Several hundred years ago, beaver populations suffered because of hunting. Beaver fur hats were the height of men's fashion in Europe and the demand was such that the animal's numbers were decimated, becoming extinct in Britain.
"We wanted to see whether the beavers would help tip the balance back in favor of the open habitats, which is so important for lots of butterflies and wildflowers and a whole range of species," says Mark Elliott, one of the Trust's ecologists.
Beavers build dams to protect themselves. By raising the water level, the amphibious rodent creates a waterlogged area that allows it to escape from predators, originally animals like bears, wolves and lynx. The bark of the trees they fell is their primary source of food.
"When we put them in here in 2010 and started to see what they did to the watercourse, it was really, really profound," says Elliott. "We all suddenly became much more conscious of just how powerful this animal was."
The dams also regulate water flow, preventing floods downstream in times of heavy rainfall and droughts in dry periods. This could make beavers an unlikely tool to help combat the effects of the climate crisis, which is predicted to bring drier summers and wetter winters in the UK.
Back in the wild
In 2014, a breeding pair of wild beavers of unknown origin was discovered on the River Otter. A year later the government granted the Trust a license to run the River Otter Beaver Trial -- the first legally sanctioned reintroduction of an extinct native mammal to England.
The River Otter Beaver Trial came to an end in 2020. It was viewed as such a success that the government allowed the beavers, now up to 15 family groups spread across 15 territories, to remain in the wild.
It also noted that dams had reduced the flooding risk for a vulnerable local community, and removed pollutants from rivers and streams.
The River Otter study found that beavers created problems for some local farmers and property owners, noting that "the reduction of flood risk in communities downstream may come at a cost of water being stored on farmland upstream." But it added that these issues could be "straightforwardly managed with the right support and intervention."
"None of us ... quite realize the significance of the animal that we were talking about," Elliott says. "The opportunity to bring them back is an amazing one."