OOS 2-3
Initial and decadal responses of riparian bird and plant communities to the landscape-scale removal of livestock on Hart Mountain National Antelope Refuge in the northwestern Great Basin
The most pervasive anthropogenic disturbance across public lands of the American West is grazing by cattle, but the ecological consequences of cattle removal at a landscape scale are poorly understood. In 1990, the USFWS removed all livestock from two large national wildlife refuges in the northwestern Great Basin following >120 years of livestock grazing. In 1991, a series of 1.5 ha study-plots was established in riparian and mesic habitats on the refuges to monitor changes in vegetation and avian abundance in years 1-3 (Phase 1) and 10-12 (Phase 2) after cattle removal. In each plot, vegetation structure and composition were sampled annually on 6-12 100-m transects, and birds were sampled on fixed-width 150-m transects three times during each breeding season.
Results/Conclusions
During the first three years, grass, forb, and mesic shrub cover in riparian areas increased, and avian abundances began to increase, especially among species that nest or forage on the ground or in the understory. For aspen, the most species-rich community, both riparian and snowpocket aspen produced extensive regeneration of new shoots in both phases; a 64% increase in medium-diameter trees in riparian stands in Phase 2 indicated successful recruitment into the overstory, which made the stands more multi-tiered. By phase 2, native forb cover had increased by 68% and 57% in riparian and snowpocket stands, respectively, mesic shrub cover had increased by 29% and 58%, and sagebrush cover had decreased by 24% and 31%. By years 10-12, avian abundance had increased strongly in meadow, willow, and aspen communities. In riparian and snowpocket aspen, respectively, avian abundance in Phase 2 increased by 33% and 39%, with the largest increases seen in ground-understory nesters (133% and 67%). We interpret the increased avian abundances, increased densities of riparian forbs and shrubs, and the substantial regeneration of aspen shoots as a multi-trophic-level response to the total removal of livestock herbivory and a significant movement toward recovery of biological integrity.