What You Need to Know About Irreplaceable Habitats and BNG

Biodiversity net gain (BNG) ensures habitats affected by development are left in a measurably better state than before work began. It covers all kinds of spaces in England, except irreplaceable habitats.

While the biodiversity of most habitats can be enhanced by the legally required minimum 10%, irreplaceable habitats cannot. Instead of the standard 10% calculation, they're excluded from the BNG trading rules and require bespoke compensation agreed with the local planning authority.

Their presence on a development site also triggers separate requirements and protections that developers must understand from the earliest planning stage. This guide explains them.

What Are Irreplaceable Habitats?

Irreplaceable habitats are specific environments which, due to their age, uniqueness, rarity, or diversity of species, cannot practically be restored or replaced and function normally within any realistic timeframe.¹

They provide essential ecosystem services, including carbon storage, water regulation, and contribution to local communities' landscape character, that make their protection important beyond any regulatory requirement.

Climate change makes their protection even more urgent, since many irreplaceable habitats play important roles in climate adaptation.

Types of Irreplaceable Habitats

Ancient Woodland

Defined as land that has been continuously wooded since at least 1600 AD, ancient woodland is the most widely known category of irreplaceable habitats. It includes four categories: ancient semi-natural woodland, plantations on ancient woodland sites, ancient wood pasture and parkland, and infilled ancient wood pasture and parkland.

This irreplaceable habitat supports thousands of species that depend on old trees, undisturbed soils, and centuries of leaf litter. Ancient woodland is incredibly difficult to restore, since the soil ecology that defines it develops over centuries.

Ancient and Veteran Trees

Ancient trees are the most mature specimens, and while veteran trees are younger, both support complex communities of rare lichens and fungi, as well as invertebrates, bats, and birds.

Both are irreplaceable habitats because their structure and species diversity cannot be recreated within any realistic timeframe.

Blanket Bogs

These are deep peat systems that form in wet, cool upland climates. Blanket bogs can take over 1,000 years to form one metre of peat, and can store enormous quantities of carbon. Their loss releases stored carbon and destroys habitat that is functionally impossible to restore.

Blanket bogs are rich in biodiversity, often home to rare or vulnerable species, and play a key role in flood management.²

Lowland Fens

Lowland fens are waterlogged peat-forming habitats. This complex mosaic of habitats supports over half of the UK's dragonfly species, alongside rare plants and invertebrates.³

Those that remain are classified as irreplaceable habitats because the centuries-long peat-forming processes that define them cannot practically be restored once destroyed.⁴

Limestone Pavements

Limestone pavements are exposed outcrops of rock that have a distinctive clint-and-grike (or grykes) structure⁵ formed since the last ice age.⁶

They cover approximately 3,300 hectares in the UK⁷ and host highly specialised plant communities. Limestone pavements take thousands of years to form and cannot be recreated.

Spartina Saltmarsh Swards and Mediterranean Saltmarsh Scrub

Coastal habitats where Spartina grass grows support a wide range of biodiversity, particularly birds, including curlew and redshank.

Mediterranean saltmarsh scrub is key to coastal protection and economies, and is also relied on by numerous species, including invertebrates and glasswort.⁸

Coastal Sand Dunes

England's centuries-old coastal sand dunes are home to an array of biodiversity, including slow worm, skylarks, rabbits, and dune tiger beetles.⁹

Irreplaceable Habitats and the Biodiversity Gain Plan

Developers of all projects subject to mandatory BNG (the list of exemptions is set out on gov.uk)¹⁰ must include irreplaceable habitats in their baseline survey and record them in the statutory biodiversity metric tool,¹¹ using the irreplaceable habitats sheet,¹² even if there is no loss or deterioration.¹³

However, irreplaceable habitats are excluded from the BNG trading rules and the 10% net gain calculation that applies to all other habitats on or affected by the development site.

Local planning authorities will expect the biodiversity gain plan to clearly identify any irreplaceable habitat types present on the site.

Developers are expected to detail any proposed enhancements, confirm any adverse impacts on irreplaceable habitats are subject to exceptional circumstances justification and, where needed, outline an appropriate compensation plan.¹⁴

Compensation Strategies for Irreplaceable Habitats

Under the mitigation hierarchy laid out in the National Planning Policy Framework, planning permission for any project leading to "loss or deterioration" of irreplaceable habitats should be refused, unless "there are wholly exceptional reasons and a suitable compensation strategy exists."¹⁵

Where they are allowed to move forward, a compensation strategy will be needed. Each is unique to a particular development, but reflects the valuable nature of the irreplaceable habitat affected.

It could include long-term management commitments for the remaining irreplaceable habitat that go beyond the minimum 30-year requirement,¹⁶ extensive habitat restoration or creation elsewhere, or other measures that the planning authority considers appropriate under the specific circumstances.

The developer's biodiversity gain plan must include all details of the compensation deal, as well as evidence that irreplaceable habitats have been identified and confirmation that any adverse impacts have been minimised.¹⁷

If the local planning authority is satisfied, the BNG gain plan will be approved, and only then can work begin on a development.

We Can Help If Your Site Impacts Irreplaceable Habitats

If your development site could impact irreplaceable habitat, and you need clear guidance on how to address it within your biodiversity gain plan, talk to us.

Our expert team can help you navigate any bespoke compensation requirements, and engage effectively with the relevant local planning authority at an early stage.

Email us at sales@greenshank-environmental.com or fill in this contact form and we'll be in touch as soon as possible.

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