CHEATGRASS (BROMUS-TECTORUM L) DOMINANCE IN THE GREAT-BASIN DESERT - HISTORY, PERSISTENCE, AND INFLUENCES TO HUMAN ACTIVITIES

Cheatgrass (Bromus tectorum L), an exotic annual, is a common, and oft en dominant, species in both the shadscale and sagebrush-steppe commun ities of the Great Basin Desert, Approximately 20% of the sagebrush-st eppe 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 a nd dissemination of cheatgrass in the Great Basin, examines the proces ses 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 cheatgras s was introduced accidentally to the Great Basin as a grain contaminan t at the end of the 19th century at the same time that large-scale dom estic grazing was occurring, Imported from Mediterranean Europe and ce ntral and south-western Asia, seeds of cheatgrass exploited an ecologi cal niche, as no native annual was dominant in the Great Basin. Cattle , sheep, and feral horses facilitated establishment, for they spread t he seeds in the same areas that they disturbed. Once established, chea tgrass promoted the likelihood of fire to the detriment of the native species, In addition, other factors, such as the effects of the lack o f vesicular arbuscular mycorrhizae and selective lagomorph grazing hav e worked in concert to further establish cheatgrass dominance. The eco logical 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 long-lived perennial shrubs now are replaced with either nearly p ure patches of cheatgrass or swaths of cheatgrass and short-lived pere nnial shrubs, Some consequences to human activities involve the numero us ramifications of rangeland fires with costs of approximately US$20 million annually, the undependability of cheatgrass as a source of for age for cattle and sheep, and the value of biotic diversity as numerou s plant and animals species undergo high amplitude population fluctuat ions, Management of these Great Basin vegetation communities should be approached using the state and threshold range condition model. Copyr ight (C) 1996 Elsevier Science Ltd.