A ‘BNG’ Biodiversity Net Gain Assessment compares existing habitats with proposed post-development habitats and uses a matrix prepared by DEFRA as a tool to compare the pre development bio diversity with the post development bio diversity and improving it by a mandatory 10%. The matrix will confirm how many biodiversity credits are needed improve the biodiversity of the post development habitat (the biodiversity offset). An ecologist will recommend the types of grasses and wildflowers that need to be grown to get the required credits. With regard to the scoring system, trees and hedges do not score well which initially surprised me. The view is trees can be damaged in storms, take a long time to grow or be felled and hedges can be removed. It seems that different grasses, wildflowers and gorse score well. Sites which are arable land before being developed have a lower bio diversity base than grass fields.
Biodiversity Net Gain (BNG) is more problematic on small sites as they often cannot accommodate the biodiversity offset. The off set area in the schemes I have been involved with ranges from 30-40% of the land area. As an alternative to providing habitat on site there are schemes being developed that will accept a payment and they will then provide the biodiversity net gain on land that they control elsewhere. The land set aside and used for BNG has to be maintained for a period of 30 years.
BNG is an issue developers need to address now with Local Authorities requiring BNG land or an off set payment as part of granting a planning permission for development. I hope as the DEFRA Metric is developed that less land can be used to provide BNG. Developers and landowners will need to work together to provide BNG.