Aylesbury Vale Area

Biodiversity Accounting Supplementary Planning Document

Ended on the 19th March 2021
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6.0 The Biodiversity Accounting Tool

6.1 The Biodiversity Accounting Tool uses a spreadsheet for the user to input information about the habitats on-site, and also for what is planned for existing and new habitats as a result of the development. The tool applies formulae (based on the latest available Defra metric calculations and guidelines) to work out whether the plans for the habitats on-site result in an overall residual biodiversity gain or loss. The Biodiversity Accounting Tool also includes separate assessments for hedgerows and rivers.

6.2 Overall, the tool works to calculate:

  • the 'units' of habitat required to ensure that there is at least a 10% biodiversity gain compared with the pre-development calculation;
  • the length (in metres) of distinctive (quality) hedgerows that must be replaced, if hedgerows are removed on-site; and
  • river impacts and any compensation required.

6.3 For habitats - using the Biodiversity Accounting process allows a standardised formula to be used to calculate the overall biodiversity impact of a development. This 'residual habitat impact score' is based on the condition and extent of habitats affected, comparing the before and after of the proposed development. The tool also takes into account:

  • plans for current habitats to be retained, enhanced or lost;
  • the value of losses to habitats from indirect impacts of development;
  • proposed on-site mitigation (creation or enhancement) and;
  • the required minimum percentage net gain.

If, after all opportunities on-site to avoid, mitigate and compensate have been exhausted (which may involve alternative designs), the applicant's development still results in a residual loss, then habitat compensation will be required to ensure at least the minimum biodiversity gainis achieved post-development,compared with the pre-development value of the habitats.

Only where on-site opportunities are exhausted should off-site compensation be sought. The off-site compensation could be on land either already owned by the applicant or elsewhere; and the nature of the compensation could be creating new habitat or by restoring current, degraded habitat.

6.4 For hedgerows – (including those on the development boundary) should be retained, enhanced and created on site where possible in line with the mitigation hierarchy. However, if they are removed, they must be assessed for their distinctiveness (quality)and replaced by at least or a higher distinctiveness hedgerow, of a length calculated through the Biodiversity Accounting Tool.

6.5 For Rivers - River impacts are calculated using same formulae to that of habitats, however they are measured in kilometres. The factors that influence the distinctiveness and condition are Time to Target Condition, Difficulty to Create, Strategic significance, and water-course or riparian encroachment.


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