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Sagebrush Steppe Restoration and Cheatgrass
David A. Pyke, USGS Forest and Rangeland Ecosystem Science Center, Corvallis, OR
Cheatgrass (Bromus tectorum) is the greatest threat to the sagebrush steppe ecosystem and it becomes the primary roadblock for successful restoration of the structure and function of the sagebrush steppe. Structurally, the invasion and spread of cheatgrass has lead to the destruction of the dominant shrub of the ecosystem, sagebrush. This destruction occurs by cheatgrass providing a continuous fuel source across the landscape. This is the greatest problem for Wyoming big sagebrush. This sagebrush is incapable of resprouting after being burned and its seeds are thought to be short-lived, but in the past this was not likely the problem it is today because fires likely consumed less area. Islands of sagebrush would likely remain unburned and would provide a seed source for recovery. Now, the continuous fuels provided by cheatgrass mean larger fires and greater distances for seeds to travel to re-establish throughout the burned area. So structurally the system has changed from one having shrubs to one often lacking shrubs. Functionally, cheatgrass germinates earlier than most native herbaceous plants and it may impact both the water (drier) and nutrient cycles (rapid turnover of nitrogen and more labile sources of carbon) in the ecosystem. These appear to influence the soil microbial communities as well shifting microbes from fungal to bacterial-dominated. We generally believe that cheatgrass is more competitive than native species seedlings, but that competitive advantage may not be just its superior ability to access and use resources. It may also create a soil environment that provides a positive feedback for cheatgrass growth that enhances its dominance over that of native species. Restoration may require more than just reintroducing the desired species; it may require soil amendments to balance the competitive field.