The UK faces a biodiversity crisis. It is one of the most ‘nature-depleted’ countries in the world. The 2019 State of Nature report found that a quarter of UK mammal species and nearly half of birds are at risk of extinction, largely due to urbanisation and agricultural intensification.
In response, the UK Government has proposed a suite of new policies to protect and enhance biodiversity, including the Environmental Land Management Scheme, Local Nature Recovery Strategies and – the focus of this blog – Biodiversity Net Gain (BNG). The BNG policy is currently in draft, but it is intended to require property developers to demonstrate a 10% increase in biodiversity habitat on or near development sites. Since development will generally result in some habitat being lost, this requirement is in effect mandatory ‘biodiversity offsetting’, with a 10% gain.
It sounds like a good idea – but will the BNG policy, as it currently stands, actually improve biodiversity; or is it more likely to fund habitat projects that fail to meet the real needs of nature recovery?
The answer depends in large part on how we define biodiversity. Do we consider biodiversity to consist of resilient, species-rich ecosystems? Or is any aspect of nature that provides ‘ecosystem services’ an instance of biodiversity? These two perspectives may have overlapping elements but represent fundamentally different views of biodiversity. I would argue that to avert a ‘biodiversity crisis’ we need to create resilient, species-rich ecosystems; and that the proposed BNG policy is unlikely to deliver this vision of biodiversity.
To understand why this may be the case, we first need to understand roughly how the BNG proposed policy is intended to work. It uses ‘habitat’ as a proxy for biodiversity and assumes that if suitable habitat is provided, wildlife will occupy it. Habitat is measured in terms of ‘biodiversity units’. If a developer’s plans would destroy a number of biodiversity units, they would be obligated to create 110% of that number to compensate. As a result, there will be a ‘net gain’, as the total number of units present after the completion of the development will be 10% greater than previously. Units are to be calculated using the draft Biodiversity Metric 3.0, which quantifies and multiplies scores for habitat area, distinctiveness, condition, and ‘strategic significance’.
The number of units generated by new compensatory habitat is adjusted to account for the difficulty of creating the habitat, the time taken for habitat to become established and whether the habitat is ‘local’. The policy has an explicit aim to ‘replace like for like in the local landscape’ so habitats created outside the Local Planning Authority area or National Character Area (i.e. the ‘local area’) where the development is constructed generate half as many units as those created within the local area. This creates a strong incentive to ‘offset’ locally. In fact, given the value that greenspace can add to properties, most developers are looking to create their offset on the development site by upgrading a small area of it.
Sedum and sedummer
One key issue with the tool is that if there is a difference in the cost per unit of creating different kinds of habitats, developers are likely to choose the cheapest unit. This can result in habitat repetition, not diversity. This is exactly what happened in Malmo, Sweden, as a result of a similar ‘Green Points System’. Developers discovered the cheapest unit was sedum roofs, so the city just ended up with lots of those. Without diversity, we risk creating a limited range of habitats that support a small group of common species rather than the full diversity of UK flora and fauna, leading to the continuing decline of endangered species.
Even if the metric could be adjusted to ensure that all units cost the same, there is still a danger that developers choose to create more familiar, easy-to-create habitats that carry low risk of failure, like hedges, over less well-known and more complex habitats of substantial value that may be riskier to create and sustain.
A second key issue is that the BNG policy aims to maintain and marginally increase the status quo, by ‘replacing like for like in the local landscape’. But what if the status quo isn’t good enough? If the habitats destroyed by development are small-scale, static and homogenous so that they don’t support resilient wildlife populations and only suit a limited range of species, should we be trying to replace them? Or should we be looking to use the available funds to create habitat suitable for more diverse, resilient and endangered populations? Money and land are both scarce resources, so how can we get the most (biodiversity) bang for our buck?
Resilient biodiverse ecosystems benefit from habitat scale and contiguity. This does not mean large areas of uniform habitat, but large areas containing a ‘dynamic mosaic’ of habitats. The 2010 Lawton Report concluded that the existing patchwork of protected spaces in England cannot reverse biodiversity loss, and that we need an approach that is ‘bigger, better and more joined up’. The Biodiversity Metric 3.0 recognises habitat scale but the weighting system means that 10 totally unconnected 10-hectare (ha) sites within the local area will generate the same number of units as a single 200ha site outside the local area. Yet the 200ha site arguably has more biodiversity value. Connectivity was removed from the updated metric because ‘the connectivity tool was not often used and the approach did not work for all habitats’. Whilst connectivity can be hard to measure it remains a critical attribute for biodiversity.
The BNG policy prioritises local offsets over scale and connectivity. Therefore, it is likely to create fragmented areas of habitat that are unable to sustain viable ecosystems and may require long-term management to maintain an unstable status quo. This management requirement may be problematic given that developers are only obliged to manage compensatory habitat for 30 years.
Furthermore, certain habitats with extremely high and globally important biodiversity value can only exist in specific places, constrained by geography, hydrology and even patterns of migration. For example, there are 175 sites in the UK designated under the Ramsar Convention as wetland sites of international importance. Many of these high-value habitats are remote from areas of substantial property development potential, but in real need of restoration and extension. However, Biodiversity Metric 3.0 only recognises ‘strategic significance’ within the local area. National significance is not considered. A ‘strategically significant’ area identified within a local plan can generate 15% more units, but if outside the local area it does not generate any extra units.
To efficiently use the land and money we have available we need a national strategy that allows us to enhance places where the greatest biodiversity gain can be achieved. Only once we have established this can we work out how locality fits into this broader strategy and work within the local structures and strategies to implement change. The BNG local requirement appears to be driven by a different agenda from genuine biodiversity gain, and thus is likely to lead to suboptimal biodiversity outcomes.
Don’t park the issue
One important reason for prioritizing local ‘offsets’ rather than taking a national approach is to ensure the provision of ecosystem services is spread evenly around the country. These ecosystem services include air quality improvement, flood management, pollination and, in particular, amenity value. Nature is extremely important for our mental and physical health, and the pandemic has only increased our awareness of this. One estimate suggests that parks and green spaces save the NHS over £100 million per year. However, whilst small parks and gardens can provide a range of hugely important ecosystem services, they provide relatively limited ‘biodiversity’ value.
The main direct funding mechanism for local greenspace is local authority expenditure, which is under pressure. It appears that the government may be trying to supplement this source through biodiversity offsets. Clearly, greenspace can and should be managed to benefit biodiversity wherever possible. However, the emphasis on maintaining amenity through local replacement is likely to prove significantly suboptimal in achieving biodiversity outcomes. By seeking to deliver on too many policy priorities, BNG risks doing none of them well.
So, will the BNG policy improve UK biodiversity? In its current form, the proposed BNG policy will maintain and marginally increase the availability of local greenspaces. These will support some wildlife species and provide a range of important ecosystem services. However, the policy is unlikely to create habitat that supports resilient, species-rich ecosystems. I would argue the UK needs to improve, not just maintain, the status quo. We need to decide how to maximize sustainable biodiversity at a national scale and then focus on how to implement the necessary changes locally.
The BNG policy is therefore likely to achieve modest improvements in some local ecosystem services, which is admirable. However, it has far less prospect of delivering meaningful biodiversity improvement nationally, in the way its name suggests. If the government is serious about increasing biodiversity, it needs to tailor its flagship biodiversity policy accordingly.
Featured image: Alexas_Fotos via Pixabay