Biodiversity net gain (BNG)

Biodiversity net gain is a policy requirement, most developed in England's planning system, that a construction or land-use project must leave measurable biodiversity higher after the work than it was before, rather than merely avoiding harm. It reframes habitat loss from a cost to be minimized into a metric that must finish positive.

Gain is measured with a habitat-based scoring tool that assigns each habitat type a unit value based on its size, distinctiveness and condition; developers must deliver a net increase over a baseline survey, commonly a 10% uplift under the English scheme, through on-site habitat creation, off-site habitat units, or, as a last resort, statutory biodiversity credits. This differs from carbon offsetting in that units are tied to specific, monitored habitat types rather than a fungible tonne of emissions, and from ad hoc habitat fragmentation mitigation, which addresses connectivity rather than a net quantity.

Analysts working on BNG track baseline habitat surveys, model post-development habitat condition, and monitor delivery sites over the required multi-year period, since gains are legally required to persist, not just be planted. Common pitfalls include weak baseline surveys that inflate apparent gain, and treating any single species distribution model as sufficient evidence of ecological outcome when the metric is habitat-based, not species-based. It sits alongside broader ESG reporting on nature-related impact.