England's statutory biodiversity metric enhances plant, but not bird nor butterfly, biodiversity

• Published in: The Journal of applied ecology 2024-08, Vol.61 (8), p.1918-1931
• Main Authors: Marshall, Cicely A. M., Wade, Kristian, Kendall, Isla S., Porcher, Hannah, Poffley, Jakob, Bladon, Andrew J., Dicks, Lynn V., Treweek, Jo
• Format: Article
• Language: English
• Subjects: Biodiversity; Biodiversity loss; biodiversity net gain; biodiversity offset; Birds; ecological impact assessment; Environment Act; Flowers & plants; Habitats; nature recovery; no net loss; Offsets; Planning permission; Plant species; Plants; Policies; Population decline; restoration; Species richness; Statistical models; statutory biodiversity metric; Threatened species; Wildlife conservation
• ISSN: 0021-8901; 1365-2664
• DOI: 10.1111/1365-2664.14697

Biodiversity net gain is a policy focus worldwide, acknowledging ongoing losses of biodiversity to development, and a commitment to offsetting any residual impacts on biodiversity elsewhere. At least 37 countries have mandatory offsetting policies, and a further 64 countries enable voluntary offsets. Offsets rely on credible and evidence‐based methods to quantify biodiversity losses and gains. Following the introduction of the United Kingdom's Environment Act in November 2021, all new developments requiring planning permission in England must demonstrate a biodiversity net gain of at least 10% biodiversity net gain from 2024, calculated using a statutory biodiversity metric framework. The metric uses habitat as a proxy for biodiversity, scoring habitats' intrinsic distinctiveness and current condition. We carried out a study of the metric's performance across England in terms of outcomes for biodiversity. We used generalized linear mixed models to regress baseline biodiversity units against five long‐established single‐attribute proxies for biodiversity (species richness, individual abundance, number of threatened species, mean species range and mean species range/population change). Data were gathered for species belonging to three commonly used indicator taxa (vascular plants, butterflies and birds) from 24 sites, including all terrestrial broad habitats except urban. In baseline assessments, metric‐derived biodiversity units correlated with most plant biodiversity variables, but not with any of the bird or butterfly biodiversity variables used in this study. Plant species recorded in habitats with higher baseline biodiversity units had slightly more restricted ranges (slope −16.22 ± 1.52, p