Biodiversity accounting on farms: Relating diversity of bird assemblages to ecosystem condition.

Natural capital accounting can help farmers and producers meet global demands to disclose supply chain impacts on biodiversity and to reverse biodiversity declines in farmland. To date, methods have been limited in their ability to reliably represent biodiversity, especially fauna, and are typically prepared at the regional scale, not at the farm scale - the scale at which many decisions that impact habitats for species are made. We surveyed birds at 1155 sites across 50 farms (total area = 135,890 ha) in south-eastern Australia to relate site-level species richness of groups of birds to spatially discrete ecosystem condition states that are based on the structure and composition of vegetation and to develop a framework for farm-scale biodiversity accounting. Site-level species richness of bird groups was strongly related to ecosystem states. Spatially explicit models enabled calculation of the proportion of a farm that provides high-quality habitat for each bird group. This metric represents farm-level diversity and can be used to quantify a farm's impact on biodiversity and contribution to biodiversity conservation. This approach could be applied to agriculture regions within Australia and could be replicated in agricultural landscapes around the world where it is possible to establish applicable state and transition models with a reliable 'best-on-offer' or 'reference' condition state. Farm-scale accounts that incorporate biodiversity provide a robust tool for strategic farm management, rigorous environmental reporting, greater traceability through supply chains, and improved access to global sustainability markets.