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Mitigation Hierarchy

This online resource paper provides information about the Mitigation Hierarchy, which is a widely used tool for limiting as far as possible the negative impacts of development on biodiversity

Definition and Purpose

The mitigation hierarchy is a widely used tool that guides users towards limiting as far as possible the negative impacts on biodiversity from development projects. It emphasises best practice of avoiding and minimising any negative impacts, and then restoring sites no longer used by a project before finally considering offsetting residual impacts.

Key points to consider

  • Following the hierarchy is crucial for all development projects aiming to achieve no overall negative impact on biodiversity or on balance, a net gain – also referred to as no net loss and the net positive approach, respectively;
  • It is based on a series of essential, sequential – but iterative – steps taken throughout the project’s life cycle in order to limit any negative impacts on biodiversity.

What this means for spatial planning and development management

Local authority officers can assess if the applicant has appropriately followed the sequential steps below in their development proposal. Craven Local Plan policy ENV4: Biodiversity does not specifically mention the mitigation hierarchy, although elements of it are referred to (i.e. no adverse effects on international, national and local sites, encourage recovery/enhancement of ecological networks/habitats/species). The NPPF 2021 also refers to elements of the mitigation hierarchy, for example section 179, Habitats and Biodiversity, discusses the enhancement and restoration of natural habitats. 

The mitigation hierarchy can be described as a more general approach to considering impacts on biodiversity that developers and agents should keep in mind when formulating their proposals and carrying out the work. Applicants can benefit by working through the steps of the mitigation hierarchy because it can help them to satisfy the requirements of Policy ENV4 and wider national policy.

1. Avoidance: the first step of the mitigation hierarchy comprises measures taken to avoid creating impacts from the outset, such as careful spatial placement of infrastructure, or timing construction sensitively to avoid disturbance. Examples include the placement of roads outside of rare habitats or key species’ breeding grounds, or the location of development away from known flood plains (which often also have value for biodiversity). Avoidance is often the easiest, cheapest and most effective way of reducing potential negative impacts, but it requires biodiversity to be considered in the early stages of a project. Applicants can implement the most effective avoidance mechanisms by engaging in pre-application engagement with the local planning authority, and also with key stakeholders in the subject area in terms of biodiversity;

2. Minimisation: these are measures taken to reduce the duration, intensity and/or extent of impacts that cannot be completely avoided. Effective minimisation can eliminate some negative impacts, such as measures to reduce noise and pollution. This stage is of particular importance during the construction of an approved planning application on a site. Minimising water, noise, and air pollution mechanisms can be permanently implemented for the duration of the project;

3. Rehabilitation/restoration: The aim of this step is to improve degraded or removed ecosystems following exposure to impacts that cannot be completely avoided or minimised. Restoration tries to return an area to the original ecosystem that was present before impacts, whereas rehabilitation only aims to restore basic ecological functions and/or ecosystem services – such as through planting trees to stabilise bare soil.  Rehabilitation and restoration are frequently needed towards the end of the development project.  For example at the end of a quarry’s usage excavated ground can be converted to a water body, or restored to a viable, functioning grassland habitat; or the implementation of a tree planting programme can create or extend an existing woodland.

Collectively, avoidance, minimisation and rehabilitation/restoration serve to reduce, as far as possible, the residual impacts that a development project has on biodiversity. Typically, however, even after their effective application, additional steps will be required to achieve no overall negative impact or a net gain for biodiversity.

4. Offsetting: Offsetting aims to compensate for any residual, adverse impacts after full implementation of the previous three steps of the mitigation hierarchy. Biodiversity offsets are of two main types: ‘restoration offsets’ which aim to rehabilitate or restore degraded habitat, and ‘averted loss offsets’ which aim to reduce or stop biodiversity loss in areas where this is predicted. Offsets are often complex and expensive, so attention to earlier steps in the mitigation hierarchy is usually preferable. Please refer to the Biodiversity Offsetting resource paper.

In summary:

1. Avoid - damage to habitats should be avoided

2. Minimise - damage to habitats should be minimised

3. Rehabilitate/restore - damaged or lost habitats should be restored

4. Offset - as a last resort, damaged or lost habitats should be compensated

Relevant Craven Local Plan policies

Relevant Craven Local Plan policy guidance

March 2022. This webpage provides general information about relevant planning topics and we hope you find it helpful. Please be aware that it is not a statement of Council policy and does not provide formal policy guidance. For those things, please refer to the Craven Local Plan and supplementary planning documents.