Aras Napal – The European explorers who penetrated deepest Sumatra in the 18th century recoiled in awe at the beauty of the "dark and savage" forest that covered the Indonesian island. Today, there is hardly any of it left.

As is the case across much of Indonesia, huge swathes of tropical woodland have succumbed to the ravages of deforestation, in the process destroying the natural habitat of endangered species including tigers and the Sumatran rhino.

"70 percent of the logging is illegal. At the current pace, the tropical forest will have disappeared within 10 years," said Arbi, a 29-year-old activist with the environmental group Telapak.

Satellite images show a huge green mass in the north of Sumatra where the forest has survived. This is the Leuser national park and the protected eco-system that surrounds it is one of Asia's most stunning natural sanctuaries.

It is the last place where Sumatran rhinos, whose numbers have dwindled to less than 80 in the wild, still share the forest with tigers, elephants and orangutans.

The park's forests and valleys stretch for as far as the eye can see – the blanket of green broken up only by the sudden appearance of a brilliant red bird.

Greater serenity, it seems, could not be found anywhere on the planet – or at least that would be the case if it was not for the distant drone of the chainsaw.

"I can't see them, they are a few kilometers away, but I can hear the sound, says Tina, a young Dutch zoologist. "The local people here say 'that's the sound of the forest.' It's not a very nice sound, is it?" The teams of local farmers who operate the chainsaws are paid less than two dollars a day for their toil in the stifling humidity of the mosquito-infested forest.

Already a fifth of the park has been seriously damaged by illegal logging. Fragile marshland areas have been transformed into plantations. In broad daylight, lorries loaded with wood can be seen on the roads leading to the city of Medan.

"Illegal logging is not a poverty problem," insists Mike Griffiths, one of the directors of a European-backed project to defend the Leuser park. "That's a myth. Its a greed problem." The loggers are only the last link in a chain from which the principal beneficiaries are powerful businessmen, the wood barons.

"Here everyone knows who they are and nobody does anything about it," says one local ecologists. Campaigners are happy to name businessmen who they say benefit from contacts in the security forces and forestry companies who cut down far more trees than they are authorised do.

In 1997 and 1998, millions of hectares of forest were destroyed in huge fires designed to clear land for planting.

Such practices are not new: millions of hectares were destroyed by companies linked to cronies of former ruler Suharto such as "Bob" Hassan, who has since been jailed.

Since Suharto was toppled in May 1998, local barons have taken over, using the same combination of corruption and violence to get their way, according to Telepak.

Indonesia's moves to devolve power to the regions has played into their hands, the environmentalists argue.

"We want to stop illegal logging," North Sumatra governor Nurdin Tengku Rizal recently told EU ambassadors. But he added: "The new autonomy law gives us responsibility, but not power." The ambassadors had come to demand greater efforts to protect the park, which the EU has funded to the tune of 32.5 million euros (36.5 million US dollars).

"Catching those involved in cutting or transporting logs illegally is not enough," said Sabato Della Monica, the head of the European Commission's Indonesian office. "A legal process in a court of justice is necessary. And not only those involved in cutting and transporting should be punished, but more important is that those behind the scenes who are involved in buying and trading illegally should be dealt with severely." To date only a handful of drivers have been arrested, some of whom have been convicted on largely symbolic charges.

Local officials say Indonesia's myriad economic problems, the lack of efficient security forces to impose order and the strong international demand for tropical hardwood mean combatting illegal logging is an uphill struggle.

The environmentalists insist that the real problem is how to put an end to the corruption and nepotism that allows it to continue. Above all, they argue, there has to be an end to the culture of impunity symbolised by the fact that one of the country's most notorious wood barons, Abdul Rasyid, sits in parliament.