Challenges to developing mitigation hierarchy policy: findings from a nationwide database analysis in France

While the mitigation hierarchy, which is designed to achieve no net loss of biodiversity, is being adopted in many countries, comprehensive evidence of its effectiveness at a national scale is lacking. Only a few major development projects covering specific natural habitats or a limited geographical scale are used as illustrative cases. There is a critical need for nationwide, up-to-date datasets to assess the scope of the implementation of mitigation hierarchy. In this study, we used a national database consisting of 2588 development projects to assess how this policy is implemented in France. We found that the objective of no net loss is primarily targeted through reduction measures implemented during the construction phase of development projects or through compensation measures, and that both of these are mainly based on technical solutions rather than geographical or temporals solutions. When offsets are required, these tend to be dispersed over many small sites and are mainly implemented in agricultural and natural areas, including areas of high ecological interest (similar to 50%). These results suggest that ecological and financial additionality to other environmental policies may not be achieved. The findings also highlight significant differences in the treatment of small and large development projects, reflecting that the extent of this policy is uneven. These results demonstrate the importance of the availability of national data in providing an overall vision of the implementation of the hierarchy. However, a precise definition of stakeholders' roles and responsibilities is imperative to ensure information is entered into the database effectively and to allow the long-term monitoring of the achievement of no net loss at a national scale.