The resurgence of bush and forest fires in Indonesia has raised fears of a return of the massive blanket of smog that smothered much of Southeast Asia last year. The haze of 1997 was caused by thousands of blazes across the country, but why were they so widespread?

The cause of last year's fires in Indonesia remains the subject of heated debate. Environmental activists blamed the timber and plantation industries for using uncontrolled burning to clear land, while many Indonesian government ministers said it was the result of unusually dry conditions brought by the El Nino weather pattern.

The truth is probably a combination of the two. Most of the fires were started deliberately, some by individual farmers hoping to plant a few crops under the jungle canopy, others by commercial plantations cashing in on demand for rubber and palm oil. But the growing hunger for land coincided with the worst drought for half a century. The fires simply refused to go out.

Human causes

The World Wide Fund for Nature says that many of the world's forest fires last year were started deliberately, and often illegally, in order to clear land for planting or development, or to cover up illegal logging. Setting fire to the land is the quickest, cheapest way of clearing land. Any other method in the former tropical forests of Indonesia is much more difficult.

Don Henry, Director of WWF's global forest programme: "While the causes are complex, the smoking gun in almost all cases is widespread forest destruction and land clearing for plantations.

"Rainforests should not burn. But by clearing vast areas through destructive logging practices, loggers have made them tinderboxes waiting for somebody to strike a match. As more and more rainforests are destroyed, it will be easier and easier to set them on fire."

The WWF has called for the strict enforcement of national laws controlling forest fires and the introduction of new laws where necessary. The fund wants improved management of the world's forests.

But environmentalists argue that most fires in Indonesia were started by large conglomerates and politically-influential businesses who had been given licenses to turn vast areas of Borneo and Sumatra into commercial plantations.

Environmentalist Emmy Hafild: "Without government ability to control the attitude of the big business and the vested interests groups, I think the forest fires will not be able to be controlled or be prevented. It depends on the political will of the government to really implement laws and rules that have been in place but never been implemented."

For years Indonesia's forests have been viewed as the country's green gold - a rich source of revenue for the government, and of profits for the companies which have been allowed to exploit them. Environmental campaigners believe the fires are just the latest chapter in a long history of unsustainable forestry practices by big business.

Unsurprisingly the forestry industry disagrees. Bob Hasan, timber tycoon and close friend of Indonesia's President Suharto, is unrepentant. He admits lighting fires in the forest, but dismisses the complaints of his critics.

"When we do deforestation, we do organised burning. Organised burning means we clean up the shrubs, we clean up the grass, because if you do not clean the shrubs, it might become a fire hazard. We want to develop our country on a sustainable basis, but sometimes some of the NGOs come in and say you're violating environment rules, you're violating human rights, but usually things like this comes from communist individuals."

The Environment Minister, Sarwono Kusumaatmadja, says that in the past licences for lighting fires have been given away very cheaply to all kinds of people. During last year's crisis, he called for tighter controls.

A list was drawn up of firms which were to lose their licenses, but some managed to escape the clampdown. Two of Mr Hasan's companies were originally on the list, but were removed a few days later.

The current financial problems faced by Indonesia could increase the harmful effects of the economy on the forests this year. Mr Kusumaatmadja said most of the recent blazes had been lit by farmers or by plantation companies desperately trying to recoup losses by clearing more land for cultivation. He added that poor people who could not afford fuel were also chopping down trees.

El Nino

Although Indonesia is used to forest fires breaking in the dry season, it was caught out by the severity of the 1997 inferno.

The blazes were made much worse by prolonged drought, exacerbated by the century's most severe El Nino weather event, which dried out the usually lush rainforests and left them more susceptible to fire.

So-called greenhouse gasses released from the fires may in turn have contributed to the increased severity of El Nino producing what the WWF describes as a vicious cycle of destruction. The environmental group estimates that six months of fires in Indonesia could release more carbon dioxide into the atmosphere than the combined annual production of cars and power stations in Western Europe.

To make matters worse, last year's fires set alight peat deposits that will remain burning deep underground for months or even years and surface during the dry season.