A scheme is being set up in north Devon and Somerset to help support the reintroduction of red squirrels.
Red Squirrel South West was awarded government funding to establish a management programme for grey squirrels between Ilfracombe and Minehead.
It will involve culling the animals in a 35-mile (56km) corridor of coastal woodland.
Red squirrel populations were decimated in most of the UK after grey ones were first introduced in 1876.
Grey squirrels, which are larger and faster breeding than reds, are much more successful in competing for food, the Woodland Trust said.
Greys are also carry squirrel pox, which they are immune to, but red squirrels are not.
Red Squirrel South West told BBC Radio Devon it wanted to "drastically reduce" populations of the invasive animal to help pave the way for the eventual reintroduction of the native species.
It said the animals needed to be culled - through methods such as shooting or trapping - because plans to trial the use of contraceptives were still years away.
Project coordinator Mish Kennaway said ancient oak woodlands in Devon were "going backwards" because grey squirrels were destroying young saplings.
Animals such as songbirds, dormice and even bats were also threatened by the animal, he said.
"Nobody likes killing grey squirrels or any other animals for the sake of it - and certainly conservationists don't - but we humans have put the imbalance in nature," Mr Kennaway said.
"In a way we have a social responsibility to do something about that because our native species are literally dying out."
The group is setting up a group of volunteers to control grey squirrel populations in the management area.