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Writer's pictureJeremy Dickman-Wilkes

Preliminary Ecological Appraisals and Biodiversity Net Gain: What They Are and When They are Required for Planning Applications


When planning any type of development, whether it’s a residential housing project, a commercial complex, or infrastructure expansion, environmental considerations are more critical than ever. As biodiversity becomes a focal point in urban planning and development, two key concepts often come up: Preliminary Ecological Appraisals (PEA) and Biodiversity Net Gain (BNG).


Badger walking through leaf litter in woodland

These ecological assessments are fundamental to ensuring that development projects do not just minimize environmental harm but also contribute positively to the natural world.

But what exactly are PEAs and BNGs? When are they required in the planning process, and what kind of information do these assessments need to include? This blog explores these questions in detail, offering a comprehensive guide to understanding these crucial components of sustainable development.


Understanding Ecological Assessments: Preliminary Ecological Appraisals (PEA)


What is a Preliminary Ecological Appraisal (PEA)?

A Preliminary Ecological Appraisal (PEA) is the first step in the ecological assessment process for any proposed development. This appraisal provides an initial overview of the ecological value of a site and its surroundings. It identifies potential ecological constraints that could affect the development and outlines any further surveys or mitigation strategies that may be required.


The PEA typically includes two key components:

  1. Desktop Study: A review of existing ecological data relevant to the site, including previous surveys, records of protected species, and information about nearby designated sites (like Sites of Special Scientific Interest, Special Protection Areas, or Local Nature Reserves).

  2. Field Survey: An on-site visit to assess the current ecological conditions. This includes identifying different habitat types (e.g., woodlands, grasslands, water bodies) and assessing the potential for the presence of protected species such as bats, birds, badgers, or great crested newts.



When is a PEA Required?


A green-coloured newt sitting on a moss covered log














A PEA is usually required when:

  • Development is proposed on a greenfield site where natural habitats are likely to be impacted.

  • There are existing natural features such as mature trees, hedgerows, or ponds that could support protected species.

  • The site is near or within a designated nature conservation area (e.g., SSSI, SPA, or SAC).

  • The development involves demolition or significant modifications to existing buildings that could provide roosting opportunities for bats or nesting sites for birds.

In essence, if there’s any potential for the development to affect wildlife or habitats, a PEA is essential. Local planning authorities often require this appraisal as part of the initial planning application, ensuring that ecological impacts are considered from the outset.


What Information Does a PEA Include?

The PEA report typically covers the following:

  • Site Description: Details of the site location, size, and current use, along with its ecological context within the wider landscape.

  • Habitat Survey: A map and description of the habitat types present on the site, using recognized classification systems such as the Phase 1 Habitat Survey methodology.

  • Protected Species Assessment: Identification of any potential for protected species to be present, based on habitat suitability and signs observed during the field survey.

  • Constraints and Opportunities: Discussion of any ecological constraints that could affect the development, such as the presence of protected species or high-value habitats. The report may also highlight opportunities for biodiversity enhancement.

  • Recommendations for Further Surveys: If necessary, the PEA will recommend more detailed surveys, such as specific species surveys (e.g., bat surveys, reptile surveys) to inform the planning application.

  • Mitigation and Enhancement Suggestions: Initial recommendations for mitigating any identified impacts on biodiversity, as well as potential measures to enhance the site’s ecological value.


What is Biodiversity Net Gain (BNG)?



Biodiversity Net Gain: A Positive Step Forward

Biodiversity Net Gain (BNG) is a key principle in modern urban planning that aims to leave the natural environment in a better state than before the development. The goal is to ensure that any adverse impacts on biodiversity from a development are outweighed by positive contributions to nature, resulting in a net gain.

Five bats hanging from roof beams of a derelict building

BNG requires developers to quantify the impact of their projects on biodiversity, often using standardized tools like the Defra Biodiversity Metric. The calculation includes assessing the value of existing habitats, the impact of the development, and the benefits of any proposed habitat creation or enhancement.


When is Biodiversity Net Gain Required?

The requirement for BNG is becoming increasingly common across the UK, especially following the enactment of the Environment Act 2021. From late 2023, it will be mandatory for most developments to achieve a minimum of 10% net gain in biodiversity.

BNG is required in the following scenarios:

  • All major development projects—including residential, commercial, and mixed-use developments—are subject to BNG requirements.

  • Any development that impacts natural habitats—whether it's a greenfield or brownfield site—needs to demonstrate how it will achieve net gains in biodiversity.

  • Projects in ecologically sensitive areas—such as those near protected sites or within areas identified as biodiversity priorities—must consider BNG as part of the planning process.


What Information Does a BNG Assessment Include?

A BNG assessment typically involves the following steps:

  • Baseline Biodiversity Assessment: An evaluation of the current biodiversity value of the site before any development takes place. This is usually quantified using the Defra Biodiversity Metric, which considers factors like habitat type, condition, and size.

  • Impact Assessment: Calculation of the anticipated loss or degradation of biodiversity due to the development, again using the Biodiversity Metric.

  • Biodiversity Net Gain Plan: A detailed plan outlining how the development will achieve at least a 10% net gain. This can include on-site measures such as creating new habitats, enhancing existing ones, or implementing green infrastructure. Off-site compensation measures may also be considered if on-site gains are insufficient.

  • Long-term Management and Monitoring Plan: BNG isn’t just about initial gains; it requires sustained biodiversity benefits over time. The plan should include details on how the new or enhanced habitats will be managed and monitored for at least 30 years to ensure that the net gains are maintained.


The Integration of Ecological Assessments into Planning Applications



Why Are PEAs and BNG Important?

Both PEAs and BNG are critical for ensuring that developments are sustainable and environmentally responsible. They help developers understand the ecological value of their sites, avoid or mitigate harm to wildlife, and contribute positively to local biodiversity. Moreover, they are key to meeting legal and policy requirements, particularly under the UK’s planning system and the Environment Act 2021.


How to Prepare for Ecological Assessments

For developers, early engagement with ecological assessments is essential. Undertaking a PEA at the initial stages of a project can identify potential constraints and opportunities, allowing for a smoother planning process. Similarly, planning for BNG from the outset ensures that the development not only meets legal requirements but also contributes to wider biodiversity goals.


Conclusion

Ecological assessments, including Preliminary Ecological Appraisals and Biodiversity Net Gain assessments, are now integral to the planning process.


They ensure that developments do not just minimize their environmental footprint but actively contribute to enhancing the natural world.


By understanding when these assessments are required and what they entail, developers can better navigate the planning process, leading to more sustainable and environmentally friendly outcomes.


Incorporating these assessments early in the development process is not just a regulatory necessity—it’s a vital step towards creating resilient, thriving communities that coexist harmoniously with the natural environment.


This blog offers a clear understanding of Preliminary Ecological Appraisals and Biodiversity Net Gain, focusing on their importance and requirements in planning applications.

By keeping the focus on "Ecological Assessments," the content remains relevant and accessible to both professionals and those new to the subject.

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