Biodiversity net gain: creating lasting value for nature and communities

Why place-based delivery will determine whether BNG succeeds beyond the metric

Mandatory biodiversity net gain for Nationally Significant Infrastructure Projects in England creates an opportunity to turn compliance into lasting value. To achieve this, developers must combine ecological evidence with community insight and put long-term stewardship at the heart of design, say Mott MacDonald senior principal consultant for social impact Sarah Marshall and global market lead for nature Julia Baker.

Biodiversity net gain (BNG) – an approach to development that leaves habitats in a measurably better state than before – becomes mandatory in England for Nationally Significant Infrastructure Projects (NSIPs) from 2 November 2026. This change means that developers will need to deliver measurable improvements and maintain them for at least 30 years. Meeting those requirements is essential, but achieving at least 10% net gain is only part of BNG. The long-term success of BNG will depend on where habitats are created, how they fit within their wider landscape and whether they reflect the needs of local communities.

Habitats must work in their ecological setting, respond to the needs of the places affected by development and have credible arrangements for long-term care. Bringing community evidence into design earlier is not an optional social value exercise. It can expose risks that a biodiversity calculation cannot, build legitimacy and help avoid opposition, redesign and consent challenge later.

As the statutory tool for measuring mandatory BNG, the biodiversity metric rightly focuses on habitat value, using factors such as area, condition and ecological importance to calculate biodiversity units. Combining this assessment and BNG technical expertise with community insight offers an opportunity to identify solutions that deliver measurable gains for nature while responding to local needs and strengthening people’s connection with their natural surroundings.

Plan for place, not simply for units

There is no simple choice between biodiversity and community benefit. Large, connected habitats can deliver stronger ecological outcomes away from densely populated areas, while unrestricted access can damage sensitive wetlands, grasslands or young woodland. Requiring every gain to be immediately accessible would be as reductive as assuming that the highest unit score always represents the best result.

A place-based spatial strategy can help balance ecological recovery with community benefit. Rather than applying a one-size-fits-all approach, developers should combine ecological expertise with an understanding of each location’s landscape and communities to identify the BNG solution that works best. This means assessing opportunities for local habitat enhancement and wider landscape-scale recovery in their specific context, with access designed around habitat sensitivity and community needs. Carefully positioned routes, viewpoints and site edges can provide contact with nature without undermining restoration where appropriate.

A 30-year management agreement is not the same as 30 years of stewardship

Treat community insight as design evidence

Engagement often begins before and alongside technical work and can be used to explain decisions that have effectively already been made. This detailed local knowledge about species, seasonal conditions, historic land uses and valued spaces that a time-limited survey may not reveal. Used early, that insight can improve site selection, identify overlooked risks and shape interventions around the character of a place.

However, meaningful involvement should go beyond gathering information. Co-designing habitat priorities, access, use and stewardship can create places that reflect local identity rather than generic planting, strengthen ownership and reduce the risk of conflict, vandalism or maintenance problems.

On a major transport infrastructure scheme, place-based analysis was used to assess potential BNG sites against ecological opportunity, socio-economic deprivation, access to green space and demographic factors. Mott MacDonald’s BNG and social and community teams brought these datasets together, creating a richer picture of where intervention could support nature while responding to community need. This demonstrated the value of working as an integrated team from the outset, before decisions about location and design narrow the available options.

Nonetheless, the initial design is only part of the change being brought in by mandating BNG for NSIPs – there must also be a plan for the long term. A 30-year management agreement is not the same as 30 years of stewardship. Project teams, suppliers and landowners may change as habitats establish and adapt to a changing climate. Effective governance must set out responsibility, funding, monitoring, maintenance and accountability from the beginning, while building local ownership through organisations and communities with an enduring connection to the place. Citizen science, community-based monitoring, where local residents and groups collect, share and analyse environmental or scientific data to address local priorities and other forms of local participation can help sustain that connection and provide continuity and oversight over the long term.

Move from compliance to lasting value

What is clear is that the technical disciplines needed to deliver better outcomes are already present on most major programmes. The difference will come from whether ecology, landscape, social value, engineering and engagement teams are able to shape the scheme together before sites and outcomes are fixed. If they work sequentially, opportunities could be lost and problems can reappear later as redesign, opposition, examination delay or weak long-term delivery.

The practical response is to treat BNG as a shared design challenge from day one: define nature restoration and social outcomes together, combine ecological and community evidence before selecting sites, plan access according to habitat sensitivity and secure the ownership and funding needed for long-term care. 

Mandatory BNG will improve wildlife-rich habitat through infrastructure. The bigger test is whether those habitats enhance places nearby the development and remain valued for decades to come. Developers that combine ecological expertise with community insight from the outset will be better placed to deliver both.