The elevational ascent and spread of exotic annual grass dominance in the Great Basin, USA

Sweeping sagebrush and salt desert shrublands typify the Great Basin - a 200,000-square-mile landscape that encompasses much of Nevada and parts of Utah, Idaho, Oregon, Wyoming, and California. Across this broad geography - a mix of privately owned ranches interspersed with public lands - invasive annual grasses are displacing native perennial vegetation. New research supported by Working Lands for Wildlife (WLFW) quantifies the spread of this threat.

Displacing native plants with annual grasses like cheatgrass, medusahead, and ventanata, reduces forage productivity and carbon storage, degrades wildlife habitat, and increases the threat of wildfires. Understanding the extent and spread of these annual invasive grasses is key to crafting a landscape-scale approach for maintaining these productive and resilient rangelands.

Lead author Joe Smith, a WLFW-affiliated researcher at the University of Montana, used recently developed remote sensing-based rangeland monitoring data from the Rangeland Analysis Platform (RAP) to produce yearly maps of annual grass-dominated vegetation communities from 1990-2020. With these images, Smith and his team quantified the rate of spread of annual grasses and characterized changes in the distribution (elevation and aspect) of those transitioning areas.

Supported by and co-produced with USDA's Agricultural Research Service (ARS) scientists in Burns, OR, the team documented a more than eight-fold increase in annual grass-dominated areas since 1990. In 2020, annual invasive grasses dominated approximately one-fifth of the Great Basin. Smith also determined annual grasses were spreading to higher elevations and to slopes that faced a generally northern direction.

Through the Framework for Conservation Action in the Sagebrush Biome, WLFW works to defend relatively uninvaded sagebrush cores from annual grass conversion and expand them through restoration to maintain productive working lands that are resilient to fire and resistant to invasive annuals.

WLFW’s approach for tackling this threat relies on statewide maps identifying large, intact core areas with relatively low, or no, annual grass invasion. Core areas serve as anchor points for conservation action and inform a proactive strategy for management: Defend the Core, Grow the Core, Mitigate Impacts.

Smith’s research reiterates the urgency to implement preventative measures for intact, yet vulnerable, landscapes as annual grasses continue to invade the Great Basin and other rangelands across the American West.

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