Biodiversity Net Gain

Biodiversity Net Gain (BNG) is a concept which aims to leave development sites in a better state than what was there originally. 

It takes a baseline of the habitats and linear features on a site, assesses against the loss a development will create, and a 10% gain will be required, once the loss is found.

All planning authorities now have a legal duty to ensure that mitigating and enhancing biodiversity within a development is undertaken via the Environment Act 2021. 

This includes Ecological Mitigation and Enhancement Plans, and more recently, Biodiversity Net Gain assessments.

Biodiversity Net Gain is a government policy in which developers must aim to enhance the state of the natural environment by increasing the natural habitats and ecological features across a site. 

It is a legal obligation, when the site is not exempt (see below), to achieve a minimum of 10% biodiversity net gain prior to a planning application being approved as part of the new Environment Bill.

There are a few exemptions which can be found here https://www.gov.uk/guidance/biodiversity-net-gain-exempt-developments

The type, condition, and area of habitats on site are determined prior to the development. Then, each habitat included in the proposed development is calculated, with each habitat assessed on its condition, size and location.

This habitat data, along with information on local biodiversity action plans (Nature Recovery Strategies), are input into the Biodiversity Metric (versions are currently being updated regularly, but the statutory metric is the main one), which results in the calculation of Biodiversity Units. The difference between the baseline and proposed development biodiversity units provide a percentage loss or gain – this is the Biodiversity Net Gain result.

With a minimum of 10% biodiversity net gain needed for a development to be approved in both habitat and linear units, we then recommend the best ways in which to achieve this.

For example, on a recent project, the biodiversity net gain was calculated for the proposed development where a +8.96% net gain was achieved. Therefore, to meet the minimum 10% net gain, a further +1.04% was needed.

We recommended using a species-rich grass seed mix, such as WFT-Species-Rich-26, for the proposed amenity grassland. We calculated that enhancing 0.8 Ha of the proposed amenity grassland would meet the minimum 10% net gain. 

Another option was to include patches of mixed scrub, totaling at least 0.1 Ha, which would also meet the 10% net gain requirement.

An emerging BNG unit market is being created by the private sector, whereby sites that can’t make the 10% on site can buy the required units off-site. These normally need to be in the county and landscape character area e.g. if grassland is required you have to replace that with grassland in the same or better condition.

A Biodiversity Net Gain calculation and subsequent report can be carried out any time of the year.

Following grant of planning and if the 10% is possible on site, it is likely that a Habitat Management and Monitoring Plan (HMMP) will be required to detail the management of habitats for a 30yr period. These are substantial documents and require both ecological knowledge and habitat management knowledge.

If you are buying units, the habitat bank will have already had an ecologist undertake this work.

The final piece of paperwork is called a BNG Gain Plan, this is a fairly straightforward document that brings all the info into one place, this is usually a condition of the planning permission.