CONSERVATIONISTS have drafted in a small army of sheep to nibble away at a prickly problem.

With rare plants near Derwent Reservoir, County Durham, disappearing under a sea of bracken, a small flock of rare Soay sheep is halting the spread by eating the plant stalks.

Soays date back to Roman times and are descended from a population of feral sheep living on Soay, in the Western Isles of Scotland.

Native breeds such as Swaledales could not be used because they avoid bracken, which can be poisonous.

The North Pennines AONB Partnership’s Living North Pennines project is funding work on Northumbrian Water’s land to clear bracken and re-introducing grazing.

Bracken is a difficult plant to control and normal methods – such as a chemical application or trampling by cattle – have been ruled out on water quality and safety grounds.

Andy Lees, the partnership’s conservation officer, said the area’s fen and heath habitats were home to many rare plants and featured in local and national biodiversity action plans.

He said: “As well as being important habitats in their own right they have also, in the past supported rare species of butterfly such as the green hairstreak and small pearl-bordered fritillary.

“Green hairstreak caterpillars feed on bilberry, which still survives below the bracken, and small pearl-bordered fritillary caterpillars feed on marsh violets in the wet fen areas, which are slowly drying out and being invaded by bracken.

“Our plan is to slowly reduce the area of bracken which dominates the slopes with a combination of annual cutting by a tractor-mounted topper and the introduction of Soay sheep.

“Sheep and cattle do not eat bracken as it is poisonous to them, however Soay sheep are known to chew the base of the bracken stalk for some unknown reason, and this helps keep the plants at bay.”

The sheep are being provided by Flexigraze, a North-East conservation grazing project, and will be looked after by staff from the project and from Northumbrian Water.