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Avoidance, mitigation and compensation of impacts


Avoidance of adverse impacts on habitats and species as a direct or indirect result of development must always be the first consideration. It is often possible to move the site boundary to avoid damaging a particular habitat feature, or to carry out works at a time of year when vulnerable species are least likely to be present.  In many cases it is also necessary to design specific mitigation measures that will significantly reduce the impacts to the habitats in or next to the site and the wildlife species that they support.


Mitigation must be realistic and effective, drawn from a defensible evidence base and should aim to build on cumulative national and international knowledge of habitats and species and the potential adverse impacts that may affect them. It is therefore advisable to engage the services of a consultant ecologist to advise and assist with the design of effective mitigation.

Mitigation must be designed around the specific ecological systems on the site and impacts of the development, avoiding the use of broad brush "worst case scenario" solutions.

The mitigation must be designed to maintain the environmental conditions that exist at the site, that are paramount to the existence of the habitats and species that the site supports:

  • Temperature
  • Slope aspect
  • Availability of natural light
  • Avoidance of light pollution
  • Prevailing wind etc

Mitigation schemes should be submitted as an integral part of the planning application for consideration by the Local Planning Authority (LPA) ecologist and planning officer.

A monitoring schedule should be built into the design of mitigation that details how often and for how long the mitigation will be monitored. It must also include prescriptions for review of monitoring data and a mechanism by which the mitigation can be altered if found to be ineffective in any way.

The developer must make sure that the necessary funding is set aside specifically to address any necessary alteration to mitigation measures, if found by monitoring to be ineffective. Approved mitigation and monitoring schemes will be made conditional of any permission granted and will be enforceable through normal planning enforcement procedures.

Where European protected species are present at a proposed site, the consultant ecologist should advise the developer on the requirement to obtain development licences for the relevant species and the criteria that must be met to satisfy the granting of a licence.

The LPA ecologists will review and approve mitigation designs for all proposals. If the mitigation is unlikely to satisfy the licensing criteria (i.e. a licence for development is likely to be refused), then planning permission must be refused.

Ecological compensation

This will only be considered after all other options have been explored without finding a sufficient solution. In a very small percentage of cases it will not be possible either to avoid adverse impact on the ecology of the site, or to mitigate to reduce the adverse impact. In these cases, the local authority will consider proposals for ecological compensation; however this must be strictly as a last resort, after the first two options have been thoroughly explored. All options for onsite compensation should be investigated and given preference over offsite compensation options.

The basis of ecological compensation will be to produce "like for like" habitat. It will not be acceptable, for instance, to create an area of chalk grassland in compensation for an area of woodland lost to development.

The location of compensation sites must be appropriate to habitats and species they are designed to support, taking into account the soil substrate, slope aspect etc., and the long term integrity of the location.

Compensation sites must be subject to management agreements as part of a legal document, to ensure the long term integrity of the site for wildlife benefit. Offsite compensation sites must be in the control of the person or organisation eligible to sign a Section 106 agreement for the planning permission i.e. with a legal interest in the development site; otherwise it will be necessary for any third party land owners to enter into a separate legal agreement with the LPA.

The consultant ecologist and the developer should liaise on the design of the compensation and the resulting design must be approved by the LPA ecologist.

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