Impacts of Black-tailed Jackrabbits at Peak Population Densities on Sagebrush-Steppe Vegetation

Abstract

In the northern Great Basin, populations of black-tailed jackrabbits (Lepus californicus) are cyclic, reaching high densities at approximately 10-year intervals. This project examined impacts of jackrabbits during a peak in their cycle on sagebrush-steppe vegetation in southeastern Idaho. Total vascular plant cover was significantly lower on plots open to jackrabbit herbivory than on exclosure plots, but in no case was cover of a specific species significantly reduced on open plots. The most severe impacts were on shrubs during winter; most aboveground tissues of both winterfat (Ceratoides lanata) and green rabbitbrush (Chrysothamnus viscidiflorus) plants were completely eaten by spring. However, these impacts were largely ameliorated by compensatory growth during the following growing season, and there was no difference in total biomass for either species between the open and protected plots by July. New growth of winterfat plants that had been browsed the previous winter was significantly greater than that of protected plants. Thus, although the cumulative effects of herbivory reduced total plant cover, no single species was irreparably impacted. Over a year, jackrabbits exert feeding pressure on nearly all of the important species in these communities; therefore, these hares do not appear to apply differential grazing pressure that would alter the course of vegetation development on northern Great Basin rangelands.