Winter 2023

IMPLEMENTING BNG
A FOCUS ON
BIODIVERSITY NET GAIN
By Richard Tomlinson, Chartered Landscape Architect
and Associate Landscape Manager at The Environment
Partnership (TEP) Ltd.
What is Biodiversity Net Gain
(BNG)?
You may have come across the term
in recent months as the government
moves towards implementing a
mandatory minimum 10% increase of
biodiversity on all new developments
by January 2024 – small scale
developments and Nationally Significant
Infrastructure Projects will follow later.
But what does this actually mean and
how is it implemented?
Wildflowers on roof
Image cedit: TEP
Definition
The standard definition from UK
Government states that “Biodiversity
net gain (BNG) is a way to contribute to
the recovery of nature while developing
land. It is making sure the habitat for
wildlife is in a better state than it was
before development”.
The process, however, is like a lot of
things, fairly simple to explain but
rather more difficult to pull off. Of
course with some developments it
will be easier to achieve a net gain in
biodiversity than on others.
Understanding Biodiversity Baseline
The first point of call is to understand
the site’s biodiversity baseline value.
This is achieved by completing a
structured and formal assessment using
a standard tool. Natural England, along
with the Department for Environment,
Food & Rural Affairs (DEFRA), developed
and created the Biodiversity Metric
(current version is 4.0). The metric
tool takes a habitat-based approach
to measure a site’s biodiversity value.
First a detailed site appraisal, marking
the condition of existing habitat against
Below: Figure 1 – Baseline habitat and pre-intervention score.
pre-determined condition assessment
criteria (UKHab), which assigns a grade
of poor, moderate or good condition.
The site assessment information is then
uploaded into the DEFRA Metric, which
then further appraises the habitat’s
strategic significance within the
landscape, to arrive at a total habitat
value for the site. These are scored as
baseline biodiversity units, which is the
currency of the metric.
BNG proposals
The proposed development is then
overlaid on to the baseline survey,
which reveals the potential impacts
on the baseline habitat and identifies
opportunities for enhancement of
retained features. For example, a
retained habitat in poor condition
could be enhanced to moderate
condition through specific management
interventions. There are a number of
guiding principles and best practice
documents that provide a structured
approach to developing a BNG
strategy. British Standard 8683.2021
sets the requirements for the BNG
assessment process, and the Chartered
Institute of Ecology and Environmental
Management (CIEEM) has developed
guiding principles for designing,
implementing, maintaining and
monitoring a site’s Biodiversity.
The landscape and habitats that will
be implemented post development
are entered into the metric. They must
demonstrate a minimum 10% net gain,
along with satisfying predetermined
18 GREENSCAPE WINTER2023 • www.greenscapemag.co.uk