Biodiversity net gain – what is it and is it a sensible policy?

From 12 February 2024 a change to the planning system requires that most planning permissions will have to deliver a 10% biodiversity net gain (BNG).  So what does it all mean?

 

What is biodiversity net gain?

Biodiversity net gain (BNG) is an approach to development, and/or land management, that aims to leave the natural environment in a measurably better state than it was beforehand. The word ‘biodiversity’ comes from the term ‘biological diversity’. It refers to the variety of all living organisms, including animals, insects, plants, bacteria and fungi.  Biodiversity net gain delivers measurable improvements for biodiversity by creating or enhancing habitats in association with development. Biodiversity net gain can be achieved on-site, off-site or through a combination of on-site and off-site measures.

 

[Local Government Association]. 

 

Natural England state “BNG is additional to existing habitat and species protections. Intended to reinforce the mitigation hierarchy, BNG aims to create new habitat as well as enhance existing habitats, ensuring the ecological connectivity they provide for wildlife is retained and improved.”

 

Natural England, 2023, Biodiversity net gain, An introduction to the benefits.

 

 To assess current and biodiversity how much work is required to meet the BNG, a biodiversity tool is used.

A biodiversity metric is a tool, such as Defra’s statutory Biodiversity Metric used to measure changes in biodiversity. Metrics do not take protected species into consideration, focusing only on habitats.  Metrics assign every habitat on a site a ‘unit value’ according to its relative value for biodiversity. Once this value is determined for both the existing site and the proposed development, comparisons can be made and used by the local authority to inform planning outcomes.The metric helps developers and landowners to ensure their project increases the overall biodiversity value of a site.

 

https://www.rpsgroup.com/services/environment/ecology/biodiversity-net-gain/

 

 

 

The process

To achieve BNG there are four elements to follow in the mitigation hierarchy – avoidance, minimisation, on-site restoration, offset (off-site compensation).  A number of businesses have been established

 

A number of businesses have been established which will carry out assessments of a site while another group of businesses have developed which trade in Biodiversity Net gain units. These work with landowners who have land of biodiversity value and with developers who need to offset the loss of habitat on a development.  The BNG units are traded between the two. 

 

Does it work?

A number of problems have emerged. zu Ermgassen et al in a paper in 2021 identified a number of issues with existing projects:

The metric was not designed with rewilding areas in mind, so scrubland value is minimized;

There was a loss of 34% of green space – offset by a 20% increase in biodiversity;

The metric trades wildlife losses today for uncertain future gains.

 

Jamie Robins, projects manager at Buglife, said a huge number of mitigation commitments from developers were already failing to be delivered. A fundamental problem was that habitats that had existed for decades or centuries could be destroyed and replaced by a habitat present there for 30 years. https://www.theguardian.com/environment/2021/jul/21/biodiversity-metric-algorithm-natural-england-developers-blight-valuable-habitats-aoe

 

There are other contentious issues:

The BNG approach:

ignores the value of land for food production;

the importance of a site in the landscape;

ignores the carbon cost and other environmental impacts of the development itself, such as those associated with the construction phase and those arising from users;

land which is used for off-site mitigation should be enhanced anyway not used to allow development. 

 

Conclusion

BNG may appear to offer a means of offsetting the environmental costs of development yet by ignoring significant contributors to environmental costs it creates the illusion of a solution.

 

 

References

 

Guardian, 21 July 2021.  https://www.theguardian.com/environment/2021/jul/21/biodiversity-metric-algorithm-natural-england-developers-blight-valuable-habitats-aoe

 

Local Government Association.

https://www.local.gov.uk/pas/environment/biodiversity-net-gain-local-authorities

.

Natural England, 2023, Biodiversity net gain, An introduction to the benefits.

 

zu Ermgassen et al, 2021, Exploring the ecological outcomes of mandatory

biodiversity net gain using evidence from early-adopter jurisdictions in England, Conservation letters.