Biodiversity Net Gain (BNG) in principle is about developments leaving biodiversity in a better state than it was before by creating and improving natural habitats. BNG makes sure developments have a measurably positive impact on biodiversity, compared to what was there before development. BNG is founded on the appropriate application of the mitigation hierarchy – avoidance, mitigation, compensation, and enhancement.
In England, BNG will become mandatory on 12th February 2024 under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act 2021), meaning planning applications must deliver a minimum of a measurable 10% net gain in biodiversity, in order to validate their application.
Under the current legislation, BNG has four distinct ‘rules’:
The Trading Rules is satisfied.
The minimum of a 10% net gain for each unit type is distinct.
The Biodiversity Metric Calculation Tool must be used.
In exceptional ecological circumstances, deviation may be permitted.
The word ‘must’ is used frequently in the current legislation, which highlights there is a legal requirement. There are also nine ‘Principals’ of BNG, which do not have a legal basis; however, there is still a requirement to have regard to the user guide, so the methodology should still be followed.
The trading rules set minimum habitat creation and enhancement requirements to compensate for specific habitat losses, up to the point of no net loss. They are based on the habitat type and distinctiveness of the lost habitat. Habitats proposed must be like-for-like or better. Trading down must be avoided, where possible. Ideally, new, or restored habitats should aim to achieve a higher distinctiveness and habitat type, and the same condition or better. Baseline habitats onsite that are proposed to be replaced by either habitats of lower distinctiveness or a habitat which is not like-for-like, is calculated as trading down by the Biodiversity Metric.
There must be a minimum of a 10% net gain in each habitat type that is present in the baseline: Area habitats, Hedgerow habitats, and Watercourses habitats.
The change in biodiversity units is calculated by subtracting the baseline biodiversity units from post-development biodiversity units and there should be a minimum of a 10% increase in biodiversity units. This is calculated using the statutory biodiversity metric calculation tool. Post-development biodiversity units include all the baseline habitats that will be retained, all the new habitats that will be created, and all the baseline habitats that will be enhanced. The post-development habitats must be realistic for the site and deliverable for the project.
If a measurable 10% net gain in biodiversity cannot feasibly be achieved on site, then there are two options. Firstly, there is offsite habitat creation/enhancement, where new habitats are created or existing habitats are made better on land outside of the red line boundary of the development, which can be used to make up the deficit in biodiversity units onsite. This is the preferred option for Local Planning Authorities. An off-site provider can create or enhance habitats to generate biodiversity units for developments and allow them to meet their BNG requirement. An offsite provider could be a land manager, a landowner, or an organisation acting as a habitat bank.
The final option is purchasing biodiversity credits, which is the last resort. Buying statutory credits means that as well as, or instead of, creating and enhancing biodiversity on or offsite, developers can make a financial contribution, which counts towards their mandatory 10% BNG. This contribution will be used to fund biodiversity enhancements across England. More information on purchasing biodiversity credits can be found on the Government website here.
The Statutory Biodiversity Metric Calculation Tool is used to calculate biodiversity value for the purposes of biodiversity net gain. Principals and rules underpin the use of the biodiversity metric tool. The first principal is that the metric assessment should be completed by a suitable qualified individual who have the skills and knowledge to complete and review the calculations within the metric. A suitably qualified ecologist would be able to do this.
The statutory biodiversity metric tool can calculate different types of biodiversity units. There are three types of biodiversity units, which are calculated in three separate categories:
Area habitats.
Hedgerow units.
Watercourses units.
One of the rules of BNG is that a minimum of 10% net gain must be achieved for every category present in your baseline. The earlier the biodiversity metric tool can be applied in an application process, the greater the opportunity to design for biodiversity and wider ecological benefits.
Most projects should not use Rule 4 – Exceptional Ecological Circumstances. It may be used in exceptional ecological circumstances occurring when:
The site has optimal conditions (such as soil condition, hydrology, nutrient status) for restoration of a wildlife-rich or historic natural habitat,
and the project team has the expertise and resource to deliver the habitat with negligible risk of failure.
It can only be used where there are either:
Highly complex landscape scale habitat changes such as creation of heathland or a heathland grassland mosaic,
River re-meandering, or
Large-scale restoration of natural processes.
If you meet the requirements to use rule 4, the relevant planning authority should be engaged prior to the submission of the biodiversity gain plan. The LPA needs to be satisfied that the exceptional ecological circumstances in which rule 4 can be applied are occurring.