Urban growth is a major driver of biodiversity loss, as natural habitats are destroyed or fragmented. To address this, nature-positive initiatives aim to balance development with nature conservation. In the UK, Biodiversity Net Gain (BNG) was introduced through the 2021 Environment Act requiring developers to deliver a minimum 10% biodiversity increase for new developments. Despite BNG's potential, doubts exist about local planning authorities’ (LPAs) ability to implement and enforce BNG effectively, due to resource limitations, inconsistent ecological expertise, and ineffective monitoring. This study examined 44 residential developments across two case studies where biodiversity measures were mandated through prior planning policy and assessed i) how well ecological advice was integrated into planning decisions, and ii) whether biodiversity measures were effectively implemented. The study revealed significant gaps between approved plans and actual implementation. The ecological advice transposed into planning decisions and approved documentation, was biased towards European protected species (EPS) or more charismatic fauna. Additionally, many developments failed to properly implement biodiversity measures, with frequent deviations from approved plans for artificial and semi-natural habitats. Solution: Improved awareness and knowledge of biodiversity, increased LPA resource, better communication between planners, ecologists, and developers, stronger enforcement, and improved monitoring are essential for BNG’s success. Without these actions, BNG may fail to leave the natural environment in a measurably better state.

This study uses two case studies, covering 44 residential developments across six LPAs. Specific details of the planning applications have been withheld to protect anonymity. Case Study 1 covers 35 developments in five LPAs with decisions made (including three refusals) between 2012 and 2016, and informed Stage 1 and Stage 2 of this study. Case Study 2 considers 9 developments in one LPA, permitted between 2012 and 2018 and informed only Stage 2 of this study. All developments were within the 4-year planning aftercare period, but no development specifically required post-development monitoring embedded within the conditions that related to biodiversity (e.g., the submission of a report by a suitably qualified ecologist), nor were any financial securities attached to the delivery of ecological features.

Case study 1: Central England

In Stage 1, 29 residential developments between 2 and 100 dwellings in size, across five LPAs in Central England, whose decision was made after NPPF publication (26^th March 2012), were subject to a review of the extent to which statutory ecological advice was transposed into the planning decision notice, in Stage 2, 19 completed developments were visited and assessed for how well biodiversity measures were implemented.

Stage 1: Review of ecology advice and decision noticeStage 1: Review of ecology advice and decision notice

For each planning application, the decision notice, the ecological advice provided to the case officer, and for additional context, the case officer's report was accessed via the respective planning portal for each LPA. Where any documents were not provided, the planning authority was approached directly. Both the EA and the biodiversity-relevant condition statements within the PDN were categorized according to broad (e.g., landscaping) and specific (e.g., species) categories and counted. A count was made of the number of developments where each category was referred to at least once as, either a recommendation from the EA or as a condition within the PDN. Biodiversity and landscape management plans submitted in the discharge of a condition were further checked for the inclusion of specific measures that may have been recommended. 

Stage 2: Site inspection to assess accordance with approved documentation

Approved documents were obtained for 11 completed developments assessed in Stage 1 plus an additional 8, which contained biodiversity measures within the approved documentation, but EA was not available. ‘Approved documents’ included those within the PDN or those approved for discharge of a planning condition relating to biodiversity, although not always directly, e.g., submitted through landscaping and planting schemes.

Each development was visited between February and March 2016, with wetland or wildflower interventions revisited during June and July. Minor or major deviations were noted (Table 1) within six broad habitat features: hedgerows, trees, wetlands, wildflower grassland, artificial and other. Deviations could also be positive, such as additional bat boxes. Site visibility was variable; averaging 72.3%, min. 37.4%, max. 100% (calculated by dividing plans’ line-of-sight visible area by site area).

Case study 2: Southwest England

Nine residential developments were visited in July 2021, ranging from 9 to 433 dwellings in a single LPA in southwest England, where planning permission was granted after NPPF publication. Each development had some biodiversity measures secured as part of the planning permission, concerning species groups (e.g., artificial measures for EPS), or habitat / habitat features (e.g. trees, grasslands or hedgerows). The approach taken differed from Case Study 1, including a compliance score calculated within each feature (Table 2), as a proportion of the proposed measures that were implemented at either a unit level or species level. This value was then averaged across each development to give an overall non-compliance score.