Response of Two Sagebrush Sites to Low-Disturbance, Mechanical Removal of Piñyon and Juniper

In the Great Basin of the western United States, expansion of Pinus monophylla (singleleaf piñyon) and Juniperus osteosperma (Utah juniper) out of historic woodlands and into Artemisia spp. (sagebrush) shrubland communities can facilitate the invasion of exotic downy brome (Bromus tectorum) and lead to decreases in ecological and economic values of shrublands. This expansion has, therefore, been the focus of management efforts, including the thinning or removal of trees in areas that were historically shrubland. Our study examined the effects of tree thinning at two sites located in eastern Nevada, near the center of the Great Basin. Such projects can be controversial, so our goal was to estimate and document the ecological effects of low-disturbance tree thinning at these two sites. Both sites were mechanically thinned using a feller-buncher and were aerially seeded with native grasses. Aerial seeding had no apparent effect at either site. The site that had lower tree cover before treatment (Ely, NV) showed an increase in native forbs and a small increase in invasives. The site that initially had very high tree cover and low shrub cover (Mt. Wilson, NV) showed increases in native forbs and species diversity and a substantial increase in invasives. We conclude that low-disturbance methods for thinning encroaching trees can have positive ecological effects in shrublands but that the initial cover of both trees and native herbaceous species should be considered to determine the potential of the site to recover naturally from the seedbank and the risk of invasion by downy brome.