A workflow for impact indicators of alien species: A demonstration with Acacia species

The negative impact of alien species is recognised as a major threat to biodiversity. An impact indicator, a measurable proxy of the status of alien species impacts over space and time, is essential for informing biological invasion policies and management strategies. We introduce an open-source workflow for computing impact indicators of alien species, combining occurrence data from the Global Biodiversity Information Facility (GBIF) with assessments of Environmental Impact Classification for Alien Taxa (EICAT). To implement the workflow, we developed an R package, impIndicator, which allows users to compute and visualise impact indicators for individual species and sites, as well as regional impact indicators. This tool can support ecological research and management by providing standardised insights into where alien species pose the greatest threats and whether current interventions are effectively reducing them. Such information is directly relevant to policy frameworks, including Target 6 of the Convention on Biological Diversity’s Kunming–Montreal Global Biodiversity Framework and the Sustainable Development Goals. We demonstrate the workflow using Acacia species in the Iberian Peninsula, South Africa and California, showcasing the spatiotemporal dynamics of their impacts and highlighting sites with higher impact risk. The resulting impact indicators were sensitive to variation in sampling effort and the completeness of the underlying occurrence data, highlighting the importance of well-sampled and systematically curated biodiversity datasets for robust impact assessment.