A 'very serious' new disease is killing native oak trees across a wide swathe of Britain. Experts have warned could alter the British landscape more than Dutch elm disease.
The Forestry Commission said the condition acute oak decline (AOD) is hitting both native species of oak, which show black bleeding on the trunks and stems.
The trees can suffer rapid dieback and death within three to five years, experts are warning.
Acute Oak Decline causes black bleeding on the trunks and stems on affected trees (as shown)
The practice note from the Forestry Commission, whose research arm Forest Research recently identified bacteria thought to be involved in the disease, is urging woodland managers to be vigilant about the health of their oak trees.
Roddie Burgess, head of the Forestry Commission's plant health service, said: 'It's one where I think they need to take this very seriously.
'We tend to be cautious about what might be seen as scare-mongering, but the signs here are that we are dealing with something that has the markings that it could become something very serious indeed.'
He added: 'We've 200 million oaks in the UK, so if this thing did really take off in the same way as Dutch elm disease, the impact on the landscape and biodiversity would be very significant.'
An oak tree in all its glory. Experts have warned a new disease could devastate the English tree
Woodland owners and managers are being encouraged to inform visitors and walkers in woods if trees are suffering from acute oak decline and give advice on how they can help prevent its spread.
The Forestry Commission suggests notices should be put up advising the public not to touch infected trees or remove wood from the area, and to clean walking shoes and bicycle tyres used in infected areas before going to places which are disease-free.
According to the Forestry Commission, cases of acute oak decline should be monitored and reported, but generally the infected trees should be left in place unless there is immediate concern about safety - such as branches falling.
But the commission suggests that if there are only a few trees infected - and they are mostly the same oak species - it might be worth felling and destroying the diseased trees.
It also stresses the importance of limiting access to infected trees, disinfecting boots, vehicle wheels, machinery and equipment to help prevent the spread of the disease.
Forest Research is continuing to investigate the disease, which has infected hundreds of trees across the Midlands and Wales, to get a better understanding of it and how it spreads.