Calculation of biodiversity level between different land-uses to improve conservation outcomes of biodiversity offsetting

The goal of the mitigation hierarchy is to counteract the losses of biodiversity due to development projects by avoiding, reducing and as a last resort, by offsetting these losses. However, the implementation of offset measures is currently very unsatisfactory from a biodiversity perspective, and many development projects do not incorporate them. Here, we proposed a method for comparing biodiversity level between different land-uses to propose a set of alternative offset measures offering the same biodiversity outcomes. Biodiversity level (including both bird and bat communities) was calculated from the variation in biodiversity from each land-uses (fallow, grass strip, bush, grass strip with bushes, hedgerow) compared to crops (control). In order to account for local specificities of environmental assessment studies, we modulated the calculation of the biodiversity level following three examples of scenarios that differed according to the weights assigned to different species. For each scenario, hedgerow was always the land-use that generated the greatest biodiversity level, and was found to be the best alternative in terms of effect size. The advantage of this method and its weighting system is that the opinions of local stakeholders and specificities of species, such as their sensibility level to the development project or their conservation status, can be taken into account, resulting in the results being better appropriated. Thus, offset measures could be implemented more efficiently thanks to multi-taxonomic calculations and weighing possibilities, improving biodiversity outcomes. This method can also be used to compare the residual loss of biodiversity and biodiversity gains from implemented offset measures, using the same biodiversity metric.