Draft:Biodiversity Net Gain

Biodiversity Net Gain is England's domestic ecological compensation policy, due to first be implemented nationally in January 2024, designed to compensate for the ecological harms caused by new developments. . Biodiversity Net Gain is implemented through a modification to the Town and Country Planning Act, requiring that new developments demonstrate their intention to leave biodiversity better off after the proposed development than beforehand. Biodiversity under Biodiversity Net Gain is measured using a standardised Biodiversity Metric, designed by Natural England and Defra in consultation with relevant stakeholders and industry. Whilst Biodiveristy Net Gain is frequently thought of as a biodiversity offsetting policy, in practice offsetting represents a small proportion of the biodiversity enhancements delivered through the policy, with the majority of biodiversity enhancements coming through habitat managmeent activities implemented within the boundaries of the new developments themselves.

Biodiversity Net Gain in practice
In England, developers must show that their proposals result in a positive impact on biodiversity, using a government-defined metric, in order to obtain planning approval from local planning authorities. Assessments for Biodiversity Net Gain are conventionally integrated into the Ecological Impact Assessment (EcIA) process. This involves utilizing data gathered from pre-development ecological surveys, which is then processed through an Excel-based tool (the Statutory Biodiversity Metric), to give a measure of the ecological value of a site in 'biodiversity units'.

In order for development proponents to secure planning permission, the Biodiversity Metric needs to demonstrate that biodiversity will increase by at least 10% after development relative to the pre-development scenario. Failure to meet this criterion obligates the developer to adjust their project plan, or compensate for the shortfall in biodiversity units through the purchase of biodiversity offsets, which are delivered either through a payment to the council or a third party, such as a broker managing a habitat bank. If no compensation sites are available within the local planning authority where the development is planned, compensation is permitted in other local authorities, triggering an increase in compensatory units required due to a spatial multiplier within the Metric. As a final option, developers can purchase 'statutory biodiversity credits' from the national government.

The Biodiversity Metric
The Metric is a habitat-based proxy for biodiversity combining various factors such as area, habitat condition, distinctiveness, and multiple parameters (like risk, the time required for habitat development, and the ecological significance of the site on a landscape scale) for each habitat section within the development area. It generates an overall biodiversity score, measured in biodiversity units. Data necessary from the project site encompass both quantitative information (like the area of each habitat patch pre and post development) and qualitative assessments made by ecological experts regarding habitat condition and classification. Additionally, it includes landscape-scale data, such as whether the site falls within an area of significant biodiversity importance such as the Local Nature Recovery Network.

This Metric computes the baseline biodiversity units within the development area and any associated compensation areas owned or managed by the developer. It then compares these with anticipated biodiversity units after development. The Metric includes trading rules that constrain the kinds of ecological trades permitted as a result of the development. For example, if a developer damages a 'high distinctiveness' habitat, then they are required to compensate with a habitat of the same type, rather than trading it for a less ecologically-valuable habitat.

Scientific evidence
The preliminary scientific evidence on the ecological outcomes of Biodiversity Net Gain suggests the policy facilitates the trade of habitat losses from construction for smaller, but more ecologically valuable habitats to be delivered in the future. There are concerns that the governance (monitoring and evaluation) of the biodiversity benefits delivered through the poicy is insufficient to ensure these future biodiversity outcomes are effectively secured. Additionally, there are concerns that the Biodiversity Metric may not be an effective proxy for biodiversity, and therefore that a net gain in biodiversity demonstrated by the metric may not translate into real-world improvements in biodiversity such as wildlife populations