An ancient swathe of woodland is being severely damaged by over-amorous squirrels who are destroying trees in an effort to impress their mates, forestry experts warned.

Grey squirrels in the Forest of Dean in Gloucestershire, have created havoc this summer by tearing bark from the trees in order to show off to their partners.

The rodents, which number more than 20,000 in the forest, strip the bark away from the trunk and some of the higher branches of the younger trees.

In severe cases, this damage can kill the trees and leads to fungus attacking the weaker exposed parts of the trees.

This kind of damage occurs during the breeding season each year but the recent warm winters and glut of autumn fruit has led to more squirrels breeding in the forest and damaging more and more trees.

Ben Lennon, from the Forestry Commission, said squirrel damage to the trees in the forest this year could be extremely severe.

He said: "The damage is at its peak in the grey squirrel's breeding season which runs roughly from April to July.

"If you walk around the forest at the moment you can start to see the damage that has been caused so far this season.

"Some of the branches are bare on the trees and a lot of leaves are brown already. They are an introduced species and their population just keeps growing and growing.

"There are several theories why the squirrels rip of the bark, but the most likely one is that it is linked to mating and the squirrels are trying to impress females." Grey squirrels were introduced to Britain from America in the late 19 century.

The grey is bigger and more adaptable than the native red squirrel and they have pushed the reds out of their former strongholds to the extremities of the country.

Explaining the squirrels' growth in population, Mr Lennon added: "The animals have been in good condition to survive the winters in the past few years because recent fruit harvests have been good.

"It gives them a good chance of getting through the winter which means there's more of them around in the mating season.

"We don't even bother planting some species in the forest now because it's not worth it - the squirrels just destroy them."

He added that various schemes have been tried out to deter the grey squirrels from destroying the trees but so far all have failed.

The results of the damage inflicted on the forest this year are expected to be known in the next few months.