Exploration of the rain forest canopy
Tropical rain forest canopy has been of interest to some of the greatest biologists for nearly two centuries.
Alexander von Humboldt (1815) was perhaps the first scientist to write specifically about tropical forest canopy. He described the treetops of the Amazon as a "forest above a forest". Tropical rain forest canopy is full of epiphytes (or air plants) and lianas; consequently to the viewer on the ground it appears almost as if there are separate layers or strata of plantlife - one living above the other.
A decade before Alfred Russel Wallace proposed the theory of evolution by natural selection he made an essential expedition to the Amazon and was immediately impressed by the bio-diversity of arboreal fauna and flora high in the treetops. Recalling the observations made on July 4th 1842, Wallace wrote*:
"A few forest trees were also in blossom; and it was a truly magnificent sight to behold a great tree covered with one mass of flowers, and to hear the distant hum of millions of insects gathering together to enjoy the honeyed feast. But all is out of reach of the curious and admiring naturalist. It is only over the outside of the great dome of verdure exposed to the vertical rays of the sun that flowers are produced, and on many of these trees there is not a single blossom to be found at a less height than a hundred feet. The whole glory of these forests could only be seen by sailing gently in a balloon over the undulating flowery surface above: such a treat is perhaps reserved for the traveller of a future age."
The age that Wallace imagined has now arrived!
* This exact quote was used in Jacob Bronowski's television series "The Ascent of Man", in the programme "The Ladder of Creation" first broadcast by the BBC, July 30th, 1973. See http://www.drbronowski.com/
Professor William Beebe who is famous for his deep ocean dives in a Bathyshere with Otis Barton, spent many years studying the flora and fauna of Guyana. In 1917 he wrote: "Yet another continent of life remains to be discovered, not upon the Earth, but one or two hundred feet above it, extending over thousands of square miles..."
Today we know that the canopy of tropical rain forests represents one of the richest biomes on Earth. It has been described as the "high frontier", a zone that is difficult to access, but where millions of species coexist, including epiphytes (air plants), lianas, bromeliads, monkeys, birds, frogs, ants, beetles and even earthworms.
Professor E. O. Wilson has written:
"We may think that the world has been explored. Almost all the mountains and rivers, it is true, have been named, the coast and geodetic surveys completed, the ocean floor mapped to the deepest trenches, the atmosphere transected and chemically analyzed. The planet is now continuously monitored from space by satellites; and, not least, Antarctica, the last virgin continent, has become a research station and expensive tourist shop. The biosphere, however, remains obscure. Even though some 1.4 million species of organisms have been discovered (in the minimal sense of having specimens collected and formal scientific name attached), the total number alive on earth is somewhere between 10 and 100 million. No one can say with confidence which of these figures are closer." E. O. Wilson, The Diversity of Life, 1994.
"More than half the plant and animal species of the world are believed to occur in tropical rain forests. From these natural greenhouses...many of the world's records of biodiversity have been reported: 425 kinds of tree in a single hectare of Brazil's Atlantic Forest, for example, and 1,300 butterfly species from a corner of Peru's Manu National Park. The record for ants is 365 species from 10 hectares in a forest tract of the upper Peruvian Amazon. I have identified 43 species from the canopy of a single tree in the same region, approximately equal to the ant fauna of all the British Isles." E. O. Wilson, The Future of Life, 2002.
Ghillean Prance (former Director of Kew Gardens) was once asked about the value of (tropical forest) biodiversity. His reply was:
"...No ecosystem is stable; it is constantly changing, and the turnover resulting from disturbance is one of the factors that produces diversity in the forest. I have looked at this from the point of view of the interdependency of organisms, pollination, dispersal, mychorrhizal relationships, and so on. So many things are concerned with the maintenance of just one species that it is easy to see that species removal is bound to have wide consequences. Take the Brazil nut, for example; this is a tree that I have studied in great detail. It is pollinated by a bee that in turn needs epiphytic orchids, which attract the female bee and permit mating to take place. So the tree needs the orchids to support the bees. Then an agouti on the forest floor is responsible for dispersing the seeds, and so on. There is a great complexity of interrelationships, and the loss of species can have surprising consequences.
It is also very important to bear in mind the importance of the structured, multi-species forest canopy on a global scale, modifying the chemistry of the atmosphere and world climate patterns. So the biodiversity of this system has an importance that extends beyond the operation of the ecosystem itself, affecting whole global systems. In this way it also extends beyond the more obvious values to humanity as a source of crops and pharmaceuticals. These global values, however, are much more difficult to quantify in economic terms than is the case with forest exploitation for drugs and food".