Does ecological offsetting really allow to achieve no net loss of biodiversity?

Since 2016, the mitigation hierarchy in France, which requires projects with impacts on biodiversity to avoid, reduce and then offset these impacts, aims for no net loss of biodiversity. The offset measures taken in this framework must generate sufficient ecological gains, which implies that they are carried out on sites in bad ecological condition. In this article, we study the ecological context in which 1 153 offset measures were carried out between 2017 and 2021 in metropolitan France. To this end, using data on the "potential wilderness of metropolitan France", we compare the biophysical integrity scores of the selected sites on the one hand and the ecological quality scores, including an index of landscape connectivity around the sites, on the other hand, in relation to national scores. Our results show that 64% of the surface area of the offset sites is located in areas where the biophysical integrity score is higher than the French median, and that 40% is located in areas where it is higher than the last quartile. On the other hand, the majority of offset sites are located in landscapes with a lower ecological quality. These results suggest that the strategy for locating offset measures is not primarily aimed at generating a significant ecological gain, but probably responds to other economic and land constraints that prevail over the ambition of the ecological actions taken. They therefore raise questions about the effectiveness of offsets in achieving no net loss of biodiversity.Keywords: territorial planning, biodiversity, anthropogenic impact.