Comparing biodiversity offset calculation methods with a case study in Uzbekistan

Biodiversity offsets are interventions that compensate for ecological losses caused by economic development, seeking 'no net loss' (NNL) of biodiversity overall. Calculating the ecological gains required to achieve NNL is non-trivial, with various methodologies available. To date, there has been no comparison among methodologies for a common case study. We use data on industrial impacts in Uzbekistan to provide such a comparison. We quantify losses from 40 years of gas extraction, using empirical data on vegetation impacts alongside estimates of disruption to mammals. In doing so, we implement a novel technique by estimating spatial 'functional forms' of disturbance to calculate biodiversity impacts. We then use a range of offset methodologies to calculate the gains required to achieve NNL. This allows a crude comparison of the potential biodiversity outcomes of in kind offsets (here, vegetation restoration) with out of kind offsets (protecting fauna from poaching). We demonstrate that different methods for calculating the required offset activities result in divergent outcomes for biodiversity (expressed in habitat condition x area, or 'weighted area'), and different trajectories in biodiversity outcomes over time. An Australian method is currently being considered for adoption in Uzbekistan, but we show that it would require careful adjustments to achieve NNL there. These findings highlight that the method used to quantify losses and gains strongly influences the biodiversity outcomes of offsetting, implying that offsets generated using different methodologies are not transferable between jurisdictions. Further, conservation gains from out of kind offsets may outweigh those from strict in kind NNL interpretations. (C) 2014 The Authors. Published by Elsevier Ltd.