Unpublished Government figures, obtained last week for the Independent on Sunday, show that levels of ozone have exceeded official danger limits for trees for weeks, and often months, over most of rural Britain since May.
In areas as far apart as Sussex and Scotland, Devon and North Yorkshire, the pollution, mainly from car exhausts, stayed above the internationally agreed limits for almost every day throughout the height of the summer.
The figures, compiled from official computerised records by Friends of the Earth, show that up to last Monday the gas exceeded the limits laid down by the World Health Organisation on 89 days in Cumbria, 93 days in North Yorkshire, 101 in Devon and the South-West and 103 in Sussex. (The highest figure, 123 days, was recorded in the Scottish Highlands, but this is distorted because the monitoring station is high on a mountain, where ozone levels are elevated.)
Ozone - one of the factors in the asthma epidemic which currently affects one in every seven British children - is now being implicated in an alarming sickness sweeping through the country's woods and hedgerows. By one official measurement, more than half of Britain's trees are seriously or moderately affected - nearly three times as many as seven years ago.
For the second year running, trees throughout Britain have begun changing colour from mid-August. This 'early autumn' is a classic sign of the sickness; another, bare or sparsely foliated treetops, has been even more widespread in the past few summers.
Last year the Forestry Commission acknowledged that 'early autumn' was taking place, but blamed drought - in what proved to be an exceptionally wet summer. This year it denies it is happening: 'There is some yellowing of leaves, but no early autumn.'
At the Department of the Environment a senior official did admit: 'As a member of the public I feel that autumn has started early. But there has not been a systematic survey that would tell us that this is true.'
A DOE review group, which six years ago dismissed suggestions that pollution might be damaging trees, has also admitted, in its latest report, that 'the available evidence suggests that ozone is likely to adversely affect tree health in parts of Britain'. It calls for cuts in pollution levels.
This is a significant change from the department's position throughout the 1980s, when, together with the Forestry Commission, it insisted that Britain's trees were healthy, and later denied that pollution was to blame. When European foresters reported widespread forest sickness in the early 1980s, and attributed it partly to ozone, sulphur dioxide and nitrogen dioxide pollution - making trees vulnerable to pests, diseases, frost and drought - senior commission officials rubbished their findings.
Even when the commission published a report with evidence of such damage, it presented it as showing that 'Britain's trees are in good health'.
But research by both the commission's own scientists and the Government's National Environment Research Council has gradually undermined this position and increasingly pointed to ozone as a source of the blight. Experiments with beech seedlings have shown that they grow poorly when exposed to even relatively low levels of ozone and thrive when the air is cleaned. Even a single exposure to ozone can blight the development of a young tree.
Fiona Weir, senior campaigner for Friends of the Earth, said last night: 'Many factors are involved, but pollution plays an extremely important role. We cannot do much about such factors as drought, pests or disease, so we had better tackle pollution if we are concerned about the plight of Britain's trees.'
The Forestry Commission says it will 'shortly' embark on its first research to measure pollution around blighted trees. Meanwhile, it has reported an apparent dramatic improvement in the health of Britain's trees. Its annual survey shows that only 16.9 per cent of them are moderately or severely damaged, down from 58.3 per cent last year, which was the worst figure reported anywhere in Europe.
But in fact, it admits, almost all of this change comes from adopting a different method of assessing damaged trees to give 'a more satisfactory comparison with results obtained elsewhere'. By the old method of counting the figure would have been 54 per cent, a slight improvement but still more than two and a half times as great as the 20 per cent the commission recorded seven years ago.Reuse content