Two Eurasian beavers released into a fenced enclosure in North Yorkshire’s Cropton Forest have cut peak river flows, expanded wetland habitat and built the largest beaver dam in England across a five-year trial. That is according to Forestry England, which ran the five-year trial with the University of Leeds under a licence from Natural England.
The trial began with the pair’s release in April 2019, and the animals have since grown into an extended family of 11 kits living across four lodges. They have built six dams in that time, one of which is now the largest recorded anywhere in England.
Researchers tracked river flows, drought response, vegetation and wildlife before and after the release, marking the first time so many measures had been recorded at a single site. Mark Smith, professor at the University of Leeds’ School of Geography and the study’s lead author, said the enclosure changed in ways the team had not expected.
Smith said the shifts spanned flooding, drought, and biodiversity, with peak flows declining and plant and animal diversity rising over the five years. “The site was transformed by the beavers in ways we never imagined,” Smith said.
The beaver dams worked alongside existing leaky-dam structures already built for natural flood management, slowing and reducing the volume of water moving downstream. Although the human-built structures lost more than half their storage capacity during the trial, the beaver dams made up for that loss.
Researchers also found that the beavers were repairing and extending the lifespan of those degraded structures, adding to the catchment’s flood storage rather than competing with it. The enclosure now holds water in the upper catchment through dry spells and slows its release when rivers run high.
Biodiversity gains were recorded across the site, with greater aquatic plant diversity and higher fish and amphibian species richness than a neighbouring stream. Bat numbers also rose in the areas and at the times that matched beaver activity.
Cath Bashford, species recovery officer for Forestry England in Yorkshire, said returning the beaver to the county after several hundred years had been remarkable to watch. “They have created a complex wetland habitat connecting the river with the floodplain,” Bashford said.
Natural England has extended the licence until 2029, allowing Forestry England and the University of Leeds to continue the work and shape any future wild releases.
For further information: Puttock, A., Graham, H. A., Ashe, J., Luscombe, D. J., & Brazier, R. E. (2021). Beaver dams attenuate flow: A multi-site study. Hydrological Processes, 35(2), e14017. https://doi.org/10.1002/hyp.14017
