Visitors to the Yorkshire Dales National Park are being asked to help stop the spread of a disease that is killing thousands of trees throughout Europe.

Hikers are being asked to take extra care when walking in woods as experts from the Yorkshire Dales National Park Authority (YDNPA) work to assess the impact of ash dieback disease on the fragile landscape.

The disease was discovered in the UK earlier this year. It causes leaf loss and kills off the tree’s crown, often resulting in the death of the ash tree. It is caused by the fungus Chalara Fraxinea, which is thought to be transmitted by the wind, insects and rain splash.

Geoff Garrett, the YDNPA’s Senior Trees and Woodland Officer, said:

"Ash is such an important tree in the broadleaved woodlands of thelimestone uplands of the Yorkshire Dales that we are treating thepotential impact of the disease very seriously. It is impossible to say with any accuracy how many well-established ash trees we have in the National Park but it’s in the order ofhundreds of thousands – perhaps even millions. On top of that, we have planted about 250,000 new ones in the last 10 years – and they are all at risk from this disease."

No symptoms of the disease have been found so far but the Park Authority is asking visitors to take extra care.

"If they have to go into an area full of trees, we would ask them not to visit other similar areas within a 24-hour period and to make sure they clean their boots, car and bicycle tyres, dogs and anything else that may have come into contact with leaves or wood."