A flock of sheep has been drafted in to halt the spread of bracken at a country park on the Northumberland and County Durham border.
The vegetation has been taking over the slopes above Derwent Reservoir, putting native plants at risk.
The plant is poisonous to local breeds of sheep and cattle, so Soay sheep have been brought to the area.
The sheep, descendents of a feral population on the Scottish island of Soay, eat the base of the plant.
The Pow Hill Country Park, in the North Pennines Area of Outstanding Natural Beauty (AONB), is home to rare plants such as bog asphodel, lesser skullcap, and marsh violets, the food of small pearl-bordered fritillary caterpillars.
On a remote Scottish island, the sheep are shrinking, and the cause appears to be the warming of winter.
The wild Soay sheep that live on the island of Hirta in the North Atlantic have been under careful scientific observation since 1985, partly because the island ecosystem is a simple one consisting of the sheep and the vegetation they eat.
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