10 min read | May 26, 2023

How irreplaceable habitat works in BNG

In this blog, we explore the concept of irreplaceable habitats, their importance in maintaining ecosystems, and how they are safeguarded in BNG and in other government plans and policies.
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This blog was updated in October 2023 following the release of new information from the Government.


Irreplaceable habitats hold immense biodiversity value and are incredibly difficult (if not impossible) to restore, recreate, or replace once destroyed. These rare sites are vital parts of our national environmental heritage, and they cannot be compensated. This means that there are special rules that apply to irreplaceable habitats for the purposes of Biodiversity Net Gain (BNG).

In this blog, we explore what irreplaceable habitats are, how they are safeguarded in BNG and in other government policies, and their wider importance to the environment.

What are irreplaceable habitats?

Debates about what ‘irreplaceable habitats’ are can often be intense. However, in October 2023, the Government said that, for the purposes of BNG, the following are ‘irreplaceable habitats’:

  • Ancient woodland
  • Ancient and veteran trees
  • Blanket bog
  • Limestone pavements
  • Coastal sand dunes
  • Spartina saltmarsh swards
  • Mediterranean saltmarsh scrub
  • Lowland fens

This means that, if you have any of these habitats on your site, you will have to follow certain rules in order to comply with BNG.

Biodiversity Net Gain and irreplaceable habitats

Under the Environment Act, irreplaceable habitats are excluded from the quantitative mandatory BNG objective. In other words, you cannot simply destroy these habitats - you have to follow the rules set out below.

  • Irreplaceable habitats must be recorded in the biodiversity metric but the 10% requirement will not be applied. While you must note if these habitats are on your site, any impacts to these habitats will be flagged as unacceptable and they will require bespoke compensation to be agreed with the Local Planning Authority (LPA). You’ll still need to achieve 10% BNG on any other non-irreplaceable habitat present on your development site.
  • Compensation requirements must be agreed with the LPA. The planning authority must ensure that any mitigation or compensation plans for such habitats meets the requirements outlined in relevant policies and guidance, and decisions on planning applications should be made in line with the NPPF. Compensation should be informed by ecological expertise and typically exceed the requirements set through BNG.
  • There is a prohibition on using biodiversity units or statutory biodiversity credits: Off-site biodiversity units and statutory biodiversity credits cannot be used to compensate for the loss of irreplaceable habitat. Instead, appropriate compensation should be informed by ecological expertise and typically exceed the requirements set through BNG.
  • Enhancements to irreplaceable habitats: Where there are no direct or indirect negative impacts on an irreplaceable habitat, appropriate enhancements could be made to it as part of a net gain plan. These enhancements would be included as part of the overall biodiversity metric calculation.

How irreplaceable habitats can be protected

Developers and planning authorities play a crucial role in protecting irreplaceable habitats. If such habitats are on a site both parties should engage in early consultation and adopt a nature-first approach in decision-making, prioritising the avoidance of harm to irreplaceable habitats. This can be achieved by thoroughly assessing site suitability, exploring alternative development locations, and implementing robust mitigation measures when necessary. Developers should also engage with LPAs and make sure that local strategies are consulted to identify and protect irreplaceable habitats.

Such documents include (as examples) Local Nature Recovery Strategies; National Character Areas Objectives; Local Ecological Networks Shoreline Management Plans; Estuary Strategies; Green Infrastructure Strategies. These local strategies help identify areas of high ecological value, including irreplaceable habitats, and guide development plans accordingly.

Understanding the debate around irreplaceable habitats

As noted above, debates about what constitutes ‘irreplaceable habitat’ often get heated, but one area of agreement is that these habitats often support rare or endangered species and provide critical ecosystem services, such as water purification, carbon sequestration, and flood prevention. It’s also widely agreed that their loss can result in significant, long-term, and sometimes irreversible negative impacts on local and regional ecosystems, as well as the communities that depend on them.

Irreplaceable habitats are a prime example of why a comprehensive biodiversity assessment process should include both qualitative and quantitative evaluations. A purely quantitative approach, such as only calculating the number of biodiversity units gained or lost, may fail to account for the unique characteristics and complexities of these habitats.

To be clear, quantitative assessments, which primarily focus on measuring and comparing the numerical values of biodiversity units or habitat sizes, can provide useful insights into the overall ecological health of an area - and underpin the new BNG system. However, they may not adequately capture the unique attributes of irreplaceable habitats, such as their rarity, age, uniqueness, or the presence of specific species that are critical to maintaining ecosystem function. This can result in an underestimation of the true value and importance of these habitats and potentially lead to suboptimal conservation decisions. On the other hand, qualitative assessments consider the full ecological values of habitats, which are often difficult to quantify.

A mixed approach allows for a more comprehensive understanding of the factors that contribute to a habitat's irreplaceability, such as its role in supporting the life cycle of rare or threatened species, its role in maintaining ecosystem processes, or perhaps even its cultural and historical significance.

Integrating both qualitative and quantitative assessments in the biodiversity assessment process can help to ensure that the unique characteristics of irreplaceable habitats are recognised and considered in decision-making processes. For example, a quantitative assessment may reveal a loss of biodiversity units due to a proposed development, while a qualitative assessment could provide insight into the potential impacts on rare or threatened species and the overall ecosystem function. This holistic approach allows for a more robust evaluation of potential impacts and can inform the development of targeted conservation measures that address the specific needs of irreplaceable habitats.

(As an aside, it’s worth noting that this definition of Irreplaceable Habitats set out in October 2023 for the BNG system aligns with the National Planning Policy Framework (NPPF). The NPPF defines irreplaceable habitats as those that are technically very challenging or time-consuming to restore, considering factors such as age, uniqueness, species diversity, or rarity. However, the definition is not exhaustive, which has led to ongoing debates about which habitats qualify as irreplaceable).

The future of irreplaceable habitats

Although irreplaceable habitats are afforded special consideration and protection, challenges remain - not least the lack of a comprehensive and universally accepted list of irreplaceable habitats, which can lead to inconsistencies in their identification and management (note that the Government has said it will need to update its list of habitats for the purposes of BNG). Furthermore, the complex nature of these habitats makes it difficult to measure their true ecological value and accurately assess the impacts of development.

To overcome these challenges, it is essential to invest in research, monitoring, and data collection to improve our understanding of irreplaceable habitats and the factors that influence their resilience and recovery. Additionally, strengthening collaborations between government agencies, researchers, conservation organisations, and local communities can foster the development of innovative and effective strategies to safeguard these vital ecosystems.

How Joe’s Blooms helps

With Joe’s Blooms tools we are able to automatically note if a habitat has been designated as an ‘irreplaceable habitat’ by the Government and apply the relevant rules when helping a user compile a BNG assessment of their site and fill in a Biodiversity Metric sheet.

We will also be able to give LPAs a chance, via our new portal service, to ensure that local priorities and needs are brought into the user journey.


Irreplaceable habitats have a special status in the BNG system. There are specific rules that must be observed. People who need to comply with BNG need to make sure that they understand these rules, or use digital tools like Joe’s Blooms which incorporate the rules surrounding irreplaceable habitats.

Beyond making sure that you comply with the new rules, it is worth being aware of why these habitats are so special - and how, if you find such habitats on your site, you should consider incorporating qualitative assessments. A comprehensive assessment process that takes into account the ecological, social, and cultural dimensions of irreplaceable habitats can help to ensure that these vital ecosystems are preserved for future generations and continue to provide essential services to support the health and well-being of our planet.

Irreplaceable habitats are critical to maintaining the Earth's biodiversity and providing essential ecosystem services. As we move forward, continued research and monitoring efforts, along with the development and implementation of innovative conservation strategies, will be crucial in preserving these invaluable habitats. By prioritising the protection and enhancement of irreplaceable habitats, we can contribute to a more sustainable future for our planet and all its inhabitants.

Oliver Lewis

Oliver Lewis

Founder of Joe’s Blooms
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Oliver Lewis is the founder of Joe’s Blooms, providing end-to-end digital solutions to help you create best-in-class Biodiversity Gain Plans. Expert in this field, he shares his knowledge on the Environment Bill.

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