The underlying cause is natural enough - the drought-like conditions which have existed all over south-east Asia since last year, caused by the El Nino weather pattern. This should be Indonesia's wet season, but rainfall has been low all over the country, and especially in East Kalimantan, in the Indonesian part of Borneo.
Borneo's original vegetation - tropical rain forest - is very resistant to fire, but over the years large areas of it have been cut down for logging and plantation. The thinner secondary forest which replaces it contains much less moisture, and in these dry conditions fires start and spread easily, although experts agree that almost none of them are started spontaneously or accidentally, by lightning, for instance, or stray cigarette ends.
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 lack this expertise and, in trying to clear a few hundred yards of forest, they often succeed in inadvertently burning hundreds of hectares.
The third element 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. For these businessmen, as for the small farmers, burning is the quickest and cheapest way of clearing forest, despite being technically illegal. Companies are accused of using fire to drive out local people, who may then retaliate by setting fire to company plantations.
Last year, under pressure from Singapore and Malaysia, President Suharto called on companies to desist from burning. But enforcement is weak and ministers have little power to act independently of the president. Many of the companies carrying out forest clearance, like the timber magnate Bob Hasan, are personal friends of Mr Suharto. And this year, with the precipitous decline of the Indonesian economy, the government has other things on its mind.Reuse content