Categories of flexibility in biodiversity offsetting, and their implications for conservation

Abstract

Biodiversity offsets ('offsets') are an increasingly widespread conservation tool. Often, offset policies have a like-for-like requirement, whereby permitted biodiversity losses must be offset by gains in similar ecosystem components. It has been suggested that some flexibility might improve offset outcomes - such as out-of-kind offsets, which channel compensation towards priority species. But there has been little formal exploration of other types of flexibility, and the possible ecological consequences.Building upon an existing framework for analysing conservation interventions, we first categorise the types of flexibility relevant to offsetting. We then explore ecological outcomes under two types of flexibility in offsetting, using a model which tracks biodiversity value (via the surrogate of 'habitat condition' × area) over time for multiple vegetation communities. We simulate offset policies that are flexible in time (i.e., offsets implemented before or after development) and flexible in type (i.e., losses in one habitat compensated for by gains in another).Our categorisation of flexibility identifies categories previously not explicitly considered during offset policy development. The simulation model showed that offsets that were flexible in time resulted in biodiversity declines happening sooner or later than they would otherwise - important, as conservation priorities change with time. Incorporating flexibility in type resulted in significantly different outcomes in value for each vegetation community modelled, including some counter-intuitive results.We emphasize the importance of considering the full spectrum of flexibility in biodiversity offsets during policy development. As offset policies become increasingly prevalent, insufficient consideration of the consequences of flexibility could lead to undesirable biodiversity outcomes.