A Guide to Biodiversity Net Gain

If you’re seeking planning permission for your site, you’ll probably need a Biodiversity Net Gain plan. Biodiversity net gain puts the natural environment at the forefront of planning decisions, meaning that developers must factor improved biodiversity into their pre-development plans so that habitats are retained as far as possible to avoid biodiversity loss. The primary objective is for them to leave the development site in a better condition than they found it in.

Biodiversity net gain is designed to ensure that all development achieves improvements to the natural environment. It does this by assessing the biodiversity losses resulting from development, and the biodiversity gains post-development, to calculate measurable net gains in an area following development. It will become a mandatory planning obligation for development projects in England from November 2023.

Species-rich hay meadows are important wildlife habitats.

What is biodiversity net gain?

It aims to ensure that the state of biodiversity in an area is not only left in the same condition as it was prior to a development project, but is also improved by 10% to compensate for the potentially negative impact of the scheme. Importantly, the net gains must be maintained for at least 30 years. A specialist consultant can calculate biodiversity net gain by using the Biodiversity Metric 4.0 calculation tool. This will assess an area’s biodiversity unit score, and a plan can be drawn up to incorporate biodiversity improvements into the scheme.

Biodiversity net gain is now an integral part of planning policies for all projects and local planning authorities are expecting it from developers and anyone managing a planning project. Biodiversity net gain must be factored into small projects as well as multiple developments such as independent, commercial, and nationally significant infrastructure projects.

A developer must understand statutory biodiversity credits, the current biodiversity metric, and recognise the ecological importance locally of net gain in terms of development biodiversity value on the pre-development site. Their development proposal must demonstrate how they will achieve a measurable net gain 10% uplift post development of the site, and how this uplift in biodiversity is to be looked after for the next 30 years.

A biodiversity net gain consultant can ensure the land is preserved as far as possible during the development by having an environmentally considerate plan. This can include retaining priority habitats, avoiding biodiversity loss and protecting ecological networks. Sometimes, of course, there’s no choice but to safely relocate inhabiting animals and destroy or move veteran trees and plants that interfere with the scheme.

Biodiversity net gain principles

The Chartered Institute of Ecology and Environmental Management (CIEEM), states that there are ten key good practice principles of biodiversity net gain. When these are followed correctly, net gain and habitat enhancement should result.

Mandatory biodiversity net gain principles:

1 Utilise the mitigation hierarchy to minimise the impact on biodiversity.

2 Eliminate negative impacts on biodiversity that cannot be offset elsewhere.

3 Involve all pre-development and post-development stakeholders in forming mandatory net gain solutions.

4 Understand the potential risks and variable factors to achieving biodiversity net gain.

5 Determine a suitable method to secure measurable net gain for biodiversity.

6 Ensure the best possible outcomes from biodiversity net gain.

7 Offer nature conservation that exceeds the biodiversity net gain requirements.

8 Focus on generating long-term environmental benefits from biodiversity net gain.

9 Cover all areas of sustainability, incorporating economic and societal factors.

10 Communicate all biodiversity net gain outcomes with complete transparency.

An ecological consultant inspects a tree during a biodiversity net gain survey.

Examples of biodiversity net gain

Every plot of land will offer different ways of achieving net gain. For sites with no animal species or trees, it can be relatively straightforward to offset and increase the level of biodiversity value to the required level of net gain required on completion of the project.

However, if protected animals or plants are found on the site, a British standard licensed ecologist would need to ensure they won’t be disturbed because of the development. A protected species survey may be required to fully assess the species inhabiting the site and guarantee its safety. In cases where disruption or destruction to animal habitats and plant species cannot be avoided, as a last resort, the ecologist would need to offer expert advice on ways of compensating for recognised biodiversity losses, such as by relocating or creating new habitat types and suitable locations for plant species on-site, off-site or a combination of the two. The biodiversity net gain rules allow for the changes to be made off-site, as long as the 10% net gain is achieved.

Anyone seeking planning consent must work within the mitigation hierarchy guidelines for mandatory biodiversity net gain to be successful. The mitigation hierarchy is a suggested structure for working out the most suitable course of action on development sites, with the aim of protecting the animal species present, enhancing habitats, and delivering net gains for biodiversity using the current biodiversity metric.

The top priority in this planning system mitigation hierarchy is to completely avoid harm or disruption to the environment on the site. If this is not possible the ecologist must develop mitigation measures that minimise the impact. These may include alterations to the plans to avoid impacting certain areas or providing extensive training to construction staff about working on a site that’s home to wildlife species and delicate plant life.

The importance of biodiversity

Biodiversity is important for many reasons, including:

1 Aiding the production of raw materials.

2 Enhancing the earth’s visual appearance.

3 Enabling a scientific understanding of the natural world.

4 Offering recreational activities.

5 Providing jobs for farmers and other agricultural vocations.

6 Supplying oxygen and water to the ecosystem.

Habitat creation provides great opportunities for helping endangered species such as barn owls.

Biodiversity net gain legislation

The concept of biodiversity net gain was announced by former environment secretary Michael Gove in December 2018 before the UK government introduced the new Environment Bill in October 2019. This became the Environment Act after achieving royal assent and was passed into law in November 2021. While there was existing legislation regarding the environment and development projects prior to this under EU policies, following Brexit on 31st December 2020, these no longer applied to the UK.

While biodiversity net gain finally becomes law in autumn 2023, it’s already a requirement of planning permission with many local planning authorities. As such, it’s advisable to start thinking about it now if you are about to embark on a planning application to avoid delays to your development proposal.

Why was biodiversity net gain introduced?

The concept grew from the realisation that healthy ecosystems mean good air quality and clean water, and conserving the natural capital contained in our green spaces contributes to mitigating climate change. Biodiversity improvements can add value to the economy, our well-being, the value of land, and developments on it.

While the UK’s irreplaceable habitats are already protected – such as sites of special scientific interest, and areas with key ecological features such as ancient woodland – mandatory biodiversity net gain extends protection to all sites.

Is the biodiversity net gain policy bad news for developers?

Some might see the requirement for more environmental protections as yet another hurdle to jump in the pursuit of planning consent. However, the UK has some of the worst biodiversity figures in the world. Our natural environment has been in decline for decades: a report from 2019 stated that 41% of UK species were in decline and only 26% saw increases. The net gain concept promotes development while incorporating biodiversity improvements and can be seen as a way of preventing further damage to the environment, in line with the goals of Natural England, Defra, and the British Standards Institution.

Habitat creation can benefit pollinators.

Net gain metrics, calculations, and assessments

Biodiversity net gain metrics

Developers must submit and receive approval for a biodiversity net gain plan to secure planning consent for a development. The legislation states that permission should only be granted on the condition that development can enhance the biodiversity value of your site, i.e., it should be `in a measurably better state than it was beforehand.’

While the existing National Planning Policy Framework began to make this necessary in 2012, now the difference is the word `measurable’, with the current measurement tools making it easier for a developer to achieve net gain. The main tool is the Defra biodiversity metric 4.0, replacing Defra biodiversity metrics 3.1 and 3.0. and 2.0, and it can calculate net gain or loss on any proposed development.

Biodiversity net gain calculator

The 4.0 tool looks at several factors:

  • Habitat type, both on and off-site.
  • The size of habitat parcels in hectares or kilometres.
  • The condition of habitat parcels.
  • Locations (if they are local nature priorities).

More information regarding irreplaceable habitats on the land will be based on the results of the relevant habitat survey undertaken during pre-development. Findings from a habitat survey can be used to gauge the habitat’s size, type, condition, and location to create a biodiversity metric 4.0 score. The resulting net biodiversity gain score will then be measured into biodiversity units or credits.

The government website also provides a biodiversity metric 4.0 calculation tool for calculating your unit score in a way that translates to the standards of your local planning authority.

How to measure and calculate net gain on and off-site

So that recent, deliberate harm to the biodiversity value of your site is taken into consideration, the measurement should happen when a planning application is made to prevent damage to existing flora and fauna from reducing the biological value of the land, making the 10% improvement easier to achieve. If this is found the be the case, and this or other work is discovered to have taken place without permission, their consequences won’t be taken into consideration during the site assessment.

The first step is usually a preliminary ecological appraisal – a baseline walkover ecological impact assessment, where priority habitat can be identified for input into the biodiversity metric. Further surveys will be undertaken post-development and the site will be scored again to work out whether a 10% net gain has been achieved and can be maintained for at least 30 years.

Surveyors carry out an ecological assessment.

How to deliver 10% net gain on your site.  

A conservation covenant is one option – this is a legally binding agreement between a developer and a responsible body aimed at protecting natural sites of strategic significance. A conservation covenant is indefinite even after a landowner sells or otherwise parts with the land. Practically, they are likely to make further development of the land and management more difficult, operating in a similar manner to biodiversity net gain. Also, along with putting assurances on the retention of biodiversity value and acknowledging the development biodiversity, landowners receive benefits from opting into a conservation covenant such as receiving offsite compensation, financial assistance, and tax benefits for any form of conservation work carried out on the site, even if the works could gain net biodiversity and lead to being suitably maintained for at least 30 years.

The biodiversity net gain assessment process divides the overall biodiversity value into two categories – hedgerow and habitat. Each net gain unit is assigned a relative value, giving comparable development biodiversity value between pre-development and post-development caused by a balance of an ecologically rich habitat and one with relatively poor biodiversity.

Offsetting and biodiversity credits

The local planning authority will ideally want you to demonstrate onsite biodiversity net gain, which can be achieved in different ways according to location, condition, and past and present habitats. Frequently used methods of improving biodiversity include habitat creation such as planting native tree and shrub species, allowing wildflowers to thrive, and managing eutrophication (an overabundance of nutrients, common on many urban development sites).

In cases where it’s impossible to improve the biodiversity units on a site, it doesn’t mean that your application will fail. It will be examined by the local planning authority which may grant consent if you can create biodiversity net gain through offsite habitat enhancement, perhaps on council land, areas of local importance or local nature recovery strategies. The delivery of off-site biodiversity net gain is up to the individual planning authority; they will consider it on a site-by-site basis. Alternatively, you may be able to purchase statutory biodiversity credits, or biodiversity units, from or through funding schemes that will generate the equivalent number of units elsewhere.

Using an ecological consultant at the design stage and later stages of the planning process is likely to reduce the possibility of having to deliver net gain off-site. It’s often possible to devise pragmatic solutions to achieve biodiversity net gain requirements.

When to engage an ecologist to help you deliver biodiversity net gain

Some local planning authorities are requiring developers to demonstrate how they can achieve biodiversity net gain, taking account of the biodiversity metric, prior to November 2023. Your local planning authority should be able to give you detailed guidance and you may want to engage a consultant ecologist for advice to get the full picture. If the local planning authority can’t give clarity, public bodies such as Natural England, Defra, or the British Standards Institution can provide further detail.

What does a biodiversity net gain plan cost?

Costs will depend on your site and the environmental consultancy firm that you use; as an example, Arbtech provides British standard biodiversity net gain assessments which cost from £469+VAT, depending on the scale and complexity of the site. The price for buying biodiversity units and credits in an offsetting scheme will be decided by local decision makers, based on supply and demand and negotiations with key stakeholders.

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