competitive advantage during periods of drought. Overall, study-long reductions ranged from 30% to 60% of the original amounts with cattle-grazed treatments showing the greatest declines. Recall that one of the major vegetational changes resulting from the century-long history of intensive sheep grazing of these ranges was a shift from a tall-forb dominated community to one dominated by grasses, typically with an abundance of Letterman needlegrass. From that history, one might deduce that sheep do not place enough grazing pressure on the plant to affect its presence in the plant community, whereas the results of this study suggest that cattle have some capacity to reduce its abundance.
Figure 8
Figure 8.
Figure 8
Frequency (%) of Kentucky bluegrass in pastures grazed by cattle alone, sheep alone and by both
Frequency (%)
species in combination. Bars with different letter at P= 0.05. a superscripts b differ statistically ab 100 80
Frequency (%)
100 100
Frequency (%)
80 80 60 60 40 40
aa
bb
ab ab
60 40 20 0 Cattle
20 20
Sheep
Both
00 Cattle Cattle
Sheep Sheep
Both Both
Figure 9.
Figure 9 Frequency (%) of Kentucky bluegrass in pastures grazed by cattle alone, sheep alone and by both
species in combination over the 12-year study.
Figure 9 100 100
Cattle Cattle Sheep Sheep Both Both
Frequency (%)
80
60
40
Frequency (%)
100
Frequency (%)
80 80 Cattle
Sheep 60 60 Both
40 40 20 20 00 1980
1980
20
24
1982
1982
1984
1986
1984
1986 Year
1988
1988
1990
1990
1992
1992
Year 0 1980
1982
1984
1986
1988
1990
1992
Year