The metric used for implementing England’s biodiversity net gain (BNG) policy does not accurately capture invertebrate biodiversity abundance, a pre-print paper has suggested.
The pre-print study, led by researchers at the University of Oxford, tested the relationship between invertebrate biodiversity and scoring by the UK government’s statutory biodiversity metric.
Researchers said there was no significant connection between invertebrate abundance and metric scores. The document is a preliminary version that has not yet cleared the peer review process required for publication in a journal.
“Invertebrate communities were highly variable across sites that had the same type and condition under the BNG metric,” said the study. Invertebrates are animals without backbones like insects, spiders, and worms, making up most animal species on Earth.
“Our results highlight the need to incorporate factors beyond habitat type and condition into site evaluations, and to complement metric use with species based surveys.”
THE METRIC
The metric allows companies to calculate biodiversity changes across a site to ensure an overall minimum 10% biodiversity gain, as mandated by the BNG framework.
Some landowners have also used it to calculate the natural value of their property to try to enter the nascent voluntary biodiversity credit market.
The size of an initiative, habitat distinctiveness, and condition are factors that influence the BNG metric.
“We found no evidence for a relationship between a habitat parcel’s distinctiveness and condition score calculated using the BNG metric and the abundance of ground invertebrates, for grassland and arable habitat parcels surveyed in Aug. and Sep. 2022,” said the study.
“In 2023, using a more efficient pitfall trap design and surveying a different set of habitat parcels encompassing a wider range of grassland and arable habitat types, there was similarly no significant relationship between distinctiveness and condition score and mean total ground invertebrate abundance.”
In June, a separate final study said there was no evidence that BNG units developed using the metric result in improved habitats for birds and butterflies.
The BNG requirements are expected to generate a nature market worth an estimated £135-274 million ($176-358 mln) annually.
NOT RELIABLE
“If, as we found here, combined area-condition metrics are not reliable proxies for wider biodiversity value, sites with high faunal biodiversity value but low metric scores will be undervalued in offsetting calculations,” said the study.
The metric has become influential worldwide, with derivatives emerging globally, including the Singapore Biodiversity Accounting Metric developed by US-headquartered consulting firm AECOM, and Wallacea Trust’s biodiversity credit methodology, according to the study.
“For voluntary biodiversity credit initiatives, an inaccurate proxy metric would lead to investment in credits with uncertain or even overinflated biodiversity benefits,” added the study.
“If such biodiversity credits become central to how businesses claim to achieve nature positive objectives or address their nature-related risks under prevailing Corporate Sustainability Reporting frameworks and policies, using a metric that doesn’t reliably capture faunal diversity risks creating the illusion of biodiversity gains.”
Although it has been praised as world-leading, BNG legislation has faced numerous early 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 UK’s National Audit Office warned that BNG launched before ensuring all the necessary elements were in place for success.
By Sergio Colombo – sergio@carbon-pulse.com
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