A global review of horizon scanning exercises for invasive alien species

Résumé fourni par la source

Invasive alien species (IAS) are a major driver of global biodiversity loss, generating substantial ecological, economic and social impacts. Prevention and early intervention are widely recognised as being more cost‑effective than long‑term management. As a result, IAS policy frameworks increasingly rely on predictive strategies and tools to guide prioritisation. Horizon scanning has emerged as a key approach, providing structured, forward‑looking assessments of IAS that are likely to arrive in a new area in the near future, establish invasive populations and cause harm. Despite widespread uptake of the method, there has, to our knowledge, been no global synthesis of how IAS horizon scanning exercises are conducted, how methodologies are developed, and what their potential policy implications are. Here, we present a global review of over 50 IAS horizon scanning exercises undertaken up to 2026, drawing on published and grey literature. We examine how horizon scans were designed across multiple taxonomic groups, geographic scales, regions and environments, evaluate their underlying objectives, such as informing policy and biosecurity, and review their recommendations. Our review shows that the number of horizon scans has been steadily increasing in recent years. Across the horizon scanning literature, terrestrial and freshwater environments were more frequently represented than marine systems, and exercises more often covered a range of taxonomic groups (including plants and animals) rather than focusing on a single group (e.g. invertebrates) alone. Furthermore, the majority of horizon scanning exercises to date have been undertaken in Europe, predominantly at a country level, although transnational- and regional‑level exercises have also been conducted. Impacts on native biodiversity were the dominant focus, although consideration of economic and human health impacts have been increasing in recent studies. Horizon scanning outputs are most often intended to inform biosecurity planning and policy implementation, including the prioritisation of species for further risk assessment and risk management. Most exercises follow a broadly consistent workflow: compilation of large species longlists; application of exclusion criteria to focus further effort and review; structured scoring of likelihood of arrival, establishment, spread and impact; and the application of consensus‑based prioritisation through expert elicitation and moderated group discussions. However, we identified variation in how species lists are compiled/generated, how climate or habitat suitability is assessed, which risk‑scoring frameworks are applied, and whether management feasibility or socio‑economic considerations are formally incorporated. Many studies report uncertainty associated with scoring the likelihood of arrival, establishment, and impact, particularly for understudied taxonomic groups and emerging pathways. Recurring challenges include inconsistent reporting of methods and assumptions, and limited evaluation of whether identified species inform regulatory or other action. We highlight the value of horizon scans for the effective prevention of IAS and discuss how greater standardisation of reporting and systematic evaluation could strengthen the policy impact, e.g. by facilitating the transfer of outcomes between ecologically similar regions and allowing for the upscaling of local results to larger geographic scales. Similarly, as horizon scanning practice expands, this might allow the integration of big data analytics and machine learning methods to identify emerging patterns, pathways, and taxonomic or functional trends associated with invasion risk. This could facilitate more data-driven, automated and rapid screening processes, improving the scalability and consistency of assessments, and strengthening proactive decision-making.

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