Interactions of grazing and plant protection on basin big sagebrush (Artemisia tridentata ssp. tridentata) seedling survival.

Abstract

The impact of grazing animals and plant protection on shrub seedling establishment was studied in 2 separate experiments. A total of 3,665 seedlings were monitored for survival during a sheep grazing trial in 1994, and 5,755 seedlings were monitored during a cattle grazing trial in 1986. Approximately 1/2 of the seedlings were located under the canopy of mature plants and 1/2 were located in the interspaces between plants. The presence of domestic livestock and the seedling location affected both the overall survival at the end of the growing season and the pattern of survival during the growing season. The interaction between these independent variables resulted in the highest survival (0.11) for sheltered seedlings in the grazed pastures and the lowest survival (0.009) for unprotected seedlings in the grazed pastures. Seedlings in the ungrazed pastures had survival rates intermediate between these 2 rates. The pattern of seedling survival was similar in both experiments. Seedlings in the grazed pastures experienced high mortality during the actual grazing event and immediately after grazing. Seedlings which were unsheltered experienced the lowest survival due to trampling. Survival rates late in the summer were not affected by grazing but were dependent on receiving precipitation during this normally dry period of the year. The interaction between grazing and seedling location may partially explain the aggregated distribution of Artemisia found in many communities. This aggregation should affect interspecific competition and may play a role in later stages of plant succession within these shrub-dominated communities.