The study, by a team of scientists overseen by Professor Richard Brazier from the University of Exeter, revealed “measurable benefits to both people and wildlife” at the River Otter, in East Devon, where a study of a wild population of beavers began in 2015.
The research team said that while the reintroduction of the beavers had created “localised problems for a handful of farmers and property owners”, these issues can be easily managed.
Meanwhile, local wildlife has “greatly benefitted from the beavers’ presence, while their dam building activities have also helped reduce the risk of flooding to some flood threatened human settlements”.
At the beginning of the trial in 2015, there were two breeding pairs of beavers in the River Otter – they had escaped from a captive population two years earlier. After public outcry at plans to cull them, the scientific trial was agreed upon by the government.
The work was carried out by Devon Wildlife Trust, Clinton Devon Estates, the Derek Gow Consultancy and the University of Exeter.
They found by October 2019 there were at least eight pairs of beavers in the River Otter and that the population has now spread to the connected River Tale, as well as some smaller tributaries.
The impacts the beavers have had on the surrounding area including mitigating risks to the flood-prone community of East Budleigh. A family of beavers have constructed six dams upstream of the village, with the result that peak flood flows through the village have been measurably and significantly reduced.
The report highlights the ability of beavers to help clean water supplies, removing large quantities of soil, manure, slurry and fertilisers from rivers and streams. In one location where beavers had built 13 dams and ponds, researchers found the animals were playing “a significant role in filtering these pollutants from water”.
Perhaps even more impressive is the extent to which beaver populations create perfect conditions for so many other species to thrive.
“The effect of beaver engineering and feeding has delivered significant ecological benefits,” the authors said, “with new areas of wetland habitat created and managed, with benefits for amphibians, wildfowl and water voles”.
Fish numbers were found to have significantly increased where beavers built their dams. Surveys in the River Otter catchment area showed the pools created by beaver dams contained 37 per cent more fish than in comparable stretches of the river where there were no dams. Researchers also recorded trout leaping up and passing over beaver dams during high river flows.
Prof Brazier, who is chair of the Science and Evidence Forum that published the report, said: “Following five years of detailed research work, the report concludes that the positive impacts of beavers outweighed the negatives.
“A summary of the quantifiable cost and benefits of beaver reintroduction demonstrates that the ecosystem services and social benefits accrued are greater than the financial costs incurred.
“However, it also makes clear that those who benefit from beaver reintroduction may not always be the same people as those who bear the costs, highlighting that the reduction of flood risk in communities downstream may come at a cost of water being stored on farmland upstream.”
Devon Wildlife Trust’s Mark Elliott, who has led the River Otter Beaver Trial for the past five years, said: “I think we’ve all been surprised by these amazing animals’ ability to thrive, once again, in our wetland ecosystems.
“It also shows their unrivalled capacity to breathe new life into our rivers and wetlands, very few of which are in good health.
“We have seen over these five years how beavers really do have the ability to help to restore the natural processes that all our wetland wildlife depends on.
“As a society, we get so much benefit from healthy rivers and streams that function naturally – we just need to give them greater space and appreciate them more – beavers play a crucial role in helping with that.
“The key to success will be to provide support for all landowners to make space for wetlands on their land – ensuring those who enable these far-reaching benefits to be provided are also able to manage their thriving rural businesses.”
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