Biodiversity Net Gain, guidance for developers and ecological consultants

Important issues to consider when planning how to meet your BNG requirements.

Mitigation hierarchy 

While the introduction of a metric that generates numerical values to quantify losses and gains of habitats is one of the most striking aspects of Biodiversity Net Gain, the metric is only a tool to help to estimate the value of what is being proposed. The purpose of Biodiversity Net Gain is to require development to have a positive impact on biodiversity overall through the creation and enhancement of habitats, and so at every stage of the process it is essential that ecological principles are being followed and the process is being considered in terms of how to achieve best outcomes for nature rather than just best numbers in the metric.  

Importantly, the mitigation hierarchy set out in paragraph 193a of the NPPF remains paramount - harmful impacts must first be avoided. Where they are unavoidable, they must be adequately mitigated, with compensation being a last resort. 

Enhancement should then be secured over and above that. Accordingly, the net gain process can be seen to apply right at the end of that process - to the compensatory and enhancement stages. It does not remove the need to avoid impacts as the first priority.  

To help ensure that good ecological outcomes are secured through the Biodiversity Net Gain process, a series of nine metric principles are set out in section 3 of the Statutory Biodiversity Metric user guide (opens new window), in addition to the four metric rules that must be adhered to in all circumstances. The principles exist to ensure that expert ecological advice and established ecological principles are always used throughout the BNG process. A guide called Biodiversity Net Gain: Good Practice Principles for Development (opens new window) has also been produced by CIEEM, IEMA and CIRIA, which provides extensive advice to ensure that best ecological outcomes can be secured through the BNG process.  

The use of the biodiversity metric does not override existing biodiversity protections, statutory obligations, policy requirements, ecological mitigation hierarchy or any other requirements. 

Interim arrangements for the Strategic Significance Section of the Metric until the South of Tyne Local Nature Recovery Strategy is published 

Strategic significance describes the local significance of the habitat based on its location and the habitat type. 

All habitat parcels (both baseline and post-development) must be assigned a strategic significance score; it should be considered separately for each individual habitat parcel in the metric and not on a site-wide basis.  

On an interim basis, until the South of Tyne Local Nature Recovery Strategy (LNRS) is published, strategic significance categories should be based on: 

• Mapping of the Gateshead Wildlife Corridors as shown on the policies map (opens new window) ; and
• Habitats listed as Priority Habitats for Durham Vice County 66 in Appendix 16 of Making Spaces for Growing Places (MSGP) (PDF, 8 MB) Local Plan Document for Gateshead (Gateshead Council February 2021).

High: Where the project delivers a local priority habitat within a Wildlife Corridor: 

• Record the strategic significance as low in the baseline tab
• Record strategic significance as high in post-development tab  
• Record the documents used in the user comments 

Medium: Cannot be applied given that the habitats and locations to be considered have been specified by the local planning authority (as above).(See table 7 of Statutory Metric User Guidelines) 

Low: Where the definitions for high strategic significance are not met. Even if your project is within a Wildlife Corridor, if it does not deliver a local priority habitat you should: 

• Record strategic significance as low in the baseline
• Record strategic significance as low in in post-intervention sheet

Provision of BNG on the development site

In principle, the development site itself is the preferred location for the created or enhanced habitats that will satisfy the BNG requirement, so that there isn't a spatial separation between where habitats are being lost and where they are being established, and to ensure that local communities benefit from a nature-rich environment. However, there are significant issues to be considered when determining whether this is realistic, especially on residential sites where open space is going to be used by local residents for a range of uses such as informal play and exercise, including dog-walking. 

This imposes some extra considerations on top of the normal considerations such as soil nutrient status in determining what habitats could realistically be sustained and managed, and what condition could realistically be achieved for those habitats.  

Disturbance levels and lighting must also be considered when determining whether habitat types/conditions can be deemed realistically representative of targeted habitats. 

Once they have been created, significant on-site habitats will need to be managed and monitored for a 30-year period, , to determine if the required gains are being achieved and to identify remedial measures if not. It is therefore in everyone's interests to ensure that BNG proposals are realistic and achievable. 

Significant onsite enhancements

Significant on-site enhancements are areas of habitat enhancement which contribute significantly to the proposed development's BNG, relative to the biodiversity value before development. 

Retention of existing habitat does not count as an on-site enhancement. 

What counts as a significant enhancement will vary depending on the scale of development and existing habitat, but these would normally be:  

• habitats of medium or higher distinctiveness in the biodiversity metric 
• habitats of low distinctiveness which create a large number of biodiversity units relative to the biodiversity value of the site before development
• habitat creation or enhancement where distinctiveness is increased relative to the distinctiveness of the habitat before development 
• areas of habitat creation or enhancement which are significant in area relative to the size of the development   
• enhancements to habitat condition, for example from poor or moderate to good 

View further guidance on significant enhancements on the GOV.UK website (opens new window)

Meeting the BNG requirement through the purchase of biodiversity units

Habitat Banks - areas of land where habitat is created or enhanced to sell the resulting biodiversity units to developers - may be established in Gateshead.  

In order to do this, landowners will need to conclude legal agreements with the Council and then register the sites on the Biodiversity Gain Site Register. More information can be found on the DEFRA website (opens new window).