Impacts and mechanisms of biological invasions in global protected areas

Protected areas underpin global biodiversity conservation and sustainability goals, but remain at risk from biological invasion impacts. Anticipated expansions of protected lands and waters towards 2030 under the Kunming-Montreal Global Biodiversity Framework (GBF) will concurrently increase the burden of biological invasions within and from these newly protected areas. To prioritise management efforts and assess the potential risks of current and future designations to address multiple GBF targets, it is essential to quantify impact patterns at large scales across contexts. Here, we provide the first comprehensive global assessment of non-native species impacts in protected areas using the Environmental Impact Classification for Alien Taxa (EICAT)—a semi-quantitative, standardised protocol for evaluating their environmental impacts. We analyse taxonomic, ecological, and spatiotemporal predictors of harm and compare the distribution of impact mechanisms across contexts, using 579 impact cases from a literature review. Harmful impacts from non-native species have been documented across all taxonomic groups and environments, including irreversible extinctions. In particular, non-native plants and fish most often affect native plants and insects. Competition, predation, and structural changes were the most impact mechanisms recorded. Studies have been biassed geographically towards Nearctic, Palearctic and Neotropical protected areas, reinforcing the need for regional strategies to mitigate impacts. Our findings culminate in a series of recommendations to directly and indirectly address GBF targets by managing biological invasion impacts. Overall, expanding the range of studies towards whole ecosystem levels across regions can enrich the understanding of how biological invasions affect protected areas. Based on our results, managers should seek to reduce invasion rates in general across all taxa, but especially prioritise those conferring impacts through consumptive and structural mechanisms.