Rethinking standard biodiversity offset calculations: Combining standard offset metrics with more ecologically relevant measures to improve biodiversity persistence

Abstract

Biodiversity offsetting has been increasingly used around the world to compensate for the rising environmental impacts caused by development[1]. There is considerable scepticism about the effectiveness of offsets to achieve ‘no net loss’, particularly due to the lack of consistent metrics for measuring biodiversity losses and gains[1]. Current habitat based metrics often fail to capture biodiversity values at development sites [2], resulting in offsets which rarely compensate effectively for what is lost. Here we aim to understand how commonly used offset metrics differ from the larger pool of biodiversity metrics in science, and to identify options for improvement.

We reviewed 259 publications within the fields of offsetting, conservation planning and ecology. The offsetting literature was, as predicted, dominated by habitat and area based metrics. However, within the offset research, those focused on the outcomes of offsets tended to employ more explicit metrics of population ecology and biodiversity. These metrics were also prevalent in the conservation planning and ecology literature. The discrepancy between the metrics used to calculate and assess offsets reveals a clear mismatch in the way biodiversity is represented in current offset practices and in conservation/ecology research[3]. This raises the question of whether simple area and habitat based metrics can truly capture aspects relevant to preventing biodiversity loss. Our literature review highlighted several relatively simple metrics, such as estimated abundance and diversity, that could potentially be incorporated into offset calculations to improve their ecological relevance.

We conclude that the performance of offset metrics should be more systematically tested, as accurately measuring losses and gains is essential to maximising biodiversity persistence and facilitating progress toward sustainable development practices.

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