BNG applications ask for detail beyond earlier habitat classification systems

As developers move forward to comply with biodiversity net gain (BNG) application requirements, they will need to consider the differences between how habitats are mapped for BNG and how they are mapped in habitat classification systems they’ve previously used.

Developers may have experience with other classification approaches, such as the Joint Nature Conservation Committee (JNCC) Phase 1 survey, as well as UK Habitat Classification (UKHab). While these methods thoroughly describe habitats and vegetation, they do not completely align with the BNG classifications established by the Defra Statutory Biodiversity Metric.

Phase 1

Phase 1 habitat classifications were originally published by the Nature Conservancy Council and later revised by JNCC, the public body that advises the UK Government on nature conservation.  This standardized system for classifying and mapping wildlife habitats includes an associated field survey technique to record semi-natural vegetation and other wildlife habitats. It assesses and classifies the overall area under consideration.

• Extended Phase 1 — This survey includes a Phase 1 Habitat Survey but goes beyond basic habitat classification by gathering additional details like species composition, condition, management, vegetation structure, and age. It also assesses the suitability of habitats and features to support specific fauna, typically protected or notable species, and it is commonly employed as the foundation for a Preliminary Ecological Appraisal or Ecological Impact Assessment.
• Translation — Defra’s Statutory Biodiversity Metric tool does contain a translation sheet for all Phase 1 habitats into the BNG metric habitats. However, note that BNG does not replace Phase 1.

UKHab

UKHab (UK Habitat Classification) was developed to provide a consistent and standardised approach to classifying habitats and vegetation across the UK. Its main aim is to unify and modernise habitat mapping methods, improving accuracy and repeatability in biodiversity assessments. UKHab is widely adopted in the UK for ecological surveys and is central to delivering the Biodiversity Net Gain (BNG) requirements mandated under the Environment Act 2021.

Because UKHab is a detailed and flexible system, it serves as a foundational tool for many applications, including Defra’s Biodiversity Metric. Several habitat types and definitions within Defra’s Biodiversity Metric—used to calculate biodiversity units for BNG assessments—are directly derived from UKHab classifications. This alignment allows ecologists to use UKHab data as a baseline when assessing biodiversity impacts and potential net gains from a development project.

The Defra Small Site Metric draft guidance does have a translation tool for landscapers who might want to translate the UKHab system into the simplified Small Site Metric. However, this only applies to habitats within the Small Sites Metric and is not appropriate for use on larger sites.

The issues

Defra’s Statutory Biodiversity Metric habitat types are derived from a number of sources, including:

• UKHab
• Natura 2000 Annex 1 Habitats
• European Nature Information System (EUNIS) — habitat type hierarchical view
• Water Framework Directive — lake typologies

The result is a system that draws on all four, but it is unique to Defra’s Statutory Biodiversity Metric and includes guidance specific to the metric that is not from any other sources.

Difficulties can arise when translating from one system to another where:

• BNG applications require different details than what might be gathered in a traditional UKHab or Phase 1 survey.
• Mapping is not always congruent. At times you may be unable to map directly from Phase 1 or UKHab to BNG application reporting due to different approaches to habitat classification. Neither Phase 1 nor UKHab translate entirely to BNG applications. Additional work may be needed to convert earlier survey data in UKHab or Phase 1 to the BNG application.

If classifications are not fully accurate, then a developer’s BNG application has a high likelihood of being rejected by their local planning authority (LPA).

Practical Implications for Developers, Planners, and Ecologists