Integrating EICAT and EICAT+ assessments and expert knowledge to classify invasive alien plants in France, based on their ecological impact

The EICAT and EICAT+ methods were developed to assess the negative and positive environmental impacts of alien species respectively. While both methods are theoretically applicable across spatial scales, their use has thus far been predominantly at the global level. In the case of EICAT, this reflects its original design for global assessments, whereas for EICAT+, which was only introduced in 2022, its application across different spatial scales remains to be assessed. At this stage, it remains unclear to what extent EICAT and EICAT+ can effectively support national regulations or local management strategies. Here we put forward a series of adaptations with the aim of enhancing the applicability of EICAT and EICAT+ at the national level. The main adaptation was to incorporate expert knowledge from botanists and wildlife specialists into the assessments, in addition to the literature review. To this end, a key was designed to facilitate the translation of field observations into impact categories using standardised criteria. We then tested the formal EICAT and EICAT+ protocols and EICAT and EICAT+ based protocols in France on 228 invasive alien plants. This test demonstrated that expert knowledge is an essential source of data for national-scale assessments, as it allowed reducing the proportion of Data deficient species from 39% to 5% for EICAT and from 86% to 37% for EICAT+. Consequently, this study represents the most thorough evaluation to date of the current ecological impacts of alien plants in France, highlighting 129 out of 228 taxa with harmful impacts: 71 taxa with a Moderate impact, 56 taxa with a Major impact and two taxa with a Massive impact. Furthermore, when using both EICAT and EICAT+, it is crucial to emphasise that directly comparing the two methods is not appropriate. National priority lists should be formulated solely based on EICAT, while EICAT+ can serve as a valuable tool for guiding managers on the risks associated with management actions and strategies to mitigate unintended consequences.