Assessing ecological equivalence in biodiversity offset schemes: Key issues and solutions

Habitat loss through development is one of the major causes of biodiversity loss. The increasingly common legal requirement to first avoid, then reduce and, if necessary, offset impacts of plans and projects on biodiversity has however not always been appropriately enforced. The blame lies mainly in bad governance such as patchy monitoring or poorly defined liabilities. Biodiversity offsets also suffer from the lack of formal methods for designing and sizing offset requirements. We address this gap by reviewing different tools, methods and guidelines that have been developed in different regulatory contexts. We then formulate a typology of approaches that variously combine these methods and guidelines. We discuss how these relate to the objectives of offset policies and the components of biodiversity and ecosystems to which they apply. Together, these perspectives should contribute to improving existing methods (e.g. by incorporating time-related issues) and our typology should support the development of offset policies.

► Biodiversity offsets require formal methods for assessing ecological equivalence. ► Methods must compare losses and gains for each impacted biodiversity components. ► Existing methods rely on circumstantial reasoning or standardized scoring. ► Setting ratios of acceptable loss is an alternative when gains are not realistic.