Biodiversity Net Gain has been described as a measurable target for development projects where impacts on biodiversity are outweighed by a clear mitigation hierarchy approach to first avoid and then minimise impacts, including through restoration or compensation. Adhering to these Net Gain principles (i.e. pursuing all principles together) will help in under-pinning good practice for achieving and sustaining Net Gain.
The Defra Biodiversity Metric calculation spreadsheet tool quantifies the BNG value. Sites under 0.5ha qualify for assessment using the slightly simplified Small Sites Metric. In exceptional circumstances with either negligible value habitats (confirmed during the Phase 1 Habitat or PEA survey) or only minor proposed changes with restricted impacts, completion of the Metric may not be required.
Overall biodiversity value
The Metric calculates the baseline value of the existing site. By inputting the proposed development areas and habitat types (retained, enhanced, created or lost), the overall biodiversity value of the proposed development is given a unit value and percentage. It informs of the number of habitat units which need to be met to achieve a minimum 10% net gain. Where there is insufficient space or scope to meet these targets on site, then the credits must be purchased for off-site gain, within the wider locality (e.g. same County).
Biodiversity Enhancement Plan (BEP)
In addition to the formal Metric output, a Biodiversity Enhancement Plan (BEP) document which outlines the specific actions required to ensure a net gain in biodiversity of the above site (as required by NPPF, 2023), can be produced. The biodiversity enhancement plan specifically caters for the species and habitats (protected or common) which are likely to either inhabit the site or be present on a more transient or local basis. The plan includes specific information on recommended plant species, habitat creation and maintenance. Optimal locations for ecological enhancement features, such as bird, bat and hedgehog boxes and bee bricks is also included.
