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Biodiversity Net Gain – making it real

biodiversity net gain redrow atkins mitigation housing development

Claire Wansbury and Dr Kate Vincent (Atkins) take a look at what a commitment to biodiversity net gain may actually look like for an individual developer (Redrow Homes)…

Defra’s 25 Year Environment Plan makes inspiring but challenging reading for ecologists. Exciting headline statements such as “We will: Embed an ‘environmental net gain’ principle for development, including housing and infrastructure” are tempered by subtlety different details like “We will seek to embed a ‘net environmental gain’ principle for development to deliver environmental improvements locally and nationally.” This sentence is followed by an aspiration that is challenging in itself “This will enable housing development without increasing overall burdens on developers.”

One of the things the Plan recognises is that some industry leaders are already making commitments to work towards biodiversity net gain, so in some ways the UK government is, one hopes, actually catching up with industry best practice.

biodiversity net gain redrow atkins housing

Wildflower area created at Redrow’s head office (Photo credit: Redrow)

Defra has produced a draft biodiversity metric, which allows calculations of net losses and gains. It is a proxy, and no-one pretends that a simple metric score could capture all the effects of land use change on rare and common species and habitats or the effects of changes in habitat connectivity, but it does provide an indicator of broad effects on biodiversity.

The basic concept and some ideas for ecologists on biodiversity net gain have been explored in previous Inside Ecology articles [1] [2]. However, what might a commitment to net gain actually mean for an individual developer?

As part of their sustainability strategy, Redrow Homes is looking to create a company-wide biodiversity strategy. This will look to benefit people and wildlife on Redrow’s sites across the country. Redrow obtained help from SCN Lavalin’s Atkins business to help explore the options that can be included in this strategy, including a retrospective application of the Defra biodiversity metric, to a sample of Redrow’s development sites.

Atkins applied the Defra biodiversity offsetting metric retrospectively to three of Redrow’s existing development sites. Atkins also undertook a literature review and explored wider net gain principles to help Redrow’s thinking on the next steps. Of the three sites that were analysed, two of the sites, Caddington and Saxon Brook, had a positive residual value and a biodiversity net gain for the development, whereas the third, Woodford, had an overall net loss after development.

Pollinator friendly planting, Caddington Woods (Photo credit: Redrow)

Caddington had an overall net gain of +20.03 units. The main reasons for the net gain are the current low value of the site (hard standing car park) and the retention, but more importantly the improvement through management, of the existing woodland.

Saxon Brook had an overall net gain +5.48 units. The main reasons for the net gain are the current low value of the site (agriculturally improved grassland) and the species-rich habitats such as species-rich grassland, orchard planting and pond creation that will be created post development.

Woodford Phase 1 had an overall net loss of -4.58 units. The main reason for this net loss is the fact that there aren’t large enough areas of medium or high distinctiveness habitat being created to compensate for the loss of plantation woodland. This highlights that consideration of biodiversity net gain calculations in the masterplan design at the earliest opportunity could benefit the biodiversity score. However, as only Phase 1 was measured as part of this project, the design team, working with Atkins, will now be measuring biodiversity on the remaining phases to achieve an overall net biodiversity gain on the development.

The hedgehog highway – Redrow’s 2017 CIRIA big challenge award-winning project, Glenwood Park. (An effective message despite the non-native pygmy African hedgehog used on the signage board).  (Photo credit Andrea Ormesby)

It must be noted that the metric is recognised as a proxy for biodiversity and does not take specific account of particular notable or protected species or habitats, or designated sites. For example, where an impact on a protected species cannot be avoided, a mitigation licence may be required and is likely to involve provision of compensation, but effects on individual species are not not recognised in the metric. However, application of the metric can help plan and demonstrate contributions individual development sites can make towards a net positive impact on biodiversity. Undertaking this study has given Redrow good insights that will inform the development of the company’s net positive biodiversity strategy. Redrow is now progressing the strategy based on this learning and is developing measurable targets to enhance biodiversity on all its developments.

SNC-Lavalin’s Atkins business and Redrow recognise that true commitment to biodiversity gain includes sharing experience, so a summary of the project and its findings is available to download for free. In 2016 CIRIA, CIEEM and IEMA published biodiversity net gain principles, and later this year, CIRIA will be publishing a guide to good practice, which will share stories such as Atkins’ study to help developers, planners and consultants aspiring to make net gain real in practice.

Header Image: Carey Fields development. Credit: Redrow.


[1] Six steps to mainstreaming Biodiversity Net Gain
[2] How developers enhance the environment: Introducing Biodiversity Net Gain

About the Authors: Claire Wansbury (FCIEEM CEcol CMLI CEnv) is an Associate Director of Ecology at SNC-Lavalin’s Atkins business. Claire has over twenty-five years experience as a professional ecologist. She advises on mitigation and enhancement relating to habitats and species, general biodiversity, and on valuing natural capital and the ecosystem services it provides. She is currently chairing the Project Steering Group for CIRIA’s practical guide to biodiversity net gain.

Dr Kate Vincent (MCIEEM CEnv) is an ecologist with over sixteen years experience in the academic, conservation and the private sectors, of which the last twelve has been within consultancy. She is a Principal Ecologist at SNC-Lavalin’s Atkins business, where her goal is to incorporate her passion for designing in biodiversity, and promoting and implementing biodiversity net gain in all projects she manages.