Interspace/Under-canopy Foraging Patterns of Beef Cattle
in Sagebrush Communities
Kevin France, Chad Boyd, and David Ganskopp
Introduction
Livestock grazing has been
related indirectly to sage-grouse declines in the western United States
and southern Canada. However,
there is a lack of scientific research that directly relates the two.
Sage-grouse typically nest beneath
sagebrush plants where residual
bunchgrass provides protection
from predators. Past studies have
concluded that nesting success
is highest in areas with the most
residual cover. Livestock grazing
potentially can reduce cover and decrease concealment of sage-grouse
nests. However, there is only limited research documenting livestock
foraging patterns in sagebrush habitat. Research is needed to determine
the effects of grazing intensity and
duration on cover availability at
sage-grouse nesting locations. Here
we present preliminary (1st-year)
data from a 2-year study designed
to relate livestock grazing behavior
in sagebrush plant communities
with grazing occurrence on undercanopy and interspace vegetation.
Experimental Protocol
An 18-day (July 5–23) trial
was conducted in 2003 with four
pastures fenced in a Wyoming big
sagebrush community. Four 15-acre
pastures were each stocked with
four yearling heifers (average 850
lb). Within each pasture, 30 sagebrush plants were selected randomly and a perennial grass was marked
permanently under the canopy of
each sagebrush and a second grass
plant marked in the nearby interspace. Area and volume of the sagebrush were measured, and the angle
of accessibility was measured for
the under-canopy grass to assess the
effects of sagebrush plant structure
on grazing occurrence. Grass plants
were checked every 2nd day and
given a grazed or ungrazed score.
Changes in pasture standing crop
and utilization (by weight) were
assessed weekly by clipping 20 randomly located approximately 11-ft2
plots in each pasture.
Results and Management
Implications
Structure of sagebrush plants
was not related to occurrence of
grazing on under-canopy grasses;
however, the effect of plant location (under canopy or in interspace)
was significant. Grazing of undercanopy plants was negligible at
light to moderate levels of pasture
utilization but increased at heavier
Objectives
1. Use small pastures to determine
the level of whole-pasture utilization at which cattle begin to
use grasses under the canopy of a
sagebrush plant.
2. Investigate the influence of individual sagebrush plant structure
on livestock use of under-canopy
grasses.
Figure 1. Percentage of interspace and under-canopy grass plants that were
grazed compared to pasture utilization (by weight).
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levels (e.g., at 30 percent pasture
utilization, less than 10 percent
of under-canopy plants had been
grazed, compared to more than 60
percent of interspace plants; Fig. 1).
This indicates that livestock prefer
more easily accessible interspace
plants and suggests that, at moderate levels of pasture utilization,
grazing has a negligible impact on
the reduction of under-canopy nesting cover for sage-grouse and other
ground-nesting bird species.
From a management perspective,
measurement of livestock utilization
may or may not include sampling
of under-canopy grasses. Our initial
data suggest that measurement
of utilization based on interspace
plants alone is not representative
of that for under-canopy plants,
and that under-canopy plants will
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be used with increasing frequency
beginning at around 35–45 percent
pasture utilization. Readers should
keep in mind that the data presented
here represent the 1st year of a
2-year study and that 2003 was a
dry year. In years and/or on sites
with increased forage production,
the nature of the relationships we
describe may be altered.