The mitigation hierarchy is a fundamental part of delivering a net gain for biodiversity and is embedded in good practice.
The NPPF sets out the mitigation hierarchy in paragraph 180:
When determining planning applications, local planning authorities should apply the following principles:
if significant harm to biodiversity resulting from a development cannot be avoided (through locating on an alternative site with less harmful impacts), adequately mitigated, or, as a last resort, compensated for, then planning permission should be refused;
Principle 1 of the Good Practice Principle is ’apply the mitigation hierarchy. It says:
Principle 1. Apply the Mitigation Hierarchy
Do everything possible to first avoid and then minimise impacts on biodiversity. Only as a last resort, and in agreement with external decision-makers where possible, compensate for losses that cannot be avoided. If compensating for losses within the development footprint is not possible or does not generate the most benefits for nature conservation, then offset biodiversity losses by gains elsewhere.
So, how do you evidence compliance with the mitigation hierarchy for BNG?
The CIEEM Biodiversity Net Gain Report and Audit Templates provide guidance on how to address compliance with the mitigation hierarchy:
Measures to avoid and minimise biodiversity loss and to rehabilitate/restore biodiversity affected by the project are: 1) defined and documented, 2) implemented and monitored; and 3) managed for the duration of the project’s impacts. For example, maintain records of the consideration of alternatives as evidence of avoidance measures implemented.
Here is how I might define and document measures to avoid and minimise biodiversity loss.
Avoid
Define: Avoidance means retaining the best and/or most valuable habitats on a site. More than this, it means measures that also reduce indirect impacts on retained habitats, such as from lighting, recreation or domestic pets.
Document:
‘Woodland on site has been retained…’
‘The area of species rich grassland on the site has been retained and enhanced as part of this scheme’
Minimise
Define: Minimising impacts means either retaining as much habitat as possible, or retaining the best areas of a habitat. Minimising impacts can also mean creating new habitats to provide buffers to other habitats, e.g. woodland buffers, or hedgerow buffers.
Document:
‘The areas of grassland with the greatest diversity have been retained and incorporated into the on-site open space.’
‘Key hedgerows that act as commuting corridors for bats have 10 metre buffers…’
Mitigate
Define: Mitigation means reducing the severity of impacts. This could mean providing new habitats of value for biodiversity, or enhancing retained habitats.
Document:
‘New grassland will be created to mitigate for the loss of grassland on the site’.
Compensate
Define: Compensation means providing equivalent new habitat for the loss of priority habitat. This is usually in addition to biodiversity net gain.
Document:
‘A new orchard will be planted, with orchard trees translocated from the existing orchard, to compensate for the loss the current orchard.’
Offset
Define: Offsetting means delivering biodiversity units on land not associated with the development, either on other land in the control of a developer or via a habitat bank.
Document:
‘2.5 biodiversity units will be purchased from a habitat bank to achieve a net gain for biodiversity.’
‘An additional area of land has been identified for enhancement to offset on-site impacts.’
It is also important that any consideration of alternative designs have properly documented. Document the alternative options for a scheme, and the evolution of the design, to demonstrate how the mitigation hierarchy has been applied.
This could be as a series of annotated layout drawings or proposed development maps showing how the scheme has evolved and the key biodiversity considerations of each design and the changed from the last layout. Or it could be a running list of design changes and the impact on the metric calculations.
This requires good communication with the wider design team so that they understand your requirements as an ecologist.
References
CIEEM (2021). Biodiversity Net Gain Report and Audit Templates. Chartered Institute of Ecology and Environmental Management, Winchester, UK
CIEEM, CIRIA, IEMA (2016) Biodiversity Net Gain: Good practice principles for development. Winchester, UK
Ministry of Housing, Communities and Local Government (2021). National Planning Policy Framework. London, UKMinistry of Housing, Communities and Local Government