How can civil engineers improve the biodiversity of their sites?

Biodiversity net gain is a process which aims to leave wildlife habitats in a measurably better state as a result of development than before.

The Environment Bill currently before the UK Parliament proposes to make biodiversity net gain mandatory for planning applications in England, subject to certain exclusions.

The concept has been around for a few years and wording to encourage delivery of biodiversity net gain via new development is included in the National Planning Policy Framework. Indeed, many developers are already using net-gain calculations to inform and improve their planning submissions.

Wildlife and habitat losses

One of the key drivers of the new requirement is the substantial losses of UK wildlife and habitats over the last 40 years. The latest State of Nature Report highlighted sharp declines in farmland birds like skylark and turtle dove, as well as overall reductions in insect populations.

Since rigorous scientific monitoring began in the 1970s, there has been a 13% decline in average abundance across wildlife studied, with declines continuing seemingly unabated. Biodiversity net gain aims to halt and start to reverse some of these losses.

The new Environment Bill proposes that all new development in England will need to deliver a 10% biodiversity net gain, via an amendment to the Town and Country Planning Act 1990. This has significant implications for all developers, house builders and those wishing to develop land in England. Planning applications will need to be accompanied by a biodiversity net gain plan showing how the 10% gain will be achieved.

Measuring improvements

In establishing a site’s existing biodiversity baseline, all habitats on site will need to be measured and assigned a condition assessment using The Biodiversity Metric 2.0. The 10% gain can either be provided on site through enhancements in the scheme design and landscape strategy, or offsite. Net gains need to be maintained for at least 30 years and secured via a conservation covenant.

Exemptions include irreplaceable habitats (e.g. ancient woodland), which will continue to be protected by requirements of existing law and policy, and certain types of development which, for the time being, will not need to provide net gain. These latter comprise: nationally significant infrastructure projects; marine development; some urban brownfield sites; permitted development and householder extensions. Some developments such as small sites could also be subject to a simplified assessment process.

Mitigation hierarchy

A series of good-practice principles accompany the net-gain approach. Key to these is the application of the ‘mitigation hierarchy’, so that developers look first at conserving and enhancing the best of the on-site habitats and features and look to provide the 10% net gain on-site if possible. Where this is not possible, offsite mitigation (previously piloted by Defra as ‘biodiversity offsetting’) can be pursued.

The net gain requirement will come into effect during a two-year transition period commencing with royal assent of the Environment Bill.

This article is based on the authors’ briefing article in the latest issue (173 CE2) of the ICE Civil Engineering journal.