Oak trees fall to mystery disease

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The Independent Online
BRITAIN'S OAK trees are dying at an alarming rate, prompting fears of a new "Dutch Elm Disease", which hit the country-side with such devastating consequences in the 1970s.

One of the greatest species of oak, the common oak or quercus robur, which lives for 400 years, is dying before it reaches the age of 40, raising fears that a classic feature of the British countryside might disappear.

In Sherwood Forest, oaks have lost more than half of their density, and in a test sample in London's Richmond Park 14 per cent of oak trees died in 1997.

On average, three out of four oaks have lost more than 25 per cent of their leaves, according to scientists working with the European Union.The phenomenon is called "oak dieback" and is characterised by dead branches and dropping leaves. The trees take on a "stag-headed" appearance, where the surviving large leafless branches push upwards like a stag's antlers. Many trees remain in this half-living state for years before they die.

The problem is not yet classified as an epidemic but is described as "extremely serious" in localised areas. The worst hit counties are Hertfordshire, Cheshire, Northamptonshire, Lincolnshire, Shropshire and Herefordshire.

The cause is unclear. Scientists suspect a strain of fungus, which may be thriving because of global warming. Or, they say, a simple natural process may be happening and oak numbers may slump drastically in the short term, but eventually recover. Scientists are puzzled because Britain's other 40-odd native species of tree, including the only other oak, the sessile oak, appear immune.

"We're sure drought and insect defoliation are part of the problem," said a spokesman for the Forestry Commission. "The problem is caused by long periods of attack by more than one factor. Many trees are at the point of no return."

The Woburn Estate in Bedfordshire has had 27 trees hit by the problem in five years. "It's had a terrible effect on the landscape and I think it will get even worse," said Cyril Read, head forester on the estate. "The oaks take five years to die off completely." Mr Read is felling trees as they become infected, but the cause still puzzles him.

An international research project, funded by the European Union, is investigating a fungal disease, phytopthora, which has been linked to dying oaks in France and Germany. Phytopthora develops in warm, dry conditions and spreads rapidly in wet conditions - the typical British weather pattern of the 1990s. The fungus is in soil, and spreads by infecting oak roots.

Climate change may have aggravated the problem, bec- ause one key factor in the plight of the oak is thought to be "water stress". Like humans, if trees are under stress, they are more prone to disease.

"This aggressive fungus [phytopthora] is typically found in southern Europe, where summers are hot and winters are mild," said Claude Delatour, co-ordinator of the European Union study. "We can't exclude the possibility that this disease is moving north as the climate changes."

The situation is causing serious concern. Dutch Elm Disease altered the countryside and removed an important part of the eco-system. The oak is home to more insects than any other tree, a haven of food for birds and the density of knotted branches help birds to breed.

Many dying oaks are on managed woodlands, grown commercially for furniture. Within decades a slump in commercial production would jeopardise furniture making.

"Trees are dying 50 years short of their normal felling dates, so owners lose considerable timber value," said the Forestry Commission spokesman.

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