Love-struck squirrels are damaging ancient woodland by ripping bark off the trees to impress their mates.
Thousands of grey squirrels in the Forest of Dean have been showing off to partners during the breeding season, trashing the trees in the process.
Damaging bark can leave trees open to fungus attacks, which can kill them.
Squirrels often destroy trees from April to June, but this year the damage is severe because squirrel numbers are up thanks to a warm winter and spring.
The Forest of Dean in Gloucestershire is home to 20,000 grey squirrels, which were introduced to Britain from America over 100 years ago.
Experts have tried to stop the rodent vandals from harming the trees, but efforts so far have failed.
Ben Lennon, from the Forestry Commission, said: "The damage is at its peak in the grey squirrel's breeding season which runs roughly from April to July.
"We don't even bother planting some species in the forest now because it's not worth it - the squirrels just destroy them."