Mapping the disintegration of Intermountain West ecosystems by invasive grasses: Potential limiting factors

The intermountain west is characterized by high deserts dominated by shrublands, especially sagebrushes (Artemisia spp.).  Several exotic annual grasses have colonized this region and have been rapidly expanding in recent decades.  These grasses produce fine fuels in shrub interspaces, increasing the ability of vegetation to carry wildfires.  These grasses also quickly reinvade burned areas, often to the exclusion of native species, thus creating a positive feedback mechanism that enables them to convert shrubland ecosystems to annual grasslands on a landscape scale.  Satellite sensor data (imagery) is being used to map the progression of these grasses in Nevada, Oregon, and Idaho (particularly Bromus tectorum).  Statistical models used for mapping include landscape-level variables to improve mapping accuracy.  Minimum temperatures correlate well with annual grass cover, suggesting the possibility of a temperature control on invasion.  There is also a mutually exclusive pattern between annual grasses and biological soil crusts, a key ecosystem component that may reduce erosion, alter soil hydrology, and resist invasion of exotic plants.