A disaggregated biodiversity offset accounting model to improve estimation of ecological equivalency and no net loss

Biodiversity offsetting is a mechanism aimed at achieving biodiversity gains to compensate for the residual impacts of development activities on biodiversity. Estimating the ecological equivalence of biodiversity lost to development with that gained by the offset requires a currency that captures the biota of interest and an accounting model to evaluate the exchange. Ecologically robust, and user-friendly decision support tools improve the transparency of biodiversity offsetting and assist in the decision making process. Here we describe a tool developed for the New Zealand Department of Conservation that offers a mechanism to transparently design and evaluate biodiversity offsets intended to deliver no net loss. It is a relatively disaggregated accounting model that balances like-for-like biodiversity trades using a suite of area by condition currencies to calculate net present biodiversity value (NPBV) to account individually for each measured biodiversity element of interest. The NPBV is used to evaluate whether a no net loss exchange is likely for each biodiversity attribute. More disaggregated currencies have an advantage over aggregated currencies (which use composite metrics) in that they account for each itemised biodiversity element of concern. The Disaggregated Model we present can be used to account for a variety of biodiversity types in an offset exchange, and for different scales and complexities of development and impacts within both statutory and voluntary frameworks