The strangest thing about the jungle near Muara Nayan, stranger than the smell of the air and the blank whiteness of the sky, is how autumnal it looks, closer to Hyde Park in October than the tropics. The smell is one of autumn bonfires and the tall trees are bare of leaves, or shedding them onto the road in orange piles.
But we are just 40 miles from the equator, and the temperature here is close to 38C. These are tropical hardwoods, not elms and sycamores, and we are in the forests of Borneo, eight hours from the nearest city, where it is hot and humid all the year round and there are no seasons.
The puzzle is answered a few yards off the dusty road, in what used to be a swampy grove of hardwoods and fruit trees. Now, for a few hundred yards on all sides, it is the skeleton of a forest - the swamp water has thickened to viscous mud, scattered with the fallen bodies of blackened trees and covered in a layer of white ash.
Even from the unburned vegetation lines of smoke rise into a dazzling white sky in which the sun is visible only as a pale orange disc. In an area the size of a football pitch, there are no insects or birds, no frogs or snakes, and no monkeys.
The Dayak tribesman who used to tend this land is at a loss. "It began three weeks ago in the middle of the night," he says, "and the first we knew was the smoke the next morning.
"We came quickly, but the fire had spread so far, and there is no water. So we had to let it burn." His durian trees, his mangoes, jackfruit and rambutans were all destroyed. "Every year, there were fruit there, for my family to eat and to sell in the market. I have lost my income, my livelihood."
In a normal year, he could rely on his rice fields - but with almost no rain since last year, the harvest is doomed to be a failure. His family have taken to weaving traditional textiles and making Dayak wood carvings - but the foreign tourists who might have bought them have been scared away by news of the enveloping smoke.
A worse and bigger fire three months ago burned several years' worth of rattan, the pliable cane which is the other local standby. But if this looks like a natural disaster, the villagers do not see it that way. "There is no proof," says the village headman, "and it is possible that some of these are accidents. But in the past, even when it was as dry, there were never so many fires as this. They have begun only after the companies came in, the companies and their politics. But we cannot prove it, so we keep silent."
Borneo is burning again. In November and December, the rains came at last, bringing respite from the fires which burned all summer, closing airports, causing deadly shipping and aviation accidents, and choking millions of people in Malaysia, Singapore and Thailand with the so-called "haze".
But in East Kalimantan, the biggest province of Indonesian Borneo, it has rained for no more than a few hours since the beginning of the year, at what is supposed to be the height of the wet season. Helicopter inspections last week revealed fires covering some 15-20,000 hectares in this province alone, and with no rains in sight the situation can only get worse. Indonesia, home of some of the world's biggest tropical rain forests, is once again on the way to becoming its biggest bonfire. But if the effects of the blaze are obvious enough, its causes are as complex and murky as Indonesia's politics, a product of greed, social engineering and the interaction of modern industry with a traditional way of life which has existed peacefully here for centuries.
If there is one thing which everyone agrees on, it is that almost all the fires burning here are man-made, the result of deliberate burning rather than accidents with cigarette ends or spontaneous combustion. For centuries, fire has been an essential tool of the slash-and-burn agriculture of the Dayak tribes who still populate Borneo's interior, as well as the "transmigrants", more recent arrivals, freighted in by the government in a controversial programme to ease congestion in poorer, more arid islands.
The former have lived here for thousands of years and their experience of the forest is enshrined in a detailed set of traditional precepts and religious rituals governing the use of fire. The latter, who often come to farming with no previous experience, lack this expertise. "The Dayak people don't cause forest fires," says Ludwig Schindler, a German expert who heads the Integrated Forest Fire Management (IFFM) project in the East Kalimantan capital, Samarinda.
"They know when it's too dry and dangerous to burn. But the outsiders don't have the close relationship with the forest, and they're careless. A man might want to clear half a hectare for himself and end up burning 200."
But the third and crucial element of the problem is the hundreds of commercial companies - rubber and palm oil planters, extractors of timber, gold and coal - who have descended on Borneo since the late 1960s, hacking and exporting its rainforests, which can be found in their virgin state only in the deep interior and in a few reserves.
For these companies, just as for the small farmers, burning is the quickest way of clearing forest, both in order to clear land earmarked for mining or planting, and to convert logged land for agricultural use.
The presence of these companies has created wounding rifts, as damaging to the local culture as they are to the environment. Many of the companies are affiliated to massive Indonesian conglomerates, run by the immediate family and cronies of President Suharto. Granted licenses by the central government, they arrive to "negotiate" with the local people who have almost no legal rights to their land, despite their ancient history.
Dayaks in Lempunah, a village near Muara Nayan, have been offered lump sums to exchange their traditional land for a small share in a palm oil plantation. So far they have held out but ever since the offer was made the village has been stricken by mysterious fires.
Evidence is sketchy, although foreign experts visiting the area say that they have seen fires being started by men who, when questioned, openly admit that they are acting on behalf of palm oil companies. And coincidentally or not, the loss of forest land benefits the companies in several ways.
With their rattan and fruit trees destroyed, locals are more likely to yield to the temptation of a windfall buy-out. The company may pay less in compensation for burned land than for productive forest - and the ruin of farmers creates a labour force of needy workers. "The company pays just 6,000 rupiah [35 pence] a day," says the Dayak man who lost his fruit trees. "But we have no other choice."Reuse content