Biodiversity is the variety of life on Earth. It includes all animals, plants, fungi and micro-organisms, the genetic variation within species and the variety of ecosystems that species create.

Biodiversity provides us with everything we need for survival from fresh water, clean air, food and medicines. We don’t receive these benefits from individual species, but from the way that the rich tapestry of living organisms works together.

For example, plants improve our physical environment, help to clean the air we breathe, limit rising temperatures providing protection against climate change, help slow the flow of water to mitigate flood risk, are the source of many medicines and provide the basis of our food production systems.

Land use change and habitat destruction converting forests, wetlands and grasslands to farmland is the biggest cause of biodiversity loss.

However, loss of land to development whether for homes, employment or roads and other transport infrastructure has made a significant contribution locally.

In future climate change will threaten many species, unless they can move to more suitable locations.

Biodiversity Net Gain is an approach to development that seeks to ensure that biodiversity is in a measurably better state after development than before it.

It seeks to address the impacts of future development, and in the process contribute to nature recovery and make up from some of the past losses due to development.

In the UK the government introduced a legal requirement through the Environment Act 2021 for most new developments to deliver at least a 10% net gain in biodiversity.

Biodiversity is measured based on the area, condition and distinctiveness of habitats present. This is converted to Biodiversity Units (BU), which are a proxy measure for biodiversity (as opposed to an empirical measure of real species richness or diversity).

The Defra Statutory Biodiversity Metric is used to measure habitat, hedgerow and watercourse Biodiversity Units. Each are measured separately. A detailed framework and guidance have been produced to ensure consistency of measurement.

New developments should seek to avoid impacts on biodiversity including high-value habitats and species.

However, this may not always be possible. In most situations except some redevelopment projects, new development will result in the loss of land even if this is made up of low value habitats. The loss of low value habitats can still result in the loss of space for wildlife and therefore contribute to biodiversity declines.

Most developments will deliver some or all their biodiversity net gain on site through the inclusion of natural greenspaces or other urban features suitable for wildlife including Sustainable Urban Drainage Systems, green roofs and green walls.

However, where this is not possible, they will need to achieve their Biodiversity Net Gain responsibilities off-site. This will involve the purchase of Biodiversity Units from off-site providers with habitat banks and other biodiversity offsetting sites.