Tim Radford, science editor
Monday March 21, 2005

The forest treetops are where the sun, rain and living things first meet. An estimated 40% of all terrestrial species are to be found more than 70 feet up, where the first wispy leaves and twigs compete for solar energy.

Almost 90% of the earth's biomass - the sheer weight of life - is in the forests. But the canopy is an almost entirely unexplored zone. "Some people say we know the surface of the moon better than we know the tops of the trees," said Andrew Mitchell, of the Global Canopy Programme, centred at Oxford.

"We find that about 80% of the insects we recover from the canopy are undescribed, new to science. There is an astonishing variety of life up there. So from the life-on-Earth point of view, it's really important to find out. It is totally undiscovered territory."

Ten cranes are already in use, mostly in temperate forests. But the greatest richness of life is concentrated in the tropical forests. The programme has just received backing from the United Nations environment chiefs and five governments.

Forests are powerful players in the carbon cycle, and have a huge role in the global warming theatre. If all goes to plan, the first five cranes will tower over the rainforests, swinging a research platform and instruments over the treetops, observing the foliage, flowers, birds, insects, epiphytes, parasites, reptiles and mammals in life's upper storeys, ideally without snapping a branch or disturbing a nest.

Researchers will measure volatile compounds from the foliage, monitor the interaction between plants and atmosphere, and watch for omens of change triggered by global warming.

Canopies are delicate environments. They are - at least from underneath - also dark places. Dr Mitchell first began high-altitude biology looking for gibbons in Borneo in 1978.

"I couldn't see them, because they were so high up in the trees and this was very frustrating, and I thought, well, if we could get up there and study the forest canopy maybe we could learn more about their lives."

He began by building a series of aerial walkways. He and other scientists have experimented with hot-air balloons, and even a dirigible.

More than 20 years of canopy science has convinced biologists that they need literally to get on top of the subject. "It is in the canopies that trees pass their genes around. This is where they produce flowers and fruits. It is where the sun's energy is beating down. It is where the forest meets the sky and as a result it is the most energy rich part of the forest," he says.

"The great thing about a canopy crane is that, with a helicopter, you can slide the crane down in between the trees without causing any damage. It stands on a concrete plinth that you do have to build but it doesn't have to be very big. It is simple technology, used every day in our towns. No other system allows you to get to that much forest, day after day, year after year."

The crane and gondola can deliver researchers to any point in almost a hectare of forest, from the highest fronds almost to the ground. Research at canopy level will be matched by remote sensing from space, and instrument readings at the forest floor. "The great thing is we have the backing of the United Nations environment programme and the backing of five important national governments," said Dr Mitchell.

Guardian Unlimited © Guardian Newspapers Limited 2005