A review of impact assessment protocols of non-native plants

Impact assessment protocols (i.e. scoring systems) for non-native species have been developed and implemented relatively recently, driven by an increasing demand for desk study approaches to screen and classify non-native species, considering their environmental and socio-economic impacts. While a number of impact assessment protocols have been developed, there are no clear guidelines to help researchers, environmental practitioners and policy-makers understand their differences, uses and limitations, and to ultimately assist in the choice of protocol and practical implementation. In this review, we compare the main structure of 26 impact assessment protocols used for non-native plants. We describe these protocols in terms of the impact types that they include, the way in which impacts are categorized and ranked, how uncertainty is considered, and how the overall score is calculated. In general, environmental impacts are included more often than socio-economic impacts. Impacts are rated by estimates of the intensity, extent, persistence and reversibility of the impact. Uncertainty is mainly estimated by the availability and quality of the scientific information, but also by the agreement and relevance of the available evidence on impacts beyond the region in which the impact is assessed (including the assessment of climatic similarity with other invaded areas). The final impact score is usually calculated as the sum of scores, the maximum score achieved across all impact types, or a rule-based aggregation of impacts in order to provide a final rank of the non-native species. We finally indicate issues related with transparency, redundancy, clarity, friendliness, scope, scaling, reproducibility and flexibility as key challenges for impact assessment improvement.