THOUSANDS of ash trees in Yorkshire are under threat with the arrival of a potentially fatal tree disease.

Ash dieback has been identified at 14 sites on the western fringes of North Yorkshire - and most are believed to be in the Craven district, which includes Skipton and surrounding areas.

One of the known sites is tourist hotspot Malham.

A spokesman for the Forestry Commission - which is leading the effort to contain the disease - said ash dieback had been found at 14 sites during follow-up surveys after cases were reported across the border in Lancashire.

He added: "It is too early to say how widespread it is. We will continue to monitor and survey the trees in the area and give advice to woodland owners."

Ash dieback is caused by the fungus Chalara Fraxinea and is thought to be transmitted by the wind, insects and rain splash. It causes leaf loss and kills off the tree’s crown, often resulting in the death of the ash tree.

The disease is not harmful to people or animals.

Yorkshire Dales National Park Authority senior trees and woodland officer Geoff Garrett said: "It is obviously very disappointing news that Chalara has started to affect ash trees in the national park.

"We will be working with the Forestry Commission and woodland owners to monitor the impact very closely."