The impact of aquatic alien plants and crayfish control methods on ecosystem services

An increasing number of field managers are engaged in actions aiming at controlling invasive species, notably in aquatic and riparian ecosystems. Though, control actions may influence how ecosystems function and provide services to humans. When faced with the choice of which control method to use, managers and decision makers typically consider the cost, feasibility or effectiveness of methods. More rarely do they consider the impact that the intervention will have on ecosystem functioning and services. This consideration is one of the focal points of the LIFE RIPARIAS project (2021-2027). Ecosystem Services (ES) evaluation typically relies on a matrix relating ES to ecosystem types. We developed a conceptual framework based on adapted ES matrices and ran a comprehensive literature review of the control methods for EU-listed aquatic plants, riparian plants and crayfish. The results of the review were screened by experts and stakeholders in order to select best practices for each species. A one-day workshop was hold with experts and stakeholders to identify the relevant ES in this context, challenge our conceptual framework and prepare an online survey. On the basis of this expert consultation, we evaluated ES evolution for each control method, considered for two different time scales: one year and five years after the intervention. The evaluation was relatively consensual among experts from different countries. The results showed that whatever the species group, the choice of a control method may influence provisioning, regulation and cultural services. When control methods had negative impacts on ecosystem services (notably for aquatic plants), the influence was typically highest after one year. Despite the inherent subjectivity of expert-based assessment, the present study illustrates how a comprehensive ES evaluation can be useful to support managers in selecting most appropriate control options.