Integrating species metrics into biodiversity offsetting calculations to improve long-term persistence.
Several methods of measuring biodiversity in development-offset trades exist. However, there is little consensus on which biodiversity metrics should be used for quantifying development impacts and assigning offsets. We simulated development impacts in a virtual landscape and offset these impacts using six biodiversity metrics: vegetation area, vegetation condition, habitat suitability, species abundance, metapopulation connectivity and rarity-weighted richness. We tested long-term impacts of metric choice during offsetting by combining simulated landscapes with population viability analyses. No net loss or net gains in habitat were achieved using all metrics except vegetation area and condition. Limited habitat and like-for-like requirements resulted in offsets exhausting available habitat in each vegetation class before offset requirements were met when using vegetation-based metrics. We also found that impact avoidance was an important driver in how much compensation offsets could deliver. When impacts avoided high-suitability habitats, all six metrics achieved no net loss or net gains for most species. However, when core habitats were developed, none of the metrics were able to consistently prevent population declines. Synthesis and application. When impacts on high-quality habitat were avoided, and assuming the protection and restoration benefits can occur in practice, vegetation-based metrics may produce offsets which deliver gains in species abundance equivalent to species-specific metrics. However, species-specific metrics outperformed vegetation-based metrics when core habitats were lost. Applying avoidance measures as a first step to minimise biodiversity impacts during development will significantly improve offset outcomes for species and result in greater long-term population benefits delivered through offsetting.