Summary

Biodiversity Net Gain (BNG) aims to ensure that developments leave the environment in a measurably improved state. However, significant flaws in both the BNG policy and the UK Habitat Classification System (UKHAB) undermine this objective. These issues include the destruction of high-value habitats, misclassification of habitat values, time lags between habitat loss and gains, challenges in implementation and monitoring, and the neglect of subterranean biodiversity. Addressing these flaws is essential to prevent further biodiversity loss and to ensure that development projects contribute positively to the UK's ecological health.

Key Issues

Destruction of High-Value Habitats

BNG allows developers to remove ecologically rich sites if they provide offsets elsewhere. Crucially, there is no requirement for developers to demonstrate that all other options have been exhausted, such as developing in alternative locations. This practice often leads to net biodiversity losses, as newly created habitats may not replicate the ecological functions of those destroyed. For instance, the HS2 railway project permitted the destruction of ancient woodlands, which are considered irreplaceable due to their unique ecological value. While HS2 claims to compensate for the loss of 20.6 ha of ancient woodland with 64.1 ha of new woodland, this does not constitute an ecological gain. The newly created woodland will take upwards of 400 years to approach the biodiversity, structural complexity, and ecological resilience of the ancient woodland it replaces, if it ever does. Meanwhile, specialist species dependent on ancient woodland habitats face local extinction, and vital ecosystem services are lost.

Misclassification of Habitat Value in UKHAB

The UKHAB system classifies habitats based on physical structure rather than ecological function, leading to several issues:

• Inaccurate Representation of Biodiversity: For example, a species-rich wildflower meadow could be classified the same as an intensively managed, low-diversity pasture, resulting in misleading assessments.

• Overlooking Time-Lag Effects: Newly created habitats are often classified the same as mature ones, despite taking decades, or even centuries, to develop comparable biodiversity. For example, a newly planted woodland is not equivalent to a mature, species-rich woodland.

• Ignoring Habitat Quality Variations: Degraded and thriving wetlands might be categorized identically, allowing developers to overestimate biodiversity gains and making projects appear more sustainable than they are.

Time Lag Between Habitat Loss and Gains

Many ecosystems require decades or even centuries to mature. Granting immediate BNG credits for newly created habitats ignores this reality, resulting in a temporal mismatch where biodiversity losses occur now, but compensatory gains, if they materialize, happen far in the future.

Neglect of Subterranean Biodiversity

Current BNG policies fail to account for biodiversity loss in excavated or compacted soils during development. Soil ecosystems host a vast array of species, estimated at 59% of all living species, including ground-nesting bees, earthworms, soil beetles, fungi, and microbial communities, which play vital roles in ecosystem function. Development often leads to irreversible loss of subterranean biodiversity due to lack of assessment and translocation efforts. Without explicit measures to quantify and mitigate these losses, BNG risks underestimating true biodiversity impacts.

Challenges in Implementation and Monitoring

Research indicates that BNG is often used to justify development rather than prevent biodiversity loss. A study by Wildlife and Countryside Link found that only about 609 hectares of off-site land and 93 hectares of on-site land have been reported by local authorities under the BNG scheme, representing less than 13% of the amount DEFRA estimated would be generated annually. Additionally, a lack of independent monitoring means many biodiversity promises remain unfulfilled.

Policy Recommendations

Implement Time-Weighted Biodiversity Accounting

• Apply a strong time penalty for destroying mature habitats to account for their slow recovery rates.

• Prevent immediate BNG credits for newly created habitats until they have demonstrated equivalent ecological function.

Strengthen Avoidance Measures

• Require developers to prove that habitat loss is absolutely necessary before considering offsets.

• Expand legal protections for irreplaceable habitats to prevent their destruction.

Revise the UKHAB System

• Introduce functional ecological assessments that consider species richness, ecosystem functions, and habitat connectivity.

• Account for time-lag effects by differentiating between newly created and mature habitats.

• Ensure that habitat classifications reflect variations in habitat quality to provide a more accurate assessment of ecological value.

Incorporate Subterranean Biodiversity Assessments

• Require surveys of excavated soils to quantify subterranean biodiversity loss, including earthworms, soil arthropods, fungi, and microbial communities.

• Implement translocation programs where possible to mitigate biodiversity loss.

• Establish long-term monitoring of soil health and subterranean species recovery in development sites.

Enhance Independent Long-Term Monitoring

• Implement third-party verification for all BNG offset sites to ensure accountability.

• Enforce long-term (30+ years) biodiversity tracking with penalties for failure to deliver real gains.

Call to Action

The UK Government must act promptly to address these critical flaws in BNG and UKHAB. We urge DEFRA, conservation organizations, and planning authorities to:

• Revise the UKHAB Classification System: Ensure it accurately reflects ecological value, considering factors such as species richness, habitat quality, and time-lag effects.

• Strengthen Habitat Protections and Avoidance Measures: Implement robust measures to protect high-value and irreplaceable habitats from destruction.

• Ensure Accountability: Establish independent monitoring and legally binding biodiversity targets to hold developers accountable for delivering genuine biodiversity gains.

• Integrate Subterranean Biodiversity Assessments: Recognize and mitigate biodiversity loss in soils during development to prevent long-term ecological degradation.

Without these reforms, BNG risks becoming a tool for greenwashing development rather than a driver of biodiversity recovery. It is imperative to act now to safeguard the UK's natural heritage for future generations.

Next Steps

This policy report aims to inform stakeholders about the critical flaws in the current BNG and UKHAB systems and to advocate for necessary reforms. We recommend disseminating this report to policymakers, environmental organizations, and planning authorities to initiate discussions and prompt action towards improving biodiversity conservation in the UK.