Trees and rare flowers have been damaged at Dole Wood, near Thurlby, and young cyclists are thought to be to blame.

Dave Vandome, warden of the wood for the Lincolnshire Wildlife Trust, said: "We've had children trying to build a BMX-style track.

"We have dismantled it and they have stopped cutting trees but the track is in ancient woodland, which is relatively rare and irreplaceable. The track will destroy spring flowers such as bluebells."

The site is protected as a site of special scientific interest and Mr Vandome said: "We don't mind them on the path but even I am not allowed to chop trees down there. We did put a sign up saying it is a valuable habitat.

"Someone in Thurlby must know who they are.

"They are causing quite a lot of damage and if they knew what they were doing they would probably stop. If it is nipped in the bud we can repair the damage."

Joyce Stevenson of Thurlby, who last month warned that rare trees were under threat because of forestry management, said: "The riders must be made aware that it is a site of special scientific interest and that this is not acceptable.

"It is vandalism."