Effects of Dormant Season and Contemporary Spring-Summer Grazing on Plant Community Composition in the Sagebrush Ecosystem

Abstract

Livestock grazing is the primary land use across sagebrush ecosystems in the western US and its effects have been subject to extensive research and debate. Historical overgrazing, annual grass invasion and associated increase in fire frequency, conifer encroachment, climate change, and human modification have resulted in the loss or degradation of 86% of sagebrush ecosystems, leading to intensified interest in how remaining intact rangelands are managed. Unlike historical, continuous grazing, contemporary practices generally incorporate planned periods of rest and recovery from grazing during the growing season. Dormant season grazing is one such practice that shows promise for improving degraded rangelands and reducing wildfire risk. However, no studies have compared moderate intensity dormant season grazing to contemporary spring-summer grazing and grazing exclusion in sagebrush rangelands dominated by perennial bunchgrasses. We evaluated the effects of contemporary spring-summer grazing, dormant season grazing, and grazing exclusion on plant community characteristics in a Wyoming big sagebrush ecosystem. We expected the effects of dormant season grazing to be comparable to grazing exclusion. Deep-rooted perennial bunchgrass cover and density and shallow-rooted perennial bunchgrass cover in grazed areas did not differ from grazing exclusion (control) sites, and we found no support that grazing altered the deep-rooted perennial bunchgrass community through time. Dormant season grazing reduced native annual forb and sagebrush cover, but increased density of the shallow-rooted perennial bunchgrass. Our results suggest contemporary spring-summer or dormant season grazing are unlikely to lead to a decline in desirable perennial bunchgrasses.