Unearthing the habitat of a hyperaccumulator: case study of the invasive plant yellowtuft (Alyssum; Brassicaceae) in Southwest Oregon, USA

Invasive species pose a critical risk to wildlife habitat, ecosystem processes, and agricultural productivity. This risk is exemplified by the spread of Yellowtuft (Alyssum murale and Alyssum corsicum), in Josephine County, Oregon. Both species have spread into protected botanical areas, which are home to a number of endemic and endangered species. ArcGIS 10 software suite, a comprehensive system used to collect, analyze and distribute geographic information, provided the platform for spatial analysis of infestation sites. The advanced statistical model, MaxEnt, was used to project the likely distribution and suitable habitat for Yellowtuft across 208,513 hectares of southern Oregon and northern California, and identify patterns of spread and habitat suitability. 12 environmental characteristics representing topography, climate, soil characteristics and vegetation cover were used to project distribution across the study area. Current infestations were not found to exclusively reside along spread pathways - roads and streams – or require serpentine soils to establish. The single most important variable related to habitat suitability was elevation, followed by slope, soil depth and vegetation cover class. The suitable map identifies 10,729 hectares as suitable habitat for both Alyssum species, with the vast majority residing within the Illinois River Valley. The final results were overlaid with the 2011 surveyed areas to identify areas that were of high suitability but not yet surveyed to identify survey gaps and possible areas to focus treatment effort for the 2012 and 2013 field season. The results were also overlaid with a prospective aerial survey flight plan to examine if the survey incorporates all areas of high suitability. With limited resources, and costly efforts like aerial surveying, species modeling and spatial analysis provided information that assisted managers to streamline efforts and identify areas of higher suitability that were not actively surveyed.