Exploring the ecological outcomes of mandatory biodiversity net gain using evidence from early‐adopter jurisdictions in England

Abstract Net outcome‐type biodiversity policies are proliferating globally as perceived mechanisms to reconcile economic development and conservation objectives. The UK government's Environment Bill will mandate that most new developments in England demonstrate that they deliver a biodiversity net gain (BNG) to receive planning permission, representing the most wide‐ranging net outcome type policy globally. However, as with many nascent net‐outcome policies, the likely outcomes of mandatory BNG have not been explored empirically. We assemble all BNG assessments (accounting for ∼6% of England's annual housebuilding and other infrastructure) submitted from January 2020 to February 2021 in six early‐adopter councils who are implementing mandatory no net loss or BNG requirements in advance of the national adoption of mandatory BNG, and analyze the aggregate habitat changes proposed. Our sample is associated with a 34% reduction in the area of nonurban habitats, generally compensated by commitments to deliver smaller areas of higher quality habitat years later in the development project cycle. Ninety‐five percent of biodiversity units delivered in our sample come from habitats within or directly‐adjacent to the development footprint managed by the developers. However, we find that these gains fall within a governance gap whereby they risk being unenforceable, a challenge that is shared with other net outcome type policies implemented internationally.