Biodiversity Net Gain Metric

The true value of the natural environment and the biodiversity it supports is notoriously difficult to quantify. What is the monetary value of pollination by bees? Or the filtration of water by oysters? These ecosystem services are often overlooked by traditional market valuation methodologies, leaving the possibility for them to be neglected by policy. Negative external factors such as pollution and habitat degradation have consequences on nature and inevitably humans, but novel legislation in the UK may begin to change the tide.

Biodiversity Net Gain (BNG) is new legislation that is being introduced as part of the Environment Act 2021 and will come into effect from November 2023. Biodiversity gain can be calculated using DEFRA’s newly published biodiversity metric 4.0 tool, which consists of a standard version which will be used for most sites, and a specific version for smaller developments with an area smaller than 1 hectare.

For net biodiversity gain to be determined, both pre-development and post-development biodiversity value must be calculated. Firstly, the pre-development biodiversity value is derived by considering habitat type, size, and distinctiveness. Multipliers such as time to achieve target condition, spatial risk, and difficulty to achieve are then applied to the pre-development biodiversity value to establish the post-development value. Finally, the pre-development biodiversity value is subtracted from the post-development biodiversity value to generate the percentage net biodiversity increase (or decrease) arising from development.

We have been busy working to understand the requirements for undertaking biodiversity net gain assessments and how this will impact development projects across the UK. We hope to provide much-needed clarity for developers on the requirements for complying with this new legislation and achieving the required 10% net gain as part sustainable development.

Exo Engineering Int. Eco Rock Armour units deployed along the Newlyn breakwater by the Environment Agency.