Forests have arguably played a larger role in the development of human societies than any other resource, bar water and soil. The prime marketable product of most forests today is wood for use as timber, fuel wood, pulp and paper, providing some 3.4 billion cubic metres of timber-equivalent a year

Poor and rich nations alike need wood. The world's leading per-capita consumers of timber include nations at all levels of economic development: Liberia and Zambia; Malaysia and Costa Rica; Sweden and the USA. By continent, Africa is the second largest per-capita consumer of wood after North America.

Half of the world's timber consumption is for fuel, but in developing countries, this figure rises to 80 per cent. For almost three billion people, wood is the main energy source for heating and cooking. Many countries, particularly in Asia, face a growing domestic shortage of wood for this basic purpose--notably Bangladesh, Nepal and Pakistan.

Among industrialised nations, the predominant use of wood is as industrial roundwood, a category that encompasses building material, paper and packaging. Global paper use has grown six-fold since 1950, using a fifth of all the wood harvested. The focus of industrial roundwood production is moving from logging natural forests towards harvesting from plantations. In the past 25 years, the extent of plantations doubled to 180 million hectares, an area the size of Mexico.

Plantations offer the potential for high yields of fast-growing species on small areas of land. They are now being cultivated in developing countries, with most of them planning to double the area of land allocated by 2010. Plantations can help to relieve the stress on natural forests--as long as they are established on land that has previously been cleared for another use. However, plantations don't provide the same protection against soil erosion and flooding as natural forests, and they are more vulnerable to fires. They are normally monocultures with little biological diversity, and offer virtually none of the non-timber forest products that sustain many local economies and cultures.

Non-timber forest products include fruits and nuts, rattan, medicinal plants and bushmeat. Many people living in or near tropical rainforests rely on wild animals caught in the forest for half or more of their protein. But just as timber can be over harvested, so too can these non-timber resources, especially when local products gain access to large urban markets. The bushmeat industry, which has become an international business, exceeds one million tonnes a year in Central Africa alone. Such levels of exploitation are clearly unsustainable.

But the greatest wealth of the forests may lie hidden in its genes. "At the dawn of the 21st century, many people believe the natural world has nothing left to offer us in the way of new medicines. This could not be further from the truth," says Mark Plotkin, a US-born ethnobiologist. "Mother Nature has been creating weird and wonderful chemicals for three billion years, and we're only beginning to sift through these hidden treasures. While today's laboratories can synthesise new molecules at a pace that was unimaginable a few decades ago, nature provides the optimum starting points. Time and again, we find that plants and animals make strange molecules that chemists would never devise in their wildest dreams."

The US National Cancer Institute has already collected and genetically screened more than 50,000 plant and animal samples from 30 countries in an effort to find drugs that fight cancer. The US Army holds gene patents on numerous traditional treatments for tropical diseases, including a plant called mamala from Samoa, as well as on forest microorganisms that could be used in biological warfare. More than 100 of the top 150 prescription drugs in the USA are derived from plants and animals, mostly of rainforest origin.

Much of the information for these finds comes from research into traditional remedies. As a result of this research, ethnobotanists have recently found treatments for Hodgkin's disease and childhood leukaemia lurking in the chemistry of the rosy periwinkle, a small forest-floor plant from Madagascar. A new blood thinner being marketed by Merek is derived from a native cure for snakebite. And an anti-viral drug used in the treatment of HIV first surfaced in the pharmacopoeia as a Samoan herbal remedy for hepatitis.

But the native wisdom that is delivering these findings is being lost at a great rate. "Tribal knowledge represents tens of thousands of years of human experience. To lose it now, just when we have developed the scientific tools to evaluate it as a source of new drugs, crops, ecological insights and conservation techniques would be extraordinarily short-sighted," says Paul Cox, director of the US national tropical botanic garden in Hawaii.

THE HIGH FRONTIER

The idea that jungles are an impenetrable tangle of vegetation is largely a myth. Undergrowth is found mainly at the borders, along river banks and clearings and wherever else light can penetrate. Because humans are now responsible for most of the clearings, the irony is that what we think of as archetypal jungle is, in fact, often man-made. Inside dense jungle, it's too dark for much to grow. For the real action, you need to look up, into the canopy, which is exposed to the full impact of the sun and rain.

This 'high frontier' is, by some measures, home to 40 per cent of all plant species. Perhaps half of all life on Earth could live up there, largely unseen and unknown. About a quarter of all our insects are reckoned to live there alone. Just as the rainforests are the hub of the planet's biodiversity, so the hub of the rainforest is the canopy.

Scientists have always had their suspicions about the rainforest canopy. In 1917, US naturalist William Beebe declared that "another continent of life remains to be discovered, not upon the Earth, but one to two hundred feet above it, extending over thousands of square miles".

Now that world is being explored more intensively. During the 1980s, a new generation of daredevil scientists began to explore the canopy using crossbows to get ropes into the high branches. Now they float above the canopy in airships and beneath balloons or climb aloft on giant construction cranes planted in the forest. This is the new biological frontier. A new great age of jungle exploration is just beginning.