The Response of Native Vertebrate Populations to Crested Wheatgrass Planting and Grazing by Sheep

Abstract

Native vertebrate population levels were examined in grazed and ungrazed habitats dominated by big sagebrush (Artemisia tridentata) and crested wheatgrass (Agropyron cristatum) in southeast Idaho. Our objective was to determine the species diversity and relative density of birds, mammals, and reptiles in these habitats with and without grazing pressures by sheep. In a habitat dominated by sagebrush, grazing did not significantly alter the species diversity or the density of reptiles or nesting birds. However, both the diversity and the relative density of small mammals were significantly reduced. Crested wheatgrass plantings, regardless of sheep use, supported fewer nesting bird species and a lower density of birds, mammals, and reptiles than did areas dominated by sagebrush. The synergistic effects of planting with crested wheatgrass followed by grazing were most evident in (1) a significant reduction in the relative density of small mammals, and (2) the occurrence of only one nesting bird species: the horned lark (Eremophila alpestris).