What are Tropical Forests?

Tropical forests are located in a loose belt that wraps around the equator between the Tropics of Cancer and Capricorn. These forests found in Latin America, Southeast Asia and Africa, are among the world’s oldest continuous ecosystems, some go back 100 million years. While they encompass only 7% of the earth’s surface area, tropical forests contain at least half of the world’s 5 to 30 million species. The most widespread and biologically rich tropical forests are the rainforests, which receive high average amounts of rainfall. The world’s largest area of rainforest lies in the Amazon region of South America. Ninety percent of the world’s non-human primates are found only in tropical rainforests, along with two thirds of all known plants 40% of the birds of prey and 80% of the world’s insects.

OK, but what’s so UNIQUE about them?

What’s unique about them is the unimaginable diversity… According to a report by the US National Academy of Sciences, a typical 1 sq. km patch of rain forest contains up to 1500 species of flowering plants, 750 species of trees, 125 species of mammals, 400 species of birds, 100 of reptiles, 60 of amphibians and 150 of butterflies. Insects in tropical rainforests are so abundant and so little is known that it is difficult to establish an average density. The same report cites that 2.4 acres might contain 42,000 species. Ten square feet of leaf litter when analysed had 50 species of ants alone! Terry Erwin, a scientist of the Smithsonian Institute, who had conducted detailed surveys of insects on tropical trees, estimates that each species of rainforest tree supports 405 unique insect species - implying that there may be 20 million or more insect species in tropical rainforests alone! The rainforests of the Amazon basin in South America contains 30% of the world’s plants and animals and one-fifth of the world’s fresh water.

With so many different species, there can be obviously only relatively few individuals of each. So most tropical forest species are rare. Most plant species occur only once in one acre. A survey of five acres of forest in the Brazilian Amazon found 1,986 plants of over five feet height, representing 502 species. This means that there was an average of only four individuals of any one species. A sixty-acre patch of rainforest in the Malay Peninsula had 381 species of trees, of which 157 occurred only once.

And that is not all… A high proportion of plants and animals are endemic to only one area - that is, they live nowhere else. This is especially true of South-east Asia and Oceania with its over 20,000 islands. Papua New Guinea has 320 endemic species of birds, almost half its total. There are 180 species of mammals in Philippines and over half are endemic to that country. Sixteen percent of all the species of mammals occur in Indonesia and almost a quarter of them are endemic. Forty percent of all birds of prey (eagles, kites, etc.) depend on tropical rainforests.

Many rainforest species have a very limited distribution; some birds, for example, live only on one island or one mountain range. This rarity itself makes rainforest species particularly vulnerable to extinction. The combination of rare species and threatened habitats means that some species have disappeared before they were ever known to modern science. There are probably 10 to 15 thousand species of flowering plants in South America alone that are still unknown to science. South American rivers have perhaps two thousand species of fish yet unnamed. In all likelihood many of these will become extinct before they are even discovered by science!

OK, but why are you telling me all this?

A few thousand years ago, rainforests covered five billion acres that’s 14% the earth’s land surface. Man has already destroyed more than half of that. Most of the damage has been done in the last 200 years, especially after the Second World War.

Tropical rainforests are being destroyed faster than any other natural ecosystem. A United Nations study from 1976 offers the most optimistic assessment of forest loss. It found that, of the 2.4 billion acres of rainforest left in the world then, 14 million were permanently and completely destroyed every year - that amounts to 30 acres a minute. National Geographic Society, in their film “Rainforest” estimate the rate to be 50 acres a minute, and a far less optimistic figure estimated by the World Rainforest Movement rates the destruction as 100 acres a minute!. The most comprehensive study, published in 1981 suggested that almost one fifth of the world’s remaining tropical forests would by destroyed by the turn of the century, which has turned out to be true.

And today, when the global warming and climate change has been acknowledged and accepted by the scientific community the world over, it is important to recognise that these large swathes of tropical rainforests are also “carbon sinks” or absorbers of carbon dioxide. Deforestation is releasing the large volumes of carbon locked in the trees back to the atmosphere… and this in turn is affecting the forest itself! Recent reports suggest that climate change and deforestation could damage 60% of what remains of the Amazon forest by 2030.

OK, forests are disappearing. Is that all? I have the answer. I’ll plant LOTS of trees and recreate a forest.

The solution is not so simple. Consider this case...
One disadvantage of highly specialised species is that, because they depend on a particular set of conditions, they are most likely to become extinct if their environment is disturbed. The United States imports about $16 million worth of brazilnuts every year, gathered by natives (Indians, as the parlance goes) and peasant collectors from trees scattered throughout the rainforests of the Amazon. Some time ago an entrepreneur decided that it would be more efficient to grow the nuts on plantation. The trees were planted, they grew well and in due course they flowered. But they produced no nuts. No one knows how brazilnuts are pollinated but they are visited by a species of bees there called euglossine bees, whose mating rituals depend on certain chemicals available only from a few species of epiphytic orchids. The plantation had none of these orchids or the other plants that the bees depend on for food. No bees no brazilnuts. Brazilnut trees must grow in a mixed forest, one big enough to encompass all the other species involved in the life cycle of the trees. Besides the euglossine bees and the plants and insects the bees may need (such as the orchid mentioned above), the seed of brazilnut needs a rabbit sized rodent called the agouti, which are the only creatures that crack open the hard fruit case that contains the valuable brazilnut. As yet no one knows what plants and animals the agoutis depend upon…

Aren’t rainforests incredible? And is it not time enough that we should be concerned about their survival?