There’s no evidence that Biodiversity Net Gain (BNG) units developed using the statutory biodiversity metric in England result in improvements for birds and butterflies, as additional conservation efforts are needed to reach 10% net gain for those species, a newly published study has found.

The research, carried out by scientists at Cambridge University and published Friday in the Journal of Applied Ecology, assessed the performance of the UK Department for Environment, Food, and Rural Affairs’s (Defra) statutory biodiversity metric across 24 sites in England, showing that units are calculated more precisely for the plant dataset than for the bird and butterfly datasets.

While the metric appears to capture plant diversity quite well, it doesn’t reflect the intricacies of ecosystems and species like birds and butterflies, which use habitats in very different ways, first author Cicely Marshall said.

However, even for plants, gains are smaller than expected.

“Using the statutory biodiversity metric to define 10% biodiversity net gain without additional species-focused conservation management is likely to translate into small gains for plant biodiversity, and negligible gains for birds and butterflies,” the study said.

“We hope our study will contribute to improving the way nature’s value is calculated, to make the most of this valuable opportunity for nature recovery,” Marshall said.

Defra’s metric allows companies to calculate biodiversity losses and gains across a site in a bid to ensure an overall minimum 10% biodiversity gain, as mandated by the BNG framework. Landowners can also use it to calculate the biodiversity value of their land so as to enter the biodiversity credit market.

The reliability of the metric has key relevance since the net gain requirements are expected to generate a market for biodiversity credits worth an estimated £135-274 million ($170-346 mln) annually, as the UK is committed to building 300,000 homes a year by the mid-2020s.

“The choice of metric is a key determinant of success in achieving no net loss of biodiversity,” the study said.

“The use of habitats as a proxy for biodiversity may overlook the value of habitats to certain species’ populations and may also fail to address the needs of species in cases where the amount, type, and quality of habitat is not the main driver for population viability.”

RECOMMENDATIONS

In light of the results, scientists made several recommendations to improve the metric’s efficacy in achieving biodiversity outcomes.

For instance, researchers said the metric gives all croplands the same biodiversity score, while there are significant differences in their ecological value depending on how they are managed.

Conventional farms that use artificial pesticides and herbicides have much lower biodiversity than organic farms that do not.

“It would be nice to see these differences reflected,” Marshall said.

Moreover, according to the scientists, achieving only a 10% net gain would result in minimal to no benefit for nature. The study urged England’s net gain goal to be more ambitious, by for example aligning with the Global Biodiversity Framework objective of a tenfold reduction in extinction risk by 2050.

“The statutory biodiversity metric is a really important opportunity, and has potential to direct a lot of money into biodiversity conservation from developers,” Marshall said.

“It’s the responsibility of conservationists and policymakers to ensure that it provides a reliable indication of nature’s diversity.”

The BNG legislation has faced numerous issues over the last year, including claims it could incentivise building in nature recovery areas, pose serious risks to ecology, and lacks a strong market infrastructure.

In May, a separate study by the National Audit Office (NAO) warned that Defra launched the BNG legislation before ensuring that all the necessary elements were in place for the scheme to be successful.

According to NAO, the statutory biodiversity net gain scheme was launched with risks to the long-term effectiveness of the policy, including uncertainty about whether the fledgling market for biodiversity units scales up to satisfy developers’ demand, risks to enforcement, and gaps in its information.

By Giada Ferraglioni – giada@carbon-pulse.com

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