In the summer of 1984, research was conducted in Utah on mule deer (Odocoileus hemionus)-induced mortality of a mountain big sagebrush (Artemisia tridentata ssp. vaseyana) community that was bisected by a deer fence. The sagebrush community was located on an exposed, west-facing slope that was generally snow-free during the winters of 1982-1983 and 1983-1984. On the freeway side of the fence, the site was essentially free of browsing animals, while above the fence, the shrubs were exposed to concentrations of mule deer. There was significant mortality and decline in vigor of mountain big sagebrush plants in the area behind the right-of-way fence where mule deer had access. Mule deer forage access was limited to the exposed slopes with less snow accumulation in the area during much of the 1982-1983 and 1983-1984 winters. These winters saw heavy snow accumulation. Mountain big sagebrush plants were quite similar in height and crown diameter on both sides of the right-of-way fence, but the number of dead plants was significantly different between the two sides of the fence. Plants in the browsed transects had an average crown dieback of 64% in comparison to a 17% dieback in the nonbrowsed transects. Dead plants were 11 times as common on the browsed side of the fence. None of the dead sagebrush had resprouted by 1986. Furthermore, the promising cohort of seedlings on the browsed side of the fence of 1984 was reduced to a very low level in 1986. It was suspected that the cohort was lost because of competition with the dense stand of annuals and normally very hot and dry mid-summer conditions. Results show that sagebrush does not tolerate heavy defoliation by native herbivores and can alter the plant community.
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