Conservationists say the rate at which Indonesia is losing its forests has doubled since the 1980s.
They say the lowland forests, the richest in the country, will not survive for long on some of the biggest islands.
They blame corruption for driving "an epidemic of illegal logging".
Indonesia's forests are home to a wealth of species and are one of the world's biological treasures.
The accusation comes from the World Resources Institute (WRI), Global Forest Watch (GFW), and Forest Watch Indonesia (FWI).
In a report, The State of the Forest: Indonesia, described as the first comprehensive map-based assessment of the country's forests, they say the deforestation rate doubled in the late 1990s.
While Indonesia was losing a million hectares (2,471,000 acres) of forest annually in the 1980s, the report says, nearly 2m ha (4,942,000 acres) are now being destroyed every year.
Forest cover has fallen from 162m ha (400,300,000 acres) in 1950 to 98m ha (242,200,000 acres) in 2000.
There for the taking
The jewels in the crown, the lowland forests, have almost entirely disappeared from the island of Sulawesi.
Sulawesi mangrove forest: Little remains
By 2005, the report says, they will have vanished across Sumatra, and by 2010 from Kalimantan.
One of its co-authors, Emily Matthews, said: "Deforestation on this scale, at this speed, is unprecedented. Indonesia is rapidly moving from a forest-rich to a forest-poor country."
The report says this doubling of deforestation rates results mainly from "a corrupt political and economic system that regards natural resources as a source of revenue to be exploited for political ends and personal gain."
Togu Manurung, director of FWI, and another co-author, said: "Indonesia's economic miracle of the 1980s and 1990s was based on ecological devastation and abuse of local people's rights and customs.
"Our findings do not provide grounds for much optimism, despite clear signs of change in Indonesia."
The report says not only corruption is to blame, but lawlessness, illegal logging, political instability and over-expansion of forest industries.
Indonesia's Ministry of Forestry says legal timber supplies from natural forests declined from 17m cubic meters in 1995 to under 8m in 2000.
The report says huge expansion in the plywood, pulp and paper industries in the last 20 years means that demand for wood fibre now exceeds legal supplies by up to 40m cubic metres annually.
Sumatra's lowland forests "will last three years" (Emily Matthews)
It says illegally cut wood accounted for as much as 65% of the supply in 2000.
Indonesia is home to 16% of the world's bird species, 11% of plants and 10% of mammals. These include the orang-utan and the Sumatran tiger, neither found anywhere else.
Two years ago the World Bank said the state of Indonesia's forests was so bad it might withdraw support for forestry protection projects.
Sea change needed
It said Indonesian maps showed the area of forest lost between 1985 and 1997 was greater than the entire state of Florida.
Thomas Walton of the Bank said: "Illegal logging has become rampant, even in national parks, on a scale that exceeds the volume of legal logging, and the authorities look the other way.
"Only a radical departure from 'business as usual' will spare the nation and the world the loss of this precious natural resource."
Dirk Bryant, director of GFW, said: "Sixty-four million hectares (158,100,000 acres) of Indonesian forest have been cut down over the past 50 years.
"There is no economic or ethical justification for another 64m ha to be lost over the next 50."
What the clearance gangs leave behind: A former forest in Sumatra
Images courtesy of Forest Watch Indonesia.