The Department for Environment, Food and Rural Affairs (Defra) has published its biodiversity net gain (BNG) metric calculation tool.

Ahead of the legislation commencement on 12 February (for large sites), Defra has laid out the statutory biodiversity metric before parliament, and published its statutory metric calculation tool.

When BNG becomes mandatory, developers will be required to use the metric to demonstrate a net gain for all planning applications (unless otherwise exempt).

Land managers supplying off-site biodiversity units to the project must also use this metric.

As laid out by Defra, the metric uses habitats as proxy for biodiversity and calculates biodiversity value for the purpose of net gain. The biodiversity value is calculated in standardised ‘biodiversity units’.

Helping developers break down their sites into ‘parcels’ whereby the biodiversity gains and losses for each habitat parcel is visible and manageable.

For landowners the metric shows the current biodiversity value of the land, as well as showing how many producible off-site units are available through additional habitat creation.

Decision-makers, such as local authorities, the calculation tool provides evidence that the statutory metric has been used by the developer to meet the BNG requirements.

It provides an objective means of determining what additional biodiversity value a development will deliver.

The small sites metric has also been published for smaller developers, for whom the legislation will be mandatory from 2 April this year.

For more information on the metric and calculation tool, visit here.