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Biodiversity Net Gains

Biodiversity Net Gain (BNG) is an approach to development that aims to “leave the natural environment in a measurably better state than before”. The Environment Act 2021 now makes Biodiversity Net Gain a mandatory part of the development process. In addition, the National Planning Policy Framework (NPPF 2021) now states that the planning system should:

‘contribute to and enhance the natural and local environment by …minimising impacts on and providing net gains for biodiversity…”. NPPF 2021 Paragraph 180 (d) states ‘opportunities to improve biodiversity in and around developments should be integrated as part of their design especially where this can secure measurable net gains for biodiversity.’


BNG will be a major change for Architects, Landscape Architects, designers and developers. Why? Because it means that we need to design with nature, leaving biodiversity in a better state at the end of the development. Developers will need to work with suitably experienced ecologists to inform the design process from the outset so that we avoid the best and enhance the poorest places for nature. In fact “an approach to development that leaves biodiversity in a measurably better state than before development took place” is the definition of Biodiversity Net Gain.


Burton Reid Associates provide expert advice related to all stages of Biodiversity Net Gains, please contact our team to discuss your requirements.



The NPPF now requires that planning policies and decisions should contribute to conserving and enhancing the natural environment by “minimising impacts on and providing net gains for biodiversity, including by establishing coherent ecological networks that are more resilient to current and future pressures”.

The Environment Bill 2019-20 sits alongside the Government’s longer-term objective for “this, to be the first generation to leave the environment in a better state than that in which we inherited it.” It makes long-term, legally binding targets for “priority areas” including biodiversity, along with the production of statutory “Environmental Improvement Plans”, the first of which was the 25 year Environment Plan (Jan, 2018).

The 25 year Environment Plan focused on requirements for developers to achieve “biodiversity net gains” of 10% through the planning system. The Environment Bill now legislates for the creation of the net gain requirement and expands the duty on relevant authorities from just “conserving” to “conserving and enhancing” biodiversity.

There are going to be some challenges to rolling out the BNG approach, for instance many of the mechanisms for delivery via a financial contribution into off-site areas managed by a third party (e.g. a local authority or Wildlife Trust) are still yet to be developed and put in place. However, there are also many opportunities, such as delivery of BNGs on land that is undevelopable for other reasons (due to topography or location) and opportunities for landowners (for instance farmers) to create BNGs that can then be sold to developers to meet their obligations. This will mean that land managers can diversify to run BNG business models which not only provide a much-needed income but also really deliver for wildlife. It’s a win win.


So how does it work?

To achieve the best outcomes for the developer, the end user and for wildlife, BNGs need to be considered from the start, preferably at or before masterplan stage so that opportunities can be sought at a landscape scale.

This will mean developing a very different kind of relationship with your ecological consultant.  Rather than employing them to undertake the minima required for planning submission, they will need to be embedded into the design team from the start, to help to guide and clarify where opportunities and constraints are present within each development. Working in this way will help to avoid risks and plan for the future, ensuring that where possible net gains are in place well before the point of impact.

In all cases, the approach should follow the 10 guiding principals for Biodiversity Net Gain as per joint guidance published by CIEEM, CIRIA and IEMA. The first and most important principal should be to do everything possible to first avoid and then minimise impacts on biodiversity. Only as a last resort, and in agreement with external decision-makers where possible, compensate for losses that cannot be avoided[1].


The guiding principals:

Principle 1. Apply the Mitigation Hierarchy

Principle 2. Avoid losing biodiversity that cannot be offset by gains elsewhere

Principle 3. Be inclusive and equitable

Principle 4. Address risks

Principle 5. Make a measurable Net Gain contribution

Principle 6. Achieve the best outcomes for biodiversity

Principle 7. Be additional

Principle 8. Create a Net Gain legacy

Principle 9. Optimise sustainability

Principle 10. Be transparent


So how do we measure net gains?

Gains will be measured using a biodiversity metric that has been developed by Defra (at time of writing the Biodiversity Metric 2.0). The metric measures with ‘units’ and these consider both pre and post construction conditions. Units include measurements for site size (ha), distinctiveness, condition, location and connectivity. These are measured against post construction and need to include risks to the delivery of proposed gains, such as how difficult is the habitat to create, how long will it take until it is functional and how far is it from the development site.

Once the unit of required gain is understood these gains can be achieved through three mechanisms, on site, off-site (but as close to the original site as possible) or via a financial contribution to a strategic net gain scheme (for instance, local authority may already be managing areas for wildlife and will set a contribution figure per housing unit or habitat feature lost to compensate for losses on the development site). As noted above, there is also scope for land managers to use land of lower value to provide sources of net gain for developers to buy.


So why do we need net gains?

We are currently undergoing a biodiversity loss of epic proportions. The State of Nature Report (2019) makes for terrifying reading, for instance since the 1970s we have lost more than half of our farmland birds, climate change is resulting in widespread and rapid changes to our ecosystems, unsustainable water abstraction practices have led to declines in freshwater species and habitats, and overall we have seen changes to the abundance of over 50% of our species.

This is important for us as we rely on a rich diversity of species and habitats for many of our own needs. We need our environment to provide clean air, soil and food, we need drinking water and rely on pollinators to secure our food production. We are dependent on all of these ‘ecosystem services’ for our own survival and if we don’t make the shift now, we are endangering not only our own future but the future of our children.

In terms of business, net gains can also help to deliver reduced planning uncertainty, allocation of the right land for development, health and wellbeing benefits, deliverability via improved stakeholder and community consultation and a sense of place and social cohesion.

[1] Biodiversity Net Gain, Good Practice Principals for Development. CIEEM, CIRIA, IEMA, 2016

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