Biodiversity Net Gain - what is the theory?

In the UK there has been a significant decline in biodiversity over the last few decades with England becoming one of the most nature depleted nations in Europe. In February 2024 the Biodiversity Net Gain (BNG) legislation was introduced to try and address the impact of development on wildlife.

The idea is to try to ensure an overall improvement to habitats for wildlife when a new development takes place. Developers are legally required to achieve a minimum 110% BNG.

Ecologists have come up with a way of ‘scoring’ land where development is being planned as follows:

●      Size - the land area in hectares

●      Distinctiveness - the area is categorised into one or more habitat types from a possible list of about 130 types (based on the geology and flora) and each habitat type has a score according to its rarity.

●      Condition - a score is assigned based on whether the condition of the land is poor, moderate or good.

●      Strategic significance - if the land is part of the local area nature recovery strategy the score is uplifted.

In addition, there is a separate scoring process for hedgerows and water courses.

The land is given an overall ‘biodiversity units’ score by multiplying all these factors together. Arable land has a relatively low distinctiveness score and will tend to attract a low biodiversity units score. This type of land is some of the most nature-depleted non brownfield land.

The developer now must show how they will produce an increase of 110% in this score. The simplest way for developers to fulfil their BNG requirements is by creating habitat onsite within the boundary of the proposed development. Where this is not possible the main alternative is to buy units from registered offsite habitat banks.

Most wildlife organisations like Suffolk Wildlife Trust believe that, done well, BNG should help to mitigate the impact of development on wildlife.  There are however concerns about how the process may work in practice.

One concern is that we may lose unique elements of on-site habitats such as a toad migration site only to be replaced by lower quality habitats elsewhere. Another concern is that whilst larger offsite habitats might be beneficial there is a danger that certain areas become built up without any local biodiversity provision.

There are also worries about the government wanting to water down the legislation. A recent consultation proposes removing BNG requirements for smaller sites which could mean the vast majority of new developments. There is also new planning legislation currently going through parliament which will weaken protection for nature.

BNG is potentially an important tool for protecting wildlife. Like a lot of well-meaning legislation, the devil is in the detail and citizens will need to play their part in making sure the process is monitored and effective.