The Potential for Ventenata dubia to Intensify the Annual Grass Driven Transformation of the American West Now and in the Future

Abstract:

Invasive exotic annual grasses have transformed native ecosystems of the Great Basin, Southwestern Deserts and California Mediterrenean regions of the western US, altering multiple aspect of ecosystem function and increasing fire frequency and extent. Wiregrass (Ventenata dubia) is a relatively new exotic annual grass that has largely been problematic in the Inland Northwest, although the species is rapidly expanding. Understanding the potential for this species to invade new areas of the western US as well as respond to future climate change could aid in early detection and rapid response efforts and the development of preemptive management approaches to curb spread. We modeled V. dubia’s present and future climate habitat for the western US using Boosted Regression Trees. Presence data was compiled from multiple sources. Bioclimatic predictor variables were derived from PRISM historical climate data. Future projections were created using 31 GCMs from NEX-DCP30 downscaled data for RCP 8.5. Model results indicate there is substantial suitable climate habitat for V. dubia in the western US. High probability areas (0.75-1.0) align somewhat with the broad geographic distribution of other problematic invasive annual grasses such as cheatgrass (Bromus tectorum); however at finer scales, abiotic drivers appear to be quite different. For example, many higher elevation mountainous areas may climatically support V. dubia. Results suggest that substantial areas of potential habitat (more than 40 % of the ecoregion) are present in the Blue Mountain, Eastern Cascade Slopes/Foothills, and the Arizona/New Mexico Mountains. At least 10% or more of the Columbia Plateau, Southwestern Tablelands, Klamath Mountains, California High North Coast Range, Southern/Northern Rockies, Northern Basin and Range, and Cascades ecoregions may also support invasions. By the end of the century, some areas may no longer be climatically suitable; however, habitat could shift northward and up in elevation. The projected low probability niche broadens geographically, while high probability areas contract. There is considerable uncertainty regarding model results; nevertheless, there is potential for V. dubia to expand the overall annual grass invasion footprint in the west and intensify ecosystem transformation.