Response of Cheatgrass and Other Vegetation to Proactive Management Using Two Consecutive Fall Herbicide Applications in High-Elevation Sagebrush Steppe

Abstract

Nonnative plants are one of the foremost concerns to public and private land managers. To help guide managers, conservation and nonnative plant management methodologies have been blended to help prioritize management under the “defend the core” management framework. This approach emphasizes the need to control low-abundance infestations of nonnative plants before they become costly to manage and result in irreversible ecosystem alterations. However, few studies have explored the impacts and efficacy of nonnative plant management when target species occur in low abundance. Our study focused on one of the most prolific invaders in the western United States, cheatgrass (Bromus tectorum). We found that at the northern edge of cheatgrass's historical range, two consecutive fall applications of the herbicide imazapic (Plateau; BASF Corporation, Research Triangle Park, NC) controlled low-abundance populations of cheatgrass for three or more years. However, cheatgrass reductions did not result in an increase in native plant richness, native plant abundance, or native perennial grass productivity, and ultimately, cheatgrass returned to pretreatment abundances in one of two areas. As a result, we conclude that imazapic can be an effective tool to control cheatgrass when it occurs at low abundance in high-diversity plant communities, i.e., “core” sagebrush areas, within the Middle Rockies ecoregion. To defend the core, we recommend herbicide as a tool within a broader adaptive and integrated management plan that includes alterations to factors that managers can control, e.g., stocking rates, timing, placement of grazing infrastructure, and off-road travel. Lastly, we suggest that monitoring should be conducted throughout the management process so managers can adapt to the real-time responses of plant communities.