Risks posed by invasive species to the provision of ecosystem services in Europe

The capacity of nature to sustain human quality of life has been deteriorating since 1970, with the spread of invasive species a major contributing factor. While the effects on native species and biodiversity are well-documented, evidence regarding impacts on ecosystem services remains scattered and geographically limited. This lack of spatial assessments is partly due to the absence of harmonized accounting and mapping for multiple ecosystem services at large spatial scales. This study addresses this gap by providing a comprehensive spatial evaluation of the risks posed by biological invasions to the provisioning of ecosystem services at a continental scale in Europe. The study's specific aims are to quantify current observed risks and map spatial patterns of future risks, acknowledging that risks vary across regulating, provisioning, and cultural services delivered by different ecosystems with varying invasion levels. The severity of impacts depends on vulnerability and exposure to the hazard; exposure is measured by the presence of invasive species, and vulnerability by the level of ecosystem service provisioning. The study focuses on Europe (excluding Russia) due to data availability and the significance of environmental policy regulations at national and pan-continental scales, allowing results to inform policy decisions, particularly regarding the EU Regulation on Invasive Alien Species (EU Regulation no. 1143/2014).

Existing literature extensively documents the negative impacts of invasive species on biodiversity. However, studies on their effects on ecosystem services are fragmented, focusing on specific species or limited areas, hindering large-scale generalizations. Global assessments reveal that invasive species significantly affect ecosystem services, but lack comprehensive spatial analyses at continental scales. The impact of invasive species on ecosystem services is recognized as a major threat to human well-being and is emphasized in reports like the IPBES Global Assessment Report. This study builds upon previous research highlighting the importance of considering both the direct impacts of invasive species on specific services and their indirect effects through interactions with other ecosystem components.

This study analyzed 94 invasive species from the European List of Invasive Species of Union Concern, including terrestrial and aquatic plants and animals. Data on potential impacts on seven ecosystem services (habitat maintenance, nitrogen retention, soil retention, flood control, crop and timber provision, and outdoor recreation) were derived from existing risk assessments. Current exposure was quantified using species occurrence data from the Global Biodiversity Information Facility (GBIF) and other sources, gridded to a 10 × 10 km resolution. Ecosystem service provision data was obtained from the European Environmental Agency (EEA). Future potential exposure was predicted using species distribution models (SDMs) based on global occurrence data, environmental predictors (climate, elevation, human accessibility), and Bayesian Additive Regression Trees (BART). A nine-category risk matrix was developed by combining three levels of ecosystem service provisioning (low, medium, high) and three levels of invasion favorability (1, 2, 3), allowing for the identification of safe areas, critical areas, and hotspots. Statistical analyses included Welch one-way ANOVA and paired t-tests.

The analysis revealed 269 potential negative impacts of the 94 invasive species on the seven ecosystem services, with outdoor recreation, habitat maintenance, crop provision, and soil and nitrogen retention being most frequently affected. Current exposure to invasive species was higher in areas with low provisioning of regulating and cultural services but significantly higher in areas with high provisioning of crop provision and nitrogen retention. Species distribution models projected a 77% average increase in potential invasion area across Europe, particularly along coastal areas and in the Atlantic and Continental biogeographic regions. The risk assessment identified safe, critical, and hotspot areas. Safe areas, representing high service provision and low invasion potential, were dominant for most services. Critical areas (low service provision, high invasion potential) and hotspots (high service provision, high invasion potential) were much smaller, but disproportionately important for service conservation. Spatial analysis highlighted variations in hotspot and critical areas across different services and biogeographic regions.

The findings highlight a spatial mismatch between the current distribution of invasive species and areas providing high levels of ecosystem services. While many areas with high service provisioning have low invasion suitability, the potential for future expansion is substantial. The study's comprehensive cross-taxonomic and spatial analysis provides a more nuanced understanding of invasive species impacts compared to previous studies. The limitations of relying on existing risk assessments and the complexities of species-service interactions are acknowledged. However, the use of a risk matrix provides a clear framework for prioritizing conservation efforts. The results demonstrate the need for proactive management strategies focused on hotspots and critical areas, ensuring the long-term sustainability of European ecosystem services.

This study offers a comprehensive, spatially explicit assessment of risks posed by invasive species to ecosystem services in Europe. The identification of hotspots and critical areas provides a valuable tool for targeted management and conservation efforts. Future research should focus on refining impact assessments, incorporating climate change projections, and examining the cumulative effects of multiple invasive species. The framework used here is applicable to other regions and species, contributing to global efforts to protect biodiversity and ecosystem services.

The study's reliance on existing risk assessments may not fully capture the complexities of invasive species impacts and the context-dependent nature of these effects. The accuracy of species distribution models is subject to uncertainties related to data availability, model assumptions, and future environmental changes. The use of categorical classifications for ecosystem service provisioning and invasion favorability introduces some level of simplification and potential loss of nuance. Future research should address these limitations.