Biodiversity Net Gain

by Paul Whitby, The Ecology Co-op

What does it mean for development and when will it be required?

Biodiversity Net Gain (BNG) has caused some controversy both in ecology and development as a whole. The principle of trying to calculate the biodiversity value of a plot of land pre-development and predicting its value post development has been around for some time; we undertook our first calculation in support of a planning application in 2018.

When it comes to BNG there is generally two camps within ecology consultancy: those who fundamentally support this approach as a way to ensure development no longer contributes to the national trend which has seen the value of UK biodiversity plummet, and those who see the approach as inaccurate, lacking in teeth and view offsetting as an inappropriate approach that only serves to enable the destruction of high value habitat.

Firstly, let’s look at how BNG is applied:

  1. Biodiversity Net Gain (BNG) has caused some controversy both in ecology and development as a whole. The principle of trying to calculate the biodiversity value of a plot of land pre-development and predicting its value post development has been around for some time; we undertook our first calculation in support of a planning application in 2018.
  2. When it comes to BNG there is generally two camps within ecology consultancy: those who fundamentally support this approach as a way to ensure development no longer contributes to the national trend which has seen the value of UK biodiversity plummet, and those who see the approach as inaccurate, lacking in teeth and view offsetting as an inappropriate approach that only serves to enable the destruction of high value habitat.
  3. Firstly, let’s look at how BNG is applied:
  4. An ecologist is required to assess the habitat values of a site prior to any work being undertaken. It is very important that the site management is not altered in any way and remains normal, as any evidence of activity intended to reduce biodiversity values in advance of a survey would mean that a retrospective assessment incorporating a ‘precautionary principle’ would have to be applied.
  5. The survey data is entered into the Defra Metric 3.0 to determine the pre-development value, which is portrayed as habitat units. The larger the site and the higher the habitat value, the higher the number of units pre-development.
  6. The post-development value of the site is calculated using the proposed landscape design plan. We often work with terra firma for this element of a project, marrying together their expertise in aesthetic design and landscaping with the creation of habitats that have a high biodiversity value and which can be compared with the habitats lost (it would not be appropriate to replace grassland with new woodland planting for example). A ‘difficulty factor’ is accounted for in the calculations in relation to new habitat, with the establishment or enhancement of some habitats subject to risk of failure.
  7. The headline figures produced within the metric indicate the losses and gains for three key habitat types: habitat units, hedgerow units and river units. Where these types of habitat are impacted, a 10% net gain must be achieved.

Managing client’s expectations through this process can be challenging. Some expect the value of the land they are developing to have little value (for example a horse paddock), but the permanent loss of habitat is weighted heavily for all but those with the very poorest value. Even a cultivated arable field has a value – it can of course support a variety of invertebrates and can be important for some ground nesting birds. For this reason, most greenfield development, where the majority of a site is proposed to be developed, will undoubtedly fall into ‘net loss’ territory. It certainly may struggle to find the key target of 10% net gain that is stated in the newly ratified Environment Act. This means that a large proportion of new greenfield development will require a ‘biodiversity offset’, whereby land off site is enhanced/created from scratch; this is typically achieved through either a financial contribution to an existing scheme(s) or via habitat offsetting within another landholding(s) under the same ownership as the proposed development site.

BNG is here to stay and my own opinion on its potential effectiveness falls somewhere in the middle of the two camps I previously mentioned. Calculating the biodiversity value of a site based on habitat values alone can easily undervalue features of high importance for key species, such as open mosaic habitats that could support nationally important assemblages of solitary bees for example. But I do think it is an improvement on current practices within the planning system and may help the government reach its target in the Environment Act to halt species declines by 2030, with offsetting sites managed for conservation value potentially popping up across the country.

Within the Environment Act, BNG is unlikely to become mandatory until autumn 2023, when it is incorporated into the Town and Country Planning Act; however, this does not mean that councils cannot request it as a validation requirement or prior to determination – something we have seen repeatedly in 2021 for larger developments. Under the National Planning Policy Framework Agreement and within existing policy of many local authorities, a requirement for ‘biodiversity gain’ or ‘no net loss in biodiversity’ is already stated. Existing case law has already illustrated that planning authorities are within their right to request a biodiversity net gain commitment through development and therefore it is sensible to establish early on through a pre-application advice service whether this is the case in your area. The adoption of BNG has not been even across local authorities in our experience this year and caution is therefore recommended, particularly as a habitat assessment is required before an initial calculation can be made.

BNG adds some additional complexity and extra consideration to the impact assessment supporting any development proposal and developers will need to be aware that this does not supersede any existing requirements for protected species or general habitat value assessments.

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