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Rainforests: A Paradise on Earth
Dr. Thomas Lovejoy
Rainforests brim with life. Collectively they harbor the single greatest repository of biological diversity: plants, animals and microorganisms. It is an awesome congregation of nature.
At first it can be bewilderingly green, filled with myriad sounds and with not much to see because every animal hides from everything else. With the right assistance and experience, however, its riches can be discerned.
Rainforest Basics
Rainforests are clustered around the equator (Central and South America, Africa, South Asia and Australia) and occur on the 7% of the dry land surface of the planet where it is both warm enough and wet enough. There are temperate rainforests such as in the Olympic peninsula, but without tropical temperatures they have much lower biological diversity. Rainforests require a minimum of 100 inches of rain a year. They normally have dry seasons but require moisture even in the drier months. In contrast, a New England forest receives about 40 inches of rain a year and the Arizona desert 7 inches.
Rain forest trees are about 100 feet tall, but there are taller trees known as "emergents" that can easily reach an additional 30 feet above the canopy. The forest is also very stratified with different animals and plants living at different levels. Virtually the only species the canopy and the rainforest floor share in common are the trees themselves. The birds of the rainforest canopy are a completely different set of species from those at lower levels. The canopy is in brilliant sunlight during the day, but it is dark (almost gloomy) at the rain forest floor, where only one to two percent of light reaches.
How Rainforests Work
The very conditions of warmth and moisture that are so favorable to the profusion of life in these forests are also responsible for rapid rates of decomposition. In contrast to cold or dry climates where decomposition is dramatically slow in comparison because of lack of warmth or moisture, in rainforests decomposition sets in almost the moment a leaf falls to the forest floor.
In a stark contrast to temperate forests, there is little accumulation of leaf litter as a consequence of this rapid decomposition. In fact right below the thin leaf litter is a vast network of tiny roots actively taking up the nutrients as decay releases them. That is why rainforests generally have the vast majority of critical nutrients in the living biomass (the living mass of plants and animals) itself. A tall grass prairie in contrast has enormous amounts of nutrients stored several feet deep in the soil. So rainforests present a paradox: the greatest expression of life on earth often occurs on very poor soils. The main exceptions are soils of volcanic origin and those that get annual deposits of silt on floodplains.
Indigenous forest dwellers for millennia have known how to practice agriculture despite the poor soils. It involves making a small clearing in the forest. When the felled trees are dry enough they are burned to release the nutrients that had been in the living mass, so the ashes act as fertilizer. (In some places indigenous peoples systematically enriched forest soils by composting). This can support agriculture for three years or so and then the forest agriculturalists move on and repeat the process elsewhere, while the previous area recovers drawing on the nutrients that were washed away by heavy rains but only as far as the neighboring forest. This works well as long as populations are small. Modern industrialized agriculture in contrast clears large areas that are slow to recover.
The Biological Richness of Rainforests
Rainforest are amazingly rich in species. Whereas a New England forest may have 20 or 30 species of trees at most and a coniferous forest may have only one or two tree species, a 25 hectare plot near Camp 41 in the Amazon has 295 species of trees. A single tree in Peru has more ant species than all of the United Kingdom. And the Amazon River system has 3000 species of fish -- more than the entire North Atlantic.
Life builds on life in these forests. Lianas loop around more than one tree at a time. Epiphytes like bromeliads and philodendrons cling to the tree trunks. Within each bromeliad there is a tiny microcosm of species living in the water trapped by the whorl of leaves: microbes, invertebrates, insect larvae and some frog species use them as a place to lay their eggs.
The richness in species in rain forests is part of a general pattern of ever more species from the poles to the equator. At the tip of South America in Tierra del Fuego there are only two species of ants. At the very edge of the tropics in Sao Paulo Brazil there are 222 species of ants, with the equator still a very long distance away. This pattern is not universal for all groups of organisms. For example, there are very few species of bumblebees in the Amazon and almost no bears in any rainforest.
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Tom Lovejoy is a biologist who went to the Amazon of Brazil in 1965, became fascinated by the living treasure chest,
and has worked to understand and save rainforests ever since.
He played a major role in bringing the issue of tropical deforestation to the
public consciousness, made the first estimation of global extinction rates in 1980, and coined the term "biological diversity".
He founded the public television series NATURE in 1982. He also pioneered
the study of the impacts of climate
change on the natural world. His advice is widely sought on policy matters relating to science, environment and sustainable development.
He built the program of World Wildlife Fund from 1973 to 1987, served subsequently as a high official at the Smithsonian Institution and at the World Bank.
Since 2002 he has been President of the Heinz Center for Science, Economics and Environment, an environmental policy center in Washington, D.C.
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The Rainforest Crisis
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More than half of the original tropical forest is gone, and in some places like the Atlantic forest of Brazil or Madagascar only a few percent remains. Much of the lowland forest in Indonesia and Malaysia is gone as well.
Each of these areas represents a "biodiversity hotspot" where there is a concentration of species that occur nowhere else and are under severe threat. In many instances there has been little gain in human welfare as a result of the deforestation; in fact it further impoverishes already poor people.
The extinction of a large number of plant and animal species looms if the trends are not stopped and reforestation instituted. As a consequence of the Convention on Biological Diversity, many rainforest countries now have active programs in rainforest protection; rainforest protected areas and indigenous areas that protect native peoples and their forests have made significant progress.
There are major conservation programs in the Amazon (ARPA: the Amazon Region Protected Area project) and in the Congo Basin, the former with World Bank assistance and the latter with US AID. Much more needs to be done.
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