Who on earth would destroy all this?

It is Britain's silent environmental disaster. A series of mysterious fires has reduced some of Britain's most precious heathlands to little more than a pile of cinders, wiping out vital nesting sites for birds and mammals at the height of the breeding season.

It is Britain's silent environmental disaster. A series of mysterious fires has reduced some of Britain's most precious heathlands to little more than a pile of cinders, wiping out vital nesting sites for birds and mammals at the height of the breeding season.

As winter ends, Britain's heather heathlands should be preparing to flaunt their glory. The purple flush of common heather, accompanied by gorse, bell heather, cranberries, bilberries and marsh violets, is one of the great sights of the remoter parts of the country.

But in the past six weeks, several dozen small fires have broken out across the West Country, from north Devon to the southernmost tip of Cornwall, causing widespread damage to more than 3,600 acres of moor and heathland.

There is probably more than one cause. But environmentalists believe the most damaging fires were started deliberately. But by whom? On one hand they say it is a classic case of mindless arsonists at work. On the other, some whisper privately about more sinister motives.

Goss Moor, near Roche Moor and St Dennis in Cornwall, is one of the heathlands worst affected. Firefighters took six hours to extinguish a blaze that destroyed 125 acres of this prime heathland. The moor's wide variety of flora and rare fauna has given it the status of a National Nature Reserve and a Site of Special Scientific Interest. It has been put forward to be upgraded to a Special Area of Conservation, an EU designated status which would protect it further against development.

Such a move would thwart any plans to develop the A30 east of Indian Queens, a notorious tourist-season bottleneck. There are those who wonder whether some, so desperate to see impoverished Cornwall receive more investment, are prepared to harm its countryside so that the A30 scheme will not be held back by further environmental protection.

There may be more innocent reasons for the destruction. Small fires break out in spring on moorland for no other reason than the land is usually bone dry. Other blazes may have been caused by fag-ends thrown by motorists.

There is an even more bizarre theory that the fires may be the work of the arsonists who last year damaged the Men an Tol and Lanyon Quoit stones in Cornwall, which date from 3,500BC. They then tried to justify their act by citing past mistreatment of the stones and claimed it was an attempt to make them more aesthetically pleasing.

So far, 15 to 20 per cent of heathland in Cornwall has been destroyed since the start of March, affecting areas across the county including Penrith and the Lizard. In mid-Cornwall, English Nature puts the figure destroyed as high as 70 per cent. The heathlands alongside the A30, the main route over Bodmin Moor and into west Cornwall, have been affected worst of all. The optimistic assessment is that it will take 10 years for the heathland to recover while precious species such as the silver-studded blue butterfly and the endangered Dartford warbler may become locally extinct.

There are fears the fires may jeopardise the Cornish Heathland Project which will recreate 1,000 acres of lowland heathland on old waste tips excavated for china clay. Despite recent wet weather, the gorse has remained dry, allowing fires to spread rapidly at speeds of up to 35mph.

Nor does there seem to be any let-up. There was a recent string fires on Rosenannon Downs, near St Columb Major. And only last week another was started at Carn Brea, near Redruth, while in Devon firefighters used beaters to put out a fire on East Anstey Common near South Molton.

Yet the blazes have received almost no publicity and, as yet, no satisfactory explanation. Fire crews have sought to play down the issue, wary of encouraging or giving a platform to the activities of arsonists.

"We're quite certain that we are dealing with heathland arsonists," said Martin Davey, site manager for English Nature in east Cornwall. "We can see that some fires have been started accidentally but the more serious ones look as if they have been orchestrated by someone who knew what they were doing."

Swaling, the controlled burning of heather to encourage regrowth, has been used to manage heathland for centuries but the nature of the recent fires has gone far beyond this traditional benefit, according to Mr Davey. "This kind of blanket burning kills off the roots and the seed bank of the heather which means it will not grow back quickly. It will take about 10 years to recover."

In the past a fire that devastated a stretch of heathland would have been a serious but manageable cause for concern. But today the heathlands of Cornwall and Devon are fragmented by the intensification of agriculture, housing and military training. The problem for wildlife is that the next stretch of heather may be five miles away, too far for some species to travel. Mr Davey said: "Some animals will just die out locally. We've got linnets and stonechats just standing around not knowing what to do because their nests have been destroyed."

Police, too, believe many fires were started deliberately, though they admit they are struggling to come up with hard evidence. They point out that the fires around Goss Moor broke out near electricity pylons which are rigorously monitored for fire risk and unlikely places for natural fires to occur.

Detective Sergeant Terry Carne of Newquay police, who is investigating the fires on Goss Moor, said: "It is significant that some of these fires have been started within a few miles of each other." The areas in question are remote and not easily policed. So, it may be that the environmentalists who first raised the alarm have a role to play. DS Carne called on wildlife enthusiasts to remain vigilant. "Bird watchers pursue their hobby in areas we can't cover so if they see anyone behaving suspiciously then we want to know about it."

Heathland is a rare and declining habitat. England has just 10 per cent of the heath we enjoyed at the end of the 18th century, and more than 40 per cent has been lost since 1950. What precious little is left, including the beautiful lilac-pink Cornish heaths, is recognised by nature lovers and statutory bodies for what it is: a national treasure worthy of gentle protection.