Compensating for lost nature values through biodiversity offsetting – Where is the evidence?. (May 2021) - Josefsson, Jonas
Abstract: Biodiversity offsetting is becoming a principal instrument for managing biodiversity and ecosystem services in society. Still, it is unclear whether biodiversity offsetting can fully mitigate losses to natural values. When reviewing published studies on offsetting, we found only 40 evaluations with primary outcome data on biodiversity or ecosystem services. Among these, we found no evidence that biodiversity gains from offsets actually compensate for development-associated losses, because losses were never estimated. The failure to quantify losses is troubling from a conservation perspective, as applying offsets that do not match up losses and gains will result in continued net loss of biodiversity. Instead, most studies (76%) included only reference habitats as comparator and evaluated singular taxa of biodiversity (66%), and rarely ecosystem services (ES). The overall meta-analysed effect size from reference habitat comparisons suggests that offsets perform poorly when contrasted to these habitats. There was a strong bias towards North American freshwater biomes, with only six published evaluations from terrestrial habitats. The bias and small number of studies precluded any detailed meta-analytical enquiries, such as identification of main drivers of outcomes. For biodiversity offsetting to be an important instrument for halting biodiversity losses, all actions must build on solid scientific evidence, and our review show that this evidence base is yet not in place. We conclude that there is a strong need for rigorous evaluation of offsetting projects, and to this end governments could request long-term monitoring programmes as an integral part of offsetting actions and make data openly available for assessment. Highlights: Biodiversity offsetting evaluations fail to quantify development-associated biodiversity losses Evidence is biased towards North American freshwater biomes Offsets perform poorly when contrasted to reference habitats There is a strong need for rigorous evaluation of offsetting projects