Biodiversity Net Gain: What’s up for debate?

At the beginning of December 2018, the Department for Environment, Food and Rural Affairs (DEFRA) announced a public consultation about their proposal to make a mandatory requirement for new developments to deliver a ‘Net Gain’ to biodiversity.
A number of the partner organisations in the Partnership for Biodiversity in Planning are likely to be responding to this consultation, but ahead of their responses, this article touches on some of the key issues raised regarding defining and delivering net gain.

Biodiversity definition: Species as well as habitats

Natterer’s Bat (Credit: Daniel Hargreaves)

How does DEFRA actually define ‘Net Gain’ to biodiversity? The principle that a new development should seek to enhance rather than reduce levels of biodiversity sounds straightforward, however the concept of Net Gain is far from simple to define and apply in practice.

DEFRA proposes 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 a 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 biodiversity but only one 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 affects the definition of biodiversity components like ‘habitat connectivity’ and raises the question, how can the Net Gain metrics find a way to better reflect the functional variation that exists between species?

Compensation for biodiversity loss

DEFRA’s consultation document  suggests that their approach to Net Gain aims to create a more ‘level playing field’ for developers through a standardised requirement regarding biodiversity. However, the aim to increase biodiversity is tempered by the government’s ambition to achieve 300,000 new homes by 2020, as DEFRA indicate:

The government will only mandate biodiversity net gain if it is satisfied that it will deliver benefits for development, including greater certainty and process cost savings.

How Net Gain will be interpreted when delivered in practice is also further tempered, as the consultation proposes 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 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 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 the 10% 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 invites consultees to consider whether there should be any exemptions to the net gain requirement e.g. for urban brownfield sites? 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?

There are clearly a number of issues that need to be addressed to effectively define and deliver the principle of Biodiversity Net Gain. DEFRA are inviting responses until 10th February 2019.


Link to consultation here.

The Bat Conservation Trust response to the consultation is available here.



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