Heathland: A burning issue

Four years ago tomorrow, in the baking July of 2006, one of the most devastating wildfires Britain has ever witnessed broke out on one of our most wildlife-rich nature reserves, Thursley Common in Surrey. It burned for nearly four days, looking like scenes from a painting of hell, it required more than 100 firefighters to bring it under control, and by the time it was finally out, it had turned 60 per cent of the 1,100-acre reserve into a black, charred, smoking desert.

The reason the fire was so fierce was its location: heathland. Lowland heath is a widely cherished wildlife habitat, but it is also incredibly flammable, as its vegetation cover consists largely of heather and gorse, both of which, once alight, burn like billy-o. (Burning gorse generates so much heat that it was the fuel of choice to fire medieval bread ovens.) And as a hot dry summer is at last succeeding the three sodden summers in a row we have just endured, concern about heath fires like the one at Thursley is now mounting again.

At the weekend, the first major heath fire of the year hit Surrey's Frensham Common and required 80 firemen to control it. Although rain is due this week, the initial six months of 2010 have been the driest start to a year since 1929, and with the high temperatures forecast to continue next week and into August, at least in the South east, the heath fires risk is regarded as very high.

The areas of concern are mainly concentrated in a broad band stretching from Surrey and Sussex through Hampshire to Dorset, although patches of lowland heath can be found in Cornwall, Norfolk, and the Wirral Peninsula in Cheshire. It is one of Britain's most special landscapes, an ancient wasteland whose acid, sandy soils were always too poor to farm for crops, so it was used as grazing for livestock and left to the heather and the gorse which could flourish there, and the silver birch trees and occasional Scots pines which sprang up among them.

Once it was seen as sinister – you may remember the Blasted Heath where Macbeth meets the three witches, or Thomas Hardy's Egdon Heath, the dark wilderness at the heart of his Wessex. But our view of it has changed, not least as its area has shrunk to but a tiny fraction of what it once was, and now the wilderness atmosphere which heathland undoubtedly engenders – in mid-heath you can occasionally feel you're in somewhere like Russia – is seen as a very attractive contrast to the placid settings of the rest of England's intimate and unthreatening countryside.

In addition, heathland has a specialised and abounding biodiversity, beginning with its ericaceous plants, its heathers, ranging from the deep purple bell heather to the lighter purplish-pink ling, and cross-leaved heath, along with other specialised plants such as sundew, which is insectivorous. Sundew can well afford to eat insects; the insect fauna of lowland heath is staggeringly rich, with thousands of species ranging from funnel-web spiders to tiger beetles which can run faster than a person can walk, and crowned with its own special butterfly, the lovely silver-studded blue, which recent research has shown spends much of its early life as a caterpillar inside ants' nests.

The bird fauna of lowland heath is similarly specialised, characterised in particular by three uncommon and fascinating species, the Dartford warbler, the woodlark and the nightjar. But perhaps the highlight of heathland wildlife is that group of creatures which is largely ignored in Britain: the reptiles. We only have six, three lizards and three snakes: the common and sand lizards and the slow-worm (a lizard with no legs), and the adder, the grass snake and the smooth snake. They're elusive, but all can be found on heathland, and on Thursley Common and a few other places, all six can be found on the same site.

A mortal shame, then, that all this wildlife-rich and charismatic habitat can go up in a puff of smoke if people are not careful – for you nearly always find people, at the origin of heath fires, says Simon Nobes (pictured above left), Natural England's senior reserve manager at Thursley Common. He laughs. "The idea of the sun shining through broken glass and starting a fire – well, I wouldn't rule it out on fine grass, but on a heathland landscape, that's a long shot. It's pretty much an old wives' tale. Heath fires are started by people."

Sometimes they're started deliberately, he says, by certain types who like to see the drama of a fire; sometimes they're started accidentally, by a camp fire, say, which the campers concerned mistakenly think they have put out. And although camping is not allowed on Thursley Common, a camp fire is the best guess for the cause of the 2006 conflagration.

It was a very hot period. We have probably forgotten, but July 2006 was the hottest month ever recorded in Britain, and five days after the Thursley fire broke out, the hottest-ever July day was also recorded, when the mercury rose to a remarkable 97.7F (36.5C) at Wisley in Surrey, a few miles away. The vegetation on Thursley Common was tinder dry, the heather and the gorse; all it needed was an act of carelessness to set it ablaze, and that appears to have happened in Spur Wood, a small copse of Scots pines in the centre of the reserve. "We suspect it was a camp fire here someone thought they had put out, but because it was on the peaty soils it smouldered and smouldered, and by the following day – whoomph!" Nobes says.

We are standing in the copse, surrounded by blackened pine trunks – some of the trees have died, but others have sprung back to life in their upper branches. "You can see the temptation to camp here, sheltered, a nice view out," he says. "That's our best guess."

They first knew of the fire in the early afternoon of Friday 14 July when a farmer phoned to say he had seen smoke on the common. By the time they got there, the flames were coming out of Spur Wood on a 20-yard front about 60 yards deep; but in one of the shifts which make heath fires very hard to fight, the wind changed, the flames began to advance to the side – and now the fire front was 60 yards wide.

Nobes, 47, who has been at Thursley Common for 20 years, has seen many heath fires (though none comparable to 2006) and is alive to their tricks and their dangers. "You've got so much combustible material, they can move very quickly, faster than you can run," he says. "Heath fires advance at a frenzy. They can start over-spotting, where hot debris falls ahead of the fire, so you can get a fire front almost leap-frogging itself as it advances with the wind.

"Then the topography can have a big effect. When a fire hits the base of a hill, it will at least double its speed as it goes up the slope, because the angle of the slope works as a fuel pre-loading system – the fuel in front is being pre-heated by the fire itself. And then it can shift direction whenever the wind changes."

All that happened, making the Thursley fire a beast to handle. Surrey fire brigade got there very quickly but the flames had taken too deep a hold to extinguish with ease, and eventually crews from four other forces had to be called in and they took nearly four days. Fire officers share Simon Nobes's view of the difficulties. "Heath fires present us with very significant challenges," says Surrey Fire Service's assistant chief officer Simon Moore. "There is often difficulty of access, difficulty getting water, and we have to think about protecting the houses which may be on the edge of the heath, the people who may be on the heath, and the fairly precious habitat itself."

When the fire was finally out, more than half of that habitat had been devastated. The landscape was black; you could find the charred corpses of snakes and foxes. The heathland vegetation had vanished, and with it, it was feared, the wonderful insect communities headed by the silver-studded blue butterfly.

Four years on, Thursley is slowly regenerating, and last week it was a pleasure to see the young heather and gorse again starting to spread over the charred landscape, and in some places, the silver-studded blues sparkling among the heather flowers. But it took a ferocious hit, and much of the wildlife has not yet come back to its previous level – the pre-fire population of 45 pairs of Dartford warblers has been reduced to six. And all because of a piece of carelessness with a campfire. Carelessness is something England's lowland heaths will not be able to afford, in the coming weeks.