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Biodiversity net gain – Dorset

Biodiversity net gain was introduced in the Environment Act 2021 to enhance nature in the face of declining biodiversity. Biodiversity net gain legislation compels developers to maintain the current standard of biodiversity on a development site on completion of a project and increase it by 10%, leaving it in a measurably better state.

While biodiversity net gain legislation was introduced after a two-year transition period to allow developers and local councils time to adapt, Dorset Council was one of several councils across England to implement the policy early.


Protected natural environment: Poole Harbour.

Biodiversity net gain explained

On gaining royal assent the Environment Bill became the Environment Act 2021. Biodiversity net gain (bng) applies to most planning applications in England and has been introduced into the National Planning Policy Framework. It means that a biodiversity net gain plan must be submitted to the local planning authority for examination during the planning process.

Biodiversity net gain became a statutory requirement on 12th February 2024 in England for major developments and minor sites of nine units or less, and it applied to small sites from April 2024: there are few biodiversity net gain exemptions.

To comply with local planning authorities’ biodiversity net gain requirements, a scheme must demonstrate a minimum 10% uplift in biodiversity value post-development compared to pre-development, evidenced by the Defra biodiversity metric. The uplift must be achieved by ecological enhancements such as installing bat or bird boxes or habitat creation. Applicants must also provide details of how the enhanced areas will be maintained for the long term, at least 30 years.

When it proves impossible to add net gain to a site area, biodiversity net gain units can be delivered off-site. A legal agreement or conservation covenant is required to determine the site management over the next 30 years. As a last resort, to achieve bng requirements habitat units may be purchased through the national biodiversity credits scheme.

Biodiversity net gain in Dorset

As a local planning authority, Dorset Council is responsible for local biodiversity net gain regulations, approving planning applications and biodiversity net gain plans. It also monitors county-wide compliance with biodiversity net gain principles.

Dorset Council’s document, Biodiversity Net Gain Guidance for Applicants and Agents 2023, explains its Natural Environment, Climate and Ecology Strategy: a vision for a nature-positive Dorset in the face of significant loss of species. Local Nature Recovery Strategies, identifying key areas for action to improve nature recovery, have been developed across Dorset and come into play if biodiversity net gain cannot be achieved on site, to determine the best location for off site bng.

Dorset Biodiversity Appraisal Protocol (DBAP)

Dorset Council created the DBAP to clarify how developments of 0.1 hectares or above must follow biodiversity net gain legislation, such as arranging ecological surveys at the correct times of the year; it guides on achieving net gain for species and habitats and gives information on installing bat and bird boxes. The DBAP states that a mitigation hierarchy must be followed, impacts on biodiversity must be avoided or mitigated, and if this is impossible, they must be compensated for.

Dorset Council will assess applications against this mitigation hierarchy and local plan policies. The council’s Natural Environment Team may request further information about a site plan to ensure it meets the biodiversity net gain hierarchy. The hierarchy must also be applied using Dorset’s Ecological Network Maps or Local Nature Recovery Strategy (LNRS) Local Habitat Map, identifying priority areas for net gain delivery via habitat creation or enhancement.

Further environmental protections

The council has also published guidance on achieving biodiversity net gain via sustainable drainage systems, planting schemes and green space design, and notes that biodiversity net gain does not override protection for designated sites such as Sites of Special Scientific Interest and irreplaceable habitats such as veteran trees and ancient woodland. Important sites such as Poole Harbour have stringent protections and international designations protect Dorset heaths. New development must ensure no adverse effects on European protected sites such as Special Protection Areas, Special Areas of Conservation, or Ramsar sites.

A Green Infrastructure Networks Strategy is underway and there should be support for schemes that would enhance geodiversity and biodiversity and offer improved access: for instance, the Purbeck Local Plan aims to protect wildlife and geological features on the coast through the Shoreline Management Plan Policy. While Dorset does not have many Nationally Significant Infrastructure Projects, there is potential for large-scale renewable energy schemes for which biodiversity net gain principles will be relevant.

Heathland at Hamworthy, Poole.

The biodiversity net gain assessment

A biodiversity net gain consultant will assess all ecological features on the site, such as European protected species and important habitats, and calculate their biodiversity value. The next step is to work out the biodiversity value of the site post-development, based on studying the development plans. Armed with two figures, the surveyor will input them into the Defra biodiversity metric 4.0 to find out if there is a deficit – if there is, changes will need to be implemented to eliminate it. Then the best way of adding a 10% biodiversity gain is worked out according to a mitigation hierarchy and described in the biodiversity net gain plan.

Creating on-site net gain is the preferred policy, for instance by creating habitats or altering the development plans. If this proves impossible, the next option is to deliver off-site bng, while the last resort option is to purchase biodiversity net gain credits.

Local planning authorities view a biodiversity net gain plan as reliable information to base a decision on when determining planning applications.

The causeway at Chesil Beach leads to the Isle of Portland on the Jurassic Coast.

Do you need a biodiversity net gain plan in Dorset?

To ensure that you comply with biodiversity net gain requirements, the first step is to identify an ecological consultancy with experience in drawing up biodiversity net gain plans for the local authority. The firm should employ fully qualified ecological consultants; this means that you can rely on receiving expert advice about the best way to add biodiversity value to leave your site in a measurably better state and secure a successful planning application.

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