The peer-reviewed study, published by Oxford University researchers in the Conservation Biology journal, is based on a review of planning applications submitted to six councils between 2020 - 2022 which have adopted BNG policies ahead of the requirement for a 10% BNG becoming mandatory next year.
As BNG policy stands, offsite BNG units must be registered on Natural England’s Biodiversity Net Gain Register, which records allocations of off-site biodiversity gains to developments and makes this information publicly available. Crucially, these biodiversity units will need to be verified to ensure they are legitimate, accountable, and transparent.
This stands in contrast to onsite biodiversity units - those created by developers on the site they are developing - which are subject to fewer enforcement controls. There is no requirement for onsite units to be registered, and while it falls to local planning authorities to monitor onsite biodiversity units, doing so is discretionary.
The government has previously estimated that 50% of units under BNG are likely to be delivered through on-site action, but the samples assessed in the Oxford University paper show that in fact more than 90% are being delivered on-site.
The study, led by Sophus zu Ermgassen and Emily Rampling, reads: “Whilst the drive for delivering on-site habitats is likely a product of one of the key policy goals to improve public access to green spaces, our evidence demonstrates that this goal is likely to conflict with the other goal to enhance wildlife and ecosystems.”
As a starting point, the researchers assumed that the developers all attempted to deliver the habitats promised in their BNG assessments, but classified those onsite, and in excess of the condition they were in before the project was started, as being exposed to governance risks.
They justify this classification on four grounds; the first that no register is required, and that failing to deliver habitats to a promised condition level in the initial planning application “falls below the threshold of what is conventionally enforced by local planning authorities (LPAs) and so enforcement action is very unlikely”.
The second ground was that habitats delivered on-site “are likely to be under intense human and pet pressure, especially as one of the key aims of the BNG is to improve public access to green space”. The third ground was what the researchers describe as “potential conflicts between residential preferences and BNG commitments which may pose a risk to habitat condition when managing green spaces”. The paper cites previous research which has shown that for some there can be an association between “wildness” and untidiness or neglect, as well as “feelings of reduced personal safety”.
Finally, the paper points to the expected skills shortages in the property management companies “who tend to be contracted to maintain properties and are used to managing the built environment intensively, not for the benefit of biodiversity”.
Based on this classification, the paper concludes that “27% of all biodiversity units fall within governance gaps that expose them to a high risk of non-compliance”.
Furthermore, it states that just under half of all biodiversity units in its sample dataset will “take longer than five years to mature” and that approximately one quarter of all developments will take twenty years or longer to achieve their commitments of woodland habitat enhancement and creation.
“It is highly unlikely that LPAs will have the resources to investigate and enforce violations of planning conditions from multiple years in the past,” the researchers state.
The paper continued: “Ideally, more robust governance mechanisms would be implemented to cover on-site biodiversity unit delivery. Alternatively, more of these units could be delivered through the off-site biodiversity offsetting; in the latter case, we estimate that the demand for offsets could rise by a factor of four, increasing the financial contributions generated by BNG for conservation activities on private land.”
The paper also uncovered that just over half of all projects containing errors in their BNG plans had already been accepted by LPAs, and that the remainder were ‘in review’.
“Of all accepted projects within our dataset, 24% of them contained errors. There was no evidence to suggest that the occurrence of errors was falling over time, with 17% of all projects using the earlier [BNG] metric 2.0 containing errors, but 39% of all projects using the more recent metric 3.1 containing errors,” it said.
Proposing potential solutions to the risk of non-compliance, the researchers say that if the government significantly increased LPA resourcing and capacity to deliver more effective monitoring and implementation practices, “there is the potential that such risks could be overcome and mandatory BNG may achieve its goals”.
The researchers also mooted that “if governance and standards were standardised for both onsite and offsite gains (at the higher-quality standards of offsite gains), then there would be no risk of proponents undercutting standards by going down the less stringent route”.
The paper continued: “We have seen equivalent levelling-the-playing-field in other compensation systems that experienced similar divergence in standards between developer-led and third-party-initiated compensation – for example, the 2008 Compensation rule in the US wetland mitigation system addressed this divergence by closing the governance gap and ensuring that the same standards were applied across all forms of compensation.”
Commenting on the findings, Richard Benwell, chief executive of the nature NGO coalition, Wildlife and Countryside Link, said: “There’s a huge gap when it comes to monitoring, reporting, and enforcement of BNG onsite. Local authorities stand little chance of checking whether gains are ever delivered, let alone maintained for 30 years.
He added that in order to give LPAs “a fighting chance”, all onsite gains should be registered in the same way as offsite gain, but warned that more support would be needed. “Mandatory gain will need to come with significant guidance and investment in monitoring and enforcement. Otherwise, we may find that the legacy of net gain is nature loss and phantom habitats that quickly vanish, or never existed at all,” he said.
A DEFRA spokesperson said that to support the implementation of BNG, which will be mandatory for all major developments with enforcement through the planning regime, the government has "already committed over £15 million to assist LPAs to prepare and has consulted extensively with stakeholders on its design.”
The department was also keen to emphasise that the Oxford University paper refers to the "voluntary implementation of this policy which is not enforced at this current time".
This article was updated to include DEFRA's comment