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ZTA245. 7 AUQUST i933

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lniegroied Brush
Monogemeni Systems (IBMS):
»- Conoepis ond Poieniiol
Technologies for Running

Mesquite ond Wniiebrush

The Texas Agricultural Experiment Station/Neville P. Clarke, Director/The Texas A&M University System/College Stati oooooo as

CONTENTS

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ii
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Conceptual Basis for Integrated Brush Management

Systems (IBMS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

The Running Mesquite Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

The Whitebrush Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Research Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Running Mesquite Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Whitebrush Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Running Mesquite Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Whitebrush Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Herbicide Application/Prescribed Burning as Potential IBMS
Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10

Running Mesquite Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Whitebrush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 12

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

CONVERSION OF
METRIC TO ENGLISH UNITS

Metric unit(s) English equivalent(s)
Centimeter (cm) 0.394 Inch

(Degrees centigrade [°C]x9/5) + 32 Degrees Fahrenheit (°F)
Hectare (ha) 2.471 Acres

Kilogram per hectare (kg/ha) 0.892 Pound/acre
Kilometer (km) 0.621 Mile

Kilometer per hour (km/hr) 0.621 Mile/hour

Liter per hectare (liter/ha) 0.107 Gallon/acre

Meter (m) 3.28 Feet (ft)

Square meter (m2) 10.758 Square feet

l“

CONCEPTS AND POTENTIAL TECHNOLOGIES
FOR RUNNING MESQUITE AND WHITEBRUSH

C. J. Scifres
Thomas M. O’Connor Professor
The Texas Agricultural Experiment Station (Department of Range Science)

J. L. Mutz
Assistant Research Scientist
The Texas Agricultural Experiment Station (Corpus Christi)

G. A. Rasmussen
Research Associate
The Texas Agricultural Experiment Station (Department of Range Science)

R. P. Smith
Research Associate
The Texas Agricultural Experiment Station (Department of Range Science)

INTEGRATED BRUSH MANAGEMENT SYSTEMS (IBMS):

.434» i» x

J

SUMMARY

Integrated Brush Management Systems (IBMS) use
two or more brush management methods in an appropri-
ate sequence to achieve specific resource management
goals within an economic framework, with cognizance of
critical needs for enhancement of environmental quality
and improvement of wildlife habitat. This concept re-
duces dependency on single methods of brush control by
developing a logical series of treatments for application
over a defined planning horizon. IBMS minimize the
weaknesses of each treatment while amplifying its
unique strengths. This can help the resource manager
capitalize on ecological and economic synergisms not
possible with single-treatment approaches. Research on
IBMS reported herein describes herbicide-fire based
systems applied with decision-deferment grazing for im-
proving South Texas rangeland supporting excessive
covers of whitebrush or the running mesquite complex (a
shrub type composed of a mixture of decumbent honey
mesquite and screwbean).

Prescribed burning in the winter, approximately 31
months after aerial application of 1.1 kilograms per
hectare (kg/ha) of 2,4,5-T + picloram in the spring, and
burning again at about 57 months after spraying, main-
tained canopy reduction of running mesquite more effec-

ii

tively than spraying or prescribed burning alone. Grass
standing crops were greater and a higher proportion of
the grass stands were composed of species of good-to-
excellent grazing value on plots sprayed and burned than
on untreated areas (periodic grazing deferment only) or
those treated with herbicide or burning alone.

Aerial application of tebuthiuron pellets at 2 kg/ha
in the fall of 1975 effectively controlled heavy stands of
whitebrush. Although the subsequent prescribed burn
could not improve brush control, forage production was
increased and botanical composition of the stands was
improved compared to areas treated with herbicide
only.

Herbicide-fire combinations appear promising for
improving rangeland supporting excessive cover of run-
ning mesquite or whitebrush. Herbicide application ini-
tially reduces the brush cover and releases herbaceous
vegetation to serve as fine fuel as well as increasing)
livestock carrying capacity. Prescribed burning expe- -
dites forage production, improves botanical composition

of herbage stands, and suppresses brush regrowth and ‘ »

reinvasion by woody seedlings. This research indicate
that such sites may be burned at 3- to 5-year intervals
during periods of average rainfall.

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INTEGRATED BRUSH MANAGEMENT SYSTEMS (IBMS):
f\ CONCEPTS AND POTENTIAL TECHNOLOGIES

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Excessive cover of woody plants on rangeland is a
primary constraint to livestock production in Texas and
much of the Southwest. Although there are accounts of
vast expanses of pristine grasslands in South Texas (Sci-
fres, 1980), there is reason to guard against conjuring
visions of early grasslands completely free of woody

“plants such as honey mesquite (Prosopis glandulosa)
(Hester, 1980). Woody plants long have been compo-
nents of range vegetation. Remains of honey mesquite
from archeological digs along the Frio River have been
dated to, 300 B.C. (Hester, 1980). The diaries of explor-
ers and travelers through Texas in the 1700’s often refer
to presence of specific woody plants which are now
considered to be serious management problems (Inglis,
1964).

Woody plants, by virtue of man’s influences (re-
ducing occurrence of fires, restricting movements of
grazing animals, overgrazing and spreading of seeds)
(Scifres, 1980, 1983), spread from the draws and water-
ways and increased in stature and density to form today’s

\“brush problem” (Bogusch, 1952; Johnston, 1962; York
and Dick-Peddie, 1969). Bray (1901) referred to the
“pigmy” forests of “chaparral” on the South Texas Plains
at the turn of the century as not yielding to mesophytic
forests because of low rainfall. In rationalizing the gener-
al dominance of woody plants instead of grassland, he
stated:

The temperature conditions are of signifi-
cance to vegetation in the province but only
indirectly do they react upon the character of
the grass formations. This indirect control
consists chiefly in permitting the occurrence
of woody species that require high annual
temperatures (Mimoseae, for example),
which, with certain artificial barriers re-
moved, the burning 0f grass notably, [em-
phasis added], are capable of waging a suc-
cessful struggle against grass vegetation.
With respect to the relations of grass forma-
tions to woody formations in the Rio Grande
Plain, the encroachment of the latter has
been so vigorous as practically to destroy
continuous areas of open grass formation.
Much of the province is covered by im-
\ penetrablethickets of chaparral.

Presently, more than 8O percent of the 43 million hec-

tares (ha) of rangeland in Texas is so heavily covered with

\brush that livestock production is reduced (Scifres,
1980).

Early workers, bent on ridding rangeland of brush,

set out to develop methods to eradicate the brush—an

f FOR RUNNING MESQUITE AND WHITEBRUSH

api/Fz/fié fia/m/zpara/é [JJ/K/fif,’  fi?

term soon found a prominent place in the vocabularies of
ranchers (Caird, 1947) and researchers (Fisher et al.,
1946). Early efforts were viewed as a “war” against an
enemy which was felt to be progressively occupying all
productive rangeland (Caird, 1947). However, there
were workers during the same period who recognized
some positive attributes of plants such as mesquite.
Parker (1943) p-ivqwfiza-tm

[c]onsidering the advantagesfarid disadvan-
tages of mesquite, the problem appears to be
one rather of control than elimination; that is,
control of further encroachment into grass
land areas and the use of practical methods of
thinning out some of the present stands,
allowing the remaining perennial grasses to
spread.

The term “brush control,” as a philosophical re-
placement for “brush eradication,” rapidly gained popu-
larity and was almost universally used by the mid-1950’s.
However, the goal of brush control, applied in the
purest sense, still connotes the desire to kill 100 percent
of the target woody plant stand. Development of brush
control methods traditionally has emphasized use of
single technologies. Each available method is charac-
terized by certain weaknesses as well as unique
strengths. Some weaknesses of standard methods (Sci-
fres, 1981) include:

1. Incomplete control of the target population of
brush resulting in rapid development of re-
growth stands which negate treatment effec-
tiveness, and which may be more difficult to
control than the original growth form.

2. Partial or ineffective control of associated species
resulting in release of “new” brush problems
after controlling the primary species. This may
be a particular problem in mixed stands where
secondary species released are more difficult to
control than the initial target population. An
example is release of yaupon (Ilex vomitoria)
and/or winged elm (Ulmus alata) after control of
post oak (Quercus stellata) and blackjack oak
(Quercus marilandica) in east-central Texas (Sci-
fres, 1980).

3. Lack of economic acceptability because of high
treatment costs and/or requirement for reappli-
cation. Multiple applications with phenoxy her-
bicides are usually necessary for effective control
of species such as the post-blackjack oak com-
plex, Macartney rose (Rose bracteata), and run-
ning mesquite (Prosopis spp.) stands.

4. Potential for damage t0 susceptible crops in adja-
cent areas by physical drift and/or volatility as-
sociated with herbicide sprays. This potential
problem is magnified when multiple herbicide
applications are required for brush control.

5. Damage to desirable species, as is the case with
use of aerial sprays that control native legumes.

Combinations of methods have been investigated to
develop complementary treatment sequences, especial-
ly use of low-cost measures to extend the effective
treatment life of costly practices and to improve degree
of eificacy. Some of these treatments, spraying and
chaining of honey mesquite as one example (Scifres,
1973), have proven highly satisfact33g~ and provide the
basis for pursuing development 61 brush management
systems. __ " w.

A coNcEPTUAL BASIS
FOR INTEGRATED BRUSH
MANAGEMENT SYSTEMS (IBMS)

The concept of brush management, “management
and manipulation of stands of brush to achieve specific
management objectives,” considers the potential values
of woody plants in the range ecosystem. The term brush
management was used in the mid-1960’s (Box and Pow-
ell, 1965) but has only recently been formalized (Scifres,
1980), and apparently is gaining acceptance. Apprecia-
tion of the concept was precipitated largely by the
increasing values of rangeland for uses other than solely
as grazing by domestic livestock, especially its impor-
tance as wildlife habitat. The emergency of wildlife as an
economically viable resource provided impetus for
managing the use of all range vegetation, not just the
grass. “Although the concept of brush management on
rangeland is not new, the time appears right for promot-
ing its general acceptance” (Scifres, 1978).

Development of brush management systems re-
quires consideration of all applicable brush control tech-
nologies. However, a brush management system, a plan
0f procedure in which the application 0f the individual
methods is coordinated by the manager in an orderly
fashion, is much more than simply a combination of
brush control methods. “Development of effective brush
management systems necessitates that all processes re-
quired for designing, implementing, and maintaining
range improvement—from the development of objec-
tives for a given management unit to assessment of
economic feasibility-be given appropriate considera-
tion” (Scifres, 1980). The systems are based on ecological
potential of the land resource using principles of sound
business and land management to achieve an economic
result. IBMS are employed to optimize rangeland pro-
duction considering all uses (livestock, wildlife, recrea-
tion) of the resource, not necessarily to maximize returns
from any given use. Brush management is integrated
with all other management inputs, especially grazing
management, to achieve the appropriate result.

The IBMS concept reduces dependence on any
given brush management method by emphasizing an

2

IDENTIFY GENERALIZED MANAGEMENT
GOALS AND OJECTIVES
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Anon Range l,’ ‘\ Identity Brush
cmldmm‘ I ‘s Problem (s)
RESOURCE

POTENTIAI.
FPROPRIATE

Conversion to
Primary Use Other NO

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Grazing and Livestock ‘\ Y“
Management Constraints \\\~ CHA"CIERIZE

TECHNOlOGICAl
ALTERNATIVES

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livestozk Management = ‘ osvnor uusu MANAGEMENT
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ESTIMATE RESOURCE REQUIREMENTS
AND PRODUCTION IMPACTS

   
        

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MODIFY PlAN

Figure 1. Processes and functions required for development of
Integrated Brush Management Systems (IBMS) (from Scifres et
al., 1983). Various persons contributed to development of the
flow chart including R. E. Whitson, W. T. Hamilton, j. M. Inglis,
and j. R. Conner.

appropriate sequencing of a series of alternatives. The
alternatives are selected such that the unique strengths i
of one compensate for any characteristic weaknesses of
the other( s).

It is beyond the scope of this paper to entertain in
detail all steps involved in developing a specific IBMS 
(Figure 1). Present IBMS concepts represent an evolu- -
tion of philosophies arising from experimentation since
the early 1970's (Scifres, 1975, 1978, 1980). Scifres et al. “ T
(1983) discuss procedures for IBMS development. How-
ever, critical considerations, briefly stated, for develop-
ing an IBMS are:

1. Management objectives. The best use (relative to
overall firm goals) of the _management unit(s)

1 l. targeted for brush management must be discern-

ed, and reasonable production goals to be
achieved in an appropriate time framework must
be established. The objectives may usually be
established to optimize economic returns from
all potential uses rather than to maximize income
from any single use.

2. Natural resource potential. Realistic manage-
ment objectives cannot be established without a
reliable estimate of production potential of the
management unit. Present production level
must be compared against potential production
b. to assess economic feasibility.

3. Grazing management. Success from IBMS can-
not be expected unless sound grazing manage-
ment is an integral part of the system. Develop-
ment of the most effective IBMS may necessitate
some changes in grazing management strategies.
IBMS may also be developed which take full
advantage of present grazing management, or
grazing management systems may be developed
simultaneously with formulation of an IBMS.

4. Available alternatives. All available alternatives
should be considered relative to such factors as
their efficacy, characteristic weaknesses, expect-
ed treatment life, biological secondary effects

'\ (positive as well as negative), application re-

quirements, and effects on wildlife habitat so
that maximum flexibility of treatment choice is
possible.

5. Proportion of management unit t0 be treated.
Often there is management wisdom to applying
the brush treatments in a pattern rather than
treating the entire management unit. Key sites
for wildlife habitat and areas for livestock shade
and loafing must be considered. The pattern
should be “tailor made” so as to best meet
management objectives for the targeted manage-
ment unit. This need has precipitated develop-
ment of some rather novel treatment designs
such as the "Variable Rate Pattern” (Scifres and
Mutz, 1982).

6. Economics. A reasonable planning horizon, in
light of management objectives, should be cho-
sen. Management benefits and treatment costs
must be projected, and alternative uses of capital
considered. Sound, practical criteria must be
selected for economic projections. These may
range from projecting simple rates of return and
payback periods on borrowed capital to more

0 detailed approaches such as present-value
analyses.

The primary purpose of this research was to investi-
Nate herbicide-prescribed fire combinations as potential
components of IBMS for improvement of rangeland
infested with running mesquite or whitebrush (Aloysia
 The research was stimulated by the effec-

tiveness of herbicide/fire treatment sequences in sys-
tems for improving rangeland supporting excessive cov-
er of diflicult-to-manage species such as Macartney rose
(Scifres, 1975).

THE RUNNING MESQUITE PROBLEM

There are 44 species of the genus Prosopis (mes-
quites) distributed in arid and semiarid areas of North
and South America, northern Africa, and eastern Asia
(Burkart and Simpson, 1977). The genus can be sub-
divided into the “mesquites” and the “screwbeans”
based on legume (seed pod) characteristics (Bensen and
Darrow, 1954). The legume of mesquite is slightly curv-
ed, creamish-tan (sometimes purple-tinged) at maturity,
and generally resembles those of garden beans. The
legume of screwbeans (also referred to as “tornillos") are
tightly coiled spirals of uniform diameter (Bensen and
Darrow, 1954) and bright yellow in some species.

Correll and Iohnston (1970) list four species of
Prosopis in Texas: P. reptans var. cinerascens, P. pubes-
cens, P. laevigata, and P. glandulosa. Gould (1975) lists
the same species as Correll and Johnston (1970), except
that he includes three varieties of P. glandulosa (var.
glandulosa [honey mesquite], var. torreyana [western
honey mesquite], and var. velutina [velvet mesquite]).
Honey mesquite (P. glandulosa) is the most cosmopoli-
tan representative of the genera occurring in virtually
every resource region of the state. Gould (1975) gives P.
reptans var. cinerascens the common name “creeping
mesquite” which also is locally referred to as running
mesquite. g

The running mesquite type consists of low, spread-
ing individuals, rarely exceeding 2 meters (m) tall (usual-
ly less than 1 m), and usually occurs on alkaline or
gypsum soils of the South Texas Plains. The stands may
be surrounded by mixed brush (Prosopis-Acacia) on the
less saline soils, and may contain various proportions of
species common to mixed-brush stands, especially prick-
lypear (Opuntia spp.). We and others have often used
the scientific name, P. reptans var. cinerascens, as the
species which typifies such stands. However, most
authorities (Vines, 1960; Burkart and Simpson, 1977;
Bensen and Darrow, 1954) describe this species as
“screwbean,” "dwarf screwbean,” or “tornillo. ” Based on
legume characteristics of individuals in the stand studied
in the present experiment and on similar sites, it appears
that the running mesquite type in South Texas is com-
posed primarily of a decumbent form of P. glandulosa
with scattered individuals of P. reptans var. cinerascens.
Therefore, future reference to “running mesquite"
herein refers to a kind of shrub stand rather than to a
specific species. There are no reliable estimates as to the
area of influence of the running mesquite brush type,
but it occurs throughout the South Texas Plains and into
northern Mexico, especially on saline clay sites.

Control of running mesquite with conventional
sprays, as with several other problem species such as
Macartney rose, requires multiple herbicide applica-
tions. Two or three successive annual applications of 0.8
kilograms per hectare (kg/ha) active ingredient (ai) each

3

of 2,4,5-T (2,4,5,-trichlorophenoxy)acetic acid are usual-
ly required for effective control (Hoffman and Ragsdale,
1967). Scifres et al. (1976) reported that three successive
annual applications of 2,4,5-T at 0.8 kg/ha killed 11
percent of the running mesquite and reduced the
canopies by 99 percent. The effective life of such treat-
ments is normally about 5 years and rarely exceeds 10
years.

THE WHITEBRUSH PROBLEM

Whitebrush, also called “beebrush,” is a serious
management problem on about 2.4 million ha of South
Texas rangeland. Almost 250,000 ha of these stands have
canopy covers of >20 percent (Smith and Rechenthin,
1964). Whitebrush may occur in mixed stands with more
than 15 other species of woody plants or in almost pure,
dense thickets. Plants rarely exceed 2 m tall and are
characterized by groups of relatively small, brittle stems
arising from the base. The greatest canopy covers usually
occur on sites of relatively high production potential.
Whitebrush stands greatly reduce forage production and
utilization by livestock, and the plant is of little value as
browse or cover for range animals.

Conventional sprays of phenoxy herbicides at rates
commonly used for range improvement do not control
Whitebrush effectively. Prior to the advent of
tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-
2-y1]-N,N'-dimethylurea), only picloram (4-amino-
3,5,6-trichloropicolinic acid) effectively controlled
whitebrush (Meyer et al., 1969; Scifres et al., 1981).
Applications of 1 to 2 kg/ha of tebuthiuron effectively
control many Whitebrush and associated species, except
for honey mesquite and pricklypear (Scifres et al., 1979).

RESEARCH OBJECTIVES

Specific objectives of this study were to determine

if:

1. a single application of 1.1 kg/ha of 2,4,5-T +
picloram (1:1) could be used to effectively con-
trol running mesquite when followed by appro-
priately applied prescribed burns, and

2. there are advantages ‘of prescribed burning fol-
lowing application of tebuthiuron pellets at 2
kg/ha ai for improvement of whitebrush-infested
rangeland.

The results of the specific experiments were then
considered as potential technological elements for inclu-
sion into IBMS.

MATERIALS AND METHODS

Running Mesquite Case Study

The running mesquite-dominated site was
Maverick clay loam (fine montmorillonitic, hyperther-
mic family of Ustollic Cambothids). The brush stand on
the study area was dominated (>90 percent of the
canopy cover) by running mesquite with scattered black-

4

brush acacia (Acacia rigidula) and lotebush (Ziziphus
obtusifolia) plants. Initial canopy cover was estimated as .
50 to 60 percent.

The site, located between Cotulla and Freer on the‘
South Texas Plains, was aerially sprayed with 1.1 kg/ha
of 2,4,5-T + picloram (1:1) in 47 liters/ha of a diesel
oilzwater (1:4) emulsion on May 24, 1977. Grazing exclo-
sures, 1 ha in size, were erected on the sprayed and on
an adjacent unsprayed area the following December. On
January 25, 1979, half of each exclosure was randomly
selected for burning with a headfire when the air tem-
perature was 24 degrees centigrade (°C), relative humid-
ity was 52 to 58 percent, and wind speed was 10 to 12
kilometers per hour (km/hr) from the southwest. Im-
mediately prior to burning, fine fuel load was harvested J
from 24 randomly placed, 0.25-meter-square (m2) quad-
rats, dried at 60°C for 48 hours (hr), and weighed.

Half of each plot sprayed in 1977 and burned in
1979 was reburned on February 16, 1982, with headfires
when the air temperature was 33°C, relative humidity
was 17 percent, and wind speed was 7.5 km/hr from the
southwest. The area had not been grazed since the
previous September 15 to allow accumulation of fine
fuel. Fine fuel was harvested to a 2-centimeter (cm)
stubble height from 20, 0.25-m2 areas equally spaced on
a diagonal across each plot, dried at 60°C for 48 hr, and
weighed. The 1982 burn resulted in five treatments in
the demonstration: untreated; sprayed in 1977; burned
in 1979; sprayed in 1977 and burned in 1979; and ~
sprayed in 1977 and burned in 1979 and again in 1982. ‘-

Reduction in brush canopy cover on each plot was
estimated in late August to mid-September each year
from 1977 until 1982. Standing crops of herbaceous
vegetation were evaluated by clipping 15 to 25, 0.25-m2
quadrats to a 2-cm stubble height in September 1977;
May and August 1978; January, May, and July 1979;
June and September 1980; July 1981; and June 1982.
Herbage was separated into grasses and forbs, dried at
60°C for 48 hr, and weighed. Means of treated areas
were compared to those of untreated areas using t-test
(a=.05). At the same time that standing crops were
harvested, botanical composition based on foliar cover
was determined from 50 inclined, 10-point frame sam-
pling units equidistantly spaced on a diagonal across
each plot. Species were grouped by grazing value ac-
cording to assessments by Gould and Box (1965), Hoff-
man et al. (1979), and the range site condition guide
published by the Soil Conservation Service. Experimen-
tal area was grazed in mid-May and again in mid-
September each year of study except the first growing
season after spraying when it was deferred until Septem-
ber. Grazing animals were removed from the area when
approximately 60 percent of the topgrowth of key species
was removed. J

Ten to 15 soil samples were recovered from 0 to 8, 8
to 15, and 15 to 30 cm deep on April 10, May 2, June 12,
and October 15, 1979; on April 1 and June 23, 1980; and l‘
on July 26, 1981. Samples were dried at 105°C for 48 hi‘!
and percentage soil water calculated on a dry-weight
basis.

Whitebrush Case Study killed about 25 percent of the plants, rapid regrowth of

The study Site, located about 16 km northeast of surviving brush had replaced nearly 90 percent of the
fiTilden, Texas, is predominantly Clareville sandy 10am Ollglllal Canopy Cover by fall l98l' _ _ _
(fine montmorillonitic, hyperthermic family of Pachic Removal of llle blush canopy by llelblclde appllce“
Arguistolls). The site was dominated by whitebrush lloll’ although temporary’ lmploved bolalllcal compo“
(canopy cover of 245 percent) but the Stand Contained tion of the grass stand compared to stands on the un-

Scattered honey mesquite Spiny hackberry (Calm, Pam; treated areas. For example, species of good-to-excellent
dd) blackbrush acacia arid lotebush grazing value accounted for nearly 50 percent (based on

Tebuthiuron pellets (20 percent ai) were aerially foliar cover) of the forage stand on the sprayed area by
applied at 2 kg/ha (an to the whitebrush site on Novem_ fall 1979, compared to less than 3O percent of stands on
be‘, 29, 1975_ Herbicide was applied to duplicate 2_1_ha untreated areas (Figure 3). Rainfall in 1978 was greater
plots alternated with untreated plots of the same size. than the lollglelm average’ prlmallly the result of fall

‘v on January 24, 1979, half of each plot was burned with a rains, but rainfall in 1979 was only 65 percent of average
headfire when the air temperature was 13°C, the relative Cable l)‘ Specles of goollloflxcellelll glazlllg value
 humidity was 19 percent, and the wind speed was 3 to 8 lllclllded _commoll Cllllylllesqlllle (Hllaria belangerl)’

' km/hr from the southeast. Prior to burning, fine fuel load plallls bllslleglas§ fseitarla (nacrostachya) and blllleL
was harvested from 50 randomlyplaced, 0_25_m2 quad_ grass (Cenchrus czlzarzs) .. Primary species of fair grazing

rats in each plot. The fuel samples were oven-dried at value were lolleglas? llldells (Trldens eragrostoldes)’
60°C for 48 hr and weighed. Immediately following solllgrass (Dlgltarla msulalfls)’ plnk pappllsglass (Pa?
burning, basal diameter (ground line) of whitebrush pophorum b ‘C9100 ’ Wlllplasll pappllsglass (Pa?
stumps and standing stems intercepted by six equally pllphorulfl vagmatum) and sllky bllleslem (Dwaw
spaced, 46ml lines were measured with a caliper_ thmm semceum). Grasses of poor grazing value included

Standing forage was harvested in 25, O.25-m2 areas wllorled dlop§e,ed (Spombolus pyramldatus)’ purple
equidistantly spaced through each plot and separated lllleeawn (Amtlda pllrpurea)’ red glallla (Bflllteloua
into grasses and {Orbs in July 1977’ and in August and tnfida) and tumble windmillgrass ChZOTIS vertzczllata).
December 1978. Immediately following the burning in Improved bolalllcél composlllon and glass l8lea§e
1979, 10 exclosures were established on each plot. In llllollgll the l978 glowlllg season llollowlllg Splaylllg lll
April and late Iuly 1979, ]une and September 1980, and 10o
August 1981, herbage was harvested from O.25-m2 quad-

Orats inside each exclosure and at 1 m from the exclo-
sures. Grazing animals were allowed access to the ex-
perimental area using the same schedule as described for
running mesquite. F oliar cover, based on 5O to 100, 10-
point frame samples equidistantly spaced on a diagonal
across each plot, by herbaceous species, was recorded at 50 ' ' Spraved 1977-
each harvest date. Initial brush cover was based on 5O to Burned 1979
6O sampling locations per plot using the point-center
quarter method. Posttreatment brush canopy reduction
was estimated visually at each herbage harvest date.

Data were subjected to one-way analysis of variance
to evaluate treatment effect. Means were separated
(ci=.05) using Student-Newman-Kuefs test (Steel and
Torrie, 1980).

Ten to 15 soil samples each from 0 to 8, 8 to 15, and
15 to 30 cm deep were recovered from each plot on Iuly
26, 1979, Iune 19, 1980, and July 23, 1981. Samples
were dried at 105°C for 48 hr and percentage soil water L
calculated on a dry-weight basis. Rainfall data were 5° ' Sgsizgg 1325's‘ 1982
obtained from the U.S. Weather Bureau recording sta- Burned 1979

. tion at Tilden.

75 _ Sprayed 1977

2s~ -

7s- -

Canopy Reduction(°/o)

RESULTS AND DISCUSSION

0 Rmmlng Mesquite ca“ Study 10971 l 19179 1991 j 1911 l 19179

Canopy reduction of running mesquite exceeded 95 year of Evguuation
percent by August the year of application of 2,4,5-T +
. picloram (Figure 2). However, the Woody plants re_ Figure 2. Canopy reduction (%) of running mesquite at various

t -' covered rapidly from the herbicide application. Canopy gyclfosraigtli; .z;fig'tal1 a1’) fgifiatigg Afljjgf ‘Jig?’ sgfjjfggffofiffgg b1;

reducltl-Qn averaged about 55 Percent b3’ fan 1979 f0now' prescribed burning on January 24, 1979; spraying followed by
ing spraying in May 1977 (Figure 2). Although the spray burning in 1979 and again in 1982; or burning in January 1979.

l l

l t
1981

    

     

     

60
1979 - Poor 1981 5
Fair Q
5° 7 Good to Excellent $ ‘
f \
q) \
5 40 >- Q _
O  \
a Q
E \
> 3° "  '
° w
C
 §
8 2o -  § -
a
s \
<> \
~ a
1o - \ —
\
\
\
No tmt. Spray No tmt. Spray Burn Spray+Burn

Figure 3. Composition (%) of grass stands based on grazing value
of grasses near Cotulla, Texas, after aerial application of 2,4,5-T +
picloram (1:1) at 1 . 1 kg/ha on May 24, 1977 and/or prescribed
burning on January 24, 1979.

1977 (Table 2) improved fine fuel load (1,935 kg/ha) and
continuity for prescribed burning. Consequently, 90
percent of the surface area was covered by the fire in
January 1979.

Prescribed burning in 1979 reduced the brush
canopy 0n the sprayed area by more than 9O percent
through the 1980 growing season (Figure 2). There was
no evidence of increased brush mortality on the sprayed
and burned plot compared to kills from spraying alone.
The burn removed much of the standing dead woody
topgrowth resulting from spraying, and caused the re-
growth to develop laterally rather than to form upright
clumps. Area covered by regrowth increased rapidly
following burning so that canopy cover was reduced by
only 5O percent in the fall 1982 on the plot sprayed in
1977 and burned in 1979 (Figure 2).

Grass standing crop by May 1979 after burning in
Ianuary equaled average standing crop on the area
sprayed only (Table 2). Grass standing crops on both the
sprayed and on the sprayed-burned plots exceeded

TABLE 1. MONTHLY RAINFALL (CM) FROM 1977 THROUGH 1981
ON THE EXPERIMENT IN WHICH HERBICIDE-PRESCRIBED FIRE
WAS EVALUATED FOR IMPROVEMENT OF RANGELAND
DOMINATED BY A STAND OF RUNNING MESQUITE NEAR\
COTULLA, TEXAS

Year

Month 1977 1978 1979 1980 1981
January 4.7 1.1 2.0 0.8 4.6
February 0.9 1.3 1.5 0.6 1.5
March 0.6 0.2 1.5 0.6 6.3
April 10.4 1.3 9.6 1.3 5.8
May 4.2 8.8 1.2 8.0 20.3
June 7.0 9.8 5.6 0 17.8
July 2.6 4.8 3.0 0.3 2.4
August 0.8 9.4 1.1 12.3 9.7
September 2.6 14.7 4.1 5.7 2.6 ‘
October 6.5 6.1 0 0.3 8.5
November 1.8 3.0 0.1 4.0 0
December 0.7 3.1 4.6 1.1 1.5
Total 42.8 63.6 34.3 35.0 81.1
% of avg 81 121 65 66 154

standing crop on the untreated area during spring 1979.
By the end of the second growing season following the
burn (September 1980), standing crop on the area
sprayed and burned exceeded (or= .05) that on the plot
which was sprayed only. Moreover, grass stands in the
fall 1981 on areas sprayed in 1977 and burned in 1979
contained a greater proportion of species of good-to-
excellent grazing value than those sprayed only (F igure.
3). Improvement in botanical composition following
burning resulted primarily from reduction in the propor-
tion of the stands composed of species of fair grazing
value, compared to stands on areas which were sprayed
but not burned.

Fine fuel accumulation (3,290 kg/ha of standing fine
fuel and 1,630 kg/ha of mulch) was adequate for installa-
tion of a second burn on the sprayed area during Feb-
ruary 1982. At the time of the second burn, water
content (dry-weight basis) of fine standing fuel averaged
7.4 percent. The heavy load of dry fuel, low relative
humidity (17 percent), and relatively high air tempera-
ture (33°C) resulted in an intensely hot fire. Flame
height was estimated to exceed 8 m during combustion

TABLE 2. GRASS STANDING CROPS (KG/HA) AT VARIOUS TIMES AFTER AERIALLY APPLYING 1.1 KG/HA OF 2,4,5-T + PICLORAM (1 :1) TO
A RUNNING MESQUITE-DOMINATED MIXED BRUSH STAND IN MAY 1977 AND/OR PRESCRIBED BURNING IN JANUARY 1979 NEAR

COTULLA, TEXAS

1977 1978 1979 1980 1981 1982
Treatment Sept May Aug Jan May July June Sept July June
Grasses
None 429 502 612 383 805 612 720 540 915 493 .,
Spray 719* 916* 1004* 1935* 1629* 940* 1152* 2143* 2218* 1464*
Burn - 4"__ _ - 533 552 691 997 1043 977*
Spray +
burn — - — — 1557* 972* 2667* 3037** 3419* 1720* \

‘Significantly different from untreated area (a= .05).

“Significantly different from untreated area and from area sprayed only (a= .05).

6

f\

I
\

I c

on areas of heavier fuel loads. The second burn reduced
woody plant canopy cover by 85 percent for the 1982
growing season (Figure 2). Grass standing was 1,653
kg/ha (data not shown) by June 1982 on plots sprayed in
1977 and burned in 1979 and 1982.

_ These results imply that prescribed burning may be
used to prolong the canopy reduction achieved by her-
bicide treatment of running mesquite stands. Based on
development rate of woody plant regrowth in this study,
prescribed burning should be applied at about 3-year
intervals to maintain brush suppression and improve
production of herbaceous stands.

Prescribed burning was not effective as an initial
treatment for reducing woody plant canopies. Pre-
scribed burning of an unsprayed area in January 1979
reduced the brush canopy by only about 20 percent,
based on evaluations in spring 1979 (Figure 2). The
unsprayed plot supported only 383 kg/ha of fine fuel
which occurred primarily in the spaces between brush
plants. Consequently, only about 4O percent of the
surface area was covered by the relatively cool burn.
Grass standing crops on the area burned only did not
statistically exceed those on the untreated plot, regard-
less of evaluation date, through July 1981 (Table 2). The
apparent difference in grass standing crops of burned
and unburned areas in June 1982 was attributed to
random chance in sampling rather than to treatment
effect.

Proportion of grasses of good-to-excellent grazing

fivalue had increased in 1981 compared to 1979, on the

I

f‘

untreated area (Figure 3), apparently in response to the
long deferments from grazing. There was little differ-
ence in the composition of herbaceous stands on the area
burned once and the untreated area. Thus, the single
prescribed burn of running mesquite stands did not
result in substantial range improvement.

Development of luxuriant herbaceous growth on
burned areas may reduce soil water contents in the
upper 13 cm soil layer (Wright and Bailey, 1982). How-
ever, soil water contents to 30 cm deep from untreated
plots and those burned only were generally less than
from sprayed plots, whether burned or not, during April
and May 1979 (Table 3). Since the most herbaceous
vegetation occurred on the sprayed plot and the area
sprayed and burned, the usual trend relative to soil
water depletion did not occur on this site.

By mid-June, the growing season after burning,
there was little difference in soil-water contents, regard-
less of treatment or sampling depth. Soil water contents
varied little among treatments by fall 1979. Thus, pre-
scribed burning alone or following spraying did not
appear to accelerate soil-water depletion rates.

Whitebrush C use Study

Control of whitebrush by fall 1976 exceeded 9O
percent after aerial application of tebuthiuron at 2 kg/ha

fWhe previous fall. Based on evaluations on January 20 and

August 9, 1978, the herbicide had completely controlled
the whitebrush. Whitebrush canopy cover on untreated
plots on these dates averaged 32 percent.

TABLE 3. SOIL WATER CONTENTS (%) AT THREE DEPTHS AT
VARIOUS TIMES AFTER AERIALLY SPRAYING RUNNING MES-
QUITE-DOMINATED MIXED BRUSH WITH 2,4,5-T + PICLORAM
(1 :1) AT1.1 KG/HA ON MAY25, 1977; BURNING ON JANUARY 25,
1979; OR SPRAYING FOLLOWING BURNING NEAR COTULLA,
TEXAS

T t‘
Soil depth reatmen
(cm) None Spray Burn Spray/burn
April 10, 1979

0-8 14.4 ab 20.2 bcd 12.8 a 16.6 abc

8-15 15.0 ab 21.4 cd 14.9 ab 19.0 bcd
15-30 15.6 ab 22.8 d 16.1 abc 20.4 bcd

May 2, 1979
0-8 15.4 a 19.2 b 16.5 ab 17.0 ab
8-15 17.4 ab 22.0 c 18.6 b 22.6 c
15-30 19.1 b 22.4 c 18.8 b 23.9 c
June 12, 1979
0-8 16.4 a 19.4 ab 18.8 ab 17.8 ab
8-15 19.2 ab 22.2b 21.5 b 21.4 b
15-30 18.9 ab 20.4 ab 20.9 b 21.1 b
October 15, 1979

0-8 7.3 ab 6.7 a 8.2 b 7.0 a

8-15 10.3 c 10.5 c 10.8 c 10.9 c
15-30 12.4 d 13.4 de 13.2 de 13.8 e

April 1, 1980

0-8 10.6 a 10.1 a 10.5 a 10.3 a

8-15 14.1 b 13.9 b 13.5 b 14.2 b
15-30 14.6 b 15.3 b 13.8 b 15.0 b

June 23, 1980
0-8 8.9 a 7.0 a 9.0 a 8.0 a
8-15 12.2 b 11.2 b 12.1 b 11.5 b
15-30 13.7 b 12.2 b 13.8 b 11.8 b
July 6, 1981

0-8 17.7 bcd 14.4 a 17.1a-d 20.1 de
8-15 16.8 a-d 15.1 ab 16.0 abc 18.9 cd
15-30 18.1 bcd 17.5 bcd 18.5 cd 22.1 e

‘Means within a sampling date followed by the same letter are not signifi-
cantly different (a= .05) according to Student-Newman-KueVs range test.

Annual rainfall in 1976 was greater than the long-
term average, and the annual average was received in
1977 (Table 4). Rainfall from March through June 1977
totaled 21.3 cm, most of which (18.4 cm) occurred in
April and June. Standing crop of grasses in July 1977
after application of tebuthiuron in fall 1975 averaged
2,561 kg/ha, approximately twice that on untreated areas
(Table 5). However, the forb standing crop was 120
kg/ha, approximately one-third that on the treated plots.

Application of the herbicide improved the fine fuel
load and continuity, compared to untreated plots. Stand-
ing fine fuel on tebuthiuron-treated plots was 1,750
kg/ha, contained 9.4 percent water, and burned uni-
formly and completely. Maximum flame height was 1O
m, and the fire front moved at 46 to 6O m/minute.
However, untreated plots did not burn because of the
marginal fine fuel load (940 kg/ha with 1O percent water)
which was not uniformly distributed.

TABLE 4. MONTHLY RAINFALL (CM) FROM 1975 THROUGH 1981 NEAR TILDEN, TEXAS WHERE A COMBINATION OF AERIALLY APPLIED

TEBUTHIURON AND PRESCRIBED BURNING WAS EVALUATED FOR IMPROVEMENT OF RANGELAND DOMINATED BY WHITEBRUSH

Year  a

Month 1975 1976 1977 1978 1979 1980 1981
January 0.9 1.2 5.7 1.3 4.6 4.0 4.7
February 2.1 T 2.0 1.6 3.5 1.7 1.9
March 1.6 0.9 1.8 T 2.3 3.0 4.5
April 5.6 11.2 8.8 2.3 9.1 0.9 6.6
May 14.6 11.3 1.1 5.3 2.5 16.0 21.6
lune 5.0 0.3 9.6 13.8 8.9 0 19.7
July 8.0 32.4 4.1 1.4 3.1 0.2 4.9
August 3.9 1.0 0.2 11.7 6.0 19.1 10.5
September 8.8 8.6 4.5 15.9 4.3 5.5 3.2
October 3.8 17.7 6.0 1.5 0.1 0.2 10.1
November 0 7.5 7.1 4.7 0.8 10.1 0 \_
December 2.0 5.3 0.1 4.3 0.9 1.5 1.6 U
Total 57.2 97.3 a 51.0 63.8 46.1 62.2 89.3
% of avg 102 174 91 114 82 111 159

The fire burned down all whitebrush stems, 0.63
cm in diameter or smaller, on the area treated with
tebuthiuron (Figure 4). Percentage burndown decreased
as stem diameter increased with only 13 percent of the
stems 1.9 cm in diameter being removed. Overall, the
fire reduced the density of standing dead stems by 6O
percent.

Grass standing crops in April 1979 after burning in
January 1979 did not differ between burned and un-
burned areas which were treated with tebuthiuron
(Table 5). Average standing crop on burned areas (3,988
kg/ha) was greater by ]uly 1979 than that on plots treated
with tebuthiuron but not burned. However, the increase
in grass standing crop attributable to burning did not
occur in 1980 or 1981. Increased grass standing crop for
only the growing season following burning was expected
because of the high degree of effectiveness 0f
tebuthiuron in controlling the whitebrush.

Primary species of good-to-excellent grazing value
were multiflowered false rhodesgrass (Chloris pluriflo-
ra), common bulfelgrass, butfalograss (Buchloe dacty-
loides), pink pappusgrass, Arizona cottontop (Digitaria
californica) and vine mesquite (Panicum obtusum).
Grasses of fair grazing value were represented primarily
by hooded windmillgrass (Chloris cucullata), sand drop-
seed (Sporobolus cryptandrus), lovegrass tridens and
filly panicum (Panicum hallii var. filipes). Grasses of
poor grazing value included oldfield threeawn (Aristida
oligantha), common sandbur (Cenchrus incertus), tum-
ble windmillgrass, gummy lovegrass (Eragrostis cur-
tipedicillata) and red lovegrass (Eragrostis secundiflo-
ra). Other grasses included Bell rhodesgrass (Chloris
gayana), common Bermudagrass (Cynodon dactylon),
common curlymesquite, southwestern bristlegrass
(Setaria scheelei), red threeawn (Aristida longiseta),
red grama, fall witchgrass (Leptoloma cognatum), and
whorled dropseed.

Application of tebuthiuron and lengthy deferments
from grazing allowed proportion of grasses of good-to-
excellent grazing value to essentially double, compared
to stands on untreated areas, by 1978 (Table 6). Much of

8

the increase in proportion of the more desirable grasses
was attributed to dramatic increases in multiflowered
false rhodesgrass. This species further responded posi-
tively to prescribed burning, accounting for the increase
in the proportion of grasses of good-to-excellent value on
plots treated with herbicide and burned, compared to
that on plots burned only.

Prescribed burning increased utilization of the gras-
ses, especially multiflowered false rhodesgrass, which

may rapidly develop rank growth. The experimental area y,

was grazed in a manner to prevent damage to burned

I I I I

100~

80-

60—

Stems Burned Down (°/o)

20—

I l

a 1
O 0.5 1.0 1.5 2.0 2.5

Stem Diameter (cm)

Figure 4. Burndown (% based on density) of whitebrush stems 

various sizes on /anuary 24, 1979 after aerial application o
tebuthiuron pellets at 2 kg/ha on November 29, 1975 near Tilden,
Texas.

--u

TABLE 5. STANDING CROPS OF FORBS AND GRASSES AT VARIOUS TIMES AFTER APPLICATION OF TEBUTHIURON PELLETS AT 2 KG/HA
IN NOVEMBER 1975 AND BURNING IN JANUARY 1979 NEAR TILDEN, TEXAS

 

 19771 1 978 1979 1980 1981
Treatment July Aug Dec April July June Aug
H Grassesz
None 1298 a 1232 a 842 a 524 a 996 a 452 a 1872 a
 Tebuthiuron 2561 b 2504 b 1750 b 1208 b 1892 b 1738 b 3624 b
 Tebuthiuron + burn — —- — 1288 b 3988 c 1960 b 3960 b
E A Forbsz
i » None 381 a 400 a 389 a 306 a 560 a 260 a 280 a
9 Tebuthiuron 120 b 100 b 180 b 332 a 320 a 180 a 240 a
Tebuthiuron + burn - - — 796 b 940 b 220 a 758 b

 

"ITTaken from Scifres and Mutz, 1982.
‘Means within a date followed by the same letter are not significantly different (a= .05).

plots the growing season following burning. For exam- moved 33 percent of the standing crops from plots
ple, cattle were excluded in late Iuly 1979 after remov- treated with tebuthiuron and burned, 36 percent from
ing 49 percent of the standing crop on the burned plots plots treated with tebuthiuron only, and 15 percent from
(use of multiflowered false rhodesgrass was estimated at untreated plots.
55 to. 60 percent). During the same period, they re- No difference in soil-water contents occurred
moved 18 percent of the grass standing crop on plots among treatments, regardless of depth, in late ]uly 1979
treated with tebuthiuron but not burned, and a negli- (Table 7). However, average water contents were re-
gible amount from the untreated plots. However, differ- duced, compared to that of untreated areas, to 15 cm
ences in utilization between burned and unburned areas deep on tebuthiuron-treated plots, both burned and
were not apparent in 1980, the second growing season unburned, on June 19, 1980. Variation in water contents
v following prescribed burning. The cattle were allowed to of the surface soil was attributed to differences in amount
 emove 7O percent of the standing crop in mid-June 1980 of herbaceous standing crop among treatments during
F from plots treated with tebuthiuron in 1975 and burned the dry period (no rainfall was received in June, rainfall
i’ in 1979. They removed essentially the same amount (64 in May came as a single early storm, and March-April
percent) from areas treated with tebuthiuron but not precipitation totaled only 3.9 cm [Table  The in-
burned, but removed only 8 percent of the standing crop creased herbaceous cover apparently increased the Wa-
fi-om untreated areas. The same trend was apparent after ter demand on the surface 15 cm of soil during this dry
a grazing period in late July 1981 when the cattle re- period (Table 7).
TABEE 6- EROPQRTKJN OE HERBAGE 5TAND5 C0MPO5ED OE TABLE 7. SOIL wATER coNTENTs m) AT VARIOUS TIMES AFTER
9RA55E5 BY GRAZWG VALUE AT VAR'OU5 TTME5 AFTER AER'AE AERIAL APPLICATION OF TEBUTHIURON PELLETS AT 2 KG/HA IN
APPLICATION OF TEBUTHIURON PELLETS AT 2 KG/HA IN NOVEMBER 1975 AND EURMNG IN JANUARY 1979 NEAR HE
NOVEMBER 197s AND PRESCRIBED BURNING OF DEN TEXAS
TEBUTHIURON-TREATED AREAS IN IANUARY 1979 NEAR TILDEN, ’
TEXAS Treatment‘
Tebuthiuron Soil depth Tebuthiuron
Grazing value None Tebuthiuron + burn (cm) None Tebuthiuron + burn
August 9, 1978 IUIX 26, 1979
GOOd-IO-EXCGIIEM 20.3 46.3 —— 0-8 13.8 b-d 12.7 CI 11.7 d
y Fair 65.9 47.0 — 8-15 17.8 ab 16.0 ad 16.2 a-d
8" POOI’ 13.8 6.7 15-30 17.3 ac 18.0 ab 16.2 a-d
 AEriI 25, 1979 June 19, 1980
Good-to-excellent 26.0 51.0 66.7 0-8 6.4 ef 5.5 e-g 3.1 g
Fair _ 50.0 36.7 18.2 8-15 11.1 a-c 8.2 c-e 5.7 d-g
CF00!‘ 24.0 12.2 15.1 15-30 13.6 a 11.7 ab 11.0 a-c
June 19, 1980 July 23,1981
Good-to-excellent 21.6 57.2 65.5 0-8 7.0 cd 5.1 de 6.0 cd
air 58.3 30.8 28.3 8-15 8.6 bC 8.8 bC 9.1 bC
_E POOI’ 20.0 21.0 6.2 15-30 12.0 a 11.2 ab 9.7 a-c

‘Means within a date followed by the same letter are not significantly
different (a= .05) according to Student-Newman-Kuels range test.

HE RBICIDE APPLICATION/
PRESCRIBED BURNING AS
POTENTIAL IBMS TECHNOLOGIES

Based on results of this research, herbicide applica-
tion and prescribed burning combinations have potential
as components of Integrated Brush Management Sys-
tems (IBM S) for rangeland supporting excessive cover of
running mesquite stands or whitebrush. Success from
such systems hinges largely on initial control of the
woody species by herbicide applications.

Running Mesquite Complex

Based on results of the demonstration near Cotulla,
prescribed burning following aerial application of 2,4,5-
T + picloram (1:1) at 1.1 kg/ha maintained the reduction
in woody canopy more effectively than where spraying
alone was used for range improvement. However, bum-
ing alone was not effective as an initial treatment. Thus,
effective performance of prescribed burning depended
on initial effectiveness of the herbicide application.
Strict attention must be given to applying the herbicide
under the optimum environmental conditions and when
the brush is in the appropriate stage of development

(Scifres, 1980). Given those conditions, herbicide appli-
cation reduces the brush canopy cover, thins the density

of live plants, and releases herbaceous vegetation fo¢

grazing as well as fuel for prescribed burning (Figure 5).

Results of this study confirm earlier conclusions that
single applications of foliar-active herbicides result in
only short-term suppression of running mesquite. How-
ever, prescribed burning was effectively substituted for
subsequent herbicide treatments, at least for the 6-year
investigation period.

Perpetuation of brush suppression with prescribed
burning was reflected by greater standing crops and
grass stands composed of a higher proportion of species
of good-to-excellent grazing value than those on un-

treated areas. A single burn of unsprayed areas did mop

generally increase forage yields compared to untreate
areas. Ineffectiveness of burning alone was attributed to
the extremely light load and discontinuity of fine fuel.
Thus, the spray application increased amount and con-
tinuity of fine fuel.

The study on running mesquite was conducted on
level to gently rolling topography, and burning plans and
expected results will vary with topography. However,
the failure of unsprayed brush to burn effectively in this
study gives us reason to believe that the desired pattern

PHASE I

HERBICIDE APPLICATION

PHASE II

IMPROVE
HERBACEOUS STANDS

PHASE III

FINE FUEL DEVELOPMENT/
BURN PREPARATION

_PHASE 1v

PRESCRIBED BURNING

PHASE V

MAINTENANCE OF
RANGE IMPROVEMENT

Reduce canopy cover and
density of running

mesquite and associated
brush to release forage.

OBJECTIVES

Use grazezrest periods to
allow increase in propor-
tion of desirable perennial
herbs in stand.

‘Build continuous load of
fine fuel adequate to
ensure hot, uniform fire.

Maintain brush suppression-
expedite increased propor-
tion of desirable grasses
and forbs.

Perpetuate desired level
of productivity with
minimal financial input.

Aerially apply l.l kg/ha
of 2,4,5-T + picloram
(lzl) or equivalent in
the spring.

ACTIVITY

Defer from grazing for 60-
90 days to allow for grass
release; increase stocking
rate in accordance with
response of key species.

Defer grazing for 90-l20
days in fall to build fuel;
prepare fire plan and
install fire guards.

Install prescribed burn
according to sound fire
plan; defer grazing to
allow recovery of key
species; then allow removal
of no more than 60-65% of
topgrowth before next
deferment.

Schedule prescribed burns
as needed (approximately
3- to 5-year intervals).

Apply in appropriate
pattern for game manage-
ment; usually treat no
more than 80% of manage-
ment unit; treatments
will likely be extremely
damaging to several pre-
ferred browse species.

CONSIDERATION(S)

First flush (first season)
of grasses usually short-
term opportunists released
from shading etc; defer-
ment designed to allow
vigorous development of key
species.

Deferment period must be
adjusted to rainfall condi-
tions; under drought condi-
tions, utilize proper
amount of accumulated fuel
and delay burn.

Late winter when wind
speed l6-l9 km/hr, RH< 60%,
fine fuel water content
120%. backfire 30-45 m
before headfiring: if RH
<20%, fuel water €l0%,
wind speed of steady 8-ll
km/hr will effectively
burn.

Grazing deferment to
build adequate fine fuel
and post burn to allow
grass recovery.

Brush defoliation >90%
for first growing season;
then 50% original cover
replaced third growing
season if not burned;
rass released by spray
ay more than double
that on unsprayed areas
irst growing season;
orbs will be controlled
y spray for at least l
rowing season.

RESULTS

Proportion of grass stand
of good-to-excellent
grazing dramatically
increases by second growing
season.

Accumulate 2,500-3,000
kg/ha of fine fuel with
only minor discontinuities.

Fire covers >90% of area;
brush stem $1.5 cm diam.
consumed or dropped; warm-
season perennials in-
creased; brush regrowth
Hlwdtogmwmlim;
forb population restored.

Continual suppression of
brush sprouts; remove
rough vegetation, improve
grazing distribution and
range condition, etc.

i»

Figure 5. Potential aerial spray-prescribed burning applications as co
improvement of running mesquite-dominated rangeland.

10

u‘

J

mponents of Integrated Brush Management Systems (IBMS) for

-\\ PHASE I

for game management can be installed with the her-
bicide sprays, and be maintained with burning without

ndue risk of removing too much brush. This opinion,
however, does not diminish the need for involving sound
fire control measures within the fire plan. Under proper
conditions, fire might be used to enlarge or reduce the
area of brush suppression. Our data indicate that pre-
scribed burning may be applied at 3-year intervals on
previously sprayed sites with positive results, except as
restricted by periodic drought.

Differential carrying capacities of the treatments
applied to running mesquite were evaluated in late
summer 1980. Based on available forage, it was es-
timated that 32 ha would be required to support an
animal unit (AU) yearlong on the untreated rangeland.

Flu comparison, estimated carrying capacities were 8

ha/AU for sprayed sites, and 6 ha/AU for areas which
were sprayed and then burned.

Whitebrush

Primary objectives for prescribed burning following
tebuthiuron application were to suppress species not
affected by the herbicide (e. g. , honey mesquite); remove
standing woody debris; improve botanical composition of
the forage stands; and improve grazing distribution and
use of species which tend to develop rank growth after

PHASE II

FINE FUEL DEVELOPMENT/

short periods of protection from grazing (e.g., multi-
flowered false rhodesgrass).

Prescribed burning in January 1979 following appli-
cation of 2kg/ha of tebuthiuron in November 1975 in-
creased forage standing crops only during the growing
season following the burn. Lack of difference in subse-
quent years was attributed to the highly effective control
of the whitebrush by the tebuthiuron. However, burn-
ing tended to improve the proportion of the herbaceous
stand composed of grasses of good-to-excellent grazing
value, and improved grazing distribution. Moreover, the
prescribed burn removed standing whitebrush stems
with basal diameters $1.0 cm and top-killed honey
mesquite less than 1.5 m tall, but did not kill the large (4
to 6 m tall) honey mesquite trees (Figure 6). As a result
the treated strips assumed a parklike appearance.

Based on forage production and using the technique
of Whitson et al. (1979), the whitebrush-infested range-
land was capable of supporting 1 AU/ 14 to 16 ha year-
long. Carrying capacity at 18 months after herbicide
application was estimated to be 1 AU/8 to 9 ha. Howev-
er, it is important to note that carrying capacity for
livestock was essentially unchanged during the growing
season of herbicide application. This is to be expected
because of the time required for tebuthiuron to com-
plete its activity (Scifres et al., 1979). Range improve-

PHASE III PHASE IV

MAINTENANCE OF

HERBICIDE APPLICATION

BURN PREPARATION

PRESCRIBED BURNING

RANGE IMPROVEMENT

\

Figure 6. Potential tebuthiuron-prescribed burning applications as components of Integrated Brush Management Systems (IBMS) for

improvement of whitebrush-dominated range/and.

Aerially apply tebuthiuron Defer grazing during fall for Install prescribed burn Schedule prescribed burns as
pellets at 2 kg/ha (a.i.) 90-120 days; prepare fire plan according to sound fire plan; needed (approximately 3-year
in fall (Sept.-Oct.) or and install fire guards. defer grazing until late April- intervals).

t late winter (Feb.). May or until reserve soil

; moisture adequate for rapid

"‘ growth; defer after 60-65% of

5 top growth removal by grazing.
Apply in strips for game Deferment period must be When wind speed 16-19 km/hr, Grazing deferment to build

g management (ex: 190-200 m adjusted to rainfall condi- RH <60%, fine fuel moisture adequate fuel and post burn to

p treated alternated with 30- tions; under drought condi- content <2S%, backfire 30 to allow grass recovery.

é 4S m untreated to improve tions utilize proper amount 45 m; if RH <209s, fine fuel

g 80-85% of area) will con- of accumulated fuel and delay moisture 5109s, wind speed of

a trol spiny hackberry and burn until next year. steady 8-11 km/hr will effec-

g several other associated tively burn.

u species but not mesquite.
whitebrush defoliation Accumulate 2,500 to 3,000 Dead brush stems El cm in Suppress brush sprouts, remove
greater than 909s by end of kg/ha acre of standing fine diam. consumed or dropped, rough vegetation, improve
first growing season under fuel of relatively uniform grass released to uniform grazing distribution, improve
average rainfall; ultimate distribution. (Fuel load on stand; warm season perennials range condition, etc.

u, kill usually exceeds 9096, research area varied from increased, annuals decreased;

S- grass release evident by about 1,000 to <2,S00 kg/ha forb population restored (wet

a end of first growing [oven-dry basis] but without springs stimulate forb pro-

Q‘ season; fall deferment major discontinuities). duction); fires usually do not

\ expedites grass release; carry through heavy brush
' forb production greatly covers on untreated strips.

reduced.

11

ment was initiated during -the second growing season
and under complete protection from grazing.

Estimated carrying capacity was 1 AU/5 to 6 ha by
the growing season following application of the burns.
Untreated (“brushy”) areas protected from grazing for
the same times were judged to be capable of supporting
1 AU/ 12 ha. These results and time-lapse between treat-
ments will undoubtedly vary with rainfall conditions.

As with the running mesquite sites, the
tebuthiuron-treated whitebrush sites may be effectively
burned at 3-year interals, depending on rainfall. The
treatment sequence in this study has left a minimal
amount of brush residuum in the treated strips. This
suggests the need for careful analysis of game re-
quirements when developing a treatment pattern and
determining percentage of the management unit to be
treated.

ACKNOWLEDGMENTS

The authors gratefully acknowledge P. H. Welder
and Dick Horton for providing land for this research.
The efforts of Julia Scifres in manuscript typing and
preparation are appreciated. The aid of numerous gradu-
ate students who helped with treatment installation and
data collection from these studies is acknowledged, and
the help of B. H. Koerth in data collection is ap-
preciated.

12

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13

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