Using Expert Knowledge to Satisfy Data Needs:Mapping Invasive Plant Distributions in the Western United States

—Lack of knowledge about the distributions of plant and animal species can severely hamper management efforts. For invasive plants, distribution and abundance data can inform early detection and rapid response (EDRR) programs aimed at treating initial infestations. These data can be used to create invasion risk models at landscape and regional scales. Further, regional maps of invasive plant abundance are useful for communicating the scope of the invasive species problem to the public and policymakers. Here, we present a set of regional distribution maps for 10 problematic invasive plants in the western United States, created from the expert knowledge of weed managers in over 300 counties. Invasive plant experts identified infestations on paper, and the results were digitized into a regional GIS. Over 40% of requests were returned, resulting in maps with good spatial coverage and distribution data suitable for assessing invasive plant abundance across the western United States. Cheatgrass (Bromus tectorum) and Canada thistle (Cirsium arvense) were the most abundant and widespread of the surveyed species; however, the high concentrations and broad spatial extents of other invasive plants, such as hounds tongue (Cynoglossum officinale), white top (Lepidium draba), and Dalmatian toadflax (Linaria dalmatica), highlight the ongoing problems invasive species pose for western ecosystems, rangelands, and croplands. These results reinforce the critical role that regional mapping efforts can play in assessing and communicating invasion risk. This study suggests that knowledge about plant invasions exists locally and that experts are willing to participate in regional efforts to compile that