Invasive annual Bromus species are widely recognized for their potential to invade, dominate, and alter the structure and function of ecosystems in the western United States. In this presentation we summarize the invasion potential and threats to fire regimes for different Bromus species within each of five ecoregions of the western United States. We characterize invasion potential and threats in terms of ecosystem resistance to Bromus invasion and ecosystem resilience to disturbance with an emphasis on the importance of fire regimes. We also explain how soil temperature and moisture regimes can be linked to patterns of resistance and resilience and provide a conceptual framework that can be used to evaluate the relative potential for invasion and ecological impact of the dominant invasive annual Bromus species in the western United States.
Results/Conclusions
We present models that illustrate how Bromus invasion potential and threats to fire regimes vary among both vegetation types and ecoregions, and among Bromus species. It should not be assumed that just because a particular Bromus is documented to pose a significant threat in one vegetation type or ecoregion, that other Bromus will pose similar threats to other vegetation types or ecoregions. We feel that these models are most reliable for B. tectorum and B. rubens, especially in the Cold Deserts, Mediterranean California, and Warm Desert ecoregions. The refinement and validation of these models would improve their reliability and utility in evaluating the relative potential for invasion and ecological impact of Bromus in western United States.