Wolf-Christian Saul’s research while affiliated with Freie Universität Berlin and other places

Due to releases and escapes from fur farms since the 1930s, raccoons (Procyon lotor) are forming growing populations in Germany, with im- pacts on humans and nature. In this setting, raccoons are perceived very differently among stakeholders as invasive or charismatic. To capture perspectives on impacts of and management options for raccoons from different societal sectors, we (i) analysed newspaper articles from 2010 to 2021, (ii) conducted semi-structured interviews with experts from urban areas in the federal states of Bavaria, Berlin, Hesse and Saxony, representing the five sectors consultancy, hunting, nature conservation, animal welfare and administration, and (iii) performed an online survey. The newspaper analysis showed that more negative press reports appear in states with a larger hunting bag and a higher hunting bag density, which served as indicators for the size or density, respectively, of the raccoon population. The interviews revealed that a wider range of raccoon impacts and management measures are known in states with high raccoon population. In Hesse and Berlin, particular emphasis is placed on coexistence strategies such as prevention of house entry, while in Bavaria the focus is primarily on hunting. Finally, interviews and online survey suggest large differences among the five sectors in terms of their assessment of impacts and management measures.

Future dynamics of biological invasions are highly uncertain because they depend on multiple social–ecological drivers. We used a scenario‐based approach to explore potential management options for invasive species in Europe. During two workshops involving a multidisciplinary team of experts, we developed a management strategy arranged into 19 goals relating to policy, research, public awareness, and biosecurity. We conceived solutions for achieving these goals under different plausible future scenarios, and identified four interrelated recommendations around which any long‐term strategy for managing invasive species can be structured: (1) a European biosecurity regime, (2) a dedicated communication strategy, (3) data standardization and management tools, and (4) a monitoring and assessment system. Finally, we assessed the feasibility of the management strategy and found substantial differences among scenarios. Collectively, our results indicate that it is time for a new strategy for managing biological invasions in Europe, one that is based on a more integrative approach across socioeconomic sectors and countries.

Invasive alien species are one of the major threats to global biodiversity, ecosystem integrity, nature's contributions to people and human health. While scenarios about potential future developments have been available for other global change drivers for quite some time, we largely lack an understanding of how biological invasions might unfold in the future across spatial scales. Based on previous work on global invasion scenarios, we developed a workflow to downscale global scenarios to a regional and policy‐relevant context. We applied this workflow at the European scale to create four European scenarios of biological invasions until 2050 that consider different environmental, socio‐economic and socio‐cultural trajectories, namely the European Alien Species Narratives (Eur‐ASNs). We compared the Eur‐ASNs with their previously published global counterparts (Global‐ASNs), assessing changes in 26 scenario variables. This assessment showed a high consistency between global and European scenarios in the logic and assumptions of the scenario variables. However, several discrepancies in scenario variable trends were detected that could be attributed to scale differences. This suggests that the workflow is able to capture scale‐dependent differences across scenarios. We also compared the Global‐ and Eur‐ASNs with the widely used Global and European Shared Socioeconomic Pathways (SSPs), a set of scenarios developed in the context of climate change to capture different future socio‐economic trends. Our comparison showed considerable divergences in the scenario space occupied by the different scenarios, with overall larger differences between the ASNs and SSPs than across scales (global vs. European) within the scenario initiatives. Given the differences between the ASNs and SSPs, it seems that the SSPs do not adequately capture the scenario space relevant to understanding the complex future of biological invasions. This underlines the importance of developing independent but complementary scenarios focussed on biological invasions. The downscaling workflow we implemented and presented here provides a tool to develop such scenarios across different regions and contexts. This is a major step towards an improved understanding of all major drivers of global change, including biological invasions. Read the free Plain Language Summary for this article on the Journal blog.

1. Invasive alien species are one of the major threats to global biodiversity, ecosystem integrity, natures contribution to people and human health. While scenarios about potential future developments have been available for other global change drivers for quite some time, we largely lack an understanding of how biological invasions might unfold in the future across spatial scales. 2. Based on previous work on global invasion scenarios, we developed a workflow to downscale global scenarios to a regional and policy-relevant context. We applied this workflow at the European scale to create four European scenarios of biological invasions until 2050 that consider different environmental, socio-economic and socio-cultural trajectories, namely the European Alien Species Narratives (Eur-ASNs). 3. We compared the Eur-ASNs with their previously published global counterparts (Global-ASNs), assessing changes in 26 scenario variables. This assessment showed a high consistency between global and European scenarios in the logic and assumptions of the scenario variables. However, several discrepancies in scenario variable trends were detected that could be attributed to scale differences. This suggests that the workflow is able to capture scale-dependent differences across scenarios. 4. We also compared the Global- and Eur-ASNs with the widely used Global and European Shared Socioeconomic Pathways (SSPs), a set of scenarios developed in the context of climate change to capture different future socio-economic trends. Our comparison showed considerable divergences in the scenario space occupied by the different scenarios, with overall larger differences between the ASNs and SSPs than across scales (global vs. European) within the scenario initiatives. 5. Given the differences between the ASNs and SSPs, it seems that the SSPs do not adequately capture the scenario space relevant to understanding the complex future of biological invasions. This underlines the importance of developing independent, but complementary, scenarios focused on biological invasions. The downscaling workflow we presented and implemented here provides a tool to develop such scenarios across different regions and contexts. This is a major step towards an improved understanding of all major drivers of global change including biological invasions.

Future dynamics of biological invasions are highly uncertain because they depend on multiple environmental, societal and socio-economic drivers. We adopted a qualitative scenario approach to explore the future of invasive alien species (IAS) in Europe and created an overall strategy for their management that considers different plausible future developments. The scenarios and strategy were developed during two online workshops with a multidisciplinary team of experts. First, we downscaled four global scenarios of biological invasions to the European level. Second, we developed a management strategy structured into 19 goals that cover a broad array of IAS-related topics (i.e. policy, research, public awareness and biosecurity), and provided solutions for achieving these goals considering the European scenarios. Third, we identified four interrelated recommendations around which any long-term strategy for managing IAS in Europe can be structured: (i) a European biosecurity regime, (ii) a dedicated communication strategy, (iii) data standardization and management tools, and (iv) a monitoring and assessment system. Finally, we identified the feasibility of the IAS management strategy, finding strong differences among the four scenarios. High levels of technological development, public environmental awareness, and effectiveness of IAS policies facilitated the implementation of the overall management strategy. Together, our results indicate that it is time for a new management of biological invasions in Europe based on a more integrative perspective across sectors and countries to be better prepared for future challenges.

Species introduced through human-related activities beyond their native range, termed alien species, have various impacts worldwide. The IUCN Environmental Impact Classification for Alien Taxa (EICAT) is a global standard to assess negative impacts of alien species on native biodiversity. Alien species can also positively affect biodiversity (for instance, through food and habitat provisioning or dispersal facilitation) but there is currently no standardized and evidence-based system to classify positive impacts. We fill this gap by proposing EICAT+, which uses 5 semiquantitative scenarios to categorize the magnitude of positive impacts, and describes underlying mechanisms. EICAT+ can be applied to all alien taxa at different spatial and organizational scales. The application of EICAT+ expands our understanding of the consequences of biological invasions and can inform conservation decisions.

a.Aim Outline of how the impact of non-native species can be defined and assessed, and how harmful non-native species can be managed across the different stages of the invasion process. b.Main concepts covered Impact as a concept in invasion biology; impact scales, levels and mechanisms; management categories c.Main methods covered EICAT and SEICAT schemes to assess the impacts of non-native species on biodiversity and socio-economics, respectively; framework for the management of non-native species d.Conclusions Efforts are needed to improve communication and understanding of researchers, policy-makers, practitioners and other stakeholders involved in the impact assessment and management of non-native species.

(a)Aim: Provides an overview of biological invasions and the invasion process, specifically: the introduction, establishment and spread of non-native species. (b)Main concepts covered: The invasion process and its consecutive stages; hypotheses about the invasion success of non-native species. (c)Main methods covered: Standardized categorization of introduction pathways; analysis of species introduction dynamics; species distribution models (SDMs). (d)Conclusions: While the establishment and spread of non-native species have been classic research foci in invasion biology, their introduction pathways are now also frequently investigated. More generally, the key role of humans for biological invasions is reflected in the increasingly interdisciplinary nature of the field.