WRASP: A spatial strategic weed risk analysis tool reveals important subnational variations in weed risks

Due to the overwhelming number and diversity of introduced invasive plants, coupled with limited weed management budgets, Government agencies are typically required to employ systems to prioritise weeds for management attention. To help tackle this problem, an analytical protocol and spreadsheet tool was previously developed for post-border weed risk management (PBWRM). The popular PBWRM tool utilises a simple framework that ignores any spatial variation in risk factors within the geographical area of risk concern. However, invasive plants vary spatially in risk factors such as invasiveness, potential impacts, and feasibility of control. The PBWRM system requires the analyst to integrate each of these spatially-variable factors into a single risk score. This process is inherently subjective, difficult to implement and conceals the variations in weed risks. To address these concerns our Trans-Tasman research team took the PBRWM logic and spatialized it, allowing weed managers to assess weed risks and management classes across geographical space. We illustrate this new spatial system using a case study of Senecio glastifolius in New Zealand, comparing the results of a spatial and an aspatial analysis of the risks it poses, and the consequent logical management options. The spatial portrayal of risks revealed locations of both higher and lower risk and suitability for management attention that were concealed within the aspatial weed risk scores of the current PBWRM system. The overall national level risk assessed using the spatial tool was also appreciably higher than that indicated by the aspatial scoring system. The spatial tool, WRASP, takes its name from Weed Risk Assessment SPatial. In New Zealand, WRASP forms part of an integrated set of tools for strategic weed management. This decision-support toolkit is described in Bourdôt & Kriticos (this volume)