Biodiversity Net Gain Mitigation for Development

Biodiversity Net Gain (BNG) is an approach to construction and development that aims to leave the environment in a better state than it was before or at the same level that it was before any development took place.

Biodiversity Net Gain was initially introduced due to the fact that biodiversity has steadily declined in recent years in the UK. Construction and developments have had a considerable impact on the environment as they produce a high amount of pollution.

BNG is being requested more frequently by local planning authorities to inform planning applications for planning permission. Therefore, it can have a significant impact during the decision making process of planning authorities when they debate whether to grant or refuse a planning application.

As such, if local planning authorities determine that a proposed development may not meet the required BNG standards, developers may be required to specify key mitigation methods that must be put in place in order to deliver the net gain required to gain planning permission.

Biodiversity Net Gain Mitigation

In order to achieve Biodiversity Net Gain, development proposals must follow the ‘mitigation hierarchy’.  This hierarchy encourages developers to avoid harm to biodiversity from the offset, then mitigate or compensate for any losses on site or off site.

Following the mitigation hierarchy is crucial for any development projects that are aiming to achieve no overall negative impact on local biodiversity or biodiversity net gain. The hierarchy is based on a series of steps that should be taken throughout a development project’s life cycle.

The biodiversity mitigation hierarchy contains the following steps:

• Avoidance – The first step in the mitigation hierarchy is comprised of measures taken to avoid a negative impact on biodiversity from the beginning. This can include timing construction to avoid disturbance to wildlife and carefully spacing infrastructure so that habitats are not affected. Avoidance is typically the easiest and most effective way of reducing potential negative impacts. However, it must be considered in the early planning stages of a project.

• Minimisation/Mitigation – This includes measures taken to reduce the duration, intensity, likelihood and extent of any impacts that cannot be avoided. Effective mitigation can help to eliminate some negative impacts. Examples of mitigation include building wildlife crossings on roads, designing powerlines to reduce harm to birds and measures to reduce pollution and improve air quality.

• Restoration/Rehabilitation – This step includes measures that will be taken when creating or enhancing habitats after development has taken place where mitigation or avoidance was not possible. Restoration aims to return an area to the original ecosystem that was present before any impacts occurred. Rehabilitation aims to restore basic ecological functions and ecosystem services. These steps are frequently required towards the end of a project.

• Offset – This includes measures that will be taken to compensate for any adverse impacts after the other steps of the mitigation hierarchy have been implemented. Offsetting can often be complex, so the steps beforehand are typically more preferable.

Biodiversity Net Gain Principles

Biodiversity Net Gain principles

According to the Chartered Institute of Ecology and Environmental Management (CIEEM), there are ten crucial good practice principles of Biodiversity Net Gain. These should help to achieve BNG if they are followed accordingly. The mandatory biodiversity net gain principles include the following:

• Utilise the mitigation hierarchy to minimise the impact on biodiversity
• Eliminate any negative impacts on biodiversity
• Communicate each BNG outcome with complete transparency
• Cover all areas of sustainability, including societal and economic factors
• Involve any pre-development and post-development stakeholders in creating mandatory net gain solutions
• Focus on producing long-term environmental benefits from BNG
• Understand the variable factors and potential risks in order to achieve and deliver biodiversity net gain
• Offer nature conservation that exceeds the stated BNG requirements
• Determine a suitable method when measuring biodiversity net gains
• Ensure the best possible results from biodiversity net gain

For case studies and a practical guide on biodiversity net gain principles, visit the CIEEM website. Following these principles alongside the mitigation hierarchy can help to ensure that your development proposal meets all of the biodiversity standards required by local planning authorities. This will mean that the planning application process will go smoothly and construction work can begin.

Calculating Biodiversity Net Gain

Metrics assign every habitat on a site a ‘biodiversity unit value’ according to its relative importance for biodiversity. This helps to compare between the existing value of a development site and what will be delivered through development or management. This may include an increase in natural habitats through retention and enhancement and/or creation, which goes over and above the environmental habitat originally on site.

Biodiversity net gain can be calculated through the DEFRA biodiversity metric 4.0, which requires a limited number of factors. These factors include:

 The type of habitat (both on and off site)

• Any locations (if they are local environment priorities)
• The size of habitat parcels in kilometres or hectares
• The condition of any habitat parcels

The government website also provides a biodiversity metric 4.0 calculation tool, which can help to determine your biodiversity unit score that translates into the standards of your local authority.