A Guide to Biodiversity Metric 4.0 | The metric for BNG planning and compliance

May 11, 2023

What exactly is Biodiversity Metric 4.0? 

Natural England describes Biodiversity Metric 4.0 (BM 4.0) as “a biodiversity accounting tool that can be used for the purposes of calculating net gain”. Under the new Environment Act 2021, the UK government introduced a mandatory biodiversity net gain obligation (which will start to become effective from November 2023) making Biodiversity Net Gain a legal requirement for nearly all new developments in England. Biodiversity Metric 4.0 is THE KEY TOOL that supports the delivery of the biodiversity net gain obligation, and its use will be compulsory. It’s important to understand it!

So what exactly is this tool? Biodiversity Metric 4.0 was designed to provide a standardised approach to assessing the biodiversity impact of development projects, and to ensure that the impact is fully accounted for and compensated for. In other words, no matter where you are in England, the tool ensures biodiversity is measured in the same way. We’ve touched on this in other blogs but to briefly review, Biodiversity Net Gain requires that any new development will be required to submit a Biodiversity Gain Plan that accounts for their on-site biodiversity score pre development and details how they will provide a minimum net gain of 10% to that biodiversity over the next 30+ years.

Natural England, along with the Department for Environment, Food & Rural Affairs (DEFRA), created Biodiversity Metric 4.0 as a habitat based approach to measuring a site’s biodiversity and then appraising the area’s importance and impact to the ecosystem at large. Biodiversity Metric 4.0 uses habitat features to assess the site’s value. This is based on a set of ecological characteristics that are important for biodiversity, such as habitat quality, condition and location. These habitat characteristics are used to assign a score to the site, counted in biodiversity units (BUs), which reflects its overall biodiversity value. The biodiversity units are then used to determine the net gain or loss in biodiversity resulting from a development.

A simplified metric for small sites

The Small Site Biodiversity Metric was created to provide a simplified method of assessing biodiversity on smaller development sites. This Metric was developed in recognition of the fact that smaller developments may not have the resources or expertise to undertake the more intricate assessments required by the full Biodiversity Metric 4.0.

It’s designed to assess the biodiversity impact of smaller development projects, those for residential developments with fewer than 10 residential units on a site area less than 1 hectare. It may also be applied to other sites, where the site area is less than 0.5 hectares.

For the purpose of this blog, we will be focusing on the details and documents of Biodiversity Metric 4.0.

How to use Biodiversity Metric 4.0 

There are a number of documents and tools listed on Natural England’s website to help anyone needing to understand and apply Biodiversity Metric 4.0 to their development project. Here’s a quick breakdown of what each is, a note on their complexity and how it should be used:

Biodiversity Metric 4.0 User Guide 

The Biodiversity Metric 4.0 User Guide is a lengthy document (69 pages to be exact) which provides detailed guidance, support and instruction on the use of the Biodiversity Metric 4.0. It is a technical document that contains complex terminology and procedures that require careful study and understanding to ensure compliance with the metric and the wider Biodiversity Net Gain policy.

Not unlike a legal document, the Biodiversity Metric 4.0 User Guide sets out a standardised explanation and framework for assessing biodiversity value, measuring the biodiversity gain achieved, and selecting appropriate mitigation measures to minimise the impact of development projects on local ecosystems. It also provides guidance on how to monitor and report on the effectiveness of the mitigation measures.

Biodiversity Metric 4.0 Calculation Tool 

The Biodiversity Metric 4.0 Calculation Tool is one massive excel file that users must understand, navigate and use to calculate the biodiversity value and biodiversity units (BUs) of a site. To use the metric calculation tool, one needs to know the following details of the on-site or the off-site area that are part of a Biodiversity Net Gain Plan:

The types of habitat. Habitat types are generally categorised into either area based, hedgerow, or watercourse. 

The size of the habitat parcel to be retained, enhanced, created, or lost. A development project’s size is measured in metres squared for area features, or in metres for linear features (rivers and streams, hedgerows and lines of trees). 

The condition of each habitat parcel which is a measure of the habitat against its ecological optimum state. This is used as a way to measure the variation in the quality of patches of the same habitat type. More on habitat condition can be found in the Technical Annexes.

The strategic significance of the site. This refers to the local significance of the habitat based on its location and the habitat type. Specifically the project developer needs to know whether the sites are in locations identified as local nature priorities

To comply with the Biodiversity Net Gain policy in England, developers will be required to use the Calculation Tool as the nationwide standard to calculate the biodiversity value of their site pre-development and compare it to the biodiversity value of the site after development. The Tool enables developers to identify the level of biodiversity gain required and to select appropriate mitigation measures to achieve this gain.

Biodiversity Metric 4.0 Technical Annexes 1 & 2

Technical Annex 1 is an excel file that provides the finer details on the assessment methodology and instruction on how to carry out condition assessments of habitats as part of the Biodiversity Metric 4.0 calculation. The file contains multiple sheets that cover hedgerow, woodland and watercourse habitat types among others, as well as guidance on how to use these sheets to assess the condition of habitats. It ensures that condition assessments are carried out consistently and accurately, so that the results of the Biodiversity Metric 4.0 calculation are accurate, standardised and reliable. 

In brief, habitats are given a condition category from “poor” to “good” correlated to a condition score ranging from zero to three. These scores affect the overall habitat valuation and Biodiversity Units of a site which are used to determine the net gain needed to achieve the biodiversity net gain mandates.

Section 5.3 of the Biodiversity Metric 4.0 details more about habitat condition.

Technical Annex 2 is an additional technical document that explains the scientific basis and methodology behind the Biodiversity Metric 4.0 calculation. It contains specific information on the ecological concepts, data sources, and algorithms used to derive the biodiversity units that are used to measure and offset biodiversity loss. Like Annex 1, it also provides detailed technical information that can be used to support the calculation of biodiversity units for different habitat types, and to ensure that the results of the Biodiversity Metric 4.0 calculation are accurate, standardised and reliable.

Both documents are complex, but need to be used for carrying out biodiversity assessments for development projects in the UK.

GIS Import Tool

The GIS Import Tool is yet another heavy excel file that allows project developers, and the BNG experts they are working with, to import existing geographic information system (GIS) data into the Biodiversity Metric 4.0 calculation. The file is meant to simplify the data collection and reporting of sites that may already have valid and up-to-date ecological and habitat data available. 

Simplifying and streamlining the complexities of Biodiversity Metric 4.0

Natural England boasts that Biodiversity Metric 4.0 has been created as a simplified, user-friendly tool to collect data and calculate the habitat value of a site. And to be fair, they’ve come a long way in each new iteration of the tool. However, complexities, technicalities and the need for competent BNG experts will always exist as the UK continues to roll out mandates on Biodiversity Net Gain. 

The implications of non-compliance for developers and landowners is huge and failing to deliver adequate biodiversity net gain according to the standards laid out in Biodiversity Metric 4.0 could be a time consuming and costly error. 

Joe’s Blooms is here to help with Biodiversity Net Gain compliance. Our platform service is designed and vetted to make compliance easy as well as affordable. With our tools, you don’t need to engage with the complex processes set out above - but instead produce fully compliant documents and metric sheets via simple interfaces and data portals. This means you can get on with your development. We are already working with the key stakeholders to ensure our system and solutions are fully comply with the 'Net Gain' policy. 

You can keep up to date with us by subscribing to our news and updates here. Or, get in touch with us today to see how we can directly help you with your biodiversity net gain plan.

Oliver Lewis

Founder of Joe’s Blooms

Oliver Lewis is the founder of Joe’s Blooms, providing end-to-end digital solutions to help you create best-in-class Biodiversity Gain Plans. Expert in this field, he shares his knowledge on the Environment Bill which will be effective in November 2023.

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