Biodiversity Net Gain: What’s it all about?

*Updated news* In the spring statement, the Chancellor has announced that the government will introduce a new mandatory requirement for developments in England to deliver a ‘Biodiversity Net Gain’, i.e. construction projects will need to enhance the existing levels of biodiversity on or near to their sites post-construction.

A number of the partner organisations in the Partnership for Biodiversity in Planning responded to the government consultation about Biodiversity Net Gain, and this article touches on some of the key issues raised regarding defining and delivering net gain.

Measuring Biodiversity gains: Species as well as habitats?

Natterer’s Bat (Credit: Daniel Hargreaves)

We are still waiting to hear the finer details about how DEFRA will define ‘Net Gain’ to biodiversity, however the principle is that a new development project should seek to enhance rather than reduce levels of biodiversity already present on a site. This will require a baseline assessment of what is currently present on a site and then an estimation how proposed designs will add to that level.

In the earlier consultation DEFRA proposed to use four components, with specific ‘metrics’ or indicators to measure an increase in biodiversity quality. A developer will assign a score under each component, to calculate the biodiversity gain or loss of a proposal in comparison with the baseline score assigned to a site before a development takes place:

  • Distinctiveness
  • Condition
  • Strategic significance
  • Habitat connectivity

All four of these Net Gain components refer to habitats as a proxy of biodiversity but only one component refers to wildlife species. A potential problem with not including species more explicitly is that individual species can use habitats in quite different ways and scales, due to their varied feeding, reproductive and migratory patterns. As the Landscape Institute points out:

Different species have different habitat requirements and will perceive and respond to a landscape at different spatial scales… what may be the matrix or barrier for some species could be habitat for others. So, both the components and connectivity of an ecological network may be experienced very differently by different species.” Landscape Institute (2016, p6)

This variation within and between species will affect the definition of biodiversity components like ‘habitat connectivity’ and raises the question, how and whether the Net Gain metrics can better reflect the functional variation that exists between species?

Compensation for biodiversity loss

DEFRA’s consultation document  indicated their aim to create a more ‘level playing field’ for developers through a standardised requirement regarding biodiversity. However, the aim to increase biodiversity is likely to be tempered by the government’s ambition to achieve 300,000 new homes in England by 2020, and it looks probably that only larger development projects will be expected to comply with the Biodiversity Net Gain requirement.

How Biodiversity Net Gain will be interpreted when it is delivered in practice is also further tempered, as the consultation proposed adopting the biodiversity ‘mitigation hierarchy’ when making decisions about a development. The hierarchy includes the option for off-site’ compensation’ if biodiversity losses are unavoidable.

DEFRA’s Biodiversity Mitigation Hierarchy

There is a concern from some conservation groups that the concept of compensation might actually enable developments that would not have been permitted otherwise, as it opens the way to developers to opt for investments to off-site wildlife areas rather than adding to the site in question. Other issues remain unclear, including regarding the geographical range of acceptable compensation sites and whether such sites would be expected to be in close proximity to a proposed development.

How much gain?

Currently DEFRA are proposing that sites seek to achieve a 5-10% gain in biodiversity from a baseline assessment. A potential issue with setting a single target is that the Biodiversity baseline present will vary at different sites and at one site it can change over time, affecting how developers measure a ‘gain’ and respond. Furthermore, a site with very low biodiversity at one time might make it very easy for a developer to achieve a 10% increase, whilst a site with a very high biodiversity baseline might make a fixed target very hard for a developer to achieve. This raises the question whether there should be a set target or an agreed proportion should be established between a Local Planning Authority and developer?

Exemptions from the Net Gain requirement

DEFRA invited consultees during the consultation to consider whether there should be any exemptions to the net gain requirement e.g. major infrastructure projects, urban brownfield sites and smaller developers. We are still waiting to see what DEFRA finally decide. Even urban brownfield sites however can have rich / unique biodiversity present. For example, open mosaic habitats supporting key invertebrate species which in turn are vital part of the food chain and plant fertilisation. So even habitats with seemingly low biodiversity may still require biodiversity protection and enhancement provisions.

Administration and enforcement

The consultation also leaves it up for debate whether Net Gain should be administered by local authorities or a national agency e.g. Environment Agency or Natural England or some combination of both local and national administrations. There is potential for the scheme to generate funds through a tariff to developers for lower performing sites. The question then arises how should the funds raised by this tariff be allocated and by who?

The spring statement indicated that further details about the mandatory Biodiversity Net Gain requirement will be presented in the government’s response to the consultation.


Link to consultation response here.

Partner responses:

  • The Bat Conservation Trust response to the consultation is available here.
  • The UK Green Building Council response is available here.
  • The RTPI response is available here.
  • The Wildlife Trust response is available here.



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