How a PEA Feeds Into Biodiversity Net Gain

A preliminary ecological appraisal (PEA) and a Biodiversity Net Gain (BNG) assessment are separate pieces of work. The PEA comes first, though, and much of what it records becomes the foundation for the BNG calculation.

Understanding how the two connect, and exactly how a PEA feeds into Biodiversity Net Gain helps you commission the right surveys in the right order. It also avoids paying twice for similar site visits.

What Biodiversity Net Gain Requires

In England, most developments requiring planning permission under the Town and Country Planning Act must deliver a biodiversity gain of at least 10% compared with the pre-development baseline. That gain must be secured for a minimum of 30 years. A biodiversity gain plan, approved before work begins, sets out how it will be achieved.

The gain is measured using the statutory biodiversity metric. The metric converts habitats into “biodiversity units” based on their type, size, condition and location. Every calculation starts with a baseline, and that is where the PEA comes in.

Where the PEA Contributes

A record of what is on the site

The field survey identifies and maps the habitats present: grassland, hedgerows, woodland and wood pasture may also change which BNG rules apply. The PEA flags these at the start of the project.

Evidence for the design stage

The appraisal shows which features are worth retaining. Keeping a mature hedgerow of a species-rich grassland is usually cheaper than losing it and compensating elsewhere. The earlier this is known, the more design options remain open.

Protected species and designated sites

BNG sits alongside protected species law, not in place of it. Bats, great crested newts and nesting birds still need their own surveys and mitigation. The PEA identifies which of these are likely to be relevant.

What the PEA Does Not Do

A standard PEA is not a BNG baseline report. Four gaps are worth knowing about.

• Habitat classification. The statutory metric uses UKHab. Older Phase 1 habitat surveys use a different system, so their results do not necessarily transfer.
• Condition assessment. The metric scores each habitat for condition using specific criteria. A general PEA may not collect this detail.
• Habitat condition is best judged in the growing season. A winter PEA may need a follow-up visit for this reason.
• A BNG baseline needs accurate area and length measurements for each habitat parcel.

How the Process Fits Together

1. PEA records habitat, features and ecological constraints.
2. The baseline assessment applies the metric, with habitat condition and area measured in detail.
3. Design retains, enhances or creates habitat on site where possible.
4. Off-site units or statutory credits cover any shortfall that on-site measurements cannot.
5. Biodiversity Net Gain plan is submitted and approved, with long-term management secured.

For farms and rural estates, this can be an opportunity as well as an obligation. Landowners with suitable land may be able to create habitat and supply biodiversity units to developers.

Plan Your Ecology and BNG Work With CWE

Understanding how a PEA feeds into Biodiversity Net Gain helps you commission the right work at the right time. Scoping the appraisal with BNG in mind saves time and avoids repeat visits. Tell us about your site and proposal, and we will advise whether a combined approach makes sense and whether an exemption is likely to apply.

Contact us at info@collingtonwinter.co.uk to discuss your project.

Frequently Asked Questions

Is a PEA the same as a BNG assessment?

No. A PEA assesses ecological features and constraints. A BNG assessment calculates biodiversity value using the statutory metric.

Can one ecologist do both?

Yes, and it is often more efficient. The ecologist can scope the survey to cover both from the start.

Will the PEA tell me how many biodiversity units I need?

Not by itself. It provides the habitat information, and the metric calculation follows from that.

What happens if the site has valuable habitat?

Higher-value habitats carry more weight in the metric and can be costly to replace. Your ecologist can advise on retention, design changes or compensation.