Biodiversity net gain is an approach to development that leaves biodiversity in a better state overall. It uses a metric to assess the biodiversity value of a site before and after development based on habitat types, areas, and conditions. The mitigation hierarchy must be followed, prioritizing avoidance and minimization of impacts before considering offsets. While biodiversity net gain shows promise as a framework, challenges include attitudes towards offsets, limitations of the metric, and ensuring proper resourcing and implementation by local authorities. Adoption of consistent net gain policies and focus on applying the mitigation hierarchy could help address these challenges.

1. Biodiversity Net Gain:
the next big thing for UK nature
conservation?
Claire Wansbury FCIEEM CEnv CEcol CMLI
Associate Director of Ecology
4th June 2019

2. Concepts and definitions – biodiversity
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The variety of life on earth –
ecosystems, habitats, species and
genetic diversity within species.
A scientific term, also used to refer
to nature or nature conservation,
including wildlife’s value to people.
Photo credit London Wildlife Trust

3. Concepts and definitions – biodiversity net gain
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Biodiversity net gain:
“Development that leaves biodiversity in a better state than before”
Can include using a metric-based means of ensuring that, for a
given site, there is an overall improvement based on increase in
habitat area and / or quality following a new development
To achieve net gain, a development must have a higher biodiversity
unit score after completion than the baseline score before
development
Natural England are currently updating the Defra Biodiversity Metric

4. Policy
developments
in England
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5. Net gain policy advances and development
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Mandatory biodiversity net gain
consultation (Dec 2018 – Feb
2019)
Announcement on mandatory
biodiversity net gain by the
Chancellor (March 2019)
Defra Biodiversity offsetting pilots
(2012)
Defra 25 year Environment Plan
launched January 2018
1992 Rio Convention on
Biological Diversity
2011 Government Natural
Environment White Paper
Plus NPPF – 2012, updated
biodiversity text 2018 (current
edition 2019)

6. Meanwhile in Local Planning Authorities and Industry…
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Councils including Warwickshire and
Lichfield introduced biodiversity net gain
requirements
CIRIA, CIEEM and IEMA created and
launched:
• 2016: Biodiversity Net Gain – Good
Practice Principles.
• 2019: Biodiversity Net Gain – A
Practical Guide.

7. Biodiversity net gain
Metric calculations
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If e = ecologist
? =
𝑘=0
𝑛
𝑛
𝑘
𝑥 𝑘
𝑒2𝜋𝑟

8. Metric: Pre-development
Each habitat given numerical ‘scores’ which are multiplied together with area
Distinctiveness x condition x area (ha) = pre-development units
Distinctiveness is based on various parameters - species richness, rarity etc.
High = 6 (e.g. lowland mixed deciduous woodland)
Medium = 4 (e.g. ponds)
Low = 2 (e.g. amenity grassland)
Baseline condition of each habitat is assessed using set criteria:
Good = 3
Moderate = 2
Poor = 1 Based on Defra 2012 draft metric
Defra 2.0 adds additional factors

9. Metric: – Post-development
Risk multipliers are introduced to account for:
 difficulty of habitat creation (delivery risk);
 distance of offset from development (spatial risk);
 time for created habitats to reach target condition (temporal risk).
Each risk multiplier is assigned a numerical ‘score’
Distinctiveness x condition x area (ha) x delivery risk x spatial risk x
temporal risk = post-development units
Based on Defra 2012 draft metric

10. But first…
Before the maths…
The Mitigation Hierarchy
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(Photo from talk by Kerry ten Kate,
BBOP & Forest Trends)

11. Mitigation Hierarchy
 Mitigation hierarchy must be implemented first and
robustly
 1 Avoid
 2 Minimise
 3 Rehabilitate/restore development impacts to
biodiversity on-site
 Offsetting offsite only adopted after this process and
seeks to address any residual gap

12. Biodiversity net gain:
the next big thing?
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Linocut inspired by the first black-winged stilt recorded
breeding at Medmerry © Lillian Tranborg

13. The next big thing?
Yes, but… challenges include:
 Attitudes: ‘want a licence to trash’, ‘need a level playing field’ and
‘don’t want to pay’
 Metric can only ever be a proxy
 Knowledge & resourcing: ecology and maths
 Knowledge & resourcing: Local Planning Authorities
 What if it doesn’t work?
 Everything else that needs funding

14. Solutions to those challenges
 Mandatory and consistent application of biodiversity
net gain
 Proper application of the Mitigation Hierarchy,
including protection of important sites and species
 Training for ecologists, designers etc (SocEnv)
 Funding and training for LPAs
 Funding for existing valuable areas From ’the Lawton Report’ Defra (2009) “Making Space for Nature: a review of
England’s wildlife sites and ecological network”

15. If you remember one thing:
Apply the Mitigation Hierarchy
Thank you – any questions?
Claire Wansbury
@ecologytweets
@atkinsglobal
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