Researchers: Joseph Smith, Brad Allred, Chad Boyd, Kirk Davies, Matthew Jones, Andrew Kleinhesselink, Jeremy Maestas, Scott Morford, and David Naugle

In the western United States, sagebrush (Artemisia spp.) and salt desert shrublands are rapidly transitioning to communities dominated by exotic annual grasses, a novel and self-reinforcing state that threatens the economic sustainability and conservation value of rangelands. Climate change is predicted to favour annual grasses, potentially pushing transitions to annual grass dominance into higher elevations and north-facing aspects. Researchers sought to quantify expansion of annual grass-dominated vegetation communities along topographic gradients over the past several decades.

Results: The team documented more than an eightfold increase in annual grass-dominated area since 1990, occurring at an average rate of >2,300 km2 year (0.6% of the area of Great Basin rangelands). In 2020, annual grasses dominated approximately one-fifth (>77,000 km2) of Great Basin rangelands. This rapid expansion was associated with a broadening topographic niche, with widespread movement into higher elevations and north-facing aspects consistent with predicted effects of a warming climate.

Main conclusions: More than a century after first appearing in the region, exotic annual grasses continue to proliferate and establish dominance in new environments across the Great Basin. Accelerated, strategic intervention is critically needed to conserve vulnerable sagebrush and salt desert shrub communities not yet heavily invaded. In this era of warming, future climate provides important context for selecting from among alternative management actions and judging long-term prospects of success.