Nature by numbers: an evaluation of how DEFRA’s Biodiversity Metric 3.0 can or cannot capture rewilding outcomes

Sammanfattning

The United Kingdom’s response to the pressing biodiversity decline in England includes the Biodiversity Net Gain (BNG) policy and is operationalised through DEFRA’s Biodiversity Metric, which quantifies biodiversity into ‘biodiversity units’. This thesis evaluates how effectively the metric reflects real biodiversity outcomes at the rewilded Knepp Estate in West Sussex. Using 2005 as a baseline and 2025 as the reference year, this study combines metric calculations for the Southern Block with aerial imagery, ecological surveys and selected species data. The findings illustrate that even though the metric 3.0 records substantial amounts of habitat-based biodiversity improvements at the Southern Block, these gains do not include any observed fluctuations in species richness or abundance, nor does it include functional diversity of the landscape. The thesis concludes that the BNG policy implementation at rewilding sites like Knepp requires complementary qualitative and quantitative indicators in order to accurately reflect biodiversity, as well as strengthened governance arrangements to support genuine and transformative biodiversity recovery in England.