Using state-and-transition models to project cheatgrass and juniper invasion in southeastern Oregon sagebrush steppe.

Many threats are jeopardizing the sagebrush steppe of the Columbia Basin, including the spread of invasive species such as cheatgrass (Bromus tectorum L.) and the expansion of western juniper (Juniperus occidentalis Hook.) into historic shrub steppe. Native sagebrush steppe provides productive grazing lands and important habitat for many wildlife species, and managers are in need of landscapescale tools to assess shrub steppe conversion risk and management options to maintain native shrub steppe. We used a state-and-transition modeling approach to project changes in sagebrush steppe vegetation across the landscape of southeastern Oregon. Models were constructed using both empirical data, including empirically derived fire probabilities, and expert opinion for processes that are still poorly documented, such as livestock grazing effects. With unrestricted grazing and no restoration treatments, future invasion by exotic annual grasses in warm, dry sagebrush steppe and juniper expansion into cool, moist sagebrush steppe are likely to accelerate in the next 50 years under current climatic conditions. Invasions are also likely to be