Forestry researchers have detected an upsurge in the disease - a fungus that can be passed from one tree to another by a beetle - in 20 elm plots planted in 1977 in the aftermath of the last epidemic which wiped out two thirds of the country's elms.
The disease has on average doubled since 1991 in southern England. In one plot the proportion of trees affected by Dutch elm disease increased from 30 per cent in 1991 to 79 per cent in 1993. At another plot, the disease climbed from 10 per cent to 36 per cent. Scientists believe the cause of the new epidemic is the recent warm summers and dry weather, which have exacerbated the effects of the fungus - which blocks the elm's water system - and helped the elm bark beetle to breed faster.
Dutch elm disease in the Seventies killed off many trees but felling left the roots able to regenerate. Many of the elms have since grown big enough for the elm beetle to breed in its bark again, Brian Greig, a forest pathologist at the Forestry Commission, said.
'The elm has made a remarkable recovery since the 1970s, but now it's being attacked by the disease once more. The beetle population is already high because of previous hot summers.'
The English elm once defined the rural landscape perhaps more than any other tree. It rarely, if ever, sets seed and spreads by producing suckers from its roots which can grow into individual trees.
It is thought that all the English elms, which are virtually identical genetically, are the descendants of one tree introduced into pre-Roman Britain from the continent. Their genetic uniformity made them highly susceptible to the fungus that causes Dutch elm disease, first identified in Holland in 1919.
'People described the epidemic of Dutch elm disease as a major ecological disaster after it destroyed more than 20 million trees. Now we are in a situation where the offspring of these trees are reaching a size where they are becoming a significant component of the countryside again and the great pity is they are being wiped out,' Mr Greig said. 'It is also a great pity that English elms are becoming akin to a shrub rather than the great majestic tree of the past.'
Mr Greig said that this year's survey is not complete but he 'fully expects' the upsurge in Dutch elm disease to continue because the epidemic is cumulative from one year to the next. 'There will be some areas where the disease kills out most of the new regeneration. The trend of increase will undoubtedly continue because of what's happened in previous years.'
The last 15 years of prolific regeneration of the English elm was a 'honeymoon period' that now appears to be over, Mr Greig said. 'This is the first generation of elm to be attacked since the major epidemic of the Seventies.'
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