Biodiversity net gain after year one

Seen from above, Kuala Lumpur is a useful reminder that dense cities and green space are not opposites. The towers cluster, but so do the parks, the planted podiums and the river corridors threaded between them. That tension, between building hard and keeping land alive, is exactly what England's biodiversity net gain regime set out to manage when it became mandatory. A year into that regime, the early lessons are worth drawing out, because they are less about ecology than about the unglamorous business of measuring, recording and proving a commitment that has to hold for decades.

What the regime asks for

Under the Environment Act 2021, most new development in England must deliver a minimum 10% biodiversity net gain, and that gain must be secured for at least 30 years (NBN; gov.uk). The duty became mandatory for major applications from 12 February 2024, and for small sites from 2 April 2024 (gov.uk). Gain can be delivered on-site, off-site, or as a last resort through statutory biodiversity credits.

The headline number, 10%, is the part everyone quotes. The part that shapes the management task is the 30 years. A planning condition or obligation that runs for three decades is not satisfied at handover. It has to be monitored, maintained and evidenced long after the developer has moved on and, often, long after the original site team has changed.

Note that biodiversity net gain is a feature of the England regime under the Environment Act 2021. The Kuala Lumpur skyline above is offered only as a picture of a dense city that has kept room for green space, not as a place where these particular rules apply.

The half-life problem

The difficulty with any obligation measured in decades is that the people change faster than the duty does. A habitat created in year one might be the responsibility of a developer, then a management company, then a new owner, then a managing agent appointed by that owner. Each handover is a chance for the commitment to slip out of view.

This is where the first year's experience has been instructive. The schemes that look most secure are not necessarily the ones with the most ambitious habitats. They are the ones where the baseline, the plan and the monitoring obligations were written down clearly enough that a stranger could pick them up and understand exactly what was promised, where, and for how long. A meadow strip or an attenuation basin is only as good as the record that says it must be maintained and the evidence that it has been.

What a manager actually has to hold

For whoever ends up running a site subject to a net gain commitment, the practical task resolves into a small number of things that have to be kept current and findable.

• The baseline and the gain plan. What was on the land before, what was committed, and the biodiversity value that the 10% was calculated against.
• The spatial extent. Precisely where each habitat sits, drawn against the site boundary rather than described in prose. Ambiguity about location is how obligations quietly erode.
• The monitoring schedule. When the habitat must be assessed, by whom, and to what standard, across the full term.
• The evidence trail. Dated records, surveys and photographs that show the commitment was actually maintained, not merely intended.
• The responsible party. Who carries the duty now, with a clear chain back to the original obligation.

Hold those five things well and the obligation survives a change of owner. Hold them loosely and it depends on memory, which over 30 years is no plan at all.

Drawing it, not describing it

The recurring theme in the first year is that biodiversity net gain is a spatial commitment trapped, too often, inside text documents. A planning obligation describes a habitat in words; the actual habitat exists in a particular corner of a particular site. When those two drift apart, disputes follow.

The buildings and sites that manage this well tend to draw the commitment onto the land directly, against a boundary that has been established once and is not in question. That is the broader argument for treating the site as a first-class object rather than an afterthought to the building on it. Where the green obligations, the drainage, the boundary and the access all hang off the same drawn site, the net gain commitment is one layer among several rather than a document filed on its own. Our note on draw the boundary once and let everything hang off it makes the case for getting that foundation right first.

The discipline that lasts

A 30-year obligation is, in the end, a record-keeping problem dressed as an ecological one. The habitat does the ecological work. The record does the work of proving, across multiple handovers and a changing cast of duty-holders, that the habitat was created, located correctly and kept alive.

A single source of truth that holds the gain plan, the monitoring schedule and the dated evidence against the mapped site, in a place that survives a change of owner or agent, is the difference between a commitment that endures and one that fades the first time the site changes hands. SAMRISK gives every plan a free site shell for exactly this kind of long-running, land-based obligation, so the thing that has to last 30 years is held somewhere built to outlast the people who set it up. A year in, the schemes that will still be honouring their commitments in 2054 are the ones that wrote them down properly in 2024.