It was intended that the largest land mammals in Europe would proliferate and create room for other species when they were brought into a woods near Canterbury.

However, West Blean and Thornden Woods have seen such success with European bison that additional space is required for them, leading to the construction of Britain's first bison bridges.

In order to allow introduced bison, which are regarded as dangerous wild animals under UK legislation, to cross the network of public routes in the old forests without coming into contact with people, four bridges totalling £1 million are being built.The massive grazers, which can weigh up to a tonne, will pass beneath the bridges, and tourists will be kept apart by trails that wind over the top to give them a fantastic view of the developing bison.

The bison herd were released into the woods near Canterbury in July 2022 in a pioneering restoration project by Kent Wildlife Trust and the Woodland Trust. Unknown to the project, one of the three female bison was already pregnant and quickly produced a calf. A bull bison from Germany was added and another calf has since been born in the woods, taking the herd to six.

Since their release, the bison have roamed in 50 hectares (123 acres) of woodland. The bridges, which are funded by the National Lottery Heritage Fund alongside National Highways, the Michael Uren Foundation, Veolia Environmental Trust, Garfield Weston Foundation and private donors, will enable the herd to traverse 200 hectares.

As the key wild engineers of the Wilder Blean project alongside free-roaming pigs and ponies, the bison are breaking up old conifer plantations to create a more natural biodiverse woodland, which will also store more carbon.

The European bison is a relative of the steppe bison, which is thought to have become extinct in Britain about 6,000 years ago. The last wild European bison was shot dead in the Caucasus in 1927 but reintroductions from captive breeding populations in zoos have created a resurgent population, with free-ranging herds in many European countries, including Germany, Switzerland and Poland.

Bison are ecosystem engineers: they strip bark from trees which creates standing deadwood that supports insects, birds and bats, and their dust-bathing forms patches where burrowing insects thrive. Their trampling of vegetation is also beneficial, creating light and space for wildflowers.

Bison help sequester carbon as well: a study in the Southern Carpathian mountains in Romania, where a herd of 170 bison have been reintroduced since 2014, has found that the animals’ impact has helped capture approximately an additional 54,000 tonnes of carbon a year, nearly 10 times more than without the bison.

Kent Wildlife Trust hopes that the bison introduction will encourage similar projects across Britain. But conservationists warn that the continued classification of bison as dangerous wild animals – requiring 27 miles of fencing in the Blean Woods complex as well as the bridges to keep them away from the public – makes it expensive for the animals to be brought into other rewilding and restoration schemes. Bison mix with the public in other countries, including on rewilding schemes in the Netherlands.

Simon Bateman-Brown of Kent Wildlife Trust said: “Our wildlife is in trouble, and we need to think differently about how we deliver conservation projects in the UK if we are to change our future. The Wilder Blean initiative is a ground-breaking proof of concept project laying out the blueprint for others to follow and we are leading the way to make it easier for other organisations to replicate.

“We recognise that miles of fencing and bridges is a barrier to rewilding projects, but we must demonstrate what can be achieved so we can advocate for change. Bison are no more dangerous than domestic cattle and, in other parts of the world, they roam freely in public areas.

"Our long-term goal is to remove the steel fencing and use electric fencing to contain the herd, but we will keep advocating for projects like this so they can be replicated until the government makes the law suitable for rewilding."

The bridges have been given planning clearance, and the first two should be finished by the end of the year.