Biodiversity Net Gain (BNG) is a mandatory requirement in UK planning, intended to ensure that developments leave biodiversity in a better state than beforehand. Recognising the specific needs and constraints of smaller developments, Natural England developed the BNG Small Sites Metric—a streamlined version of the Biodiversity Metric designed specifically for smaller projects.
This comprehensive guide explores every aspect of the BNG Small Sites Metric, ensuring you understand exactly what it is, why it matters, and how to effectively apply it.
What is the BNG Small Sites Metric?
The BNG Small Sites Metric is a simplified assessment tool used to calculate biodiversity gains and losses on smaller development sites. It provides a practical approach for measuring ecological value and planning biodiversity improvements specifically tailored to sites smaller than 0.5 hectares or developments of fewer than 10 residential units.
Key Features of the BNG Small Sites Metric:
- Streamlined data collection requirements
- Simplified habitat categories
- User-friendly spreadsheet-based calculation tool
Why is BNG Important for Small Sites?
Small sites can have a cumulative significant impact on local biodiversity. Implementing BNG ensures that even small developments contribute positively to local ecology. This is crucial in urban or densely developed areas where incremental losses can quickly degrade biodiversity.
When to Use the BNG Small Sites Metric
You should use the Small Sites Metric if:
- Your site is smaller than 0.5 hectares.
- Your development involves fewer than 10 residential units.
- Your local planning authority accepts the use of this metric for your development scale.
If your site or development scale exceeds these criteria, you must use the full Biodiversity Metric.
How the BNG Small Sites Metric Works
The Small Sites Metric measures the pre- and post-development biodiversity value, calculating the net biodiversity change.
Step-by-step Guide:
1. Initial Assessment
- Determine existing habitats using the simplified categories.
- Record the area, condition, and distinctiveness of habitats.
2. Calculating Baseline Biodiversity
- Input habitat data into the Small Sites Metric calculator.
- Calculate baseline biodiversity units.
3. Planning Development
- Design your development to minimise biodiversity loss.
- Integrate biodiversity enhancement measures.
4. Post-Development Calculation
- Project new habitats created or enhanced post-development.
- Input new data into the Small Sites Metric tool.
5. Assessing Net Gain
- Compare post-development units with baseline units.
- Ensure a minimum of 10% net gain is achieved.
Key Components of the Small Sites Metric
Simplified Habitat Categories
- Grassland
- Woodland and Scrub
- Heathland
- Wetlands
- Urban habitats
Habitat Condition
- Good
- Moderate
- Poor
Habitat Distinctiveness
- High
- Medium
- Low
Achieving BNG on Small Sites: Best Practices
Maximising Habitat Value
- Preserve and enhance high-value habitats.
- Implement native planting schemes.
- Create wildlife corridors and connectivity.
Innovative Small Site Solutions
- Green roofs and walls
- Small-scale wetland features
- Pollinator-friendly planting
Legal and Policy Context
The requirement for BNG comes from the Environment Act 2021, mandating at least 10% biodiversity gain. Planning applications must include a biodiversity gain plan demonstrating how this will be achieved and maintained for at least 30 years.
Frequently Asked Questions (FAQs)
Do all small sites need a BNG calculation?
Yes, if planning permission is required, small sites must demonstrate at least 10% biodiversity net gain.
Can I combine off-site and on-site BNG measures?
Yes, off-site biodiversity measures are acceptable if achieving net gain on-site is impractical.
What happens if I can’t achieve net gain?
You must purchase biodiversity credits or units from off-site providers to offset your biodiversity loss.
Example Calculation Using the BNG Small Sites Metric
Consider a hypothetical small residential development:
- Baseline: Poor-quality grassland (0.2 hectares).
- Post-development: Creation of enhanced wildflower meadow, native hedgerows, and trees.
The metric tool calculates baseline units and post-development units. If post-development units exceed baseline units by 10%, compliance is achieved.
Implementing the BNG Small Sites Metric Successfully
Early Ecological Engagement
Engage an ecological consultant early in your planning process to maximise opportunities for biodiversity enhancements and to streamline planning approval.
Effective Biodiversity Plans
Develop clear, actionable plans demonstrating specific measures for biodiversity enhancement, supported by evidence from the Small Sites Metric calculations.
Maintaining Long-term Biodiversity
BNG requires biodiversity improvements to be maintained for at least 30 years. Strategies include:
- Regular monitoring and reporting.
- Adaptive management to maintain habitat condition.
- Legal agreements or covenants to protect habitats.
Benefits of Applying the BNG Small Sites Metric
- Improved planning approval outcomes.
- Positive contributions to local biodiversity.
- Enhanced community and stakeholder relations.
Conclusion
The BNG Small Sites Metric offers an essential tool to simplify biodiversity assessments for small developments, ensuring compliance with UK environmental legislation. By integrating this metric into your project planning, you ensure that your development not only meets legal requirements but also contributes positively to local biodiversity, creating a legacy of ecological health and sustainability.