373 '"” "" 11361 - dBRARY hllfllil |:l\l\\\ NIMMU! wn|m‘n\u|1n\.nuuw.'u\w klllfi'{\l\l\ :IIUMWHFYIWNWLHHFIPN?!\Hi|\|i\'flll!.‘i HUN? FlFhi‘. Wt‘? {M} I ‘I HIIM"‘._KH]‘\\Y\ ?“‘A&M“¥T“e"ight Replacement ‘of Selected Woody Plants Following Burning or Shredding 1M Nl M‘ Hill HIM! HUN“ ‘I IIWWIW fhll\f\\\lll‘i'\jxh'illlll\ W ‘IW hflfll !'.l\ |l'lTIT/MlIlllllfifliilififlskflfllll‘I HWIWIMI l! Mk" NIH "W! ‘IIIM M! 11ml Hi1 '|l.Ml 7x .f'\. a Th8 T€X3S A&M UHiVETSiW SYSIEM Th8 TEXZS AQFiCU|tUF3| Experiment $113110“, N8Vi||€ P. CMFKE, Director, COIIGQG SIZCiOILTEXZS CONTENTS Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 , Introduction . . . . . . . . . . . . . . . . . ..D...D . . . . . . . Description of Study Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Materials and Methods . . . . . . . . . . . . . . . . . . . . . c . . . . . . . . . . 2 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Literature Cited .i . . . . . . . . . . . . . . . . . . . . . . . . . . . ; . . . . . . . . .7 w Metric Units -— English Equivalents . . . . . . . . . . . . . . . . . . . 8 \ Acknowledgment . . . . . . . - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 AUTHQRS HAMILTON, W. T., Lecturer, The Texas Agricultural Experiment Station (Department of Range Science). KITCHEN, L. M., formerly graduate research assistant, The Texas Ag- ricultural Experiment Station (Department of Range Science). SCIFRES,C. ]., Professor, The Texas Agricultural Experiment Station (Department of Range Science). v.1, KEYWORDS: Woody plants/height replacement/regrowth/burning/shredding/range management/Texas.‘ féleight Replacement of Selected Woody Plants Following Burning or Shredding SUMMARY y Woody plant reinvasion of tame pastures and native rangeland is a severe problem on the South Texas Plains. Shredding and/or pre- scribed burning may be employed as low-cost methods for suppres- sing woody plants, and rate of topgrowth replacement indicates how often these maintenance practices must be repeated. Honey mesquite and twisted acacia attain their pretreatment heights within the first year after shredding or burning. Blackbrush acacia regrowth attains pretreatment height by midway through the second growing season following burning. Whitebrush, lotebush, spiny hackberry, and Carolina wolfberry attain half their pretreatment heights in 10 months or less after shredding. Most other species, including blackbrush acacia, catclaw acacia, and guayacan, attain pretreatment heights within two growing seasons after shredding. Based on these regrowth rates, forage responses to the treatments, and long-term weather patterns on the South Texas Plains, it appears that burning or shred- ding regrowth of mixed-brush stands should be scheduled at intervals of 3 to 5 years. Woody species such as honey mesquite (Prosopis glandulosa var. glandulosa), blackbrush acacia (Acacia rigidula), and twisted acacia (Acacia tortuosa) aggressively reinfest rangeland and pastures in the South Texas Plains following initial brush control i practices (Scifres 1980). These woody plants are com- monly suppressed by shredding, treatment of individual plants f with herbicides. and power grubbing. Of particular concern "to livestock producers are infes- tations of woody plant regrowth following rootplowing and es- tablishment of buffelgrass (Cen- chrus ciliaris) oriCoastal bermu- dagrass (Cynodon dactylon) pas- tures. QFThe potential of fire to sup- gss woody plants is reported numerous authors (Sauer ‘Mo. Humphrey 195s. Box et al. 1967, Daubenmire 1968, Scifres INTRODUCTIQN 1980) and has received recent at- tention because of rising costs of fuel, labor, and equipment as- sociated with mechanical prac- tices, and rising costs of her- bicides and their application (Scifres 1978). Cool-season pre- scribed burns hold promise for effectively suppressing woody plants to levels-which allow im- proved forage responses from pastures. Although few woody plants are killed by cool-season burns, the live topgrowth is usu- ally reduced to near ground level and forage production is tem- porarily increased (Hamilton and Scifres 1981). Because most brush species resprout from dormant basal buds following burning or shred- ding, optimal forage production and brush suppression can be maintained only by periodic re- treatment (Scifres 1980). For ex- ample, Scifres and Haas (1974) reported about 12 sprouts per stump at 1 year after removal of post oak (Quercus stellata) tops. Sprouts averaged 94 centimeters (cm) in height and were about 4 cm in diameter at ‘the base. They also noted differences in re- growth potential of various woody species of the Post Oak Savannah, but concluded that unless maintenance brush con- trol is practiced, the brush stands can be expected to recov- er from mechanical top removal within 5 to 7 years following ini- tial treatment. Mutz et al. (1978) conclude that shredding or roller chopping must be repeated at 3- to 5-year intervals for satisfactory im- provement of rangeland infested with mixed brush on the Coastal Prairie. They suggest prescribed burning to maintain initial brush suppression from shredding or roller chopping. Huisache 1 (Acacia farnesiana) had in- creased in canopy cover, by 25 and 11 percent on shredded and on roller chopped plots, respec- tively, in 14 years after treatment compared to an increase of only 4 percent on. untreated areas. This was attributed to the rapid regrowth of huisache, which may attain half its pretreatment height within 5 months after top removal (Powell ‘et al. 1972). Although shredding is widely I practiced on the South Texas Plains and prescribed burning is gaining in popularity,cno re- search has reported regrowth rates oi woody plants subjected to these treatments. The objec- tives of this study are to (1) docu- ment and compare times re- quired for height replacement of selected woody plants following burning or shredding, and (2) ' compare height increase follow- ing burning to that of unburned plants oi the same species. DESCRIPTION OF STUDY SITES , Burned Site The experiment was con- ducted approximately l4 kilome- ters (km) south of Encinal, Texas. on an area typical of the west- central South Texas plains. Av- erage annual precipitation at the study site is about 50 cm, with peaks occurring in May and Sep- tember. The growing season is about 270 days long, with mild winters and hot summers. Soils of the study area are of the Copita series (Ustollic cal- ciorthid). The fine, loamy soil is moderately deep, moderately permeable, calcareous, and- underlain by sandstone (Stevens and Arriaga 1977). The topog- raphy is gently rolling with slopes generally less than 3 per- cent. TheilCopita soil is included in a Gray Sandy Loam range site. The experimental area was rootplowed, raked, and broad- cast-seeded to common bufiel- grass in about 1967. At initiation of this research in 1977, woody \ 2 plant regrowth on the study area was primarily honey mesquite. blackbrush acacia, and twisted , acacia. These’ species averaged 1, 1.2, and 1.6 meters (m) tall, respectively, and collectively ac- counted for more than 95 percent - of the woody plant canopy cover. Other woody species present in I the area included desert yaupon (Schaefferia cunefolia), leather- stem (Iatropha dioica), white- brush (Aloysia Iycioides), lote- bush (Zizyphus obtusifolia), Ber- landier woliberry (Lycium ber- Iandieri), spiny hackberry (Celtis paIIida), guayacan (Porlieria an- gustifolia), and tasajillo (Opun- tia Ieptocaulis). Woody plant canopy cover on the area aver- aged 8 percent prior to the burn. Shredded Site The shredding experiment was conducted near Campbell- ton, Texas, about .80 km south of San Antonio. The site supported a heavy cover of mixed brush and was composed of roughly a equal proportions of Claypan Prairie, Rolling Blackland, and Shallow range sites. Kitchen et al. (1980) presented detailed soil descriptions by site. The Claypan Prairie range site is typified by Laparita soils on nearly level to gently ‘sloping up- lands in close proximity to small drainages. Slopes are usually less than 1 percent but occasion- ally increase to*3 percent. Soils are sandy clay loams overlying clay loam subsoils which gradu- ally increase in clay content with increasing depth (Kitchen et al. 1980). The soils are acidic on the surface and slightly acidic at lower depths. i The Rolling Blackland range site is characterized by Monteola clay soils on gently undulating slopes ranging from 0 to 8 per- cent. Monteola soils are deep and homogeneous. Soil texture is 49 percent clay in the surface 3 cm and increases to 5B percent at 46 cm. Soil reaction is neutral to slightly basic, becoming more alkaline at lower depths (Kitchen et al. 1980). Fashing clay soils with sandy clay loam surface soils overlying clay subsoils 13 to 50 cm thick typify the Shallow range si the upland portions of the I iarea. These soils are on gently sloping to sloping convex sur-i faces having gradients of 1 to5 percent. Solum thickness ranges I from 25 to 50 cm and the range in thickness is common within a horizontal distance of less than 6 (m. The soil texture throughout the soil profile is a clay loam or clay. The soil is mildly. alkaline to moderately alkaline and cal- careous (Kitchen et al. 1980). All sites on the. study area @- pear to have a claypan at'a depth of 30 to 46 cm. This clay- pan is most prominent on the Claypan Prairie site. MATERIALS AND METHODS Burning Study The study area was burned February 7, 1977, with a mainte- nancelfire for suppression of woody plants and minimum risk of damage to common buifel- grass, the primary (herbaceous species present. Grazing use of the plots by livestock was de- ferred for 60 days following the burn. The area was then grazed at a stocking rate of approxi- mately 1 animal unit/8 hectares (ha) for 17 months. Grazing was again deferred for 10 months and the area was then grazed at the same stocking rate until termi- nation of the study. Rainfall was recorded as the amount ac- cumulated in a rain gauge be- tween sampling periods. I y The experiment was designed as a randomized complete block design with two replications. The fire plan employed a head- fire following backiiring of the lee sides of the plots (Scifres 1980). Four permanently-marked belt transects, 3.7 by 61 m, were established prior to the burn in each 1.8 ha plot. Woody plant height was measured in eL-‘Qh belt prior to burning and (Il/Qfi-W proximately 4, 6, 10, 17, 23fi. l 27, and 33 months following the I fire. Plant height was measured (as the distance from soil surface to the uppermost, live growing ,alon each plant in the belts. A i. ilar method for measuring height of huisache to estimate growth rate was used by Powell et al. (1972). At the same times heights were measured, canopy diameters at the point of max- imum spread were recorded by species, and the number of live plants of each species was recorded. In most studies, canopy diameter is used to assess the impact of woody plant regrowth - the range plant community. ihe validity of using height to express the influence of woody plants is evaluated in this study. The relationship between plant height and canopy diameter by species is evaluted based on the functional relationship, Y = a+bX where Y = canopy diameter as a percentage of pre- burn diameter, and X = plant height as a percentage of pre- I burn height. Height replacement following burning was best rep- resented by the functional rela- tionship Y = a+b(log X), where Y = height as a percentage of preburn height and X = time (months) after burning. Differ- ences in b-values (slope) be- tween equations from the burned and unburned areas were evaluted with a t-test at the 5 percent level of probability (Steel and Torrie 1962). Height replacement compari- sens among species were based on the predicted time required for regrowth to attain half the pretreatment height (Htso) and to- » tal pretreatment height (Htwo). Height increases between burned and unburned plants jvere compared by testing differ- ences in slopes of the regrowth response curves. Shredding Study Eight permanent, circular plots (15.6 m diameter) were es- lished on each range site. the plots were shredded %'h a drag-type shredder in Jruary 1976. At 4, 6, 8, 18, and 25f‘ months after shredding. heights of woody plant regrowth .0, were recorded by species as de- scribed for the burning study. Numbers of individuals mea- sured varied from as few as three (lotebush, Rolling Black- I lands) to 38 (spiny hackberry, Claypan Prairie) with 15 as the average. The heights as percent- shredding. Thereafter for the du- ration of the study, the pasture was stocked with ‘cows, or cows and calves, at I animal unit/9 hectares. RESULTS AND DISCUSSION age of heightsnbefore shredding , were regressed against time . (months) as the independent var- iable with the functional rela- tionship, Y = a+b(log X). Com- parisons of height replacement among species were based on predicted time required for re- placement of half the pretreat- ment height (Htso). Rainfall on the study area was monitored with a rain gauge. The study site was deferred from grazing for 6 months following: PRECIPITATION (cM) 5O 45 l5 l0 Height Replacement Following Burning Height replacement is con- sidered a valid comparative in- dex of the relative influence of brush regrowth on“ the range plant community. More than 96 percent of the variation in canopy diameters of honey mes- quite, blackbrush acacia and twisted acacia could be account- height change. Therefore, only 5/2) l 7/13 ;:E:§r§:§:§:E5E5E5E5E5EEIEIEIEIEIE ,0 ode 0 o.1h:.:,:.:.:.):.:¢:.:.:. it: .0: not‘ : : : z-t-lz! 14+!- ti nu-I-T-f- -; 1 1 j-§<1.°.°:':':': 1;I;I;-;I;I1 t“ ""'=l§:§:¥:?:?:‘I§ iii-i! ‘:1.1.-.- -1 11/10 u24l1o/1a _ 1977 1978 1979 l SAMPLING DATES Figure 1. Rainfall (cm) accumulated for the sampling periods following burning of brush- infested buffelgrass stands near Encinal,’ Texas in February 1977. ed for by measurements of. F height replacement data are re- 36o ’ UNBURNED poTllfse data do not reflect a absolute rate of growth of g woody plants on the burned 320 - y plots butindicate a rate of height t replacement based on total pre- a treatment heights. There were a 23g y ' t few plants of each species in the ‘ belt transects that were not top killed by the fire. Since cool- 24o ,_ a season burns will typically leave some woody plants unaffected, the time required for brush popu- = 101 _ 3 + 4 . 6 (LOG X) i lations to return to total pretreat- 2 = o 6 A t ment height is the most practical ' measurement. Marginal conditions at the time of the burn, including low fine fuel load (1,140 kilograms per hectare [kg/ha]), low wind ‘_‘_______.__w velocity (8 to 13 kilometers per O ' ' ‘ hour [km/hr]), high relative humidity (89 percent), high fine 30 ' ~ fuel water content (23 percent), and poor fine fuel continuity, re- sulted in a relatively "cool" fire. 40 - Fine fuel discontinuities were l most prevalent adjacent to the p older, larger woody plants. How- O y ever, an estimated 80 percent of the surface area within the plots t a y was blackened by the burns, and ,. a high percentage of woody 28o BU RN ED plants suffered visible fire dam- age. Average maximum temper- .240 _, y ature at 15 cm above soil surface during the burns was 225 de- grees centigrade (°C) (Hamilton and Scifres 1981). Rainfall distribution during g 1977 and 1978 of the study period ‘ U was typical for the area, with l O peaks during the spring and fall and relatively dry summer and winter seasons (Figure 1). Total _ , amount of rainfall during the Q study period was near the 20- year average for the area. How- ever, practically all the 1979 rainfall occurred in the first 6 0 months of the year. l Predicted times required for honey mesquite to attain half its pretreatment height (Ht50) and to Q l ' ' ' ' ' replace its full pretreatmgnt 5 l0 l5 .20 25 3o 33 height (Htwo) following burfllag MONTHS AFTER BU RN were 4.5 months and 7.8 moniigs, l i respectively. The predic§fll Figure 2. Change in height (as a percentage of initial height) of twisted acacia following equations (mCm-lnted £01’ 82 and burning in February 1977 near Encinal, Texas. ' . 92 pergent Qf the vqriqtign in 200 '- W-<> 160 - 120 r (% OF PREBURN HEIGHT) HEIGHT 200 - ‘60’ =-29.s + 53.6 (LOG X) r) , A Y f‘: .83 C 120 - 80 - 4Q- height change as related to time of measurement for the un- ned and burned honey mes-a ,1 te, respectively. According to a t-test (P<.05), burning did not affect honey mesquite height in- crease for the time of" evaluation in this study. i The predicted Htso following burning of blackbrush acacia was 7.8 months, and the Htwo was 19.3 months. As with honey mesquite, the prediction equa- tions accounted for 87 pecent of the variation in height change of blackbrush acacia. Burning did ‘ affect height increase based on comparison with unburned blackbrush acacia. Blackbrush acacia height replacement was slower than that of honey mes- quite, regardless oftreatment. The predicted Htso for burned twisted acacia was 4.4 months, w while Htwo was 11.3 months. Al- though 83 percent of the varia- tion in rate of twisted acacia height change could be ex- plained by time of measurement on burned plots, only 6 percent of y the variation was attributed to the relationship on unburned areas (Figure 2). The low coeffi- cient of determination and insig- nificant slope on the unburned plots indicate that height of twisted acacia had stabilized on ‘the site. Scifres (1980) describes twisted acacia as a low growing shrub, usually less than 1.8 m tall. The twisted acacia plants in the study area averaged 1.6 m in height prior to the burn, addi- tional evidence that twisted acacia on the unburned plots had stabilized in height in the time since root plowing. This would explain why height in- crease on burned and unburned ..plots was significantly different (P<.05). Height Replacement Following Shredding Average annual precipitation agar Campbellton is about 51 t .1. The year of shredding, 1976, _ s characterized by a rela- Qaly dry winter, but rainfall from April through October to- taled 79 cm, and the annual pre- 1976 2 0 Z Q 2 . ~.-.- 1977. E 20 - U LLI Z l l5 - fzfzffizfzf ‘izizfzfzfi 1° " 55555555555 w §:§:,5,z,z}5....... 25252555555552555555155555555555 2555555525: . . . .. 5555555555.5555555552525552525552 O . .. ._ ............................ '. g ' , ............................ _ .53.; ......... .' JFMAM, JASO'ND MON T H Figure 3. Monthly rainfall (cm) on the study site near Campbellton, Texas where bru regrowth rates were evaluated following shredding. cipitation was 100.9 cm (Figure 3). Rainfall totaled 49 cm in 1977, with 16 cm received in April. The summer dry period. was inter- rupted by rainfall in Iuly, fol- lowed by the typical fall rainfall peak. Apparent active growth of the woody plants had ceased by the first week in November 1976, about 8 months after shredding. By this time, honey mesquite, lotebush, twisted acacia, and whitebrush had regrown to half their initial height on the Clay- pan Prairie site, based on the prediction equation (Table 1). The predicted Htso for honey mes- quite on the Claypan Prairie near Campbellton was essen- tially the same as following burning (4.5 months) near Encin- pal. Estimated Htso following shredding of twisted acacia was slightly greater than following burning (4.4 months) near En- cinal. Whereas shredding uniformily removes the aerial portions of the twisted acacia plants, cool- 5 sh could have been confounded with shredding effects in the evaluation of regrowth rate this study. Scifres et al. (1974) reported TABLE 1. TIME (MONTHS) FOR SELECTED WOODY PLANTS TO REPLACE HALF (Ht50) THEIR PRETREATMENT HEIGHT (PH) AND COEFFICIENTS OF DETERMINATION (r2) AFTER SHREDDING THREE RANGE SITES IN FEBRUARY 1976 NEAR CAMPBELLTON IN THE SOUTH TEXAS PLAINS 1 . ‘Time to reach predicted 50 percent of pretreatment height exceeded evaluation period. “Not present in sufficient number for evaluation. ‘Only relationship in which regression coefficient (r) was not significant at P<.05. season burning may not result in uniform and complete kill of above-ground stems. However, honey mesquite and twisted acacia (and apparently lotebush and whitebrush [Table 1]) can be expected to replace at least half I their pretreatment heights with- in the first growing season fol- lowing shredding or burning in the dormant season. Catclaw acacia (Acacia greg- gii) and spiny hackberry re- quired an estimated l0.9land 10.1 months, respectively, to re- place half their pretreatment heights following shredding on the Claypan Prairie site (Table 1). Although the estimated time for achieving the Htso occurred in late fall, these species should probably also be considered in that group of woodyplants with potential to regrow to half their initial height in the first growing season. Predicted Ht50s for the re- maining species evaluated on the Claypan Prairie site, agarito (Berberisitrifoliolata), black- brush acacia, Carolina wolfber- ry (Lycium carolinianum), desert yaupon, guayacan, and knifeleaf condalia (Condalia spathulata) occurred during the second growing season after shredding. I 6 Height replacement of black- brush acacia, based on time re- quired to achieve H1505, was slower (19.5 months) following shredding of the Claypan Prairie site near Campbellton than after burning (7.8 months) near Encin- al. The estimated time to attain Htso after shredding approx- imated the Htwo (19.3 months) fol- 1 lowing burning. This is at- tributed to differences in the amount of topgrowth removal between shredding and burning. With the exceptions of black- brush acacia and lotebush. height replacements of woody plants which occurred on both sites tended to be slower on the Rolling Blackland than on the Claypan Prairie site. Most rapid growth on both sitesioccurred with lotebush, twisted acacia. and whitebrush, with slower growth rates for blackbrush acacia, catclaw acacia, and guayacan (Table 1). Agarito replaced its height the most. slowly of plants evaluated onthe Rolling Blackland site (Table 1). Agarito regrows from a discrete crown following top re- moval, and the regrowth may be heavily browsed by white-tailed deer (Odocoileus virginianus) (Scifres 1980). Browsing pressure Range site Claypan Prairie Rolling Blackland Shallow honey mesqulte regrowth In ' North Texas developed more . .2 2 :11 2 S9111 on R099 H111 p 0 r m m0 r sites than on Deep Upland range Agarito 1.27 17.0 0.04 1.17 24.09 0.06 1.06 21.7 6 0.04 sites. That relationship did not Blackbrush acacia 1.09 19.5 0.85 0.0g 16.7 0.88 1.12 14.7 0.62 hQld true with Qther speciesin Carolina wolfberry ' 0.65 19.8 0.84 NP —— —— c , 0.77 9.3 0.94 the study near Cqrnpblelltgn" Re- ‘ ese yaupon . . . — - - - - 1- Guayacan 0.34 14.6 i 0.77 0.42 14.0 0.77 0.43 21.6 0.72 bush’ Catdaw mama’ Cam ma . pwolfberry, and blackbrush Honey mesquite 1.34 4.8 0.87 NP - — NP — — . . Knifeleafcondalia 0.07 12.6 0.94 NP - - NP _ _ 9mm“ deYPIPPPd as rapldlY °r Lotebush 2 0.70 9.0 0.06 1.17 0.5 0.01 0.70 6.2 0.76 m°T° mPldlY 9n Shfilhw 511$ Spiny hackberry 0.91 10.1 0.91 1.05 14.7 0.09 1.06 10.3 0.04 ihqn °_I1 CIQYPQH P161119 (deePeI Twisted acacia 0.73 6.4 0.76 0.90 9.7 0.01 0.75 6.2 0.79 soil) Sltes- M°re0ver. regrowthof Whitebrush 1.30 7.4 0.81 0.99 0.1 0.77 NP - - most of the woody species was replaced more rapidly on the Shallow than on the Rolling Blackland range site. The only exception was guayacan, which . was predicted to replace “half its initial height on Claypan Prairie a and Rolling Blackland sites by 14.6 and 14.8 months, respective- ly, after shredding, compared to an estimated 21.6 months for the Shallow site. Management and Ecological Implications Cool-season burns of brush- infested range or pastures will commonly result in some areas either not covered by the fire or affected by the fire to varying degrees of intensity. Movement of a fire through such areas is dependent on a number of vari- ables. Inadequate fine fuel load in patches of heavy brush cover, for example, prevents the flame from reaching the woody plants. Poor fuel continuity, the influ- ence of which is usually mag- nified by low wind velocity, can also leave unburned areas in spaces between brush plants or cause reduced fire temperatures in such spots. This variation as- sociated with range burns is of- ten desirable relative to qualit wildlife habitat since it result ' 1 a vegetation "mosaic" (Scif 1980). ' ’ Because of the behavioral characteristics of fire, woody plant stands on burned areas a may appear to recover more idly than on those areas ~ated with shredding or "scalp- ilng," which removes woody plant topgrowth to a uniform stubble height. The live, above- ground tissuesof undamaged or mildly-damaged a plants become an immediate part of postburn stands. Even after the second burning of an area, the accumu- lation of adequate fine fuel load and continuity, and selection of the optimal combination of envi- ronmental factors "(wind velocity, §lative humidity, fuel moisture content) will be criticalfor uni- form suppression of woody plants. Managers are often con- cerned with the need to save "motts" of woody plants or un-. burned herbaceous material on range areas as a part of suitable habitat for game animals and birds (Box and Powell 1965). Thus, burning may be looked up- on as an effective way to suppress woody plants while minimizing damage to wildlife habitat, and may be preferred over complete top-removal by such means as shredding. These data indicate total pre- burn heights of species such as honey mesquite and twisted acacia were regained within one growing season after the fire, and others, such as blackbrush acacia, required less than two growing seasons. Planning fre- quency of burning treatment based on total height replace- ment would lead to intervals of burns between l and 2 years. This frequency is not reasonable in many parts of south, Texas be- - cause of the low rainfall and ex- tended periods of low forage pro- duction. A more practical ap- proach to determining burn in- terval would be to use herbace- ous forage production as an indi- cator. Hamilton and Scifres (1981) have shown that benefits -of a single, cool-season burn extend into the third grow- season following the fire, de- igding upon soil water con- ‘tents. A Height replacement varies considerably among species fol- lowing burning or shredding. The first aspect of regrowth is honey mesquite/twisted acacia- dominated stands on upland range sites and whitebrush dom- ination on lowland sites. As the regrowth rates of honey mes- quite and twisted acacia are so rapid on upland sites, it is possi- ble that these species could gain a competitive advantage over slower-growing species subject- ed to repeated shreddings, thus allowing the development of a mesquite/twisted acacia com- plex. I Shredding interval for effec- tive brush suppression will un- doubtedly vary with range site. as site influences regrowth po- tential and species composition of brush stands. However, these data support the conclusions of . Mutz et al. (1978) that shredding at 3- to 5-year intervals is neces- sary to suppress mixed-brush stands effectively. ‘ The influence of range site is not expressed in the traditional sense in this study. Range site obviously regulates botanical composition, but woody plant re- growth rates are not necessarily slower on the Shallow site than on other sites following shred- ding. Apparently, strong "site adaptation" is expressed by speciesin the regrowth rates. For example, blackbrush acacia occurs on all sites but is ex- tremely common on shallow, rocky uplands (blackbrush acacia-guajillo ridges) in south Texas (Scifres 1980). Height re- placement tends to be more rapidwith blackbrush acacia on the Shallow than on the deeper sites. The same trend is appar- ent with Carolina wolfberry and lotebush. Other species such as guayacan exhibit the "typical" response, with regrowth being slower on the shallow sites than on the deeper site. Still other species such as catclaw acacia and spiny hackberry exhibit no apparent difference in height re- placement among sites. These I results indicate the need for more research to elucidate the potential interactions of species growth with site. The very high levels of correla- tion between height and canopy diameter replacement following burning suggest that height measurements alone may be used to express the impact of woody plants on the vegetation community. In much of the south ‘ TexasPlains, measurement of woody plant height is more ef- fective and expeditious than measurement of canopy diameter. LITERATURE CITED Box, T. W., and I. Powell. 1965. Brush management techniques for improved forage values in south Texas. Trans N. Amer. Wildl. and Nat. Res. Conf. 30:285-296. Box, T. 1W., I. Powell, and D. L. Drawe. 1967. Influence of fire on south Texas chaparral communities. Ecology 48: 955-961. Daubenmire, R. 1968. Ecology of fire in grasslands in Adv. Ecol. Res. 5:209-266. Academic Press, N .Y. Hamilton, W. T., and C. I. Scifres. 1981., Cool season prescribed burning for maintenance of buffelgrass. I. Range Manage. 134: (In press). Humphrey, R. R. 1958. The desert grass- land: A history of vegetational change and an analysis of the causes. Bot. Rev. 24: 193-252. _ Kitchen, L. M., C. I. Scifres, and I. L. Mutz. 1980. Susceptibility of selected woody plants to pelleted picloram. I. Range Manage. 33:344-353. yMutz, I. L., C. I. Scifres, D. L. Drawe, T. W. Box, and R. E. Whitson. 1978. Range vegetation after mechanical brush treatment on the coastal prairie. Texas Agr. Exp. Sta. Bull. 1191. 16 p. Continued 7 ALNBBB 781101-13 Powell, I., T. W. Box, and C. V. Baker. Agr. Exp. Sta. Misc. Pub. II36fTl pp. 1972. Growth rate of sprouts after top removal oi huisache (Acacia farnesia- na [L.] Willd.) (Leguminosae) inisouth Texas. Southw. Nat. 17:191-195. Sauer, C. O. 1950. Grassland climax, fire, and man. I. Range Manage. 3:16- 21. Scifres,lC. I., and R. H. Haas. 1974. Vege- tation changes in a post oak savannah following woody plant control. Texas Scifres, C. I., M. M. Kothmann. and C. W. Mathis. 1974. Range site and grazing system influence regrowth after spray- ing honey mesquite. I. Range Manage. 27:97-100. . Scifres, C. I. 1978. Range vegetation management with herbicides and al- ternative methods: An overview and perspective. Symp., Use of Herbicides in Forest., U.S. Dep. Agr.-U.S. Environ. Prot. Agency. Feb. 21-22. Arlington, VA. pp. 151-165. Scifres, C. I. 1980. Brush Manage Principles and practices for Texa _ the Southwest. Texas A8zM Univ. Pr=._ College Station. 360 pp. Stevens, I. W., and D. Arriaga. 1977. Soil survey of Maverick Co. TX. U.S. Depf Agr., Soils Cons. Ser., Unnumbered Pub. 63 pp. . Metric Units — English Equivalents Metric Unit Centimeter . Hectare Kilogram t Kilogram per hectare Kilometer Kilometer per hour g Liter Meter Square meter e (Degrees centigrade >< 1.8 + 32 Equivalent 0.394 inch 2.47 acres 2.205 pounds 0.893 pound per acre 0.62 statute mile 0.62 mile per hour I 0.264 gallon 3.28 feet 10.758 square feet Degrees fahrenheit ACKNOWLEDGMENT Owners of the Cerrito Prieto Ranch near Encinal and the 74 Ranch near Campbellton furnished land for this study and partially financed the research, for which the authors offer thanks. The authors ap- preciate the efforts of Iulia Scifres in manuscript typing and prepara- tion, and of W. C. Mohr and I. L. Mutz in assisting with installation and evaluation of the experiments. Mention of a trademark or a proprietary product does not constitute a guarantee or a warranty of the product by The Texas Agricultural Experiment Station and does not imply its approval to the exclusion of other products that also may be suitable. All programs and information of The Texas Agricultural Experiment Station are available to everyone without regard to race, ethnic origin, religion, sex, or age. i 1.5M - 7-81