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Recent rules that require all new building and road projects in England to address and offset their impact on nature are excellent in principle but flawed in their implementation, leading environmental economists argue.

Under Biodiversity Net Gain (BNG), which became law this year, new building or infrastructure developments must achieve a 10% net gain in biodiversity or habitat.

In a study in One Earth, experts criticize the implementation of the policy which forces the majority of off-setting to occur within or near development sites rather than where it might most benefit biodiversity. The study is titled "Biodiversity offsets perform poorly for both people and nature but better approaches are available."

Targeting offsets to locations best for biodiversity was found to double the conservation gains, say the researchers, from the University of Exeter's Land, Environment, Economics and Policy (LEEP) Institute.

Localized offsetting—a practice supported by the National Planning Policy Framework—"treats the natural environment as homogenous," say the researchers, whose analysis shows that incorporating ecological and economic information into the targeting of offsets can greatly improve benefits to wildlife as well as help those living in some of the most nature deprived areas of the country.

The researchers employed models of biodiversity and nature services that took into consideration factors such as the density of wildlife species, the recreational benefits to humans of being around nature, and the costs of offsetting (typically from compensation to farmers and landowners for land use change).

They applied the models to estimates of housing developments across England over a 25 year period, and tested five scenarios: the status quo (where local offsetting is favored); where conservation benefits are maximized (highest improvements for priority species can be achieved); where costs (compensation to landowners) are minimized; where the ratio of recreational benefits to costs is maximized; and where recreational benefits are weighted towards those on lower incomes.

They found that when offsets are in locations where it most benefits biodiversity, the conservation gains are double the current policy of localized offsetting.

The current implementation of BNG performed poorly across all criteria, with other scenarios outperforming this on some or all counts.

Changing the rules would radically change the map of where offsetting is located, away from the environs of developments and the prime value farmland in the east of the country.

Professor Ian Bateman OBE, Director of the LEEP Institute at the University of Exeter Business School said, "Biodiversity Net Gains has the potential to help reverse biodiversity loss—but the way in which it has been implemented is significantly hampering this. Targeting BNG to places which are poor for biodiversity will do little to help our endangered wild species."

Dr. Mattia Mancini, a Lecturer in Environmental Economics at the University of Exeter Business Scholl, added that "similarly, if we are interested in providing disadvantaged communities with access to high quality environments, then tying BNG offsets near to new executive homes won't address inequality.

"Land use policy and its implementation needs to recognize variation in both the environment and inequality between locations and bring this information into the design and implementation of policy."