Identifying widespread and abundant invasive plants and their invaded regions in the U.S.

Bethany A. Bradley, Environmental Conservation, University of Massachusetts, Amherst, Amherst, MA, David Barnett, National Ecological Observatory Network (NEON), Boulder, CO, Evelyn Beaury, Organismic and Evolutionary Biology, University of Massachusetts Amherst, Amherst, MA, Dana M. Blumenthal, Rangeland Resources & Systems Research, USDA, Agricultural Research Service, Fort Collins, CO, Jeffrey Corbin, Department of Biological Sciences, Union College, Schenectady, NY, Jeffrey M. Diez, Institute of Ecology and Evolution, University of Oregon, Jeffrey S. Dukes, Purdue Climate Change Research Center, Purdue University, West Lafayette, IN, Regan Early, Centre for Ecology and Conservation, University of Exeter, Cornwall, Cornwall, United Kingdom, Haley Flickinger, Purdue University, Ines Ibanez, University of Michigan, Ian Pearse, United States Geological Survey, Fort Collins, CO, Laís Petri, School for Environment and Sustainability, University of Michigan, Ann Arbor, MI, Helen R Sofaer, U. S. Geological Survey, Hilo, HI, Cascade J. B. Sorte, Ecology & Evolutionary Biology, University of California, Irvine, CA and Montserrat Vilà Planella, Estación Biológica de Doñana (EBD-CSIC), Sevilla, Spain

Background/Question/Methods
Many non-native plants have been identified as invasive because of their negative impacts on individual species and ecological communities. Our knowledge of where invasive plants occur and our ability to predict the range where they could establish have improved dramatically in recent years. But within the invaded range, our knowledge of where those species are most abundant and have the greatest impact lags behind. As a result, we cannot provide management agencies and regulatory boards with the tools they need to identify and prioritize non-native plants likely to become invasive in their regions. Here, we present the results of a compilation of invasive plant cover data across the lower 48 United States. We compiled invasive plant percent cover data with georeferenced locations from the Bureau of Land Management, Carolina Vegetation Survey, Early Detection & Distribution Mapping Service, iMap Invasives Databases, U.S. Forest Service, National Park Service, and National Ecological & Observatory Network, along with several state invasive plant databases. We used these data to identify widespread and abundant non-native species associated with the different habitats and ecoregions of the conterminous U.S.
Results/Conclusions
The invasive plant cover database consisted of over 600,000 unique georeferenced locations from ten state and regional compilations. Based on range calculated within 50 x 50 km grid cells, the dataset encompassed 58% of land area in the lower 48 states. Invasive plants were reported at greater than 10% cover at more than half of all locations (~400,000 points) encompassing 43% of land area. The most widespread species reported at greater than 10% cover were Cirsium arvense, Bromus tectorum, and Centaurea stoebe. While these three species are well known invasives, there were 200 total species that achieved greater than 10% cover in at least ten grid cells. Similarly, 376 species were reported at greater than 10% cover in two or more Level-1 U.S. ecoregions, with Ailanthus altissima and Leucanthemum vulgare each reported at high abundance in all ten ecoregions. This analysis highlights the large number of invasive plants that are both widespread and abundant across the U.S. Species that frequently achieve high cover locally pose the greatest risk to ecosystems and should be priorities for monitoring and early detection and rapid response. This analysis provides a first step towards creating a single database of problematic invasive plants that can be used to prioritize invasive plant management.