Potential to fund arable rewilding in England with biodiversity credits

Emerging biodiversity credit markets are promoted globally as a solution to financing nature recovery at scale. In southern England, which has experienced particularly strong declines in biodiversity as a result of intensification of farming practices, the Knepp Estate has pioneered trophic rewilding of marginal arable land as a nature recovery solution. The scaling up of rewilding initiatives will require long-term funding, for example, through biodiversity credits. We used DNA metabarcoding to characterize aerial invertebrate, terrestrial invertebrate, soil invertebrate, and soil fungal populations recorded from the 20-year-old rewilded Knepp estate and a conventional arable farm proposed as a nature recovery project (Boothby). We used the Wallacea Trust framework to estimate the economic value of the arable farm's restoration on the global voluntary biodiversity credit market. We also estimated the economic value of the arable farm's restoration on England's compliance offsite biodiversity net gain market. Compared with the farm, Knepp had higher conservation value (167% more species with a conservation designation, 56% rare invertebrate species) and better ecosystem functioning (33% more pollinator species, 25% more fungal symbiotrophs, 21% fewer plant pathotrophs). Knepp had higher taxon richness (40-52%) for all taxa, except soil invertebrates (-35%) and soil fungi (-10%), and higher taxon biomass (6-123%). Following the Wallacea Trust definition, we predicted a median biodiversity uplift between 69% and 92% for the farm after 30 years, worth £1,176,169-£1,559,875 at £23/credit, around 15 times less than project costs. On England's offsite biodiversity net gain market, habitat restoration could generate revenue up to £68,902,500 over 30 years, although unit supply currently outstrips demand. Although voluntary biodiversity credits are unlikely to fill the biodiversity funding gap alone, they can be combined with carbon credits to increase a project's financial viability, have global reach, may represent an additional biodiversity contribution rather than offset previous damage, and can be used to support projects unsuitable for regulatory biodiversity or carbon markets.