A wildflower dig is to be held with the intention of removing alien bluebells from woods in South Gloucestershire.
Spanish bluebells are threatening native species
Conservationists fear native bluebells are being wiped out by unidentified cross-pollinated hybrid bluebells.
"These alien hybrid bluebells are botanical thugs and could cause devastation," said Richard Aston of South Gloucestershire Council.
The dig will concentrate on Ridge Wood, Chipping Sodbury where Spanish bluebells are multiplying.
"Pollen is carried from the Spanish variety of bluebell, or other hybrid bluebells common in people's gardens, to the native bluebells on our woods where cross-pollination takes place and seeds are set," said Mr Aston. "It's a downward spiral from then on."
The dig will be led by local wildflower and tree expert Tony Titchen, and will include the marking and removal of hybrid bluebells and other alien plants.
Native bluebell populations can be found in Ridge Wood and the Three Brooks and Gorse Covert nature reserves in Patchway.