The purpose of this study was to evaluate differences in aboveground biomass production by plant species between grazed and ungrazed sites on Yellowstone National Park's northern elk (Cervus elaphus) winter range. The upland bunchgrass sites on the northern range were apparently not overgrazed at the time of this study in 1986 and 1987, at least in terms of declines in aboveground biomass production, while the only minor changes in species composition were observed. There were very few differences in plant species composition or numbers of plant species between grazed and ungrazed plots, and there was no evidence of accelerated mortality of bunchgrasses from elk herbivory. Protein concentrations and the concentrations of several nutrients were enhanced in grasses by elk herbivory. Very few differences were observed on the heights or growth form of grazed grasses. An increase in bare ground and a large decrease in accumulated litter and standing dead vegetation were observed on grazed sites which, combined with higher bulk densities, contributed to slightly lower soil infiltration rates on grazed sites. Elk grazing on swales, the more productive sites, apparently resulted in stimulation of grasses, but the elk herbivory also resulted in continued persistence of a grazing resistant exotic grass, Kentucky bluegrass (Poa pratensis), following cessation of agricultural activities.
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