Frequency and Extent of Defoliation of Herbaceous Plants by Sheep in a Foothill Range Community in Northern Utah

Abstract

Defoliation of individual plants by sheep grazing a shrub-steppe community in the foothill ranges of northern Utah was examined during a spring grazing. Five sites (each approx. 120 m2) within the paddock were monitored, and populations of one or more species (Aster chilensis, Wyethia amplexicaulis, Lupinus sericeus, Poa secunda, and Koeleria cristata) within these sites were examined daily for defoliation over a 25-day period. Grazing started at different times at each site, but once grazing started each site was visited daily. The proportion of the population of A. chilensis shoots that were grazed each day varied but was highest (about 30%) several days after grazing commenced at each site. Extent of defoliation of highly palatable species did not differ over time but did increase for W. amplexicaulis (forb of low palatability) at the end of the grazing period.