Demystifying the DEFRA BNG Biodiversity Metric: How Biodiversity Units for BNG are Calculated
If you’re embarking on a new development project in England, you’ll be familiar with Biodiversity Net Gain (BNG) https://www.gov.uk/government/publications/statutory-biodiversity-metric-tools-and-guides, a cornerstone of the Environment Act 2021. The BNG principle is simple: to leave nature in a measurably better state than before.
How do we quantify something as complex as biodiversity? The answer, with regards to BNG compliance says CSX’s BNG Metric expert Steven Crosby, lies in the statutory biodiversity metric – the official government tool used to calculate the vegetation habitat biodiversity value of a site. This post will demystify the metric, breaking down how these crucial calculations are made.
What is the Biodiversity Metric?
Developed by Natural England and published by Defra, the metric is an Excel-based tool that translates real-world observations into a simple, comparable figure: biodiversity units.
When starting a project, key details like the project name, the date and the name of the person completing the calculations, are entered into the spreadsheet. Due to the complexity involved, the metric should always be completed by an ecologically ‘competent person’ – an individual with the right mix of experience, training, and qualifications.
The Core Calculation: How Biodiversity Units Work
The metric is divided into sections for on-site (within a development’s red line boundary) and off-site habitats. These are further split into three categories of habitat: area habitats, hedgerows and watercourses. Most habitats fall under the category of ‘area habitats’ – anything from grasslands and woodlands to lakes and derelict land.
For each parcel of habitat, the baseline number of biodiversity units is the result of a straightforward multiplication.
Distinctiveness x Condition x Area x Strategic Significance = Biodiversity Units
Let’s break down these components:
- Area: This is the size of the habitat parcel, measured in hectares. At CSX, we map this precisely using high resolution earth observation data, 0.75cm ground sampling distance across the whole site.
- Distinctiveness: The habitat is classified according to the UKHab system for identifying vegetation habitats, and the metric assigns a score based on the habitat’s type and rarity, ranging from 0 to 8.
- Condition: This is a rating of the habitat’s quality, which we assess using both our imagery and data models. The metric assigns a score from 0 to 3 based on this assessment.
- Strategic Significance: This score reflects how important the habitat is to the local area’s nature recovery goals. The responsible local authority designates this, and the metric gives a score between 1 and 1.15.
And that’s it! Multiply those numbers together and the resulting value is the number of biodiversity units the habitat parcel is worth, and you’ve hence completed the process of demystifying the DEFRA BNG biodiversity metric.
The same principles apply to hedgerows and watercourses, and the linear BNG units they can create, although the input measurement is in kilometres instead of hectares.
Once the baseline (pre-development) units are calculated, they are compared against similar calculations based on the post-development plans, to ensure the mandatory 10% net gain is achieved.
Navigating BNG with Confidence
Understanding the nuances of the biodiversity BNG metric is crucial for any developer in England. While the calculations are logical, they require expert handling to ensure compliance and a successful outcome.
We’re here to provide that expert support. By leveraging cutting-edge tools like ultra-high resolution digital twins, we inform and evidence your Biodiversity Net Gain calculations, delivery and compliance. CSX is here to help you navigate the complexities of BNG and achieve your project’s goals with confidence.