03 June 2004

Twice as many animals are living in rainforest treetops as had previously been estimated, making that unique aerial habitat one of the world's richest hotspots for wildlife, according to a study by two British scientists.

Martin Ellwood and William Foster, ecologists from Cambridge University, have been to one of the most inaccessible places on earth to found out what lives there. In a study published today in the journal Nature, they have calculated that the total weight of insects, spiders and other bugs living up to 200ft above the ground is twice what they had expected.

It is estimated that about 90 per cent of all animals and plants that live at the boundary between the land and the air live in the forest canopy, yet next to nothing is known about that endangered habitat, the researchers said.

Dr Ellwood and Dr Foster focused their efforts on an epiphyte - a plant that grows on trees - called the bird's nest fern, which is a popular pot plant in British homes. In the wild, some of the ferns can weigh up to 200kg (440lb) and each plant can be home to tens of thousands of small animals, ranging from giant ants and centipedes to bats. Dr Ellwood said: "The ferns represent islands in a sea of canopy. Each island has a discreet community of animals."

The ecologists found that a single large fern growing in a rainforest tree in Borneo could harbour more small animals than the rest of the crown of the tree on which the fern was growing. Using that information, they calculated that if they included the weight or "biomass" of wildlife living in the ferns, it would double the estimate of the total biomass of wildlife living within the forest canopy.

Dr Ellwood said the ferns provided a perfect aerial habitat for the smallest forest animals. "If you go into a rainforest you don't see much. The trees are not dripping with orang-utans and macaws, but what it is teeming with is ants and termites," he said.

When scientists first started investigating canopies in the 1980s they estimated there could be anything up to 30 million species of arthropods - hard-bodied animals such as insects - living there. However, those estimates were based on a method called "fogging", in which individual trees were doused with insecticide so that scientists could count and weigh the animals which fell to the ground.

"Reanalysis of the calculations has produced a range of possible estimates ranging from 10 to 80 million [species]," Dr Ellwood said. Yet scientists have formally described and named only about 1.4 million species so the vast majority of animals living in the forest canopy will be new to science.

http://news.independent.co.uk/world/environment/story.jsp?story=527677