Cheatgrass ( Bromus tectorum L) dominance in the Great Basin Desert : History, persistence, and influences to human activities

Abstract

Cheatgrass ( Bromus tectorum L), an exotic annual, is a common, and often dominant, species in both the shadscale and sagebrush-steppe communities of the Great Basin Desert. Approximately 20% of the sagebrush-steppe vegetation zone is dominated by cheatgrass to the point where the establishment of native perennial species is nearly Impossible. This paper discusses the historical factors that led to the establishment and dissemination of cheatgrass in the Great Basin, examines the processes that further cheatgrass dominance, provides examples of subsequent influences of the grass to human activities, and links the ecological history with range condition models. Evidence suggests that cheatgrass was introduced accidentally to the Great Basin as a grain contaminant at the end of the 19th century at the same time that largescale domestic grazing was occurring. Imported from Mediterranean Europe and central and south-western Asia, seeds of cheatgrass exploited an ecological niche, as no native annual was dominant in the Great Basin. Cattle, sheep, and feral horses facilitated establishment, for they spread the seeds in the same areas that they disturbed. Once established, cheatgrass promoted the likelihood of fire to the detriment of the native species. in addition, other factors, such as the effects of the lack of vesicular arbuscular mycorrhizae and selective lagomorph grazing have worked in concert to further establish cheatgrass dominance. The ecological consequences of cheatgrass establishment have been an increase in fire frequency and intensity, a decrease in species diversity, and a landscape susceptible to severe erosion. Bunchgrasses interspersed with longlived perennial shrubs now are replaced with either nearly pure patches of cheatgrass or swaths of cheatgrass and shortlived perennial shrubs. Some consequences to human activities involve the numerous ramifications of rangeland fires with costs of approximately US$20 million annually, the undependability of cheatgrass as a source of forage for cattle and sheep, and the value of biotic diversity as numerous plant and animals species undergo high amplitude population fluctuations. Management of these Great Basin vegetation communities should be approached using the state and threshold range condition model.