Urgent action is needed to prevent the world's forests being destroyed within 10 to 20 years by mining, roads and illicit logging, an extensive report claims.
Indonesia and Russia are particularly affected by the destruction. What were once pristine forests are now turning into patchworks, with serious implications for the future.
The story is repeated again and again across the world, as governments put the short-term interests of themselves and their voters ahead of the environment.
Unusually, it appears that some companies will do good where governments will not. The latest study was sponsored by Ikea, the Swedish furniture group, and supported by ABN Amro, a European bank.
The World Resources Institute (WRI), an environmental research group, said huge numbers of trees were being destroyed and corruption, often at the local government level, was allowing unsustainable "development" to damage the forests beyond their ability to repair themselves.
Worse still, many areas that had been thought of as virgin territory turned out to be suffering from human incursion.
"As we examined what we thought were still vast, untouched stretches of intact forests in the world, we came to the conclusion that they are fast becoming a myth," said Jonathan Lash, the president of the WRI.
"Much of the green canopy that is left is, in reality, already crisscrossed by roads, mining and logging concessions."
Humans, rather than environmental change, pose the biggest risk, said Dirk Bryant, the founder and co-director of Global Forest Watch, which is co-organised by the WRI.
"Much of the threats facing the remaining intact forests boil down to bad economics, bad management and corruption," he said. "We are rapidly moving towards a world where wilderness forests are confined primarily to islands of parks and reserves, with surrounding areas managed commercially for timber and other resources. The health of the planet's forests will depend on how well we manage and protect these remaining areas."
Forests are often thought of as the lungs of the planet. During the day they scrub carbon dioxide and pollutants out of the air, leading to less global warming. Burning trees means the carbon that is trapped by the them will enter the atmosphere as carbon dioxide, contributing to global warming.
The forest floor also provides the home for huge numbers of animals and plants, which could not otherwise survive. All of these are threatened by unsustainable logging, which does not allow new trees to replace those that have been removed.
In Indonesia, where illegal forest fires started by loggers have in the past few years created international environmental disasters, about 70 per cent of timber production is illegally logged.
In Chile, government policies encourage people to clear native forests that are thousands of years old to make way for plantations of exotic species. As a result, the prehistoric araucaria forests and the second oldest living trees in the world, the alerce, are in danger.
In Venezuela, logging and mining practices are threatening one of the most pristine forests on earth.
The WRI also expressed great concern about Russia, which has the largest forests in the world – the semi-Arctic taiga, or boreal, forest. Only a quarter of that area remains undisturbed, the WRI found.
The report, released yesterday after two years of research, also covers Central Africa and North America.
Indonesia contains the greatest expanse of tropical closed-canopy forest in South-east Asia. Following several decades of intense exploitation, its forest cover today is about 60 per cent of what it was a century ago. Most clearance occurred after 1950, when forest cover fell from about 162 million hectares (400 million acres) to less than 100 million today, the report said.
"Despite mounting evidence of enormous destruction, the picture in Indonesia has been clouded by poor quality data, government obstructiveness [under the former dictator Suharto] and intimidation by the powerful timber industry," the WRI said.
Last June there were separate warnings that the destruction of the Amazon rainforest could be irreversible within a decade. James Alcock, of Pennsylvania State University, said that the forest could virtually disappear within half a century due to feedback processes. He argued in the journal Science that his model could also be used to forecast the effects of logging in the other great tropical forest systems, in South-east Asia and the Congo river basin in Africa. The picture for those was similarly gloomy.
Mr Bryant and his colleagues made the first assessment of the world's intact forests four years ago, and found then that only one-fifth of the historic forest cover actually remained in that form. At the current rate of destruction, they estimated that 40 percent of what remained would be lost in 10 to 20 years.
"Our most recent studies show that we have underestimated the destruction in some countries," he said. He started Global Forest Watch two years ago to keep track of what is left of the remaining intact forests of the world.