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High Stocking Rate Potential for Controlling
Wyoming Big Sagebrush
Carl L. Wambolt
Myles J. Watts
based on the undetermined premise that sagebrush is competitive with forage plants.
Our objective was to evaluate if cattle stocking rates
normally considered excessively high could be used for a
short period of time to mechanically control sagebrush cover
and increase herbaceous production. The hypotheses tested
were: 1) that high cattle stocking rates will reduce Wyoming
big sagebrush cover, and 2) that any reduction in sagebrush
cover from high stocking rates will increase understory
production.
Abstract-Our objective was to evaluate if excessively high cattle
stocking rates over 3 years would mechanically control Wyoming big
sagebrush (Artemisia tridentata spp. wyomingensis). The hypothesis tested was that high cattle stocking rates will first reduce
Wyoming big sagebrush cover and second result in increased understory production. A Wyoming big sagebrush-bluebunch wheatgrass
(Agropyron spicatum) habitat type in southwestern Montana was
studied. A randomized complete block design with three blocks was
used. Four stocking rates, from normal up to eight times normal,
were applied for three consecutive years. Heavy stocking rates did
reduce sagebrush cover primarily through mechanical damage, but
some browsing was observed. The reduction in sagebrush canopy in
the heavy stocking treatments did not result in increased understory production. We conclude that this treatment will not increase
livestock forage but may reduce habitat quality for wildlife and
other values.
Methods _ _ _ _ _ _ _ _ __
Study Area
The study area is located in southwestern Montana approximately 50 km north of Livingston at an elevation of
1800 m. It lies within the private holdings of the Grande
family livestock operation and has been grazed by domestic
livestock since the mid-1800's. The site is dominated by a
Wyoming big sagebrush-bluebunch wheatgrass (Agropyron
spicatum [Pursh] Scribn.) plant community. The average
annual precipitation is approximately 380 mm with the
peak received during May and June. The topography is very
level with no prominent exposure. Clay loams predominate
in surface and subsurface soils. The homogeneity of environmental parameters and community characteristics throughout the study area is great.
The importance of big sagebrush (Artemisia tridentata
Nutt.) is not surpassed by any species on rangelands in the
western United States. Big sagebrush occupies nearly 60
million ha in this region (Beetle 1960). This taxon is often
valuable in wildlife habitats as both cover and high quality
forage (Welch and McArthur 1979). However, its aggressive
nature as a climax dominant and low preference as forage by
cattle are qualities responsible for it having been the subject
of control projects (Welch and McArthur 1979).
Wambolt and Payne (1986) compared controlling Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis
Beetle and Young) on the same southwestern Montana site
by burning, plowing, spraying with 2, 4-D, and rotocutting.
Watts and Wambolt (1989) furnished an economicevaluation of these treatments. However, a potential opportunity
to reduce sagebrush populations more biologically and economically efficiently was identified. The method had the
potential to prove more environmentally acceptable than
previously evaluated sagebrush control meth,ods. It would
avoid the negative aspects of herbicide use, the air pollution
of burning, and the erosion potential associated with plowing, rotocutting, and often burning.
It was conjectured that cattle stocking rates normally
considered excessive could be applied for short periods of
time to mechanically reduce sagebrush cover. The idea was
Experimental Design
The experiment utilized a randomized complete block
design of three replicates. Four stocking rates (treatments)
were tested: 1) normal stocking rate (as the experimental
control) of 1.6 ha (4 ac)/AUM, 2) twice the normal stocking
rate at 0.81 ha (2 ac)/AUM, 3) four times the normal stocking
rate at 0.4 ha (1 ac) AUM, and 4) eight times the normal
stocking rate at 0.2 ha (0.5 ac)/AUM. The treatments were
first applied in August 1987 and again during August in
1988 and 1989. This timing allowed pre-treatment measurements of sagebrush canopy cover and herbaceous production
to be taken. It also provided maximum forage production to
be reached to sustain the unusually high stocking rates.
Each block was stocked with 10 cow-calf pairs (AU's). This
allowed treatment application to be accomplished in 15
days, thus avoiding complications that might have been
encountered over a longer time with less cattle. Following
the initial treatment in 1987, no additional grazing was
allowed on the study area through the conclusion of the
study after the summer of 1990.
In: Barrow, Jerry R.; McArthur, E. Durant; Sosebee, Ronald E.; Tausch,
Robin J., comps. 1996. Proceedings: shrubland ecosystem dynamics in a
changing environment; 1995 May 23-25; Las Cruces, NM. Gen. Tech. Rep.
INT-GTR-338. Ogden, UT: U.S. Department of Agriculture, Forest Service,
Intermountain Research Station.
Carl L. Wambolt is Professor, Department of Animal and Range Sciences,
Montana State University, Bozeman, MT 59717. MylesJ. Watts is Professor
of Agricultural Economics, Department of Agricultural Economics and
Economics, Montana State University, Bozeman, MT 59717.
148
Before treatment application within each treatment replicate, 15.24 m (50 ft) transect lines (Canfield 1941) were
randomly placed to determine Wyoming big sagebrush crown
cover by line intercept. Data were taken in 3 cm units (0.1 ft).
Openings in the line canopy larger than 3 cm were recorded
as non-sagebrush intercepts.
In August 1990, one year after the last grazing treatments concluded, the study was photographed from the air.
A Cessna 150 with a camera system utilizing a Hasselblad
EUM camera with 70 mm backs was used. Color infrared
images were taken with Kodak Aero-Ektachrome film, type
2443, with the aid of a Kodak Wratten number 15 filter.
Photo flights were made at 340 m above ground level,
providing a scale of 1:6500. Thus, canopy coverage ofWyoming big sagebrush was measured one year after the final
grazing treatment was applied by sampling each entire
treatment plot with aerial infrared photographs. The photographs were projected to an image size of2 m 2 and sampled
with a dot grid. The number of sagebrush hits with the grid
was divided by the total number of dots falling in the
treatment to arrive at a percentage canopy coverage remaining following the three years of treatment.
Production data were obtained by clipping 0.5 m 2 circular
plots (Wambolt and Payne 1986). They were randomly
placed on diagonal lines beginning and ending no closer than
10 m from the treatment corners. The centers of the 0.5 m 2
plots were located no closer than 2 m apart to avoid disturbances of plants when clipping adjacent plots. In addition,
records were kept to avoid reclipping the same 0.5 m 2 areas.
Plant material was oven dried at 65°C for 1 week before
weighing. All measurements were taken as close to the peak
ofstanding crop production as practical. Numbers of transects
and plots were determined through adequacy of sample
tests.
Analysis of variance was used to evaluate relationships
among production means of perennial grasses, total herbaceous vegetation, and sagebrush canopy cover in the different stocking rate treatments. The Least Significant Difference (LSD) method (P<0.05) protected by a prior F-test
(P<0.05) was used for comparing treatment means.
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STOCKING RATE TREATMENT
(TIMES (X) PROPER STOCKING)
Figure 1-Wyoming big sagebrush percent canopy
cover means by treatment (stocking rate) one year
after the final treatments were applied. Means differ
(P<0.05) when bars have a different letter.
Results and Discussion
Figure 2-Trampling effect on Wyoming big sagebrush stocked at eight times normal for one year on
near side of portable electric fence.
We accepted our first hypothesis, that high stocking rates
will reduce Wyoming big sagebrush cover. Sagebrush cover
was equal throughout the study area before initiation of the
grazing treatments. Over the three year study the heavier
cattle stocking rates of four and eight times normal significantly (P<0.05) reduced sagebrush canopy cover (fig. 1). The
eight times normal stocking rate was significantly (P<0.05)
more effective than any other treatment. Most damage was
from trampling (fig. 2), but some browsing was observed.
The second hypothesis, that any reduction in sagebrush
cover from high stocking rates will increase understory
production, was rejected. The reduction in sagebrush canopy
with heavy stocking rates did not result in increased understory production that was equal throughout the study area
before any treatments were applied. Perennial grasses were
equal in all treatments one year after the third and final
heavy stocking treatments were applied (fig. 3). The two,
four, and eight times normal stocking rates resulted in less
total herbaceous production than the normal stocking used
as a treatment control (fig. 4).
Our results were not unexpected based on the experiences
of others. Anderson and Holte (1981) in southeastern Idaho
assessed changes in the big sagebrush type after 25 years of
grazing exclusion. Cover of perennial grasses increased
exponentially, from 0.28% to 5.8% in the 25-year period.
However, during that period, shrub cover increased 154%,
almost entirely due to changes in big sagebrush. The increase in grass cover was not at the expense of the big
sagebrush dominated overstory. Mueggler and Blaisdell
(1958) compared the sagebrush control techniques of burning, rotobeating, spraying, and railing. They found that
regardless of treatment , total vegetal production three years
after treatment was still considerably less than on untreated
149
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areas. Harniss and Murray (1973) also concluded that sagebrush must utilize resources that are not available to other
species because maximum vegetal production results when
sagebrush is present. Harniss and Murray (1973) also noted
the importance of post-treatment grazing practices.
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2X
4X
8X
STOCKING RATE TREATMENT
(TIMES (X) PROPER STOCKING)
Figure 3-Production (kg/ha) means of perennial
grasses by treatment (stocking rate) one year after the
final treatments were applied. Means differ (P<0.05)
when bars have a different letter.
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References
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Anderson, J. E., and K. E. Holte. 1981. Vegetation develop men t over
25 years without grazing on sagebrush-dominated rangeland in
southeastern Idaho. J. Range Manage. 34:25-29.
Beetle, A. A. 1960. A study of sagebrush-Section Tridentatae of
Artemisia. Wyoming Agr. Exp. Sta. Bull. 368 .
Canfield, R. H. 1941. Application ofthe line-interception method in
sampling range vegetation. J. Forest. 39:388-394.
Harniss, R. 0., and R. B. Murray. 1973. Thirty years of vegetal
change following burning of sagebrush-grass range. J. Range
Manage. 26:322-325.
Mueggler, W. F., and J. P. Blaisdell. 1958. Effects on associated
species of burning, rotobeating, spraying, and railing sagebrush.
J. Range Manage. 11:61-66.
Wambolt, C. L., and Payne, G. F. 1986. An 18-year comparison of
control methods for Wyoming big sagebrush in southwestern
Montana. J. Range Manage. 39:314-319.
Watts, M. J., and Wambolt, C. L. 1989. Economic evaluation of
Wyoming big sagebrush (Artemisia tridentata) control methods.
Weed Technology 3:640-645.
Welch, B. L., and E. D. McArthur. 1979. Feasibility of improving big
sagebrush (Artemisia tridentata) for use on mule deer winter
ranges. p. 451-473. In: J. R. Goodin and D. K. Northington (eds.)
Proc. Intern. Arid Lands Conf. on Plant Resources. Texas Tech
Univ., Lubbock.
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Cattle stocking rates up to eight times normal will reduce
Wyoming big sagebrush canopy cover, primarily through
mechanical damage, with some browsing.
No increase in herbaceous forage species will result from
reduced sagebrush canopy cover induced by heavy stocking.
Habitat quality is reduced for wildlife benefitted by sagebrush following heavy stocking.
8X
STOCKING RATE TREATMENT
(TIMES (X) PROPER STOCKING)
Figure 4-Production (kg/ha) means of total herbaceous vegetation by treatment (stocking rate) one year
after the final treatments were applied. Means differ
(P<0.05) when bars have a different letter.
150