctly older gravel unit, older gravel 1, is incised in older gravel 2 but found preserved only near the mouth of Ramshorn Creek (pl. 1€5). This unit is recognized as a separate gravel because it is incised in older gravel 2, because it has fresher surface mor- phology than the older deposits, and because of the HISTORIC FLOOD INFORMATION FOR NORTHERN CALIFORNIA STREAMS E13 FIGURE 6.-Prehistoric flood channel between older gravel 3 (left) and older gravel 2 (right). View is upstream of the right bank of the Trinity River Eagle Creek. tree-ring evidence. This unit was partially modified by erosion during the 1964 flood. Data from gaging-station records collected approximately 4 miles downstream from Eagle Creek indicate that the floods of 1964 had a peak stage of just above 12 feet. Extrapolation up- stream would suggest that probably all of older gravel 1 and larger areas of older gravel 2 were inundated. AGE DATA Ponderosa pine and incense-cedar stumps here were counted. Dates of cutting were obtained from a nearby Forest Service field office. The oldest dendrochronologi- cal sample is found on older gravel 3, yielding an esti- mated date of establishment of about 1500. However, this is only 40 years older than a stump count on older gravel 2. This suggests that the oldest gravel unit, older gravel 3, may be much older than any living tree in the area. Older gravel 1 is at least as old as 1735 but only one stump count was used to determine this and, of course, probably is the result of an event on Ramshorn Creek. No vestige of the floods of 1861 or 1955 was observed, probably because the floods of 1964 were larger, and completely obliterated any evidence. Observations of deposits laid down by the floods of December 1964 and reports by Stewart and LaMarche (1967) of eyewitness accounts may allow estimates of the relative water discharges which deposited each of the older gravel units. At least a comparison between older gravel 1 and older gravel 2 and sediments deposited by the flood of December 1964 should be attempted. Several assumptions are necessary. First, and perhaps the least acceptable, is that the average depth of flow during the floods was at least as great as the relief shown by the boulder levees. At most places this is only 5 ft. Second, that the width of the gravel deposits, as shown on the geologic maps, represents the width of the channel during the flood; this of course assumes only one channel. Using the floodmarks and distribution of 1964 gravel it is possible that older gravel 2 was deposited by an event about 50 percent larger than 1964 and older gravel 3 was deposited by an event about twice as large as 1964. Using discharge data computed at a site 4 miles downstream from the Eagle Creek site, the 1964 flood peak was about 21,000 cfs (cubic feet per second), the flood for older gravel 2 would have been about 30,000 cfs, and that for older gravel 3 about 40,000 cfs. E14 VEGETATION AND HYDROLOGIC PHENOMENA FiGURE 7.-Surface morphology. A, Gravel levee on right bank of the East Fork Willow Creek deposited by the flood of December 1964. B, Gravel levee on the right bank of the Trinity River at Eagle Creek deposited by a flood at least as old as 1540. Note asymmetry of topography. HISTORIC FLOOD INFORMATION FOR NORTHERN CALIFORNIA STREAMS EAST FORK WILLOW CREEK DESCRIPTION The East Fork of Willow Creek, just upstream from its confluence with Willow Creek, has been the site of extensive aggradation due to the 1964 flood (fig. 5). Although only 1,200 ft of the stream has been mapped, the 1964 flood debris appears as a continuous blanket from the mouth of the East Fork upstream for more than one-half mile (pl. 1F). Here only two small patches of pre-1964 gravel units could be found, but old partially buried stumps apparently rooted beneath the 1964 debris provided an unusual site for dating the pre- 1964 gravel. The older gravel was not eroded nor was 1964 flood gravel deposited on it; hence its morphology was preserved, and it was identified as an older gravel levee. Both older gravel deposits are similar in texture and morphology to the 1964 deposits and differ only in having more accumulated organic matter on their surfaces. AGE DATA Two living Douglas-fir trees, unscathed by the 1964 flood, were found on the upstream site while only stumps were found on the downstream site. Ring counts of increment cores on the living trees allow min- imum date of deposition of the upstream gravel, older gravel 1, to be at least 1749 (pl. 1F). The downstream gravel, older gravel 1, was dated by ring counts on stumps which we ascertained were logged after the December 1964 flood. The estimated date of deposition is at least 1590. Since the age of deposition of the two older gravel deposits differ by about 160 years, it may be concluded that two events prior to 1964 are repre- sented by these older gravel deposits. The probability also exists that no trees were established on the up- stream older gravel deposit in 1590 and that only one older flood event is responsible for both deposits. The interesting fact in terms of flood frequency, however, is the elevation to which the older gravel deposits and those of 1964 extend. The field evidence suggests that both flood events probably had similar stages and since the channel is straight and confined in bedrock, the discharges probably were similar. An event similar in magnitude to the flood of December 1964 occurred around 1600 and probably another around 1750. No evidence of the large floods of 1861 or 1955 were found, probably because the flood of 1964 was larger. SUMMARY AND CONCLUSIONS The concepts and techniques described here will have great utility for onsite determination of flood fre- quency, flood stage, and possible discharge, and should not be ignored when considering flood-plain zoning and possible development. E15 Age determinations from standing trees certainly have more validity than those from stumps. However, we found little difficulty in establishing the date of cutting by either "release" effects in adjacent trees or actual oral confirmation of cutting. Any regional comparison of previous flood histories in northern California probably would be premature because of the lack of more detailed local data and because of the extreme variability in unit runoff during large floods such as demonstrated during the 1964 floods. A good example is the preservation of the 1861 flood deposits along Blue Creek while no evidence of this large flood was observed at the other three detailed study localities. It does seem evident, however, that the largest flood event in the recorded history of northern California, that of December 1964, was exceeded by an earlier flood that occurred about 1600 and that floods of the 1964 magnitude have occurred in the more recent past. REFERENCES CITED Benson, M. A., 1962a, Evolution of methods for evaluating the occurrence of floods: U.S. Geol, Survey Water-Supply Paper 1580-A, 30 p. 1962b, Factors influencing the occurrence of floods in a humid region of diverse terrain: U.S. Geol. 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(Berkeley), 12 p. * U.S. GOVERNMENT PRINTING OFFICE: 1973-s4s-s78/16 UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 485-E GEOLOGICAL SURVEY PLATE 1 B EXPLANATION EXPLANATION Areas underlain by sediments deposited or Areas underlain by sediments deposited or eroded since December 1964 eroded since December 1964 s c & Blue Creek 21 23 O - 3 Approximate contact 5 = , ra To. w 5 0 tp 1700 1750 1800 1850 1900 1950 1970 T u 4 {- ests t( "" |_ {__ 1 _s #14 | | 1 2nd DENDROCHRONOLOGICAL 5 & Buri i f f I o U§J 3 uried redwood stumps in valley APRROXIMATE TIME SCALE, AD SAMPLE LOCALITIES % 5 Blue Creek 11 A w 23:2 C. a Living tree £7. 5 ma w be O G $ 1% Stump [ay ss ° Blue Creek 10 G3 . g - 2 Stump partly buried by 1964 deposits # ~ ® z 1776 . x Estimated date of establishment, A.D. 7G T w 3 E- i- aw , ae S § Blue Creek 9 # " 4+ ra = F4 1100 1150 1200 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 -R | Expo roe 1 "i_ _ mor La -a- (-~ (-il t FXG F petal o dein fest - 1 _ 1° } cell 1 esi -( APPROXIMATE TIME SCALE, AD GEOLOGIC MAP OF A REACH AT MOUTH OF EAST FORK OF WILLOW CREEK CROSS-DATING OF REDWOOD AT BLUE CREEK [- CRL CTC Seok MAPS SHOWING GEOLOGY AND GRAPHS RELATING TO CROSS-DATING OF REDWOOD, NORTHERN CALIFORNIA DECLINATION, 1973 DATUM IS MEAN SEA LEVEL * U.S. GOVERNMENT PRINTING OFFICE: 1973-s4s-s78/16