What Happens in a Biodiversity Net Gain Assessment?

An Introduction to Biodiversity Net Gain Surveys

Now one of many legal requirements within the planning system, biodiversity net gain (BNG) became an applicable part of planning law in February 2024. From that point, developers were advised to reach out to ecological consultancies for a biodiversity net gain assessment, and fortunately, Arbtech has kept a finger on the pulse of the planning policy ever since it was first referenced in the 2019 spring statement.

A developer can meet the key components of mandatory biodiversity net gain as long as they increase the biodiversity value of their development site to a measurably better state of at least 10% net gain and ensure that it can last for an estimated 30 years. While it is true that doing this without professional support will be impossible, we offer biodiversity net gain guidance to anyone staging development projects, helping to remove any tensions with the local planning authorities.

BNG was originally expected to come into power in November 2023 after a two-year transition period following the Environment Bill turning into the Environment Act 2021 after undergoing royal assent. Instead, however, the UK government delayed rolling out the mandatory BNG requirements twice until eventually enforcing them three months later, ending confusion around the actual release date. Local councils up and down the country were able to demand compliance with the policy during this stage, but since then, it has been compulsory.

Biodiversity Net Gain Principles

Over the course of the biodiversity net gain assessments we carry out, various steps go into measuring biodiversity, accounting for each habitat lost as a result of the development work and creating a positive impact on biodiversity to achieve the best possible gains. Prior to being able to complete a BNG survey and provide the client with a biodiversity net gain plan, the ecologist will need to consider biodiversity values before and after the project, the potential for habitat creation, current local biodiversity, and the types of habitat, habitat size and other relevant factors

Across the section below, we detail how we undertake a BNG assessment and outline each and every component that plays a role in our technical consultation and decision-making.

Metric Calculations

A pivotal part of the assessment process comes from using biodiversity metric calculations to determine the pre-development and post-development ecological value of a site. Using the metric provided by DEFRA, a biodiversity net gain metric calculation tool will turn all ecological features into figures. Each figure can then be combined together, producing a biodiversity unit that reflects existing habitats and any need to enhance habitats or create new habitats, and the overall ecological value throughout the site.

Forming a pre-development biodiversity net gain calculation will be based on the current standard of the site, whereas a post-development BNG calculation will involve an alternative approach. To make the statutory biodiversity metric work, the ecological consultant would need to speak to the developer and look over the development plans to predict how the site will look and accurately calculate biodiversity net gain.

The resulting number of biodiversity units will be assembled from linear habitats, area units, hedgerow units, watercourse units and the different metrics given to each existing habitat parcel present. In most cases, the biodiversity unit value will be retrieved with the biodiversity metric tool using the same exercise, but there are other biodiversity metrics depending on the nature of the site. For instance, a small sites metric was specially designed and released in April 2024 to assist with smaller developments.

Laws, Plans and Regulations

In addition to understanding BNG and the planning process, ecologists need to maintain a knowledge of any key considerations that could cause adverse impacts to the project or planning applications. Not only does this include modified grassland, protected species and other elements of the natural environment but also the plans of the development and the site itself, whether it involves nationally significant infrastructure projects, protected sites, sites of special scientific interest (SSSI) or green infrastructure techniques.

With BNG affecting minor and major development projects, obstacles could arise from local plans, neighbourhood plans, local nature recovery strategies (LNRS) and existing protections. Likewise, a commercial development or residential development could contain different obstructions to each other, and even though an ecological surveyor will abide by good practice guidelines, adhere to each legal requirement and keep on top of land management duties, their approach may need to change again if new legislation or changes to planning policies occur.

Local Authorities, Community Groups and Organisations

Such a change in development has prompted various groups to become involved, even going as far as seeing transport and utility providers factoring the BNG objective into future plans, differing massively from previous versions. Due to the correlation with planning obligations, the relevant planning authority will be perceived as the priority to satisfy, but other stakeholders include environmental organisations, nature conservation groups and any corresponding responsible body.

Via the intervention of a biodiversity net gain consultant, it is a developer’s responsibility to remain within the legally required parameters. Regulators and organisations that need to be appeased include the Chartered Institute for Ecology and Environmental Management (CIEEM), the Department for Environment, Food and Rural Affairs (DEFRA), Natural England and any relevant wildlife groups, which are likely to vary depending on the habitats on site.

Further Surveys

Featuring disciplines in numerous areas and consultants who can cater to a wide range of assessments, the ecological and arboricultural teams at Arbtech are able to provide professional judgement and expert advice at all stages of the survey process. For instance, if any specific habitat types are identified and you need further information before you can go about correctly implementing BNG, our team can continue to support you with other inspections.

In the event of the ecological connectivity of a site indicating that additional examinations are needed, other surveys could include protected species surveys for listed animals and plants, noise and air quality assessments, condition assessments, tree surveys and ecological surveys such as a preliminary ecological appraisal (PEA) or ecological impact assessment (EcIA). Whatever is required to achieve BNG, we can either deliver ourselves or recommend a trusted associate.

Off-Site Biodiversity Gains

Although the desirable outcome will be to deliver BNG on the proposed development site, it isn’t always possible. As a last resort, if the ecologist cannot generate sufficient on-site habitat, off-site enhancements will appear as an alternative biodiversity net gain approach. It plays a pivotal role in meeting the requested BNG outcome, opening the opportunity for buying statutory credits of the same quantity needed to meet BNG but using off-site biodiversity units.

Created or enhanced habitats initiated by the mitigation hierarchy during a biodiversity net gain assessment may have been unable to avoid losses and increase on-site BNG. In place of that, off-site gains can be achieved through purchasing statutory biodiversity credits from land managers who own land designated for biodiversity offsetting. A biodiversity gain site register is active to index other land available, and providing site selection has identified it as being suitable, it will satisfy the legal agreement.

Planning Acceptance

From the perspective of a developer, the main aim of ticking every box to achieve biodiversity net gain is so planning conditions can be granted by the local planning authorities. Acting as a caveat in planning decisions, a planning officer will ensure that net gains of biodiversity have been accounted for in the first place before considering the application for planning consent. Any remaining concerns will be addressed within the biodiversity gain plan.

At the planning application stage, a biodiversity net gain plan will be passed on to the local planning authority to demonstrate that every possible factor of strategic significance has been dealt with during the assessment. The plan will detail every replaceable and irreplaceable habitat present within the red line boundary along with expected habitat loss and habitat enhancement, suitable mitigation and compensation measures, areas that need to be treated differently such as any that require ongoing management, and steps necessary to deliver net gain of biodiversity, leaving the local authority with no reason to deny planning permission.

BNG Assessment Process

As for the biodiversity net gain assessment itself, the process generally follows the same set format to display consistency and reliability with the results. It has evolved multiple times since the first version, but with the legal obligation reaching a point that it has become mandatory, it is common for one type of condition assessment to be used to establish the baseline value before creating or enhancing biodiversity value to hit the target.

Biodiversity Net Gain Survey

Starting with a desk study to investigate the local importance of the development site and any known habitats that could offer biodiversity value, the ecological consultant will then take a closer look by performing an in-person physical inspection. In order to measure biodiversity on the site accurately, the ecological surveyor will need to know all animal and plant habitats present, noting them down and converting them into a unit value for the biodiversity metric.

Based on the statutory biodiversity metric and involved trading rules, it will be possible to confirm the current biodiversity value on the site. Using site design, the development plans and a prediction of the environmental impact of the project, the ecologist can then determine the likely future biodiversity value. The biodiversity gain hierarchy for mitigation and compensation will help to gauge appropriate next steps and enhance biodiversity to the required increase.

Changes to meet the necessary number of biodiversity units based on the biodiversity metric tool may include creating new habitats or enhancing habitats already on the site. An inability to achieve BNG, avoid net loss and fall short of the at least 10% increase will lead to the need for offsite compensation. A new habitat will be built on one of many suitable sites, guaranteeing that one site away from the developer’s site reaches the required level of species richness for delivering mandatory BNG.

Similar to the ecology report produced following an ecological survey, a BNG assessment will conclude with the ecologist putting together a biodiversity net gain plan and report. It will include all further information from the BNG survey, including the current biodiversity value, the biodiversity units needed to see sufficient site gains, present site habitats, and details about the area based on nearby animals and plants. The BNG plan will also provide guidance to appease the local planning authorities.

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Contact Arbtech for Help with BNG Requirements

Navigating your way through biodiversity net gain (BNG) could be stressful and worrying, especially if you aren’t aware of how many units are needed to meet the rules of the mandate specifically on your site. Arbtech can instruct a competent person with all of the relevant qualifications, skills, experience and licensing to conduct a BNG assessment for you before putting together a biodiversity gain plan full of the information needed by the local authorities as part of planning applications.

Between on-site and off-site solutions and pre-development and post-development readings of biodiversity units, our team has dealt with countless issues standing between clients and biodiversity net gain. With our help, you can be sure that the biodiversity net gain metric will be measured accurately, retained as best as possible and built on by the 10% increase and for the required minimum of 30 years. You should then possess all you need to submit a viable application for planning permission to your local planning authority.

Regardless of the size and scale of your development plans, it would be beneficial to see an accurate price of how much a BNG assessment would cost on your site. One of the perks of choosing us as your provider of surveys for planning is that we send all clients a free quote. You can receive your own quote by reaching out to us on our contact page, via email, through social media or over the phone, and as soon as we have details about your development works, we will price up a BNG survey and plan for your site and send it across to you.