Three families of beavers are to be introduced on land managed by the National Trust as part of plans to ease flooding and improve biodiversity.

Two Eurasian beaver families will be released next spring into enclosures at Holnicote estate on Exmoor, in Somerset, and another group will arrive at Valewood on the Black Down estate, on the border of West Sussex and Surrey.

Beavers were hunted to extinction 400 years ago in the UK for their fur, meat and scent glands. In recent years there has been a series of controlled reintroductions, including one by the government in the Forest of Dean, in Gloucestershire, as solutions are sought to tackle flooding. A wild colony also appears to have re-established itself spontaneously in the River Otter, in Devon.

The schemes at Holnicote and Black Down are the first led by the National Trust and have been approved by Natural England. It is not yet clear how many animals will be brought in but it could be as many as 12: six adults and six kits.

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Ben Eardley, the project manager for the National Trust at Holnicote, said: “Our aim is that the beavers become an important part of the ecology at Holnicote, developing natural processes and contributing to the health and richness of wildlife in the area.

“Their presence in our river catchments is a sustainable way to help make our landscape more resilient to climate change and the extremes of weather it will bring.”

The beavers, which will live in two wooded enclosures, are one element in a range of measures being introduced at Holnicote that includes a pioneering project to return a tributary of the River Aller to its natural path.

Eardley said: “The beavers will help us achieve a more natural flow pattern, slowing, cleaning and storing water and developing complex river habitats. The dams the beavers create will hold water in dry periods, help to lessen flash flooding downstream and reduce erosion and improve water quality by holding silt.”

Releases at both National Trust sites will be into fenced enclosures of 2-4 hectares (5- 10 acres) each so that the impact of the animals on the local ecology and the river can be properly assessed and understood.

The beavers will be transferred from Scotland, where they have been successfully breeding since being reintroduced in 2006. The National Trust beavers are expected to breed and when the young become mature they will need to be moved, possibly to other sites owned or run by the charity.

David Elliott, the lead ranger for Valewood, said: “Beavers are nature’s engineers and can create remarkable wetland habitats that benefit a host of species including water voles, wildfowl, craneflies, water beetles and dragonflies. These in turn help support breeding fish and insect eating birds such as spotted flycatchers.

“There are just a handful of sites in the British Isles that have beavers. This is a different way of managing sites for wildlife – a new approach, using a native animal as a tool.

“The beavers will live along the stream at Valewood and gradually create little ponds, dams and rivulets. Making a habitat that is perfect for them and for many birds, amphibians and invertebrates.”

Both projects will be monitored with help from Exeter University and others, to note both ecological and hydrological changes to habitat.

A footpath passes through the Valewood enclosure and close to one of the Holnicote pens so it may be possible for members of the public to glimpse the animals – though they tend to be active at dawn or dusk and can be shy.