Publication Alert: Annual Invasive Grasses Spreading Through Great Basin to Higher Elevations and Northern Aspects

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Cheatgrass is an annual invasive plant that crowds out native plants in sagebrush range.

Working Lands for Wildlife research is showing that annual invasive grasses are moving up in elevation and to more northern aspects throughout the Great Basin.

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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, decreases 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.

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 [LINK TO FRAMEWORK], 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.

STUDY TITLE, ABSTRACT, CITATION, AND PERMANENT LINK

Title: The Elevational Ascent and Spread of Exotic Annual Grass Dominance in the Great Basin, USA

Abstract: In the western US, 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 favor annual grasses, potentially pushing transitions to annual grass dominance into higher elevations and north-facing aspects. We sought to quantify expansion of annual grass-dominated vegetation communities along topographic gradients over the past several decades.

We documented more than an eight-fold increase in annual grass-dominated area since 1990, occurring at an average rate of >2,300 km2 yr-1 (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.

Citation: Smith, J. T., Allred, B. W., Boyd, C. S., Davies, K. W., Jones, M. O., Kleinhesselink, A. R., Maestas, J. D., Morford, S. L., & Naugle, D. E. (2021). The elevational ascent and spread of exotic annual grass dominance in the Great Basin, USA. Diversity and Distributions, 00, 1– 14. https://doi.org/10.1111/ddi.13440

Permanent URL: https://doi.org/10.1111/ddi.13440