EFFECTS OF DIFFERENTIAL LIVESTOCK USE ON KEY PLANT-SPECIES AND RODENTPOPULATIONS WITHIN SELECTED ORYZOPSIS-HYMENOIDES HILARIA-JAMESII COMMUNITIES OF GLEN CANYON NATIONAL RECREATION AREA

Four sites that varied with respect to grazing history were studied du ring 1990 and 1991 on an isolated 8,000 ha peninsula in Glen Canyon Na tional Recreation Area. Density and basal area of Oryzopsis hymenoides decreased with increasing grazing intensity while density and foliar cover of Gutierrezia sarothrae increased on grazed sites. Perognathus longimembris was the most abundant rodent species trapped on all sampl ed sites and demonstrated a 50% decrease in abundance at the heavily g razed site compared to the nongrazed site. Peromyscus maniculatus was the second most abundant rodent species recorded and increased with in creasing grazing intensity.