Biodiversity Net Gain (BNG) - Understanding the Metric

LEARNING OUTCOMES

1. Know how a biodiversity unit is calculated in the statutory BNG metric.

2. Understand the effect of each of the multipliers within the metric calculation tool.

3. Understand how to record degradation.

4. Use the tree helper and input watercourse data.

5. Understand the metric tool output.

6. Understand the trading rules and why they need to be satisfied for a metric to be validated.

WHAT IS THE BIODIVERSITY METRIC?

- It is a tool for auditing and accounting for BNG losses and gains.

- It uses habitat as a proxy measure, translating it to biodiversity units.

- It calculates net gain change in BNG units from (baseline) pre- to post-intervention.

- It is based on the ecological mitigation hierarchy.

WHAT ARE BIODIVERSITY UNITS?

- Unit Types: Area, hedgerows, watercourses.

- The units take into consideration on site habitat changes and off site habitat changes associated with a project.

THE PRINCIPLES THAT GOVERN THE BIODIVERSITY METRIC

1. A competent person is to complete the metric.

2. The existing biodiversity protections and obligations still apply including consents and licences.

3. The metric is to be used in accordance with good practice and professional codes.

4. The metric is not a tool for comprehensive ecological advice and not a substitute for expert advice.

5. BNG units are a proxy for biodiversity and should be treated as having relative values.

6. The metric is designed to inform decisions in conjunction with local guidance and expert advice.

7. Habitat interventions need to be realistic and deliverable.

8. Created and enhanced habitats need to be reasonable, practical and local. To deliver strategic outcomes for nature conservation.

THE RULES THAT APPLY

1. Trading rules must be followed.

2. BNG outputs for each unit type must not be summed, traded or converted to other types ie: 10% for each unit type.

3. The metric must be used to calculate BNG unit value.

4. In exceptional circumstances, deviation from the metric may be permitted by the Planning Authority. This is where there are optimal conditions for restoration of wildlife - rich habitats or extant national habitats with expertise to deliver this successfully. This requires robust ecological justification.

THE DISTINCTIVENESS RULES

1. Very high - same habitats, bespoke compensation option.

2. High - Same habitat type.

3. Medium - Same broad habitat type or higher distinctiveness.

4. Low - No trading rules.

IDENTIFYING AND MEASURING BASELINE BIODIVERSITY

Each habitat unit may be described using 4 interdependent qualities:

a. Habitat area / length.

b. Condition - This measures a habitat against its ecological optimum.

c. Habitat type or Distinctiveness - This is based on type of habitat and its features.

d. Strategic Significance - The local significance of a habitat is based on its location and type.

CLASSIFICATION OF HABITAT TYPES

A competent person identifies all habitat types on site at baseline and post-intervention. Metric habitat types use the following classification systems:

1. UK Habitat Classification (UK HAB).

2. Natura 2000 (Annex 1 Habitats).

3. European Nature Information Systems (EUNIS) habitat type hierarchical view.

4. Water Framework Directive Lake Typologies.

5. Others in the User Guide eg: watercourses, individual trees, artificial intertidal / littoral habitats.

DISTINCTIVENESS OF THE HABITAT TYPE

These are identified by distinctiveness of habitat band.

1. Very high - Priority habitats as described in Section 4.1 of the NERC Act. Highly threatened, internationally scarce and requiring conservation.

2. High - Priority Habitats as defined in Section 41 of the NERC Act requiring conservation action eg: lowland fens. Remaining Priority Habitats not in a very high distinctiveness band and other near threatened and vulnerable Red List Habitats.

3. Medium - Semi-natural habitats, not classed as priority habitats but with significant wildlife benefits eg: scrub. Arable field margins (Priority Habitat Only)

4. Low - Habitat of limited biodiversity value eg: modified grassland. Agricultural and urban landscapes of lower biodiversity.

5. Very low - Little or no biodiversity value eg: hard standing. Scores 0 in the metric.

THE CONDITION OF THE HABITAT TYPE

A competent person assesses the condition of all habitats, present at baseline and estimates post-intervention. They must use Condition Assessments developed specifically for this metric.

There are 25 assessment sheets based on broad habitat types. These sheets contain key indicators, the sum of which results in poor, moderate and good condition for that habitat parcel. The condition score in inputted into the metric.

Use of ''fairly good'' or ''fairly poor'' should only be used at baseline. Some habitats eg: developed land doesn't need a condition assessment. Rivers, streams, canals have their own Condition Assessment outside the metric, for which accreditation is required.

THE CONDITION SCORES WOR

It is better to be precautionary. Don't underestimate at baseline or overestimate at post-intervention. Where the condition is consistently different within one habitat parcel, this needs to be split into smaller parcel based on condition.

Each condition category (Poor - Good) has an associated score - automatically generated by the metric. This is based on the condition inputted by the assessor. Distinctiveness condition ranges from Good, Fairly good, Moderate, Fairly Poor, Poor.

THE STRATEGIC SIGNIFICANCE OF THE HABITAT

This is the significance rating of the habitat based on its location and habitat type.

1. Where a Local Nature Recovery Strategy (LNRS) has been published, use the LNRS to assign the strategic significance.

2. Where an LNRS has not been published yet, use documents specified by the Planning Authority eg: local plan, biodiversity action plan, species conservation and protected site strategies.

THE STRATEGIC SIGNIFICANCE OF THE HABITAT

Medium strategic significance category can only be used when:

1. LNRS is not yet published.

2. The LPN has not identified a suitable document.

3. The competent person can justify why that habitat is ecologically important in that location eg: links other strategic habitats. The multiplier ranges from 1 to 1.5.

 *LNRS = Local Nature Recovery Strategy

ENCROACHMENT

Watercourses - The biodiversity unit calculation has additional multipliers. Riparian Zone encroachment is any feature or intervention within a riparian zone that reduces the quantity, quality or ecological function of the riparian habitat. eg: buildings, structures, agriculture, footpaths.

Watercourse encroachment - Any feature that adversely affects natural function of the watercourse eg: engineered bank revetment, weir, jetty.

Landscape Institute Event.