What is Biodiversity Net Gain?

Biodiversity Net Gain (BNG) is a quantitative tool used with the aim to deliver measurable improvements in biodiversity. It can be achieved through on-site enhancement, habitat creation, and off-site measures.

• It is hoped that mandating BNG in developments will stop the loss of biodiversity through development and create and restore ecological systems and networks.
• A minimum of 10% gain is required, calculated using the Statutory Biodiversity Metric , which was published in 2023 and replaced the earlier versions. Some councils require a higher percentage net gain.

How is a BNG assessment carried out?

• A site survey is carried out to assess the baseline habitats (e.g. vegetation and bare ground areas – the soft landscaping features; and the buildings and roads – the hard landscaping features).
• The assessment includes measurement of the areas and, if required, a Condition Assessment is carried out of the habitats.
• The post-development plan for the site is finalised, showing soft and hard landscaping features.
• The baseline and post-development habitats are assessed using the Statutory Biodiversity Metric.
• The assessment includes reviewing what areas are retained, removed/loss, created, or enhanced in terms of biodiversity, both on and off site.
• The assessment is carried out for terrestrial habitats (habitat units), terrestrial linear features (hedgerow units), and linear water features (watercourse units).
• The Biodiversity Net Gain, or loss, is calculated by comparing the difference between the baseline and post-development habitat units, hedgerow units and watercourse units.

How is BNG calculated?

A Biodiversity Net Gain (BNG) calculation compares the baseline habitat against the post-development habitats. A BNG is achieved if the post-development habitat improves biodiversity overall for a site.

This is currently set at 10% net gain, although it is subject to review. As a result, to achieve a net gain, there must be an increase in ecological value. As the soft landscaping areas of a development can usually be significantly enhanced, these are often target areas for improvement.

However, if the soft landscaping areas (excluding gardens that can be changed by owners or paved over) before a development are less than the soft landscaping areas after a development, then it is highly likely that a net gain cannot be achieved on site. In this case, off-site enhancement (e.g. payment to enhance another site) would be required.

The following steps are required for a BNG calculation

A site survey is carried out to assess the baseline habitats.

• The post-development plan for the site is finalised, showing habitat areas.
• The baseline and post-development habitats are assessed using the Statutory Biodiversity Metric.
• The Biodiversity Net Gain, or loss, is calculated by comparing the difference between the baseline and post-development habitat units, hedgerow units and watercourse units.

How are habitats calculated?

Habitats are assessed based on the terrestrial area, terrestrial linear, and aquatic linear features.

Where Biodiversity Net Gain cannot be achieved on site, there is the option for off-site enhancement measures. In these instances, developers would contribute to local schemes. Ideally, local authorities will identify areas for ‘Local Nature Recovery Strategies’, which must be maintained for at least 30 years.

These local Nature Recovery Strategies are key to building a nationwide ‘Nature Recovery Network’. If local schemes are unavailable, developers would be able to invest in ‘Nationally Strategic habitats’ by purchasing government-provided ‘biodiversity credits’.

How many biodiversity metrics are there?

There are several biodiversity metrics; therefore, the preferred metric must be confirmed before the Biodiversity Net Gain calculation is carried out. The Statutory Biodiversity Metric is the most common, but other organisations and local planning authorities have their own systems.

How can Phlorum help?

Phlorum’s BNG consultants have extensive experience providing BNG consultancy, including BNG assessments and working with Biodiversity Net Gain calculators. Contact us now to book your consultation.