Survival of juvenile basin big sagebrush under different grazing regimes.

Abstract

Basin big sagebrush (Artemisia tridentata Nutt ssp tridentata Beetle) often invades rangelands seeded to introduced grass species. Livestock grazing may enhance the invasion but the effects of grazing intensity on invasion rates are not known. To investigate invasion rates, individual big sagebrush plants were marked and observed for mortality over a 4-year period within a short duration grazing (SDG) cell and continuous season-long grazed pastures. Over the course of the experiment, the survival of juvenile big sagebrush was higher in the SDG cell. However, there were no differences in survival between grazing treatments during the first year of the study. In subsequent years, declining tiller numbers and density of individual crested wheatgrass plants may have decreased the competitive pressure on juvenile big sagebrush under SDG. The intensity of grazing did not affect which individual juveniles survived. Plants with more than 50 cm2 canopy area had the highest survival rates of all big sagebrush in both grazing treatments. Plant density, which ranged from 1 to 30 plants m-2, did not affect plant survival in either of the grazing treatments. Big sagebrush survival in the SDG cell was higher in a rhizomatous grass community than in a tussock grass community.