Tropical rain forests are complex habitats that occupy four million square miles of the wettest land in the world. Tropical rain forests flourish in South America, Africa, Asia, Australia, Central America, and even in the United States (Hawaii). Although rain forests account for only 7% of Earth’s land surface, more than half of all living things reside there. As one of the most diversely populated places on Earth, one would assume that we are doing everything we can to protect and preserve this unique ecosystem. On the contrary, an estimated 71 million acres are being destroyed each year. That breaks down to one acre every second! At this rate, there will be very little left by the year 2035. The destruction is so enormous that planes at an airport in La Paz ( 5,000 feet up in the Andes) have been grounded due to dense smoke. Already half of Earth’s tropical forests have been burned, bulldozed, and obliterated. Tropical deforestation eliminates 17,000 species of plants and animals each year. Sadly, most of these species have yet to be identified and studied. Since all species of life are connected by a complex network, what happens to the rain forest does ultimately affect everyone else on Earth. Scientists divide the area between the Tropic of Cancer and the Tropic of Capricorn into three broad categories: 1) tropical dry forest 2) tropical moist forest 3) true tropical rain forest
In this unit, I will be referring mainly to true tropical rainforests unless otherwise noted. True tropical rainforests receive 160-400” of rain annually with temperatures averaging 80°F. In comparison, New York City receives an average of 43” of rain each year. Tropical rain forests contain valuable hardwoods, various food products, and vital medications, not to mention the millions of plant and animal species. More species of plant grow in the Panamanian rain forests than in all of Europe. 1,500 bird species ( 16% of all bird species ) live in the Indonesian rain forests alone. A single acre of tropical rain forest supports 60-80 tree species compared to the United State’s richest temperate forests at 25 species per acre.
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Seventy percent of the 3,000 cancer-fighting plants exist in the rain forest. For these reasons and many, many others, we must take steps to save the rain forests. Tropical rainforest vegetation grows in distinct and unique layers. The top layer, the emergent layer, towers above all the other trees and plants at 110-160 feet. Emergents endure high temperatures, low humidity, and strong winds. Many of these trees have thick buttresses which help support shallow-rooted trees. Buttresses are woody flanges that radiate from the bases of some tall tropical forest trees. (Taken from Ranger Rick’s Nature Scope)
(figure available in print form)
The next layer is the canopy. This is the most luxuriant layer at a height of 65-100 feet. Acting like a giant sun and rain umbrella, it allows only 2-5% of sunlight to reach the forest floor. Orchids, bromeliads, vines, and many of the plants and creatures in the rainforest call the canopy their home. The understory consists of small saplings, bushes, and shrubs that grow between 15-50 feet. Many of the understory’s trees have large leaves which help plants absorb as much sunlight as possible. Life at the bottom is called the forest floor. Here plant growth is limited because of the different growing conditions as compared to the top layers. On the forest floor, the air is very still, humidity is almost always 70%, and the temperature remains quite constant. Contrary to popular belief, the forest floor is actually spacious. The rainforests are often referred to as jungles. Etymologists have traced the word “jungle” to the ancient Sanskrit word “jangala” meaning “thick, impenetrable vegetation. “ People probably first used the word when traveling by boat to explore these areas. From the river banks, the rainforests do appear to have thick vegetation.
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However, once inside the forests, explorers realized that the forest floor was actually open and uncluttered. As with all habitats, the animals in the rainforests are faced with constant challenges. Many rainforest animals carve their own niche by living in one particular layer. Still others roam from layer to layer in search of food and shelter. Mammals are the largest animals in size that live in the rainforest. Elephants, deers, tapirs, wild pigs, ocelots, jaguars, leopards, lemurs, anteaters, orangutans, okapis, sloths, monkeys, gibbons, tarsiers, gorillas, bats, and chimpanzees are among mammals found throughout the world’s rainforests. The most eye-catching and colorful animals, however, belong to the bird family. Toucans, macaws, hornbills, Birds of Paradise, hummingbirds, and harpy eagles are just a few of the 2,600 bird species found in rainforests. When speaking of the largest group in number, though, the insects win hands down. Estimates are that 80 million different species reside in the rainforest. Rainforests contain an astonishing array of climbing plants, vines, mosses, and ferns. Of the 12,000 species of fern identified worldwide, 11,000 are tropical. Some vines can grow as thick as your body and some leaves can reach six feet in length ! Most tropical plants actually grow on other plants and never touch the ground. These “air plants” are called epiphytes. They derive all their water and nutrients either from the air or from materials caught in the trees far above the floor. Approximately 28,000 species of epiphytes have been identified around the world. Orchids, bromeliads, ferns, and mosses are the best known epiphytes. Unlike epiphytes, climbing vines are rooted in the ground. Some sprout on the forest floor and grow upwards while others germinate in the canopy and grow down to the forest floor. Rainforest plants have self-protective adaptations to get rid of pests. Some plants produce distasteful and poisonous chemicals in their leaves. Others have sharp spines and prickles to keep animals away. Some of the most amazing adaptations, however, involve the intricate relationships between plants and animals. The best illustration of this partnership is pollination. The majority of plants depend on animals for pollination. Insects, bats, and birds are the most common pollinators. Of these, bats are the most important; contributing up to 95% of the seed dispersal that leads to forest regeneration.
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Plants and animals are not the only inhabitants of the rainforest. Approximately 140 million people live in the rainforest. However, these indigenous tribes are disappearing forever. Their physical and cultural heritage, having existed for thousands of years, is in jeopardy. Within the last century, 87 separate Brazilian tribes have been exterminated. A particularly sad story is that of the Penan tribespeople in Malaysia. A decade ago, the government gave logging companies the right to clear the rainforests. Logging has already caused river pollution, widespread siltation, and destroyed the Penans’ food supply. With their traditions on the verge of obliteration, the Penan must now live in government built shacks suffering from malnutrition and disease. The Penan have fought back by blockading the logging roads but the government has retaliated by arresting these people. Current estimates say that the Malaysian rainforest will be completely destroyed in just seven years. As French scientist Charles Marie de la Condamine discovered in the mid-1700s when he saw native Amazonian people extracting rubber from a tree, there is a wealth of knowledge in these tribespeople. Scientists are urgently working to learn as much as they can from the indigenous tribes’ shamans before they all die out. In fact, the field of ethnobotany has gained popularity in recent years. Ethnobotany is the study of how indigenous people use local plants. Many of the rainforests’ products were introduced to scientists by indigenous people. These products have affected us in many positive ways; some have saved lives. The rainforest truly is a medicine cabinet for the world. The estimated value of these natural medicines was $51 billion just four years ago. Rosy periwinkle, for example, combats leukemia in children, Hodgkin’s disease, breast cancer, and cervical cancer. Quinine, derived from the cinchona tree, is effective against Malaria, a disease which kills millions. Many of the crops, which in the United States are considered domestic, actually originated in the rainforests. Only 2% of the United States’ crop production is from native species. Rice, coffee, tea, chocolate, lemons, oranges, bananas, pineapples, coconuts, mangoes, chicle ( chewing gum ), vanilla, and various nuts all found their way to us via the tropics. Many of these crops have developed natural defenses from insects and other damage. A majority of the citrus fruits are now cultivated and harvested in other parts of the world. Tropical plants can enhance the quality of domestic crops through hybridization.
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Industrial benefits from the rainforest include rubber trees and copaiba trees. Since up to 40% of all bus and car tires are made of natural rubber, rubber exports are worth more than $3 billion annually to rainforest countries. Another advantage of rubber is that it is a renewable resource; it can be tapped without destroying a tree. Copaiba trees produce a sap used to fuel diesel engines. Rainforests help our weather by absorbing solar energy, affecting wind and rainfall patterns worldwide, preventing global warming ( also referred to as the “greenhouse effect” ), reducing erosion, and providing natural buffers against coastal flooding. Rainforests receive almost half of all the rain that falls on land. The forests absorb this rain and eventually release it into rivers and streams. Once the trees are cut, however, rivers swell with muddy sediment after rains and shrink during dry spells. Therefore, there are either floods or drought. Soil erosion also increases. It can take 1,000 years for topsoil to develop, yet only ten years to disintegrate. Rainforests provide a natural defense against hurricanes, typhoons, and cyclones. Tropical forests absorb most of these storms’ ferocious winds saving lives and lowering damage amounts. Each year tropical storms kill approximately 20,000 people and cause more than $8 billion in damage. If there were no rainforests, both figures would skyrocket. Deforestation of the rainforests is the result of social, political, and economic problems. Most of this tropical land is found in poor Third World countries who view the forest as a valuable resource to be sold for profit. By selling timber, for example, some countries can build much needed hospitals and schools. This, however, does not take into account long-term ecological impacts. Deforestation rates have nearly doubled in the last ten years. Cattle ranching has destroyed more rainforest in Central America than any other activity. There is a huge market for cheap beef in the United States and other Western countries. Much of this beef comes from cattle raised in South American and Central American rainforests. In 1988, the United States imported almost 50,000 tons of beef worth more than $1 billion. Land cleared from rainforests only supports cattle for 3-7 years before the land deteriorates and ranchers move onto other areas. Ironically, a typical four ounce hamburger represents the destruction of 1,000 pounds of living matter. This includes one tree, fifty saplings, and thousands of insects and animals. Cattle ranching in the rainforests would lose much of its appeal if it weren’t for the subsidized loans of governments and world banks. Tropical Rainforest VI
Inter-American Bank and World Bank have promoted rainforest ranching by loaning almost $4 billion to ranchers in the 1970s. To meet the demand for mahogany, teak meranti, and ebony, at least eleven million acres are logged each year. Since these hardwoods take hundreds of years to mature, they cannot be readily replaced. Although only the oldest and largest trees are supposed to be felled, more than half of the forest may be damaged by the time all of the work is finished. Tropical hardwoods are especially valuable because of their beauty, durability, and resistance to insect damage. Industrial countries buy over eighteen times more hardwood today than they did fifty years ago. A lack of local political control has allowed overcutting in many forests. Studies show that logging can result in the loss of valuable economic revenues in the areas of tourism, food products, and fisheries. Increased sedimentation of many rivers threatens fish populations downstream. Alternatives to typical clear-cutting practices, such as selective logging and small-patch clear-cutting can lead to sustainable timber harvesting. Unfortunately, neither practice is widely used. According to the International Tropical Timber Organization (ITTO), such efforts have had “negligible” success. Continuing at the current pace, high profits from commercial logging will be short-lived. Presently, the tropical timber trade produces $6 billion per year. However, by the year 2000, that figure will drop to only $2 billion because of shrinking supplies and poor logging management. In many countries, slash-and-burn agriculture is a leading cause of tropical deforestation. Slash-and-burn agriculture is a farming method in which patches of tropical rainforest are cut and then burned to clear the land for crops. For the first few years, crops do quite well due to the nutrients in the soil and ashes. But eventually, the soil wears out and the plot is usually abandoned. On a small scale, slash-and-burn agriculture is sustainable but only if the land is given time to regenerate itself. Unfortunately, this is often not the case and the land does not recover. It is imperative that the rainforests be saved because the trees and plants help to keep the air around us clean. They use water, sunlight, and air to make food. Plants and trees make use of carbon dioxide and produce oxygen, which helps everyone breathe. When the rainforests are burnt down or destroyed, the trees stop using carbon dioxide and instead, produce more CO2 which pollutes our atmosphere.