A tree is a woody plant with a single, strong trunk and many branches that lives year after year. A large group of trees covering at least 25 percent of the area where the tops of the trees, called crowns, interlock to form an enclosure, or canopy, at maturity make up what is called a forest. The term rain forest is used to refer to any forest in tropical or semitropical regions. (Tropical regions are those around the equator.) Rain forests occur in a few regions with temperate (moderate) climates.
Tropical rain forests, also called jungles, are located for the most part in the belt between the tropics of Cancer and Capricorn. The term jungle usually indicates a disturbed, tangled, tropical rain forest with vines and other distinct plant and animal life. Plenty of rain and warm temperatures year-round support constant plant growth and great diversity of species. It is estimated that there are up to 260 different kinds of trees per square mile of rain forest. Trees that would normally lose their leaves during the autumn season in cooler climates retain them for several years (some trees for up to sixteen years), becoming evergreens because there are no cold and warm seasons. Rain forests cover only about 7 percent of Earth’s surface, or 4.4 million square miles (11.5 million square kilometers) of land.
Tropical evergreen rain forests occur in four main regions:
- The Americas and the Caribbean
- Africa and Eastern Madagascar
- India and Malaysia
The first forests evolved during Earth’s prehistoric past. Since then, all forests have developed in essentially the same way, by means of a process called succession.
|WORDS TO KNOW|
|Angiosperms: Trees that bear flowers and produce seeds inside a fruit; deciduous and rain forest trees are usually angiosperms.||Forbs: A category of flowering, broadleaved plants other than grasses that lack woody stems.|
|Clear-cutting: The cutting down of every tree in a selected area.||Gymnosperms: Trees that produce seeds that are often collected together into cones; most conifers are gymnosperms.|
|Elfin forest: The upper cloud forest at about 10,000 feet (3,000 meters) which has trees that tend to be smaller, and twisted.||Rhizomes: Plant stems that spread out underground and grow into a new plant that breaks above the surface of the soil or water.|
|Emergents: The trees that stand taller than surrounding trees.||Tannins: Chemical substances found in the bark, roots, seeds, and leaves of many plants and used to soften leather.|
|Epiphytes: Plants that grow on other plants with their roots exposed to the air. Sometimes called “air” plants.||Understory: A layer of shorter, shade-tolerant trees that grow under the forest canopy.|
The first forests
The first forests were very different from those found today. They were mostly composed of huge ferns and clubmosses; there were no flowers to speak of. Flowering plants developed only 65 to 145 million years ago during the Cretaceous period. Among the first to evolve were the ancestors of modern water lilies. Present day rain forests began developing shortly after the flowering plants.
Trees compete with one another for sunlight, water, and nutrients, thus a forest is constantly changing. The process by which one type of plant or tree is gradually replaced by others is called succession. Succession can occur naturally when different species of trees become dominant as time progresses and the environment changes. It can also occur from natural disasters, such as forest fires.
Primary succession of some forests in North America usually begins on bare soil or sand where no plants grew before. When the right amount of sunlight, moisture, and air temperatures is present, seeds begin to germinate (grow). These first plants are usually made up of the grasses and forbs (a nonwoody broad-leaved plant) type. They continue to grow and eventually form meadows. Over time, and as conditions change,
other plants begin to grow such as shrubs and trees, which become dominant and replace or take over where the grasses and forbs originally grew.
As primary succession continues, “pioneer” trees that are tall and sun-loving quickly take over the meadow. They change the environment by making shade. Trees with broader leaves that prefer some protection from the sun can then take root. If conditions are right, a mixed forest of sun-loving and shade-loving trees may continue for many years. Eventually, more changes occur.
The climax forest
Seedlings from pioneer trees do not grow well in shade; therefore, new pioneer trees do not grow. As the mature trees begin to die from old age, disease, and other causes, the broad-leaved trees become dominant. The shade from these broad-leaved trees can be too dense even for their own seedlings. As a result, seedlings from trees
that prefer heavy shade begin to thrive and eventually dominate the forest. These trees produce such deep shade that only trees or plants that can survive in complete shade will succeed there. When this happens, the result is a climax forest.
Few true climax forests actually exist because other changes take place that interfere with a forest’s stability. Fires, floods, high winds, and people can all destroy a single tree to acres of trees. Glaciers can mow them down; volcanoes can smother them with ash or molten rock or knock them over with explosive force. Then the process of succession starts over.
When the land has been stripped of trees, in some areas it will eventually be covered with them again if left alone. This is called secondary succession and can take place more quickly than primary succession. Seeds from other forests in neighboring regions are blown by the wind or carried by animals to the site. The seeds take root, seedlings sprout, and the process begins again.
Tropical evergreen rain forests can be classified into three main types: lowland, montane, and cloud.
Lowland wet forest
Lowland wet forests thrive close to the equator where rainfall is heavy, at elevations from sea level up to 4,000 feet (1,200 meters). They occur widely in the Asian tropics, in South America near the Amazon, and in Africa. Vegetation is wide and varied in these forests, having as many as 2,000 different species of trees. The largest lowland wet forest is currently located in Brazil (commonly known as Selva, the Spanish word for forest). Studies show that the Amazon forest may contain up to 120 different species in one acre of forest.
Montane rain forest
The true montane, or mountain, rain forests begin where lowland wet forests leave off; about 4,000 feet above sea level. There are lower and upper montane forests at lower and higher altitudes respectively. The average temperature is 66°F (19°C), and oak and laurel trees are predominant. At higher altitudes (upper montane) the cooler weather is favored by coniferous trees and myrtles. Montane forests can be found in Africa, Papau New Guinea, and South America.
Cloud forests, such as those in Costa Rica, grow on mountains but usually at altitudes higher than 5,000 feet (1,500 meters). Their name comes from the fact that low-lying clouds form around them, shrouding them in mist. At about 10,000 feet (3,000 meters), the upper cloud forest is known as the elfin forest. The trees, including some species of pines, tend to be stunted and more twisted than those at lower elevations. Mosses, ferns, and lichens are abundant throughout this forest.
The climate of a tropical rain forest is warm and humid all year long. Average annual temperatures are between 68° and 84°F (20° and 29°C), and the temperature never drops below 64°F (18°C). There is almost no seasonal temperature change because the difference between the coldest and warmest months is only 3°F (1°C).
Rainfall varies throughout the tropics, with some areas receiving as little as 60 inches (1.5 meters) annually, and others twice that amount. Dry seasons occur, especially in monsoon climates. Some precipitation (rain) falls almost every day. It may come in a thunderous downpour or in a misty shower. In general, humidity is very high, and days are often cloudy.
The geography of rain forests varies, depending upon location, and includes landforms, elevation, soil, and water resources.
The terrain over which lowland forests grow features valleys, rolling hills, old river basins, and level areas. Montane forests develop in mountainous regions, as do cloud forests. Tropical mountains tend to be volcanic in origin, and their slopes are often gentle rather than steep and craggy (rugged and uneven).
Rain forests grow at almost all elevations, from sea level to about 10,000 feet (3,000 meters). The greatest share of rain forested area exists at
elevations below 4,000 feet (1,200 meters), in what are known as lowland wet forests.
Rain forest soil tends to be red or yellow in color and low in nutrients because the vast number of plants quickly absorb its valuable minerals. Decaying vegetation continually enriches the topsoil, which is the most fertile soil near the surface. For this reason, tree roots are more likely to remain near the surface. In forests where the shade is dense, few smaller plants may grow and the topsoil layer is even richer. Where the ground is rocky and not much soil is present, trees may develop stiltlike projections from their trunks that help anchor them to the ground.
The presence of volcanoes increases the richness of soil in Indonesia and parts of Central and South America. Volcanic ash contains many minerals and adds nutrients to the soil.
In tropical regions, rivers and streams are often the primary water resources. Daily rainfall not only helps maintain them, but can also cause them to flood.
Most forests contain a mixture of many different species of trees, and rain forests contain the most species. Both coniferous (cone-bearing) and nonconiferous evergreen trees exist within their boundaries. Exploration of most rain forests is challenging for humans so many of these species are yet to be named.
The trees and smaller plants in a rain forest grow to different heights, forming layers. The crowns of tall trees create a canopy, or roof, over the rest of the vegetation that averages 120 feet (37 meters) above the ground. The very tallest trees, called emergents, pop through the canopy like lonely towers, some as tall as 200 feet (61 meters). Trees help support one another because they grow so close together. Beneath the canopy grows at least one more layer of shorter, shade-tolerant trees, which cover heights of 30 to 65 feet (10 to 20 meters). This shorter layer is called the understory. The next layer, about 16 feet (3 meters) off the ground, is composed of tree seedlings, a few small shrubs, and a few flowering plants. The very lowest layer consists of small plants, like mosses, that live atop the soil.
Non-tree plants that grow in the rain forest are often either climbers, epiphytes (EPP-ih-fites), or parasites. Climbers have roots in the ground, but use hooklike tendrils to climb up the trunks and along the limbs of trees in order to reach the canopy where there is light. Epiphytes, or “air” plants, store water in their fleshy stems and leaves. They also grow on trees and other plants, especially in the canopy, but their roots are exposed to the air. These plants absorb the nutrients they need from rain and forest debris. Parasites attach themselves to other plants and trees, but they manage to do without light and take their nourishment from their host.
The Rafflesia (rah-FLEA-e-ah) plant of Malaysia is a parasite. Its seeds burrow beneath the bark of another plant and invade it with hairlike strands that absorb nutrients. Eventually a flower bud emerges, but the bud has no stem or leaves. About nine months later, this bud produces a spectacular bloom that measures as much as 3 feet (1 meter) in diameter and 37 pounds (81 kilograms). It is the largest known flower in the world. The Rafflesia is not content to be just a parasite with a big, unattractive flower. It also produces one of the worst fragrances imaginable, the smell of rotting meat. The Rafflesia’s goal is to attract flies with this fragrance in hopes that they will carry its pollen to a Rafflesia in the next forest.
Plant life within the rain forests includes not only trees but also algae (AL-jee), fungi (FUHN-ji), lichens (LY-kens) and green plants.
Algae, fungi, and lichens
Algae, fungi, and lichens do not fit neatly into either the plant or animal category.
Most algae are single-celled organisms, although quite a few are multicellular. Most algae have the ability to make their own food in a process called photosynthesis (foh-toh-SIHN-thuh-sis). During this process they use the energy from sunlight to change water and carbon dioxide into the sugars and starches they use for food. Other algae absorb nutrients from their surroundings.
Although most algae are water plants, green and blue-green algae do appear in the rain forest where they encrust the leaves of trees. This blocks the sunlight from the trees’ leaves, but the green-blue algae may aid the tree in obtaining nutrients, such as nitrogen, from the atmosphere.
Unlike algae, fungi cannot make their own food by photosynthesis. Some fungi, like molds and mushrooms, obtain nutrients from dead or decaying organic matter (material derived from living organisms). They assist in the decomposition (breaking down) of this matter and in releasing the nutrients needed by plants back into the soil.
Other fungi are parasites. Fungi reproduce by means of spores, which are usually single cells that have the ability to grow into a new organism.
Fungi prefer moist, dim environments, and they thrive on the shadowy forest floor. Some, like the marasmius, grow directly on the litter of plant matter, while others protrude from the trunks of trees. Another type of fungi, the mycorrhizae, live in the soil and surround the roots of most rain forest trees. They absorb energy from the tree and help the tree’s roots absorb nutrients from the soil.
Lichens are actually combinations of algae and fungi that live in cooperation. Fungi surround algae cells, and the algae obtain food for themselves and the fungi by means of photosynthesis. It is not known if fungi aid algal organisms, but it is believed that fungi may provide moisture for the algae.
Lichens often appear on rocks and other bare woodland surfaces. Some grow on the leaves of lowland trees, while others favor the cooler cloud forests and dangle from the limbs of trees. Lichens are common in all types of forests and seem able to survive most climatic conditions.
Green plants other than trees
Most green plants need several basic things to grow: sunlight, air, water, warmth, and nutrients. In the rain forest, water and warmth are abundant. However, nutrients such as nitrogen, phosphorus, and potassium, which are typically obtained from the soil, may not be in large supply. Light can be scarce because the thick forest canopy obscures the forest floor, and may block sunlight. The lack of seasons means that the canopy is in full leaf all year long. For this reason, most rain forest plants grow in the canopy of the forest. Those that do grow on the ground often have very large leaves that provide more surface area to be exposed to the scarce amount of light.
Common rain forest green plants
Common rain forest plants include rattans, pitcher plants, ferns, African violets, nasturtiums, Spanish mosses, orchids, lianas, urn plants, hibiscus shrubs, and bamboo.
Liana Lianas are climbers found in rain forests throughout the world. Their roots can be large and tough, but they do not develop a thick trunk. Instead, they depend entirely on trees for support. Once they reach the canopy, they drape themselves among the branches and develop leaves, branches, flowers, and fruits. Often they send out “feeding,” or aerial (AIR-ee-yuhl), roots that dangle in midair and absorb nutrients.
A common liana is the strangler fig, which begins as an epiphyte that sends long roots down to the ground. These roots grow branches that
In the rain forests of Central and South America grows the cocoa, or cacao, tree. The seeds of this delightful tree produce chocolate. Initially, the roasted seeds were used by the Aztecs to make a hot drink flavored with vanilla and spices. In 1502, Italian explorer Christopher Columbus (1451–1506) brought the cocoa “beans” back to Spain, where the same drink was made but with sugar. Over the next 100 years, the use of cocoa spread to other parts of Europe and, by 1657, solid chocolate had been developed in France. Around 1700, the English improved hot chocolate by adding milk, and by 1850, manufacturing processes made sweet eating-chocolate possible. By 1876, its popularity had spread throughout the world.
Cocoa trees are raised on farms in Central and South America and portions of western Africa. In 1977, 1,653,000 tons (1,500,000 metric tons) of cocoa seeds were produced, and 20 percent of all the exports went to the United States. However, Americans consume only about 10 pounds (4.5 kilograms) of chocolate per person annually. The largest consumers are the Swiss, who eat 21 pounds (9.5 kilograms) per person each year.
Although the names are sometimes confused, the cocoa tree is not the source of the drug cocaine. Cocaine comes from the coca shrub, an unrelated plant.
surround the host tree, blocking the light. Eventually, the host dies and decays, leaving a hollow ring of stranglers.
Urn plant Urn plants are epiphytes found in Central and South America that belong to the pineapple family. The plant’s overlapping leaves form an urn, or cup, which collects rainwater and any dead plant matter that falls into it. Little hairs on the leaf surface absorb the water and dissolved minerals. Urn plants provide homes for many aquatic (water) insects and even frogs.
Hibiscus Hibiscus shrubs grow on the ground around the edges of the forest where they can obtain light. In Africa, they quickly attain heights of up to 7 feet (2 meters). Their large, colorful flowers are bell shaped and may be scarlet, pink, yellow, or white.
Bamboo Bamboo is a woody grass that can grow as tall as a tree. Dense forests of bamboo are found in Asia and Central Africa where plants may reach 130 feet (40 meters) in height. Bamboo tends to grow in thick, tightly packed clumps. Flowering occurs several years later, after which the plant dies. There are 480 species of bamboo. Its uses vary from food to instrument to paper.
It is always growing season in the tropical rain forest. At any given time, at least one species will be flowering.
Most green plants are seed plants, and most seed plants are flowering plants that reproduce by means of pollination. Pollination involves the transport of pollen from the stamen, the male part of the flower, to the pistil, the female part of the flower where seeds develop, by visiting animals or the wind. The seed’s hard outer covering protects it while it waits for moisture and light to stimulate its growth.
Instead of pollination, some plants reproduce by means of rhizomes—long, rootlike stems that spread out below ground. These stems develop their own root systems and send up sprouts that develop into new plants.
Rain forest trees
Most trees have a single strong stem, or trunk. This single trunk gives them an advantage over smaller woody plants in that most of their growth is directed upward. Some large rain forest trees develop buttresses, winglike thickenings of the lower trunk that give tall trees extra support.
As a tree grows, its trunk is thickened with a new layer, or ring, of conducting tissues that carry water and nutrients from the roots to the branches. As the tree ages, the tissues from the center outward become hardened to produce a sturdy core. In cooler climates, the rings are formed seasonally and, when a tree is cut down, its age can be determined by how many rings are present. In the rain forest there are no seasons, so rings do not form regularly and cannot be used to accurately estimate a tree’s age. Other methods are used to determine the age of rain forest trees, such as measuring the increase in the tree’s circumference during a year and dividing that number into its total girth (size). Based on these calculations, one species in Malaysia may be 1,000 years old, a baby compared to the 4,900-year-old bristlecone pine of North America, but unusually old for the rain forest, where most trees only live 100 to 300 years.
Rain forest trees seldom exceed 200 feet (61 meters) in height, although the tualang of Malaysia has been recorded at 260 feet (80 meters). It is a common misconception that the world’s tallest trees grow in the rain forests. The tallest trees grow in drier, more temperate climates.
The leaves of rain forest trees are often waxy and develop a “drip tip;” a long, narrow point that allows rain to run off easily.
Common rain forest trees
Common rain forest trees include black ebony, cinchona, mahogany, and mango.
Black ebony Found in the rain forest of Africa, the black ebony tree is almost white in color, but its heartwood is black and extremely hard. Valued for its heaviness, color, and durability, ebony heartwood is considered a precious wood. It has been commonly used to make the black chord keys on a piano.
Cinchona The cinchona (sing-KOH-nah) is native to Central and South America where it is found in lower montane rain forests. Its flowers grow in white, pink, and yellow clusters and its bark is an important source of several medicines, including quinine (KWY-nine), a treatment for malaria. During the 1800s, cinchona seeds were brought to Java in Indonesia, where the trees are still raised commercially.
Mahogany The term mahogany is applied to almost 200 species of trees with reddish-brown wood, winged seeds, and small, greenish-yellow flowers. The first trees given the name are native to the West Indies, but the most commercially important mahoganies come from Central and South America. They are used in fine furniture and paneling. African and Philippine mahogany are also economically important.
Mango The mango tree was originally discovered in East India. In its wild state, it produces a fibrous fruit that tastes like turpentine. In some species, this fruit is poisonous. Cultivated trees produce a delicious fruit that is enjoyed throughout the world. In the fifth century BC the mango was brought to Malaysia and eastern Asia. In India, the mango tree is sacred, believed to be a symbol of love and having the potential to grant wishes. The tree can reach heights of about 90 feet (27 meters) and is popular for its dense shade.
Trees are woody perennial plants, which means they live more than one year, or growing season. When temperatures are warm year-round and rainfall is constant, as they are in the rain forest, trees become evergreen and grow almost continuously. Some rain forest trees shed their leaves periodically for a short time; however, this shedding is not simultaneous, even among trees of the same species.
Many rain forest trees do not bear fruit every year and thus do not regenerate readily. Seeds that lie on the forest floor may remain dormant (inactive) for many years. Those that sprout grow very slowly after the nutrients stored in the seeds are used up. If a tree falls and creates a gap in the canopy allowing sunlight to enter, these seedlings make up for lost time. They grow quickly toward the light and soon the gap is closed again.
In general, trees are divided into two groups according to how they bear their seeds. Gymnosperms produce seeds inside cones. Most conifers, like the pine, are gymnosperms. Angiosperms have flowers and produce their seeds inside fruits. Broad-leaved trees, such as maples, are usually angiosperms. Some species of gymnosperms are found in rain forests, but most rain forest trees are angiosperms.
The seedlings of some rain forest trees do not develop large amounts of chlorophyll, the substance in leaves that gives them their green color, until they reach light in the canopy. The leaves of these young trees are often red, blue, purple, or white instead of green.
Vast areas of rain forest have been destroyed by uncontrolled logging and clearing of the land for farms. From 2000 to 2005, tens of thousands of miles of rain forest in Brazil were lost due to deforestation. In more mountainous regions, such as Papua New Guinea, the land is less useful for farming and huge tracts of rain forest still remain untouched.
Many individual plants are threatened as the forest is destroyed. The African violet, for example, which is commonly cultivated as a house plant, is found in only a few forests in Tanzania, where it is rapidly disappearing.
Animal life in the rain forest is as diverse as its plant life because the warm temperatures and plentiful moisture aid survival. Most animals live in the trees, especially high in the canopy.
Microorganisms, like their name suggests, can not be seen without the aid of a microscope. Bacteria are microorganisms that are always present in forest soil. They help decompose dead plant and animal matter. They grow quickly in the warm, humid rain forest environment where they feed on the leaves, twigs, and other matter that falls from the canopy.
The Web of Life: Biotic Potential
The highest rate of reproduction under ideal conditions is a population’s biotic potential. For most creatures, this potential is enormous. A single bacterium, for example, could set off a chain reaction of births that would cover our planet within thirty-six days.
What keeps bacteria, as well as mosquitoes, frogs, and alligators reaching their full biotic potential? The answer is that, while creatures are determined to reproduce, life is not easy. Each life form is opposed by limiting factors that keep population growth in check. Cold temperatures, for example, kill mosquitoes. A shortage of mosquitoes starves frogs. A shortage of frogs keeps alligators hungry, preventing them from reproducing more quickly and taking over the world.
Animals without backbones are called invertebrates. They include simple animals such as insects and worms, and more complex animals such as the click beetle or the trapdoor spider. Certain groups of invertebrates, like mosquitoes, must spend part of their lives in water. In general, these types are not found in the trees, but in streams or in pools of rainwater. The humid rain forest is an ideal environment for many soft-bodied invertebrates, such as leeches, because there is little danger of drying out.
Common rain forest invertebrates
In addition to bacteria, invertebrates remain the least known variety of life in the rain forest. Among those that have been identified are the Hercules beetle, the forest termite, the orchid bee, the Queen Alexandra’s birdwing butterfly, the postman butterfly, the blue hunting wasp and the army ant.
Postman butterfly The postman butterfly lives in jungles of Central America. In its larval state as a spiny caterpillar, it is a voracious eater with a preference for the passionflower vine. The adult butterfly feeds on this vine’s protein-rich pollen and nectar. The added protein gives it a longer lifespan than most butterflies, usually from six to nine months. The passionflower is a highly poisonous plant, so female butterflies lay their eggs on its youngest leaves, which contain less poison. As the larvae grow, they gradually absorb some of the poison and become immune to it.
The Web of Life: How Ants Help to Make Rain
Seventy-five percent of the rain that falls on the rain forests is recycled. It evaporates and creates clouds that protect the forest from too much sun. Many creatures help in this process. For example, the forests of the Amazon are home to vast armies of ants. Ants produce formic acid, which they use for defense and as a means of communication. They spray approximately 200,000 tons (181,400 metric tons) of formic acid into the air each year. This formic acid makes the rain that falls in the area slightly acidic and promotes the decay of dead wood. As the wood decays, bacteria are released into the atmosphere, where ice crystals tend to form around them. The ice crystals fall as rain, and the cycle continues.
Blue hunting wasp The blue hunting wasp prefers dining on crickets, which it hunts by flying low over the forest floor. It grips a victim in its powerful jaws and then paralyzes it with its stinger. Female wasps drag the paralyzed victim into a burrow and then lay their eggs on it so their larvae have food when they hatch.
Army ant Army ants are some of the most feared residents of the rain forest because they travel in huge colonies of up to 20 million individuals. The army’s number demands that food be plentiful. The army usually empties an area of insects, small lizards, and snakes, leaving them no choice but to continue moving. They take shelter at night by linking themselves together with their strong legs beneath the fallen leaves and trees. When they are on the march, worker ants carry any developing larvae with them.
Many invertebrates eat plants or decaying animal matter. The larvae of insects, such as caterpillars, are the primary leaf eaters. Weevils drill holes and lay their eggs in nuts, which their larvae use for food. Bees gather pollen and
nectar from flowers, as do butterflies and moths. The arachnids (spiders), which are carnivores (meat eaters), prey on insects and sometimes, if the spiders are big enough, small lizards, mice, and birds.
Most invertebrates have a four-part life cycle. The first stage of this cycle is spent as an egg. The eggshell is usually tough and resistant to long dry spells in tropical climates. After a rain, and during a period of plant growth, the egg hatches. The second stage is the larva, which may be divided into several stages between which there is a shedding of the outer skin as the larva increases in size. Larvae often spend their stage below ground where it is cooler and moister than on the surface. The pupal, or third stage, is spent hibernating within a casing, like a cocoon. In the fourth and final stage, the animal emerges from this casing as an adult.
Amphibians are vertebrates (animals with a backbone) that usually spend part, if not most, of their lives in water. Frogs, toads, and salamanders are all amphibians. They live in significant numbers in rain forests where humid conditions are ideal. Amphibians are cold-blooded, which means their bodies are about the same temperature as their environment. In the rain forest they can be active year-round because the temperature is always warm.
Amphibians breathe through their skin, and only moist skin can absorb oxygen so they must usually remain close to a water source. Mating, egg-laying, and young-adulthood all take place in ponds, lakes, or pools of rainwater. When they mature, amphibians leave the pools for dry land where they feed on both plants and insects.
Common rain forest amphibians
Amphibians commonly found in rain forests include tree frogs and poison arrow frogs.
Tree frog Eighty percent of frogs and toads live in tropical forests. Some, such as the fringe limb tree frog, may leap out of a tree to escape a predator. Webs of skin between their limbs act like parachutes, enabling them to glide from one branch to another. Other species of tree frogs have suction pads on their toes that secrete a sticky mucus, enabling the frog to cling to tree trunks and branches.
Poison arrow frog Poison arrow frogs are usually brightly colored. This color warns potential predators that to bite the frog may mean death. One ounce of poison from the kokai frog can kill up to 100,000 average size humans. These frogs, abundant in South America, are used by the local people, who tip their arrows and darts in the poison (hence the frogs’ name).
Most adult amphibians are carnivorous, feeding on insects, slugs, and worms. Salamanders that live in the water suck their prey into their mouths. Those that live on land have long, sticky tongues to capture food. Salamander larvae are mostly herbivorous, feeding on vegetation. Frogs and toads feed on algae, plants, and insects such as mosquitoes.
Mating and egg-laying for amphibians must take place in water because male sperm are deposited in the water and must be able to swim to the eggs in order to penetrate them. Some amphibians lay their eggs in the cups of plants where water has collected and where insect larvae may grow. As the young develop into larvae and young adults, they often have gills for breathing. They, too, require a watery habitat.
Reptiles that live in rain forests include snakes and lizards. Since a reptile’s body temperature changes with the temperature of the surrounding air, the warm, humid rain forest is a comfortable environment for them.
Many rain forest reptiles are capable of camouflage (KAH-mahflahj), or protective coloration. Their skins are often patterned or colored to resemble the forest background in which they live, and they may be able to alter their coloration to a darker or lighter shade. Many reptiles living in the forest canopy have a prehensile (grasping) tail to help them climb and may prevent falls. Rain forest reptiles may have grasping claws to ensure a firm, steady hold as they climb through the trees.
Common rain forest reptiles
Common rain forest snakes include the vine snake of West Africa, the bushmaster and fer-de-lance of Central and South America, the gaboon viper of Asia, and many tree snakes. Lizards include the Jesus Christ lizard of Central America, the crested water dragon of Asia, Parson’s chameleon of Africa, and the Komodo dragon of Indonesia.
Chameleon The chameleon (kuh-MEEL-yuhn) lizard is an expert at camouflage. A resident of the canopy, it can change its coloration to resemble that of the leaves, and it may even tremble slightly to mimic leaves swaying in a breeze. Its feet and tail are perfect for grabbing hold of tree limbs, and its long, sticky tongue flicks out with amazing speed to catch the insects that make up its diet.
Tree snake Many species of tree snakes are found in rain forests. The emerald tree boa of the Amazon is not poisonous, and kills its prey with by squeezing it. Pythons, anacondas, and cobras are found in the rain forest. Pythons can be found in Africa and Australia, cobras in Africa and Asia, and the anaconda in South America.
Komodo dragon The Komodo dragon, the world’s largest lizard, is found in Indonesia, especially on Komodo Island for which it is named. Komodo dragons can measure up to 10 feet (3 meters) in length and weigh up to 366 pounds (166 kilograms). Komodo dragons are carnivores and eat animals as large as buffalo or as small as geckos and other insects. They have long, sharp claws and jagged teeth that enable them to tear meat from their prey. In 1992, komodo dragons hatched at the Smithsonian Zoo, the first of their kind to ever have been bred outside of Indonesia.
A lizard’s diet varies, depending upon the species. Some have long tongues with sticky tips for catching insects, while others eat small mammals and birds. The water they need is usually obtained from the food they eat.
All snakes are carnivores, and one good meal will last them for days or weeks. Some snakes kill their prey with venom (poison) injected through their fangs.
Most reptiles lay eggs. Some females remain with the eggs, others bury them in a hole and abandon them leaving the young to hatch by themselves. Snakes that live in the canopy often bear live young. They produce fewer babies, but the babies, being mobile, have a better chance of survival.
The South American rain forest provided the setting for Green Mansions, a novel by British author W. H. Hudson (1841–1922) that was written in 1904. It is a fantasy love story about Rima, a strange half-bird, half-human character who lives in the forest and cannot leave it. A statue of Rima was erected in 1925 in the bird sanctuary at Hyde Park in London, England.
All rain forests have large bird populations. Most do not need the protection of camouflage, having only to compete with bats, and their feathers are usually brilliantly colored. Their songs vary from the scream of the eagle to the haunting warble of many smaller birds. Bower birds and pittas seem to be able to “throw” their voices like ventriloquists.
Rain forest birds have developed short, broad wings that do not require much room for flying because the vegetation is so dense. Some species, such as toucans and parrots, have feet adapted to climbing.
Common rain forest birds
Common birds of the rain forests include toucans, hummingbirds, birds of paradise, jacamars, eagles, parrots, and junglefowl.
Harpy eagle Harpy eagles live high in the forest canopies of Central and South America, often sitting in one of the emergent trees where their sharp eyes can spot prey. Harpies do not soar high above, but move from tree to tree in short flights. Their large nests are built of sticks, leaves, and fur about 165 feet (50 meters) above the ground. Females produce two eggs. Harpies like to catch monkeys or sloths in their huge talons, and, if their victim attempts to cling to a tree, they are strong enough to wrench the victim free.
Parrot Parrots are brightly colored birds with a loud, harsh call. There are 328 species of parrots, including the commonly known parakeets, macaws, and cockatoos. They tend to be social and roost in large groups. Their feet are strong enough to make it possible for them to hang upside down from a branch for long periods. Their nests are usually in holes in trees, where the female sits on the eggs, and the male brings her food. Preferring to eat seeds, parrots use their tongues to position a seed at the front of the strong, hooked beak and then crack the seed apart. Parrots, well know for their ability to mimic humans, are popular and desirable pets.
Junglefowl The junglefowl of Asia is the ancestor of the chicken and, as such, has affected human life more than any other bird. Male junglefowl crow like roosters and have a red comb. In the wild, they are very aggressive; much of this behavior has been bred out of the domesticated species over the years. They live primarily on the forest floor where they feed on seeds, fruits, berries, and insects. They are good runners, but their flight is weak.
Rain forest birds may fly considerable distances in search of trees bearing fruit. Different birds seek food in different layers of the forest. Parrots, for example, hunt for seeds in the canopy and insects along the trunks of the trees, while pittas dig around on the ground for snails and ants.
Birds reproduce by laying eggs, for which many species build a nest. Some, such as the macaw, prefer to use a hole in a tree. Females usually sit on the eggs until the young birds hatch. The female hornbill of Southeast Asia walls herself into a hole with mud and other materials and the male feeds her until the young can leave the nest. Both parents of most species usually feed their young until they are able to fly. Some young birds, such as the hoatzin of the Amazon region, are uniquely adapted to life in the forest. The hoatzin chicks have two claws on each wing, enabling them to climb through the branches.
Mammals of all kinds live in the rain forest, from the monkeys that swing from the tops of its trees to the shrews that scamper about the jungle floor.
Common rain forest mammals
Rain forest mammals include monkeys, antelopes, coatis, bats, sloths, okapis, gorillas, and jaguars.
Bat Bats are the only mammals truly capable of flight, which they do primarily at night. During the day, they sleep hanging upside-down from branches or holes in trees. Some species are very social and roost in groups of 100 or more. At night they leave their roosts to seek food. A rain forest bat’s diet is either insects or flower nectar and fruits. Many trees are dependent upon them as an aid in pollination.
The God of the Air
The quetzal, or resplendent trogon, of the mountain jungles of Central America has some of the most colorful plumage of any bird. To the Mayas and Aztecs, the quetzal’s emerald and crimson feathers symbolized spring vegetation. They used its tail feathers in religious ceremonies and worshiped the bird as a god of the air. The beautiful quetzal is the national emblem of Guatemala, and its name is given to a unit of Guatemalan currency.
Sloth Sloths are slow-moving creatures with large claws that spend their lives hanging upside-down from tree limbs in Central and South America. Adults are only about 2 feet (0.6 meters) long, and the claws by which they grip the trees measure about 3 inches (8 centimeters). Sloths are so well adapted to their life upside-down that even their hair grows that way, from stomach to spine. They are herbivores that almost never leave the trees because, on the ground, a sloth cannot stand or walk but rather drags itself around with its claws.
Okapi The okapi, a short-necked relative of the giraffe that lives in the rain forest of eastern Congo, was not discovered by European explorers until 1901. It feeds on understory vegetation, such as shrubs and leaves. The coat is purplish brown, with black and white stripes on the upper legs and buttocks. Okapis are unusual in that females are larger than males.
Gorilla Gorillas are found only in Africa, where there are three species: the western lowland gorilla, the mountain gorilla, and the eastern lowland gorilla. These types vary slightly in physical characteristics, such as color.
The gorilla is the world’s largest living primate (group of animals including apes, monkeys, and humans). Males may be as tall as 6 feet (1.8 meters) and weigh between 300 and 400 pounds (135 and 180 kilograms). Gorillas live in groups and rarely change locations if they can help it. They spend most of their day, apart from a midday rest period, foraging for food, primarily nuts, berries, fruits, and leaves.
World’s Smallest Mammal
The world’s smallest mammal is only 1 inch (2.5 centimeters) long, about the size of a bumblebee. It was first catalogued by researchers in 1974. It may have been overlooked until then because it only comes out at night and might have been mistaken for an extremely large mosquito. This little mammal is the Kitti’s hog-nosed bat, and it lives in the rain forests of Thailand.
Jaguar The largest cat in the western hemisphere, jaguars are found mostly in South America. A male jaguar may be 6 feet (1.8 meters) in length with a 2-foot (0.6-meter) -long tail, and may weigh more than 300 pounds (135 kilograms). It has a tan coat and is spotted like a leopard, though some are completely black or white. Jaguars feed on both small and large animals. They hunt mostly on the ground, but they are agile (skilled) climbers and swimmers.
Small mammals, such as the fawn-footed melomys (a type of rodent), often eat plants and insects. Herbivores (plant-eaters), including the agouti, the paca, and the royal antelope, feed on leaf buds and fruit. Cats, such as the palm civet, the ocelot, and the servaline genet, are carnivores (meat-eaters). Many mammals, such as the orangutan, are omnivores, which means they eat both plant and animal foods.
The young of mammals develop inside the mother’s body, where they are protected from predators. Mammals produce milk to feed their young and must remain nearby until the young can survive on their own.
The list of endangered rain forest animals is long. Many species of parrots are endangered, especially in Central and South America, because they are sought by animal dealers to sell as pets or because their habitat is disappearing. An example is the Spix’s macaw, found in Brazil. In 1999, only one bird remained alive in the wild. Concentrated efforts to bring the bird out of near extinction resulted in sixty birds living in captivity. Reintroducing them to the wild has been difficult. Biologists are attempting to send females into the wild in hopes that they will mate with the lone male.
Orangutans and gorillas are in danger because they require deep forest cover and their habitat is rapidly disappearing. For some, their only hope of preservation seems to be zoos and wildlife sanctuaries. Many rain forest cats are also endangered because they have been hunted extensively for their skins. Although many are now protected, their numbers are so low there may not be enough animals left for successful breeding.
Only five species of rhinoceros remain in the world. They are protected, but remain threatened by poachers who kill them for their horns, and by the loss of their habitat. Rhinos live in Africa, India, and Southeast Asia. Although their senses of smell and hearing are well developed, they can not see very well, making them susceptible to attack from both humans and forest predators.
Humans are creatures of the forest. Until they learned to hunt, humans gathered their food and made their dwellings among the trees of the forests.
Impact of the rain forest on human life
Forests have an important impact on the environment as a whole. From the earliest times, forests have provided humans with food and shelter, a place to hide from predators, and many useful products.
Rain Forest Cousins
Chimpanzees are great apes, the closest living relatives to the human species. They resemble humans in some important ways, including their use of tools. Some chimp populations in western Africa use stone and wooden hammers to break open nuts. In eastern Africa, chimps have been observed to stick plant stems into termite nests to drive the termites out so they can eat them, and during a heavy rain they use leafy tree branches as umbrellas.
Trees, soil, animals, and other plants all interact to create a balance in the environment from which humans benefit. This balance is maintained in what can be described as cycles.
The oxygen cycle Plants and animals take in oxygen from the air and use it for their life processes. This oxygen must be replaced, or life on Earth could not continue. Animals breathe in (inhale) oxygen and breathe out (exhale) carbon dioxide. Trees convert this carbon dioxide into oxygen during photosynthesis, releasing the oxygen into the atmosphere through their leaves.
The carbon cycle Carbon dioxide is necessary to life, although too much is harmful. During photosynthesis, trees pull carbon dioxide from the air. This helps maintain the oxygen/carbon dioxide balance in the atmosphere. When trees die, the carbon in their tissues is returned to the soil. Decaying trees become part of Earth’s crust, and after millions of years, this carbon is converted into oil and natural gas.
The water cycle The root systems and fallen leaves of trees help build an absorbent covering on the forest floor that allows rain water to trickle down into the soil to feed streams and groundwater. In this way, forests help conserve water and protect the soil from erosion caused by heavy rain. When forests are cut down, the soil washes away and flooding is more common. For example, heavy rainfall in Indonesia has caused severe flooding, in part due to tree removal. Trees take up some of this rain water through their roots and use it for their own life processes. Extra moisture is released through their leaves back into the atmosphere, where it helps to form clouds.
The nutrient cycle Trees get the mineral nutrients they need from the soil. Dissolved minerals are absorbed from the soil by the tree’s roots and are sent upward throughout the tree. These mineral nutrients are used by the tree much like humans take vitamins. When the tree dies, these nutrients, which are still contained within parts of the tree, decompose. They are then returned to the soil making them available for other plants and animals.
Forests are the home of game animals, such as birds, that provide meat for hunters and their families. Forests also supply fruits, nuts, seeds, and berries, as well as vegetation for livestock. Vanilla, for example, is made from the seed pod of a type of orchid found in Central and South American rain forests; nutmeg and cloves come from Asian rain forests; coffee beans are native to Africa and are products of Central America along with cocoa beans; and starfruits grow in Asia. It is estimated that rain forests contain more than 3,000 species of edible fruits and vegetables, and only about 200 of these have been cultivated for commercial use. With correct management these species might yet provide more food varieties for both humans and animals.
During prehistoric times, humans lived in the forest because it offered protection. Today trees can provide building materials. Trunks are cut into planks or used as poles, while fronds (branches) and grasses can be cut for thatch and used to make huts or roofs for wooden structures.
Forests are important to the world economy. Many products used commercially, such as wood, medicines, tannins, dyes, oils, and resins (sap) are obtained from forests. Forest land is also important to the farm and tourist industries.
Trees produce one of two general types of wood, hardwood or softwood, based on the tree’s cell wall structure. Hardwoods are usually produced by angiosperms, such as the mahogany tree, while most coniferous trees, such as pines, produce softwoods. These names can be confusing because some softwood trees, such as the yew, produce woods that are harder than many hardwoods. Some hardwoods, such as balsa, are softer than most softwoods.
Coffee—The World’s Most Valuable Agricultural Product
In the mid-1990s, imports of coffee beans to the United States totaled $1.5 billion each year. The United States is the world’s largest importer, and the average American drinks about 27 gallons (102 liters) of coffee annually.
Coffee trees grow in montane forests, and coffee beans are the roasted seeds of the tree. The birthplace of coffee was probably Ethiopia, the tree’s native environment. Its use was first developed by the Arabs, and it did not arrive in Europe until the sixteenth century where it was introduced as a medical potion. Coffee became popular as a beverage around 1652. Coffee plantations were soon established in Indonesia, the West Indies, and Brazil, and coffee cultivation became important to colonial economies. Latin America and Africa produce most of the world’s coffee; Central and South America grow about 60 percent of the world’s total production.
Wood is used for fuel, building structures, and manufacturing other products, such as furniture and paper. Wood used for general construction is usually softwood. In order to conserve trees and reduce costs, some manufacturers have created engineered wood composed of particles of several types of wood combined with strong glues and preservatives. Engineered woods are very strong and can be used for many construction needs.
In an effort to preserve the natural forests, plantations are developed to supply the world’s demands for wood. India, South America, and Africa combined have 102,000 square miles (264,178 square kilometers) of tree plantations.
Although rain forest land is poor for farming, more and more of it is being cleared for that purpose. It supports crops for a few years, and then it is used for cattle pasture. When its nutrients are completely exhausted it is abandoned.
Since the earliest times, plants have been used for their healing properties. It is estimated that at least 70 percent of cancer fighting plants are tropical plants from the rain forest. Quinine, from the cinchona tree, is used to fight malaria.
Deadly Traveler on the Kinshasa Highway
The Kinshasa Highway crosses central Africa, linking remote areas to airports in the large cities of Nairobi and Mombasa, both in Kenya. Any traveler starting from deep inside the rain forest who reaches one of those airports is within 24 hours of every other place on Earth. During the 1970s one traveler made such a journey, a journey of deadly consequence.
The traveler was HIV, the human immunodeficiency virus, and by 2007, only twenty-five years after its emergence from the rain forest, it had infected 40 million people worldwide. Already 25 million people have died of AIDS (acquired immune deficiency syndrome), which appears to be caused by HIV.
For millennia, potentially deadly bacteria and viruses have remained undisturbed in the rain forests. If humans caught them, villages were so remote and travel so slow that infected people seldom lived long enough to reach large populated areas where the disease could spread unchecked. As humans penetrate farther into the rain forest and destroy the natural balance that often keeps disease carriers under control, more and more problems are being created. The latest cause for concern is the hemorrhagic fever viruses, such as Ebola zaire, another rain forest resident, which is even more deadly than HIV.
Tannins, dyes, oils, and resins
Tannins are chemical substances found in the bark, roots, seeds, and leaves of many plants. It is used to cure leather, making it soft and supple. Dyes used to color fabrics can be obtained from the bark or leaves of such trees as the brazilwood. Palm oil and coconut oil are used as cooking ingredients. Resins, or saps, are used in paints and other products. Chicle is a resin from the sapodilla tree used in chewing gum, and natural rubber is made from the resin of the South American rubber tree.
Rain forests have become popular with tourists who are interested in hunting, nature study, and environmental issues (ecotourism). Some tropical countries have found it economically desirable to set aside large tracts of forest for tourism.
Impact of human life on the rain forest
While forests have had a positive effect on human life, human life has had a mostly negative impact on forests. Nearly 60,000 square miles (155,399 square kilometers) of forest are cleared each year. Most of the forest loss has occurred in developing nations where wood is used for fuel and trees are cleared for farming. A large number of trees are also lost each year to commercial use.
Rain Forest Explorers
When Europeans first encountered the rain forest, they saw it from a position at its edge, where light could penetrate and foliage ran rampant. The forest soon gained a reputation for being impenetrable, and the first men who ventured into it had remarkable courage. Many were seekers of knowledge about the world; others had a hunger for riches that they believed they would find in the jungle.
At first, valuable goods were the primary target. The Portuguese penetrated Africa by means of its rivers but gained little knowledge of the interior. Few who entered it, such as Portuguese explorer Vallarte in 1448, came back alive. The first European to explore the rain forests of the Amazon in South America was Francisco de Orellana who went in search of cinnamon trees and gold in 1541.
In the 1700s, scientific curiosity became the primary motive for exploration. Between 1799 and 1803, Alexander Baron von Humboldt and Aime Bonpland explored thousands of miles of South America in order to study plant and animal life. During the nineteenth century, journalist Henry Morton Stanley (1841–1904) made a dangerous voyage the length of the Congo River in Africa. Prince Maximilian of Wied-Neuwied, Henry Walter Bates, Alfred Russel Wallace, Jules Crevaux, and, in the twentieth century, Theodore Roosevelt (1858–1919), Percy Fawcett, and Michael Rockefeller also undertook journeys into unexplored regions.
Use of plants and animals
Rain forests are disappearing at alarming rates each year, especially the montane forests. Much forestland is being lost as populations grow and want the land for farms and cattle pasture. Slash and burn agriculture is a routine procedure in which trees are cut and burned. When the land will no longer support crops, it is abandoned and additional forest is cut down somewhere else. As a result, many animals and plants are permanently losing their habitats.
Our ability to harvest trees for wood is greater than the forest’s ability to regenerate. Mechanical harvesting with huge machines makes clear-cutting (cutting down every tree in an area) cheaper and more efficient than selecting only certain trees for harvesting. Replanting may not be done, or a fast-growing species may be replanted rather than the original species. The original species may never grow back. Clear-cutting endangers wildlife by destroying natural habitats.
Quality of the environment
Destruction of the forests does not mean just loss of their beauty and the products they provide. Water quality suffers because the trees are gone and rain no longer seeps into the soil. Instead, it runs off and underground water reserves are not
replaced. Topsoil is eroded away and often ends up in streams and rivers. If the quantity of soil is large enough, fish may die.
Air quality is also reduced by the destruction of forests. Trees not only put oxygen back into the air, but soot and dust floating in the air often collect on their leaves and are washed to the ground when it rains. When the trees are cut down, the dust and soot remain in the air as air pollution.
With the popularity of the automobile, carbon dioxide and other undesirable gases have built up in the atmosphere. Most scientists believe these gases are helping raise the temperature of Earth’s climate (the greenhouse effect). Forests help remove carbon dioxide from the air, so cutting them down may be a factor in global warming. If Earth grows warmer, many species of plants and animals could become extinct.
Most rain forests grow in developing countries that need forest resources for economic reasons. Since 1945, more than 50 percent of the world’s rain forests have been cut down and cleared away. Some countries have realized that they must use their resources wisely, and conservation efforts are under way. Malaysia and Uganda, for example, are making better use of trees that were formerly wasted, and replanting programs have begun in Gabon and Zambia.
Native people have been found in all the major rain forests of the world. They include the Yanomami of South America, the Asanti and Bambuti of Africa, the Andaman of Asia, the Aeta of the Phillipines, the Penan of Borneo, and the Aborigines of Australia.
In general, forest dwellers are hunter-gatherers who make few changes to the forest environment. Changes other people are making may destroy their way of life.
The Yanomami tribe, comprised of four smaller tribes, are scattered across Brazil and Venezuela. Only about 20,000 of them remain, as their population has decreased by over 10 percent in the last twenty years. The Yanomami live in villages as few as 40 residents to as many as 300 people. Trade and marriage keep the villages in contact with one another; sometimes peacefully and other times not. They seldom leave the forest, as it provides them with all they need to survive. Huts are built from timber and vine and food is either grown or hunted.
The Asante (sometimes referred to as Ashanti) of Africa make their home in Togo and the Ivory Coast. Like many native tribes, they began as forest dwellers. Loss of their home due to the clearing of the forest has caused some to move to nearby towns. Farming is their main livelihood. They export plantains, bananas, yams, and other staples to the local market.
Although mostly a peaceful tribe, the Asante have their share of war and strife. In the seventeenth century, firearm trade caused a power struggle in which the Asante prevailed. Then in the nineteenth century, they fought the British seeking an independent government from the Republic of Ghana. This battle was lost, but the Asante were allowed to live in peace, and they now number over 600,000 people.
The Andaman tribe is the only tribe of natives that never learned to make fire. They waited for fire to naturally occur, such as lightning fires, and then were careful to preserve the fire as long as possible.
Located on the Andaman and Nicobar islands in the Bay of Bengal, they survive by hunting, and their diet consists of no plants or vegetables. As islanders, they seek out iron from nearby shipwrecks and use it to make their weapons.
The transfer of energy from organism to organism forms a series called a food chain. All the possible feeding relationships that exist in a biome make up its food web. In the rain forest, as elsewhere, the food web consists of producers, consumers, and decomposers. An analysis of the food web shows how energy is transferred within the biome.
Green plants are the primary producers in the forest. They produce organic materials from inorganic chemicals and outside sources of energy, primarily the Sun. Trees and other plants turn energy into plant matter.
Animals are consumers. Plant-eating animals, such as certain insects and mice, are the primary consumers in the rain forest food web. Secondary consumers, such as anteaters, eat the plant-eaters. Tertiary consumers are the predators, like owls and leopards. Some, such as orangutans and humans, are omnivores.
Decomposers feed on dead organic matter and include fungi and animals like the vulture. In the moist rain forest, bacteria aid decomposition. When leaves fall to the ground, bacteria feed on the leaves and speed up the decomposition process.
Rain forests of South America
More than half of all the world’s rain forests are located in South America. The South American region contains all three types—lowland, montane, and cloud forest—and is dominated by the great Amazon River and its tributaries. The forests of South America claim 2.7 million square miles (7 million square kilometers). The region on the northwest coast of Colombia is not well explored, in contrast to the much-explored forests of northern Brazil. Bordering Paraguay is the Mato Grosso forest. Cloud forests occur in the mountains of Venezuela, Brazil, Peru, and Guyana.
Rain forests of South America
Location: Brazil, Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana, Surinam, and French Guiana
Annual rainfall is more than 236 inches (600 centimeters), which makes this one of the wettest places in the world.
An estimated 70,000 species of plants can be found in South American rain forests, which includes about 2,500 species of trees. Some trees, such as mahogany and rubber trees, have gained worldwide commercial importance.
No one knows how many species of insects live in the South American rain forest because so many remain to be identified or even discovered. Among those that have been catalogued include the malachite butterfly and the postman butterfly.
More than half of the world’s species of birds make their home in the Amazon basin. A few are migratory but most live in the rain forest year-round. They have the short, broad wings of true jungle birds and range in size from the large-billed toucan to the tiny hummingbird.
Comparatively speaking, this area supports few mammals. They tend to be small and shy and include deer, pacas, agoutis, capybaras, anteaters, tapirs, jaguars, bats, and many species of monkeys, including spider monkeys, woolly monkeys, and capuchins.
In the 1970s, a network of highways was constructed through the Brazilian rain forest in an attempt to develop the land for farming and provide access to mineral and timber resources. This has proved disastrous. Rain forest soil is poor; after a few years farms are abandoned and more land is cleared. In addition, roads are often impassable from January to July, during the season of heaviest rain and severe flooding.
Rain forests of Central America
Before the sixteenth century, the small countries of Central America were covered by rain forest. Forests now cover only about 196,000 square miles (507,000 square kilometers) of land. Some forests are protected, such as the Monteverde Cloud Forest Reserve in Costa Rica.
Rain forests of Central America
Location: Parts of Mexico, Panama, Costa Rica, Nicaragua, Honduras, Guatemala, and Belize
Like the South American forests, the Central American forests are rich in diversity, claiming to have 43,000 to 48,000 different species; 20,000 to 25,000 of these are not found anywhere else in the world. Flowering plants include the hotlips, the brown violet-ear, and many species of orchids. Trees include the massive guanacaste and the Gunnera.
Paper wasps, red-kneed tarantulas, tiger moths, false-leaf katydids, golden beetles, termites, land snails, and sally lightfoot crabs are among the invertebrates that live here. Frogs and toads are exist in great numbers. While some depend on camouflage, others are brightly colored or patterned. Boa constrictors and iguanas are representative of reptiles. Bird life is extremely varied, and Panama supports more species than the whole of North America. Some birds are migratory, spending only the winter months here. Mammals include howler monkeys, tapirs, peccaries, deer, and jaguars.
For more than 3,000 years, Central America was home to the great Aztec and Maya civilizations. The Aztec were centered in Mexico and the Maya in Belize and Guatemala. They were primarily agricultural peoples and had developed methods of irrigating (watering) and fertilizing crops such as corn, beans, and squash. These civilizations also developed forms of writing, books, maps, astronomy, and a very accurate calendar. But by 1521, Hernán Cortés (1485–1547) of Spain had conquered the Aztecs, and by 1550 the Mayans were also overcome and their great civilizations destroyed.
Rain forests of Africa
The lowland wet forest lines the West African coast, from Senegal to the Congo. Montane forest is found in central south Africa. The total area is much smaller than covered by rain forest in South America or Southeast Asia. Here the forest measures about 780,000 square miles (2.02 million square kilometers), or one third of the continent.
Rain forests of Africa
The climate in Africa is warm and wet, and annual rainfall is greater than 60 inches (1.5 meters). This helps to support plant and animal life, including the African mahogany, obeche, and ebony trees. African forests are also home to many flowering plants. One, called the “flame of the forest” or the “flamboyant tree” yields huge scarlet flowers. Animals commonly found in the African forest include gorillas, bats, monkeys, apes, and many others.
Rain forests of Madagascar
Rain forest in Madagascar covers the east side of the island along the coast. Rainfall is about 139 inches (353 centimeters) annually. The island is vulnerable to storms at sea and much damage occurs periodically.
Rain forests of Madagascar
Location: Madagascar Island, off the east coast of Africa
Vegetation is dense and of the montane variety. Trees include traveler trees and palms. Ferns, lianas, and epiphytes dominate the understory.
Invertebrates include grasshoppers, termites, cockroaches, mosquitoes, moths, and butterflies. Reptiles include chameleons, geckos, and lizards. Birds are numerous and include guinea fowls, herons, flamingoes, and owls. At one time, Madagascar was part of Africa, and animal life in both places has similar origins. The current island broke away from Africa some 50 million years ago. As a result, the animals in Madagascar developed in isolation, creating a home to many unique species. These include many species of chameleon, the mesite, the lemur, the tenrec, and the fossa.
Rain forests of Southeast Asia
Tropical forests in Asia can be found in Bhutan, Myanmar, Bangladesh, India, the Malay peninsula, Indonesia, and the Philippines. Together, it covers 864,000 square miles (12.2 million square kilometers) of land. Within that, 566,000 square miles (1.47 million square kilometers) is covered in lowland wet forest.
Rain forests of Southeast Asia
Location: Malayasia, Indonesia, the Philippines, Thailand, Cambodia, Laos, and Vietnam
In terms of tree species, the rain forests of Asia differ from others in that they support coniferous trees. The dipterocarps is a large family of hardwoods bearing winged fruits. It dominates these forests. Examples of dipterocarps include the Shorea and Dipterocarpus species. Other trees include kapoks, palms, and even pines. Smaller plants include mosses, ferns, rattans, ginger, orchids, and ant plants.
Asian forests are rich in fruit, such as breadfruit, jackfruit, and durian. Jackfruit is one of the largest fruits in the world, with some species weighing up to 55 pounds (25 kilograms). Durian has a very distinct, unpleasant odor, but is popular among the natives of Asia.
Mammals are well represented and include rats, squirrels, tigers, elephants, rhinoceroses, tapirs, wild pigs, leopards, deer, antelopes, marbled cats, and many species of monkeys and their relatives.
Rain forests of New Guinea
The eastern half of New Guinea, Papau New Guinea, is an independent country, while the western half, Irian Jaya, belongs to Indonesia. As a whole, the island boasts that 77 percent of its lands are mostly lowland wet forests. Ranges of mountains run through the center of the island, the tallest peak is 16,535 feet (5,040 meters) high. Much of this region is unexplored. Steep gorges and rolling valleys punctuate the mountains.
Rain forests of New Guinea
Location: Pacific Ocean, north of Australia
Rainfall is heavy and, on the north coast, totals about 100 inches (254 centimeters) annually. Lowland temperatures remain at about 80°F (27°C) throughout the year.
The forest is rich with kamamere, lancewood, New Guinea base-wood, and walnut. Moretan bay pines and klinki pines can be found at higher altitudes in the montane forest. The klinki pine is the tallest tree in all of the tropical forests in the world, measuring 292 feet (89 meters) tall.
Constant rain removes nutrients from the soil, and most inland soils are poor. In regions around volcanoes soil quality improves. In the montane forests, dead vegetation several feet thick often covers the ground.
Animal life resembles that found in Australia, especially the mammals. Ants, cockroaches, sand flies, butterflies, mosquitoes, and giant snails are representative of invertebrates, and the island is home to many snakes, most of them poisonous. Other reptiles include lizards, tortoises, and crocodiles. Birds are similar to those found in Malaysia and Australia; the cassowary and the bird of paradise are examples. Many mammals are found here, all of which are marsupials (mammals that carry their young in a pouch) except for the spiny anteater, the bat, and non-native rodents. An example of a marsupial is the tree kangaroo.
Native peoples depend upon agriculture, and the rain forest is gradually being cut down to accommodate farms. Crocodile farming is common for the sale of their skins.
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Since rainfall controls tropical vegetation in the tropics, rain forest types may be classified with reference to local climate. These include lowland, montane , subtropical, and temperate rain forests. Their common features are at least 1,500 millimeters (approximately 33 inches) of annual rainfall and evergreen vegetation with lianas and epiphytes . Most widespread are lowland tropical rain forests, accounting for less than one-third of the tropical land surface, growing in areas receiving between 2,000 to 5,000 millimeters of annual rainfall, with relatively high and constant air temperature (annual mean ±25°C) never below freezing point. They persist in Central America, the Amazon Basin, the Congo Basin, Southeast Asia, New Guinea, and northern Australia. Their canopy is often 25 to 45 meters or higher.
In the monsoonal tropics, characterized by similar total annual rainfall, but unevenly distributed between dry and wet seasons, a related type of lowland forest is found, which becomes partly leafless during the driest months. These tropical evergreen seasonal forests occur in Central America, the northern coast of South America, Africa, India, Southeast Asia, and in some of the Pacific Islands.
Montane tropical rain forests grow in the same regions that lowland forests do, but at higher altitudes, often above 1,000 meters. Local climate is cooler (15 to 25°C), with high annual rainfall (2,000 to 4,000 millimeters or more). The canopy is often 15 to 35 meters in lower montane forest, while above 2,000 meters, in upper montane forests, it is only 10 meters or less. Fog is frequent, and in moss forests relative humidity varies little from saturation point.
Subtropical rain forests are found in the southeastern United States, southwestern South America, southern China, Japan, eastern Australia, and New Zealand, often within cooler climates (15 to 20°C) and lower rainfall (1,500 to 2,000 millimeters). The canopy generally ranges between 35 and 40 meters. Temperate rain forests occur mostly along the Pacific Coast of North America (where the canopy may be 60 meters or higher), Tasmania, and New Zealand. Although temperatures often fall below freezing point, annual rainfall remains high. In addition, wetland forests include mangrove forests, occurring in saline coastal waters, and various peat and freshwater swamp forests. The rest of this overview concentrates on tropical lowland rain forests.
Rain Forest Structure
Rain forest structure is highly complex and determined by competition for light among plant species. Isolated trees, emerging above the canopy, are often present and can be 70 to 80 meters in height. Different tree species grow following various architectural models related to bud location and branching patterns and may or may not form distinct forest layers. Lianas rooted in the ground and epiphytes (e.g., ferns, orchids, and bromeliads) growing on support branches are common in the canopy. Leaves are often medium to large in size, lustrous, and tough. Their shape is often simple, ending with a "drip tip" to shed rainfall. Compound leaves are thought to represent an adaptation to rapid upward growth or seasonal drought and occur more commonly among plants growing in light gaps, in early successional vegetation, or in tropical evergreen seasonal forests. Very little of the light falling on the canopy reaches the ground (0.5 to 2 percent of the illumination available in the canopy), so that the herb layer is much reduced but also includes some saprophytes and root-parasites. Although larger herbs from Zingiberales and Arales may occasionally form denser understory, in mature rain forests it is usually not difficult to penetrate.
This structural complexity is complicated by the temporal dynamics of the rain forest. Often, leaf fall occurs during the driest months and leaf flushing (budding and growth) during the wettest. Furthermore, rain forest trees show a variety of leafing phenologies , from continuous leafing, intermittent flushing to deciduous habits. Within the same species or individual crown, flushing may be synchronous or not. Patterns of flowering and fruiting are equally complex, with sometimes mass flowering or fruiting. Understory leaves are often long-lived, more than five years, and covered with mats of epiphytes (such as mosses, lichens, and algae).
Plant Diversity in Rain Forests
Several theories account for the higher plant and animal diversity in tropical forests compared to temperate forests. First, a greater stability may have existed in the tropics, in comparison with temperate lands, where biotas have been depleted by recent glaciations. During the Pleistocene epoch, ten thousand years ago, climatic changes transformed many rain forests into drier savanna. Some rain forests persisted as refugia (isolated refuges), later rejoining together as the climate became more favorable, increasing species richness within. Second, tropical ecosystems may provide more ecological niches than temperate ones, thereby supporting more species. Third, predation and competition in the tropics may promote higher speciation rates. Last, high species richness in the tropics may result from solar energy controlling biodiversity in near-saturated humid conditions.
The great majority of plants in rain forests consist of dicotyledonous trees. For example, the genera Ficus (Moraceae) and Piper (Piperaceae) are diverse throughout the tropics, whereas Eperua (Caesalpiniaceae) and Shorea (Dipterocarpaceae) are species-rich in Neotropical and Asian forests, respectively. Some families that are herbaceous in temperate areas develop as woody trees in rain forests (e.g., Verbenaceae, Urticaceae, and Polygalaceae). Monocotyledons are less common but include palm trees, various herbs, orchids, and grasses. Abundant woody climbers (often dicotyledons) are characteristic of rain forest vegetation. Their broad stems may cover several kilometers of canopy. Herbaceous or shrubby epiphytes, semiparasitic mistletoes, and strangling figs (Ficus ) are also species-rich.
Although tropical rain forests cover less than 6 percent of land masses, they may sustain half or more of Earth's biodiversity. For example, the Malay Peninsula contains about 7,900 plant species compared to Britain's 1,430. Further, a typical hectare of rain forest may include 150 to 200 species of trees with a diameter greater than 10 centimeters, with records of 300 species per hectare in Peruvian Amazonia. In contrast, a hectare of temperate deciduous forest might contain only one-tenth as many species. Still, many rain forest tree species are rare, with average densities of 0.3 to 0.6 trees per species and per hectare. This results in a large average distance between trees of the same species that may affect pollinating and foraging animals, as well as the plants themselves. Indeed, pests or diseases are rarely a problem in mixed rain forests, while uniform vegetation in the same area, such as plantations, is often heavily defoliated.
Contrasting strongly with mixed rain forests, monodominant rain forests are dominated by a single canopy species, such as Mora (Caesalpiniaceae) in the Neotropical region, Gilbertiodendron (Caesalpiniaceae) in Africa, and Dryobalanops (Dipterocarpacea) or Nothofagus (Fagaceae) in Australasia. These are competitively superior, shade-tolerant, slow-growing, long-lived species with large and poorly dispersed seeds.
Animal Diversity in Rain Forests
Rain forests sustain more faunal diversity than any other habitat on Earth. In particular, the Amazonian forests of Peru and Ecuador are the most diverse for mammals, birds, reptiles, amphibians, and butterflies. Arthropods are particularly diverse in rain forests since they exploit every niche from the soil to the canopy. For example, one large tree in Peru yielded 43 species of ants, equivalent to their entire British fauna, and 134 species of leaf beetles (Chrysomelidae) were collected from ten tree species in New Guinea in comparison with a total fauna of 255 British species.
The most abundant vertebrates in rain forests are frugivores, feeding on fruits and seeds. Among invertebrates (aside from earthworms in soil and epiphytes), the dominant groups rely on a variety of food ressources. These include ants (Formicidae: predators, herbivores , or fungal-feeders), rove beetles (Staphylinidae: predators, scavengers, or fungal-feeders) or weevils (Curculionidae: leaf-chewers, wood-, seed-, or flower-eaters). Other important invertebrate groups in rain forests include parasitoid wasps, moths, leaf beetles, and spiders. However, most of these species are little known and many are yet to be described.
In 1982, entomologist Terry Erwin suggested that there may be as many as 30 million species of arthropods, instead of the previously estimated 1.5 million, although this has not been substantiated. Erwin's estimates attracted considerable attention to the vast, but endangered, reservoir of genetic diversity represented by rain forest arthropods. In 1988, Erwin stated "no matter what the number we are talking about, whether 1 million or 20 million [arthropod species], it is massive destruction of the biological richness of Earth."
Rain Forest Dynamics: Regeneration
Rain forest regeneration and continuity is assured through the important processes of pollination and seed dispersal, which occur primarily through the movements of rain forest animals. Their loss in severely disturbed rain forests drastically affects regeneration capacity. Wind pollination, common in temperate regions, is rarer due to the absence of wind currents; 90 percent of rain forest plants may be insect-pollinated, with nectar the reward for pollinators. They may be strong fliers that forage over long distances, such as birds, bats, hawk moths, and large euglossine bees , which may fly up to 23 kilometers. Other short-range pollinators may include stingless, carpenter, and bumblebees, wasps, butterflies, thrips, beetles, midges, and flies. Depending on the timing of flower opening, pollinators may be either diurnal or nocturnal.
Another important aspect of pollination is fidelity to particular plant species, which ensures cross-pollination. Some pollinators are generalists (e.g., stingless bees) but restrict their visits to particular plant species. However, many rain forest plants have developed intricate relationships with their pollinators. For example, the petal tube of many flowers corresponds exactly in length and curvature to either the beaks of hummingbirds or to the tongue of certain hawk moths. Further, pollinator activities are attuned to different flowering phenologies, the most specialized of these involving figs (Ficus ) and fig wasps (Agaonidae), the former totally dependent on the latter for pollination. Usually, one particular species of fig is pollinated only by its own species of wasp.
Some rain forest plants may be dispersed by wind or gravity. However, many of them rely on animals such as ants, fish, reptiles, birds, bats, primates, deer, pigs, civets, rodents, and elephants to disperse seeds. This ensures pollination and cross-fertilization of distant tree populations to produce more vigorous and successful offspring and that seedlings have enough space and light to grow and develop. Fruits represent fleshy rewards for animals; swallowed with their seeds, the latter emerge intact in feces and ready to germinate. Animals often specialize in particular seeds or similar seed types, with larger animals often dispersing the seeds at great distance from the parent tree.
Figs are a year-round resource for rain forest frugivores and are particularly important when other fruits become scare. Fig trees are referred to as a keystone species, those that have a crucial importance in the maintenance of the rain forest ecosystem.
Insects (e.g., Bruchidae and Curculionidae), parrots, or squirrels may overcome the chemical defenses of seeds, feeding on them without dispersal. Many insects and fungi also attack the leaves and stems of seedlings. Patterns of herbivore attack below the parent trees may depend on seedling density and decrease with increasing distance from the parent. This may result from specific insect herbivores colonizing seedlings from parent trees, promoting botanical diversity by prohibiting the establishment of young trees near conspecific parents. However, this is not universal, and this model requires validation and refinement.
Rain Forest Dynamics: Succession
Natural disturbance induces a succession of vegetation. After clearance, rain forest succession may start with almost bare soil, proceed with a different kind of vegetation (called secondary forest or growth), and end with the restoration of the original, climax, vegetation. For example, the fall of a large crown of 20 meters in diameter may produce a forest gap of 400 m2. Some plants will be damaged from the tree fall, but others will have improved growth opportunities, due to increased access to light. Forest gaps are common and promote local plant and animal diversity.
Secondary rain forests contain smaller trees, with many small climbers and young saplings in an understory that is often difficult to penetrate. The floral composition of these forests is different from primary rain forests. Although a few secondary species may live in natural gaps created by treefalls in primary forests, they are more abundant in secondary forests. These are dominated by a few plant species and are less species rich than primary forests. Secondary genera include Cecropia (Cecropiaceae) in the Neotropical region, Musanga (Moraceae) in Africa, and Macaranga (Euphorbiaceae) in Asia. Typically, these "pioneer species" (as opposed to the shade-tolerant species of primary rain forests) produce large quantities of small seeds carried by wind or small animals. In contrast, shade-tolerant species often bear large seeds in fleshy fruits that are dispersed by large animals. Pioneers germinate and grow rapidly (often several meters in two to three years), producing thin, short-lived, and large leaves on weak stems that break easily. Secondary vegetation is not long-lived, since species needing much sunlight to germinate and grow eventually die in the shade of their parents. These stands of pioneers are unable to regenerate under new ecological conditions, giving way to slower-growing, stronger trees that regenerate primary forest, a process that takes place over many centuries.
Herbivory and Decomposition in Rain Forests
Both herbivory and decomposition hasten the return and recycling of nutrients in the ground and promote regeneration of the forest. Most rain forest plants contain more chemical defenses than temperate plants. This may be a response to year-round high herbivore pressure, particularly from insects that represent the bulk of leaf-eating, sap-sucking, flower- and seed-eating fauna. Chemical defenses are often by-products of plant metabolism and are termed secondary metabolites, including lectins, resins, alkaloids , protease inhibitors, cyanogenic glycosides, or rare amino acids. Each plant species may contain fifty or more in its leaves, bark, or seeds. Many may be pharmacologically active, with subtle differences often due to the high genetic variation of rain forest plants. Since 99 percent of rain forest plants have not been yet chemically screened, biological prospecting for secondary metabolites was undervalued until recently—with an even greater percentage of arthropods untreated.
Herbivorous insects have developed assorted strategies to counter the plants' chemical defenses and concentrate their damage on young leaves. They may produce enzymes capable of breaking down secondary metabolites, thus becoming restricted to feeding on one or a few related plant species sharing similar chemical properties. About 9 percent of leaf area is usually lost to herbivores in tropical rain forests, a figure often considerably lower in forests growing on nutrient-poor soils. Since they invest most of their energy in growth and less in chemical defenses, herbivory on pioneer trees tends to be greater than those that are shade tolerant.
Decomposition of organic matter, performed by fungi, bacteria, and invertebrates, particularly earthworms, is rapid in rain forests. Termites are the primary decomposers of wood, often transporting rotting wood to great depths in their underground galleries. In terms of dominance, termites are ranked second to ants with up to 870 colonies per hectare, including underground and arboreal nests.
Nutrient Cycling in Rain Forests and the Consequences of Deforestation
Although most tropical rain forests grow on nutrient-poor soils, their primary production is the highest of any natural system, ranging from 300 to 900 tons of biomass per hectare. This is due to the efficient cycling of nutrients through a virtually leak-proof system, since up to 90 percent of nutrients may be stored at anytime in the vegetation.
The main source of nutrients is rainfall, which represents as much as 3 kilograms of phosphorus, 2 kilograms of iron, and 10 kilograms of nitrogen per hectare per year. The forest filters out nutrients from the water as it passes through. Epiphytes growing on leaf surfaces often fix nitrogen. At ground level, tree roots, which may extend near the soil surface 100 meters away from the tree trunks, may be three times as dense as in temperate forests and are very efficient at absorbing nutrients from the soil, whether from rainfall or from decaying organic matter. Symbiotic associations between roots and fungus or bacteria (termed mycorrhizae) are particularly efficient in recovering minerals, particularly phosphorus, from leaf litter.
Since most nutrients are held in the vegetation aboveground, clearing and burning of rain forests concentrates nutrients in the ground. Some nitrogen and sulfur are lost during burning, but large quantities of other nutrients are deposited in ash. Leaching, due to heavy rainfall, washes these nutrients far beyond the shorter roots of new grasses or shrubs. This severely disrupts the nutrient cycle, leaving barren tracts that remain unproductive or that require the ecologically unsound overapplication of fertilizers. Moreover, the clearing and removal of logs by heavy machinery result in soil compaction , water runoff, and, eventually, soil erosion. When a large area of forest is cleared, the soil becomes drier and warmer, and most of the mycorrhizae die out. Aided by nutrients, mycorrhizae, and seeds from nearby intact rain forest patches, regrowth occurs in small areas of clearance, but this is impossible for large clearings, where herbaceous vegetation colonizes infertile soils.
Indigenous People and Rain Forests
The indigenous dwellers of rain forests are dependent on them and, similarly, are endangered by habitat fragmentation and destruction. This includes several groups in Malaysia (the Orang Asli), Sarawak (the Penan), Sabah, New Guinea, the Philippines, the African Pygmy groups in Cameroon, Gabon, and Congo; and many Amerindian groups, such as the Yanomami of Brazil or Jívaro of Ecuador.
The encyclopedic knowledge of the natural world of many indigenous groups is well known and discussed by many rain forest ecologists. For example, Papua New Guineans know hundreds of plant and animal species living in their forests, and they have developed detailed nomenclatural systems in their local languages. This knowledge is not restricted to medicinal plants but also extends to the smallest of creatures. Indigenous knowledge is an inspiration for scientific research and an opportunity for inclusion of local assistants within research projects. Such knowledge also requires reward through the sharing of profits that may result from economically important discoveries.
Environmental Threats to Rain Forests
The major threats to rain forests are, in order of decreasing importance:
- cattle ranching and farming, leading to habitat fragmentation and destruction
- clear-cutting for timber and pulp, with similar outcomes
- plantation cultivation , creating large areas of secondary regrowth
- selective logging of particular tree species, leading to an irregularly structured patchwork of primary and secondary forests
- shifting cultivation (slash- and-burn), creating small patches of secondary growth
- natural disasters, including localized landslides and fires, leading to secondary regrowth and natural succession.
The ever-increasing and often irreversible human damage to rain forests shows no sign of slowing down. Although much controversy exists regarding rates of its loss (perhaps 50 hectares per minute) and biodiversity, it is probable that, in a few decades, large tracts of rain forests will remain only in the Guianas, upper Amazon, Congo Basin, and New Guinea. Tragically, a substantial part of Earth's biodiversity and genetic resources will be lost forever, with the potential for concomitantly disastrous effects on local and global climates. Belief that recent advances in biotechnology will remedy this situation is erroneous. The best way to slow down these alarming rates of loss is through education, conservation, and rehabilitation of the organismic components of ecology, botany, zoology, and taxonomy.
see also Biodiversity; Defenses, Chemical; Deforestation; Endangered Species; Plant Prospecting; Pollination; Rain Forest Canopy; Seed Dispersal.
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The world's rain forests are the richest ecosystems on Earth, containing an incredible variety of plant and animal life. These forests play an important role in maintaining the health and biodiversity of the planet. But rain forests throughout the world are rapidly being destroyed, threatening the survival of millions of species of plants and animals and disrupting climate and weather patterns. The rain forests of greatest concern are those located in tropical regions, particularly those found in Central and South America, and the ancient temperate rain forests along the northeastern coast of North America.
Tropical rain forests (TRFs) are amazingly rich and diverse biologically and may contain one-half to two-thirds of all species of plants and animals, though these forests cover only about 5–7% of the world's land surface. Tropical rain forests are found near the equatorial regions of Central and South America, Africa, Asia, and on Pacific Islands, with the largest remaining forest being the Amazon rain forest, which covers a third of South America.
TRFs remain warm, green, and humid throughout the year and receive at least 150 in (4 m) of rain annually, up to half of which may come from trees giving off water through the pores of their leaves in a process called transpiration . The tall, lush trees of the forest form a two- to three-layer closed canopy, allowing very little light to reach the ground. Although tropical forests are known for their lush, green vegetation, the soil stores very few nutrients. Dead and decomposing animals, trees, and leaves are quickly taken up by forest organisms, and very little is absorbed into the ground.
In 1989 World Resources Institute predicted that "between 1990 and 2020, species extinctions caused primarily by tropical deforestation may eliminate somewhere between 5–15% of the world's species...This would amount to a potential loss of 15,000 to 50,000 species per year, or 50 to 150 species per day." It is estimated that 30–80 million species of insects alone may exist in TRFs, at least 97% of which have never been identified or even discovered.
Tropical forests also provide essential winter habitat for many birds that breed and spend the rest of the year in the United States. Some 250 species found in the United States and Canada spend the winter in the tropics, but their population levels are decreasing alarmingly due to forest depletion.
Tropical rain forests have unique resources, many of which have yet to be utilized. Food, industrial products, and medicinal supplies are common examples. Among the many fruits, nuts, and vegetables that we use on a regular basis and which originated in tropical forests are citrus fruits, coffee, yams, nuts, chocolate, peppers, and cola. A variety of oils, lubricants, resins, dyes, and steroids are also products of the forests. Natural rubber , the fourth biggest agricultural export of southeast Asian nations, brings in over $3 billion a year to developing countries. The forests could also yield a sustainable supply of woods like teak, mahogany, bamboo, and others. Although only about 1% of known tropical plants have been studied for medicinal or pharmaceutical applications, these have produced 25–40% of all prescription drugs used in the United States. Some 2,000 tropical plants now being studied have shown potential as cancer-fighting agents.
Scientists studying ways to commercially utilize these forests in a sustainable, non-destructive way have determined that two to three times more money could be made from the long-term collection of such products as nuts, rubber, medicines, and food, as from cutting the trees for logging or cattle ranching. Perhaps the greatest value of tropical rain forests is the essential role they play in the earth's climate. By absorbing carbon dioxide and producing oxygen through photosynthesis , the forests help prevent global warming (the greenhouse effect ) and are important in generating oxygen for the planet. The forests help prevent droughts and flooding , soil erosion and stream sedimentation , maintain the hydrologic cycle , and keep streams and rivers flowing by absorbing rainfall and releasing moisture into the air.
Despite the worldwide outcry over deforestation, destruction is actually increasing. A 1990 study by the United Nations Food and Agriculture Organization found that tropical forests were disappearing at a rate exceeding 40 million acres (16.2 million ha) a year—an area the size of Washington state. This rate is almost twice that of the previous decade.
Timber companies in the United States and western Europe are responsible for most of this destruction, mainly through farming, cattle ranching, logging, and huge development projects. Japan, the world's largest hardwood importer, buys 40% of the timber produced, with the United States a close second. Ironically, much of the destruction of forests worldwide has been paid for by American taxpayers through such government-funded international lending and development agencies as the World Bank , the International Monetary Fund, and the Inter-American Development Bank, along with the United States Agency for International Development.
The release of the World Bank's new Operational Policy on Forests has been delayed since October 2001, and had not been released as of the first week in July 2002. The release has been delayed by a World Bank dispute over whether its new Forest Policy would apply to the World Bank's growing area of lending, which directly or indirectly finances logging activities. There has been widespread demand that the Forest Policy must apply to all World Bank operations that might have an impact on forests. It remains to be seen how the Operational Policy on Forests will handle this important question.
American, European, and Latin American demand for beef has contributed heavily to the conversion of rain forest to pasture land. It is estimated that one-fourth of all tropical forests destroyed each year are cut and cleared for cattle ranching. Between 1950 and 1980, two-thirds of Central America's primary forests were cut, mostly to supply the United States with beef for fast food outlets and pet food.
In Brazil and other parts of the Amazon Basin , cattle ranchers, plantation owners, and small landowners clear the forest by setting it on fire, which causes an estimated 23–43% increase in carbon dioxide levels worldwide and spreads smoke over millions of square miles, which interferes with air travel and causes respiratory difficulties.
Unfortunately, cleared forest that is turned into pasture land provides very poor quality soil, which can only be ranched for a few years before the land becomes infertile and has to be abandoned. Eventually desertification sets in, causing cattle ranchers to move on to new areas of the forest.
While huge timber and multi-national corporations have justifiably received much of the blame for the destruction of TRFs, local people also play a major role. Populations of the Third World gather wood for heating and cooking, and the demand brought about by their growing numbers has resulted in many deforested areas. The proliferation of coca farms, producing cocaine mainly for the American market, has also caused significant deforestation and pollution , as has gold prospecting in the Amazon.
The destruction of TRFs has already had devastating effects on indigenous peoples in tropical regions. Entire tribes, societies, and cultures have been displaced by environmental damage caused by deforestation. In Brazil fewer than 200,000 Indians remain, compared to a population of some six million about 400 years ago. Sometimes they are killed outright when they come into contact with settlers, loggers, or prospectors, either by disease or because they are shot. And those who are not killed are often herded into miserable reservations or become landless peasants working for slave labor wages.
Today, less than 5% of the world's remaining TRFs have some type of protective status, and there is often little or no enforcement of prohibitions against logging, hunting , and other destructive activities.
The ancient rain forests of North America are also important ecosystems, composed in large part of trees that are hundreds and even thousands of years old. Temperate rain forests (or evergreen forests) are usually composed of conifers (needle-leafed, cone-bearing plants) or broadleaf evergreen trees. They thrive in cool coastal climates with mild winters and heavy rainfall and are found along the coasts of the Pacific Northwest area of North America, southern Chile, western New Zealand, and southeast Australia , as well as on the lower mountain slopes of western North America, Europe, and Asia.
The rain forest of the Pacific Northwest, the largest coniferous forest in the world, stretches over 112,000 mi2 (129,000 km2) of coast from Alaska to northern California, and parts extend east into mountain valleys. The forests of the Pacific Northwest consist of several species of coniferous trees, including varieties of spruce, cedar, pine, Douglas fir, Hemlock, and Pacific yew. Broadleaf trees, such as Oregon oak, tanoak, and madrone, are also found there. Redwood tree growth extends to central California. Further south are the giant sequoias, the largest living organisms on earth, some of which are over 3,000 years old.
In some ways, the temperate rain forests of the Pacific Northwest may be the most biologically rich in the world. Although TRFs contain many more species, temperate rain forests have far more plant matter per acre and contain the tallest and oldest trees on Earth. Over 210 species of fish and wildlife live in ancient forests, and a single tree can support over 100 different species of plants. One tree found in cool, moist forests is the slow-growing Pacific yew, whose bark and needles contain taxol, considered one of the most powerful anti-cancer drugs ever discovered.
Unfortunately, the clear-cutting of most of the ancient forests and their yew trees has caused a serious shortage of taxol. Some yew trees are unavailable for harvesting because they grow in forests protected as habitat for the endangered northern spotted owl . The logging of federal land under the jurisdiction of the Bureau of Land Management (BLM) and the U.S. Forest Service (USFS) has eliminated some of the last and best habitats for the Pacific yew.
The remaining ancient forest, almost all of which is now on BLM and USFS land, is being cut at a rate of 200,000 acres (81,000 ha) a year, as of 1992. At this rate it will be destroyed within less than two decades. The consequences of this destruction will include the disappearance of rare species dependent on this habitat, the silting of waterways and erosion of soil, and the decimation of salmon populations, which provide the world's richest salmon fishery, worth billions of dollars annually.
Although the timber industry claims that logging maintains jobs in the Pacific Northwest, logging national forest often makes no economic sense. Because of the expense of building logging roads, surveying the area to be cut, and the low price it charges for trees, the USFS often loses money on its timber sales. As a result of such "deficit" or "below cost" timber sales between 1989 and 1992, the USFS lost an average of almost $300 million a year by selling timber from national forests.
Several private conservation groups, such as the Wilderness Society and the Sierra Club , are working to preserve the remaining ancient forests on BLM and USFS land through federal legislation, lawsuits, and other actions. In April 1993, President Bill Clinton attended a "timber sum mit" in Portland, Oregon, to discuss the ancient forests, endangered species , and timber jobs. But the cutting of old growth forests and "below cost" timber sales have continued much as before. The Bush administration has not supported environmental issues. In 2001, President Bush triggered international outrage when he refused to agree to the Kyoto Protocol, a United Nations approved plan to preserve the environment .
Two of the largest remaining temperate rainforests are Alaska's 16.9 million-acre (6.8 million ha) Tongass National Forest and the Russian Taiga . Tongass is the last large, relatively undisturbed, temperate rain forest in the United States, stretching over 600 mi (966 km) of coast along the Alaska Panhandle. It has the highest concentration of bald eagles and grizzly bears anywhere on Earth. In addition to reducing habitat for wildlife and salmon hatching, scenic areas are being destroyed, reducing tourism and recreation in the area.
The huge forests in the Russian Far East and Siberia are called the Taiga. The Siberian portion is the world's largest forest. Comprising some two million mi2 (5.1 million km2), the Taiga is much larger than the Brazilian Amazon and would cover the entire American lower 48 states. With Russia becoming more market-oriented and in desperate need of money, some have discussed selling the logging rights to some of these forests to American, Japanese, and Korean logging companies.
Pressure from environmentalists and increasing public concern for rain forests has encouraged world leaders to consider more environmental laws. In June 1992, at the United Nations Earth Summit conference in Rio de Janeiro, Brazil, a set of voluntary principles to conserve the world's threatened forests were agreed upon. The document affirms the right of countries to economically exploit forests but states that this should be done "on a sustainable basis," recognizing the value of forests in absorbing carbon dioxide and slowing climate change. Initial hope that the agreement on principles might eventually be turned into a binding international convention has evaporated, and throughout the world, forests continue to be destroyed. Some of the last remaining untouched forests are being opened up to poaching , logging, and other exploitation, such as the one million acre (405,000 ha) virgin Ndoke rainforest of the northern Congo Republic, a wildlife paradise full of thousand-yearold trees, along with elephants , leopards, gorillas, and other endangered species.
There is a small but positive sign of a much-needed change. In October 2001 Brazil suspended all trade in mahogany. The government's decision followed a two-year investigation by Greenpeace using ground, air, and satellite surveillance to document rampant illegal logging on Indian reservations and other protected wildlife areas. In addition, a report released in June 2002 showed that the rate of forest destruction of Brazil's Amazon jungle fell 13.4% from a five-year peak in 2000. However, the rate of destruction still deeply troubles environmentalists.
[Bill Asenjo Ph.D. ]
Caufield, C. In the Rainforest: Report From a Strange, Beautiful, Imperiled World. Chicago: University of Chicago Press, 1986.
Mitchell, G. J. World on Fire: Saving an Endangered Earth. New York: Charles Scribner's Sons, 1991.
Myers, N. The Sinking Ark: A New Look at Disappearing Species. Oxford: Pergamon Press, 1979.
Porritt, J. Save the Earth. Atlanta: Turner Publishing, 1991.
Raven, P. H. "The Cause and Impact of Deforestation." In Earth 88: Changing Geographic Perspectives. Washington, DC: National Geographic Society, 1988.
Repetto, R. The Forest for the Trees? Government Policies and the Misuse of Resources. Washington, DC: World Resources Institute, 1988.
Zuckerman, S. Saving Our Ancient Forest. Los Angeles: Living Planet Press, 1991.
Bugge, A. "Brazil's Amazon Destruction Down but Still Alarming." Reuters June 12, 2002.
Jordan, M. "Brazilian Mahogany: Too Much In Demand—Illegal Logging, Exports Are Lucrative for Criminals, Disastrous for Rain Forest." Wall Street Journal, November 14, 2001.
"United States Government Report Blames Humans for Global Warming." Reuters [cited July 2002]. <http://www.enn.com/news/wirestories/2002/06/06042002>.
"World Bank Forest Policy." World Rainforest Movement Bulletin 55 [cited February 2002]. <http://www.wrm.org.uy>.
The ethical and policy issues associated with rain forests are doubly related to technology and science: While technology has provided the tools for cutting down rain forests, science has produced knowledge about their importance that leads to the questioning of such practices.
If one compares maps of the world featuring maximum biodiversity, deserts, and desertification (for example, putting side by side Mittermeier et al., Hotspots , p. 19; the Encyclopedia of Deserts , inside cover; and the World Atlas of Desertification , pp. 44–45), the most striking feature is the proximity of maximum and minimum biodiversity in well-defined bands that circle the globe—because of the heat of the sun at the Equator and related atmospheric and climate effects. That is, the areas that contain the highest levels of biological diversity are almost all endangered to a high degree as well.
Kathlyn Gay (2001) introduces her summary of worldwide research and activism on rain forests by describing tropical rain forests as those close to the Equator and characterized by a minimum of 80 to 120 inches of rainfall per year that make up 6 percent of the surface of the Earth. These are found in parts of Central and South America, Africa, Asia, and the United States, with the best-known being in Amazonia. Others are located in Papua New Guinea, the islands of Madagascar, Malaysia, Thailand, Mexico, Colombia, and Ecuador. Gay's book covers temperate rain forests as well, such as those in the Pacific Northwest of the United States and Canada. With respect to either kind, tropical or temperate, the reason for researcher and activist interest is the impact of forests on climate, including precipitation, soil, and the carbon cycle so necessary for terrestrial life. Decimation of the rain forests would have a lasting impact on world climate, and would also affect winds, rainfall, and heat patterns, especially in the rich equatorial band around the globe.
Deforestation as Problem
Deforestation is a particularly difficult issue in certain areas. The best-known problem area is the Amazon rain forest. Susanna Hecht and Alexander Cockburn (1989) claim that Amazon deforestation is based in the policies of post-World War II Brazilian military governments. In 1964 Brazil began a massive interior settlement program that promoted forest clearing for cattle ranching. Much of the clearing also took place near gold strikes, since cattle grazing allows "large amounts of land—and the mineral rights below it—to be claimed with minimal labour" (Gay 2001, p. 46). Clearing also undermined rubber tapping in the forests, stimulating the rubber tapper Chico Mendes (1944–1988) to highlight the manifold social and environmental problems being created by deforestation (Burch 1994). His murder helped stimulate creation of the World Rainforest Movement (founded 1986) that has criticized the UN Food and Agricultural Organization (FAO) and World Bank support for national forest clearing initiatives (World Rainforest Movement 1992).
Focus on the human dimension of deforestation is further emphasized in Tropical Deforestation (1996), which makes the sweeping claim that "government management of forests often results in deforestation, whereas local community management of forests is usually more likely to contribute to forest conservation" (Sponsel, Headland, and Bailey 1996, p. xx) This broad conclusion is based on anthropological studies that detail work in Mayan Mexico, Polynesia, India, Kenya and other areas of Africa, the Philippines and New Guinea, as well as Madagascar, the Amazon, and other areas of Central and South America.
A more extensive discussion of the problem is provided by Sing Chew (2001), who traces ecological tragedies from 3000 b.c.e. to the year 2000 c.e., under a series of imperial regimes. Chew argues that in every case, from ancient Mesopotamia through Greece and Rome to the Portuguese and Spanish Empires and later European imperialism, deforestation was a constant concomitant of political aggrandizement and empire building—along with the continuing rise in population.
Few scholars challenge the link between government policies and deforestation. But some observers such as Bjørn Lomborg, while admitting that overexploitation may be taking place, nevertheless argue that the situation has been exaggerated. For instance, although in 1988 the Brazilian space agency announced that its satellites showed 7,000 fires destroying 2 percent of the Amazonian rain forest per year, subsequent corrections reduced this figure to 0.5 percent, and "in actual fact, overall Amazonian deforestation has only been about 14 percent" since humans arrived (Lomborg 2001, p. 114). Such figures raise important questions of scientific ethics and responsibility on many sides of this important issue.
A number of other scientists, especially environmental economists, argue that tree cutting—even timber harvesting on a large scale—can be managed sustainably. Eberhard Bruening, for example, maintains that it is possible "to mimic nature and utilize inherent ecosystem dynamics and indeterminism to improve self-sustainability and economic viability" (Bruening 1996,
p. x). Bruening is not overly optimistic that current managers and their government supporters can do this, but he thinks matters could change if community-orientedforestry were initiated or expanded. (In Bruening's opinion, it has begun in some places including Sarawak in Southeast Asia.) Others emphasize forest-related activities that may prove more profitable than cutting trees in rain forests. For example, Douglas Southgate (1998) discusses ecotourism and its successes in Costa Rica, along with that country's genetic prospecting agreements, debt-for-nature swapping, and offers to serve as a sink for other countries in carbon-sequestration trading deals. (Activity in Nicaragua and Guatamala underlie similarly optimistic assessments of profitable alternatives, as described at length by Olman Segura-Bonilla ).
In terms of science, technology, and ethics as related to rain forests (especially tropical rain forests), there is a broad consensus (represented here by Gay) that unethical forest management policies and practices have been implemented by governments since the Bronze Age. The science to support this claim, usually deforestation mapping from satellites, points to continuing tree cutting in spite of environmentalists' outrage—although the precise extent is contested. Indeed others argue that sustainable management (of tree cutting) is possible, even in tropical rain forests, provided that scientifically sound forest management practices are employed (Bruening 1996). Proponents of this theory also point to the ever-increasing demand for wood and wood products in the world economy, adding that rain forests can be economically productive in other ways—some even as alternatives to deforestation.
PAUL T. DURBIN
SEE ALSO Biodiversity;Deforestation and Desertification;Ecological Restoration;Ecology;Environmental Ethics;Environmentalism;Global Climate Change;Sierra Club;United Nations Environmental Program;Water.
Bruening, Eberhard F. (1996). Conservation and Management of Tropical Rainforests: An Integrated Approach to Sustainability. Wallingford, England: CAB International.
Burch, Joann Johnson. (1994). Chico Mendes, Defender of the Rainforest. Brookfield, CT: Millbrook.
Chew, Sing C. (2001). World Ecological Degradation: Accumulation, Urbanization, and Deforestation 3000 B.C.–A.D. 2000. Walnut Creek, CA: Alta Mira.
Gay, Kathlyn. (2001). Rainforests of the World, 2nd edition. Santa Barbara, CA: ABC-CLIO.
Hecht, Susanna, and Alexander Cockburn. (1989). The Fate of the Forest: Developers, Destroyers and Defenders of the Amazon. London: Verso.
Mares, Michael A., ed. (1999). Encyclopedia of Deserts. Norman: University of Oklahoma Press.
Middleton, Nick, and David Thomas, eds. (1997). World Atlas of Desertification, 2nd edition. London: Arnold.
Mittermeier, Russell A.; Norman Myers; Cristina Goettsch Mittermeier; and Patricio Robles Gil. (2000). Hotspots, CEMEX, Conservation International; and Chicago: University of Chicago Press.
Segura-Bonilla, Olman. (2000). Sustainable Systems of Innovation: The Forest Sector in Central America. Aalborg, Denmark: University of Aalborg.
Sponsel, Leslie E.; Thomas N. Headland; and Robert C. Bailey. (1996). Tropical Deforestation: The Human Dimension. New York: Columbia University Press.
World Rainforest Movement. (1992). Rainforest Destruction: Causes, Effects and False Solutions. Penang, Malaysia: Author.
Rain forests are ecosystems characterized by high annual precipitation and an abundance of many large trees, generally of very old age. (An ecosystem is an ecological community, or the plants, animals, and microorganisms in a region considered together with their environment.) Rain forests can be found in both tropical and temperate regions. (Temperate regions have mild or moderate climates; tropical regions have high enough temperatures and enough rain to support plant growth year round.) Rain forests require a humid climate, with an average precipitation of at least 80 to 100 inches (200 to 250 centimeters) per year. Because of the great amount of precipitation, forest fires occur only rarely. As a result, trees in a rain forest are able to grow to a very large size and a very old age.
Tropical rain forests
Tropical rain forests can be found in equatorial regions of Central and South America, west-central Africa, and Southeast Asia, including New Guinea and the northeastern coast of Australia. Tropical rain forests are the most complex of the world's ecosystems in terms of both their physical structure and the tremendous biodiversity of species they support. Because they support such a wide variety and number of plants, animals, and microorganisms, tropical rain forests represent the highest peak of ecosystem development on Earth.
Words to Know
Biomass: The sum total of living and once-living matter contained within a given geographic area.
Biodiversity: The wide range of organisms—plants and animals—that exist within any geographical location.
Canopy: The "covering" of a forest, consisting of the highest level of tree branches and foliage in the forest.
Ecosystem: An ecological community, including plants, animals, and microorganisms, considered together with their environment.
Old-growth forest: A mature forest, characterized by great age and many large and very old trees, with a complex physical structure.
Temperate: Mild or moderate.
Tropical: Characteristic of a region or climate that is frost free with temperatures high enough to support—with adequate precipitation—plant growth year round.
Productivity of tropical rain forests. Tropical rain forests have a very complex canopy, consisting of many layers of foliage (leaves) intertwined with each other. This canopy makes up one of the densest leafy surfaces found in any of Earth's ecosystems. The presence of so many leaves make it possible for tropical rain forests to capture solar energy and convert it to plant production with a high degree of efficiency.
In the tropical rain forests, woody tissues of trees account for about 80 percent of the biomass. (Biomass is the sum total of living and dead plants and animals.) Another 15 percent of the organic matter occurs in soil and litter (the uppermost, slightly decaying layer of organic matter on the forest floor), and about 5 percent is foliage. In contrast, a much larger fraction of the biomass in temperate forests occurs as organic matter in the soil and on forest floor. The reason for this difference is temperature. In tropical rain forests, dead biomass decays very rapidly because of warm and humid environmental conditions.
This fact explains a strange contradiction about tropical rain forests. In spite of the abundance of living and dead plants and animals they contain, they are very fragile environments. If trees are cut down, the vast majority of the forest's biomass is lost. In addition, the soil in tropical rain forests is generally not very fertile. When trees are removed, it is usually difficult to get other plants and crops to grow in the same place. The destruction of tropical rain forests in order to obtain land for agriculture, then, has had some surprising results. Very rich, productive stands of trees have been lost, but those stands have not been replaced by farms that are as rich. In fact, the land is often simply lost to any form of productive plant growing.
Biodiversity in tropical rain forests. An enormous number of species of plants, animals, and microorganisms occurs in tropical rain forests. In fact, this type of ecosystem accounts for a much larger fraction of Earth's biodiversity than any other category. Some scientists estimate that as many as 30 million to 50 million species may occur on Earth, and that about 90 percent of these species occur in tropical ecosystems, the great majority of those in rain forests.
Most of the undiscovered species are probably insects, especially beetles. However, tropical rain forests also contain immense numbers of undiscovered species of other arthropods (invertebrates with external skeletons), as well as many new plants and microorganisms. Even new species of birds and mammals are being discovered in tropical rain forests, further highlighting the fact that so much still is to be learned about that natural ecosystem.
Temperate rain forests
Temperate rain forests are most common on the windward sides of coastal mountain ranges. In such areas, warm, moisture-laden winds from the ocean are forced upwards over the mountains. There they cool, form clouds, and release their moisture as large quantities of rainfall. Temperate rain forests are found primarily along the west coasts of North and South America and in New Zealand.
Many types of temperate rain forests exist. In northern California, for example, coastal rain forests are often dominated by stands of enormous redwood trees more than 1,000 years old. Old-growth rain forests elsewhere on the western coast of North America are dominated by other conifer (cone-bearing) species, especially Douglas-fir, western hemlock, sitka spruce, red cedar, and fir. Rain forests also occur in wet, frost-free parts of the Southern Hemisphere adjacent to the ocean. In parts of New Zealand, for example, the most common tree species in temperate rain forests are southern beech and southern pines.
Most species that are found in temperate rain forests also live in younger forests. However, some important exceptions exist. For example, in temperate rain forests of the Pacific coast of North America, the spotted owl, marbled murrelet, and some species of plants, mosses, and lichens appear to require the special conditions provided by old-growth forests and do not survive well in other ecosystems.
[See also Biodiversity; Forestry; Forests ]
Tropical rain forests are large areas that are warm and wet throughout the year, and whose tall evergreen trees are so dense they form a canopy. As the richest ecosystem (an area in which living things interact with each other and the environment) on Earth, rain forests support such a diversity of life that at least half of all the world's species of plants and animals live there. Rain forests also play a role in the world's climate, and are among the most fragile ecosystems.
Most rain forests are located in the central region of Earth, near the equator, where temperatures typically range between 73° and 87°F (22.78°C and 30.56°C). Most receive some rain almost every day, averaging more than 100 inches (254 centimeters) a year, and sometimes twice that much. This rain is soaked up from the soil by the lush plants and enormous trees that then return it to the air via transpiration. Transpiration occurs in all plants as they naturally lose water vapor through their leaves.
At least half of this water released by plants falls back down again onto the rain forest as rain. Since all tropical rain forests lie near the equator, daylight lasts 12 hours throughout the year, and the steady warmth of
the land heats the air above it, causing it to rise and release its moisture (rain). Everything growing below is always green and flowers regularly.
LAYERS OF A RAIN FOREST
The largest rain forest is the Amazon in South America, and it is typical of what is called a tropical rain forest, as opposed to a temperate rain forest which is located in a cooler climate. A tropical rain forest like the Amazon is a complex system that can be divided into different horizontal layers (like floors in an apartment building). As with an apartment building, there are different things going on at different levels.
Forming the topmost layer are the tallest of the rain forest's trees. Able to sometimes grow as high as a football field is long, these giants are scattered throughout the forest. The next level or layer is called the canopy, because it shades everything below. This green roof is created by a dense thicket of trees that stand between 60 and 150 feet (18.29 and 45.72 meters) high and whose branches and leaves are so close together that they form an umbrella over the rest of the forest below. These trees grow so tightly that rainfall reaches the ground only by running down the tree trunks or the stems of other plants. The canopy is alive with animal life as well, such as iguanas, tree frogs, monkeys, and bats.
The next section is called the understory and includes smaller trees, ferns, vines and palms, and smaller bushes. Since the canopy traps and holds much of the heat and moisture, the understory is extremely hot and humid. It also does not have many flowering plants because of the lack of direct sunlight. The bottom level, or the forest floor, is covered with shade-loving mosses, herbs, and fungi, as well as dead plants and animals. The forest floor receives only 2 percent of the sunlight needed for photosynthesis (the process by which plants use light energy to make food). Dead material on the forest floor decomposes very quickly, thus providing nutrients to the soil and everything that grows in it. Masses of insects and the animals that feed on them, like the anteater, also live on the forest floor. Many of these animals, like bats, mice and rats, and porcupines, are nocturnal or active only at night. Some, like monkeys and apes, are busy during the day, while still others, like large cats and wild dogs, are most active at dusk and dawn.
PLANT LIFE IN THE RAIN FOREST
No other biome (a particular type of large geographic region) on Earth can match the tropical rain forest for its diversity of plant and animal species. All of these species, however, have the same thing in common. As rain forest dwellers, they all have adapted in many ways to life in this special ecosystem. One example of plant adaptation is a tree's buttresses or "prop roots" that spread out above ground and help support the tree in the shallow, unstable soil of the forest floor. Other trees often grow stilt roots or "air roots" which grow out from its trunk as high up as 10 to 12 feet (3.0 to 3.66 meters) and help spread the weight of the tree over a wider area.
Leaf structure is also highly adapted. Some leaves have what are called "drip tips"—a special shape that helps rainwater and condensation run off easily. This allows the leaf to breathe better. Other plants called epiphytes grow on or in trees and never actually touch the soil.
ANIMAL LIFE IN THE RAIN FOREST
Animal life in the rain forest is equally adapted and strange and fascinating. The vast majority of all species are insects, although there are twice as many mammals and birds in its tropical environment as there are in temperate zones. South America is especially rich in birds, bats, and fishes. Rain forest species often have spectacular shapes, colors, or sizes. These include the huge-billed toucan, the brilliantly colored American butterfly with a wingspan of nearly 8 inches (20.32 centimeters), the huge, scary-looking fruit bat, the goliath frog that can weigh as much as 33 pounds (14.98 kilograms), and the bizarre-looking anteater. These are but a few of the thousands of exotic life forms that crawl, slither, hop, fly, and teem about in the tropical rain forest.
CONSEQUENCES OF RAIN FOREST DESTRUCTION
Despite this great diversity and obvious abundance of life, tropical rain forests can be easily and severely damaged, and they take an extremely long time to recover. Their soil is usually ancient and poor in minerals that are mostly bound up in the incredible amounts of vegetation it has to support. Although rain forests are highly productive ecosystems, this productivity is based on the constant sunlight and steady rains, and not on rich, thick soil. When trees are cut down and burned in a typical practice called "slash and burn," the landscape suffers severely. This is usually done to clear the land for farming and roadbuilding. Logging also clears large areas. When this occurs, the thin soil is exposed and the steady rains wash it away, leaving behind "wet deserts" and causing devastating floods. An area twice the size of Maine is cleared this way every year, and with it often go the unique plants and animals it supported.
Rain forest destruction means not only plant and animal extinction because of habitat loss but possibly an increase in the "greenhouse effect" as fewer trees exist to absorb the increasing amounts of carbon dioxide people produce. This causes Earth's atmosphere to trap too much heat and could lead to global warming.
rain for·est (also rain·for·est) • n. a luxuriant, dense forest rich in biodiversity, found typically in tropical areas with consistently heavy rainfall.