Payments that enable landowners to rewild ecologically degraded land - in the form of biodiversity credits bought by investors wishing to offset their impact on nature - could be an effective component of the emerging market for nature recovery, but will not work as a stand-alone approach.
The amount investors are willing to pay is around fifteen times less than the amount needed to cover a land restoration project in England.
Cicely Marshall
A University of Cambridge-led team says that the emerging market for voluntary biodiversity credits could support the rewilding of nature-depleted land - but only as top-up funding to other market approaches that support nature restoration, like carbon credits.
Conservation projects can sell biodiversity credits, through brokers, to individuals or organisations who want to voluntarily offset their damage to nature. The money is used to carry out the restoration project, with any surplus providing a financial return to the landowners.
This study is the first to measure the biodiversity gain likely to be achieved on an arable farm undergoing rewilding, and use this to calculate the potential value of the restoration on the emerging voluntary biodiversity credit market.
The team surveyed the species present at two very different rural sites in England: a conventional arable farm and potential nature recovery site - Boothby in Lincolnshire, and a former arable farm that has been rewilded over the past 20 years to become a leading example of nature recovery - the Knepp estate in West Sussex.
Comparison of the sites indicated that biodiversity at Boothby farm will increase by between 69% and 92% after 30 years - a biodiversity gain worth an estimated £1.5 million in voluntary biodiversity credits.
But with costs to restore the site - including site management and monitoring - estimated to be fifteen times higher than this, the team says the voluntary biodiversity credit market alone will not be enough to fund nature recovery.
Despite this, the team says voluntary biodiversity credits are an important component of financing nature restoration alongside other approaches like carbon credits.
Voluntary biodiversity credits work globally, and offer flexibility to projects in terms of how they approach nature recovery - which could be a particular benefit for rewilding projects. Rather than specifying the particular habitat types that must be created, as England's mandatory 'biodiversity net gain' system does, this voluntary scheme only requires that biodiversity value increases - and pays out in proportion to that increase.
The study is published in the journal Conservation Biology.
"Voluntary biodiversity credits are important when combined with other ways of funding nature protection, like carbon credits. So it's vital to have a realistic idea of how a site's biodiversity will improve over time, in order to accurately calculate the credit value," said Dr Cicely Marshall, first author of the report, who carried out the work while in the Department of Plant Sciences at the University of Cambridge.
"Our results show that voluntary biodiversity credits alone are not enough to fund nature recovery at large scale. The amount investors are willing to pay is around fifteen times less than the amount needed to cover a land restoration project in England," added Marshall, who is now a Research Fellow at the University of Gloucestershire.
Land-use change and habitat destruction for farming - particularly the intensification of farming in the south of England - has left the country in a severely nature-depleted state. Rewilding involves leaving land to revert to its natural, uncultivated state - restoring the natural ecosystems vital for nearby farming.
Surveying the sites
The team carried out surveys to identify and compare biodiversity at the Knepp estate and Boothby farm. They focused on groups of species that give a good indication of soil recovery and ecosystem functioning, alongside classical indicators of ecosystem health like plants and birds.
Using a technique called 'DNA metabarcoding' the team accurately identified each species of flying invertebrate (including butterflies and bees), land invertebrate (including ants and spiders), soil invertebrate (including worms) and soil fungi they found.
The results showed that overall, the land at the Knepp Estate was around twice as rich in biodiversity than the Boothby land. Knepp also had improved ecosystem functioning, represented by 33% more pollinator species and 25% more species of beneficial fungus.
Comparison of the sites enabled the team to predict how much biodiversity Boothby could potentially gain over 30 years if rewilded, and then to calculate Boothby's value in terms of biodiversity credits using a method called the Wallacea Trust framework. This globally-applicable framework defines one biodiversity credit as a 1% improvement in biodiversity per hectare of land.
Voluntary versus mandatory credits
Large companies are under increasing pressure to compensate for the damage they cause to biodiversity.
Voluntary biodiversity credits are available through around 80 brokers, offering funding to conservation projects across the world. Measuring biodiversity gain is not straightforward - with no standard definition of a unit of biodiversity, various methods are used to calculate the value of a credit.
The idea is that investors sell credits to restore arable landscapes, valued using an estimate of how nature will have recovered on a site in thirty years' time. They can sell credits every five years if they can prove these biodiversity gains have been achieved. With large amounts of money involved, reliable forecasts are vital in predicting the return on the initial investment in land purchase and site management.
Defra's mandatory 'biodiversity net gain' approach allows developers to buy biodiversity credits to compensate for damage done elsewhere - ensuring that habitats for wildlife are left in a 10% better state than before the development. Management of the land under this approach is much more prescriptive than rewilding through a voluntary biodiversity credit approach.
In an alternative calculation using Defra's statutory biodiversity metric, the team found the economic value of restoring Boothby's farmland to natural habitat could be £69 million over 30 years. This covers the costs and provides a generous return to investors - but only if all the units can be sold.
Marshall, who is also associated with the University of Cambridge Conservation Research Institute and King's College, Cambridge, said: "There's increasing pressure on companies to offset their impacts on nature. Biodiversity credits are happening - and it's important that the biodiversity metrics they're based on are fit for purpose. Our project aimed to put some numbers on these credits, and de-risk them for investors and nature."
The work was carried out in collaboration with Nattergal and the DNA barcoding company NatureMetrics. It was funded by Nattergal.
Reference
Marshall, C. A.M. et al: 'Potential to Fund Arable Rewilding in England with Biodiversity Credits.' Conservation Biology, March 2026. DOI: 10.1111/cobi.70207
