Humans are creatures of the forest. Until humans learned to hunt, they gathered their food and made their dwellings among the trees of the forests. Humans and the great forests evolved together, and our lives and theirs are forever intertwined.
Forests have an important impact on the environment as a whole. From the earliest times, forests have provided food and shelter, a place to hide from predators, and many useful products.
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. However, this oxygen must be replaced, or life on Earth could not continue. Animals breathe in (inhale) oxygen and breathe out (exhale) carbon dioxide. Tress convert this carbon dioxide into oxygen during photosynthesis, releasing the oxygen into the atmosphere through their leaves. In an effort to understand forests' full impact on the oxygen cycle, a global research project to measure the overall influence of forests on the Earth's atmospheric balance is underway.
The carbon cycle: Carbon dioxide is also necessary to life, although too much is harmful. During photosynthesis, trees pull carbon dioxide from the air. By doing so they help to 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 the 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 gradually trickle down into the Earth to feed streams and groundwater. In this way, forests help conserve water and protect the soil from the erosion caused by heavy rain. When forests are cut down, the soil washes away and flooding is more common. For example, during the 1980s, villagers in the African country of Rwanda cleared so much forest that their supply of freshwater dried up.
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 back to the soil making them available for other plants and animals to use.
Forests are the home of game animals, such as birds, which 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 South American rain forests; nutmeg and cloves come from Asian rain forests; cocoa and coffee beans are products of Central America; and starfruits grow in Asia. It is estimated that rain forests contain more than 4,000 species of edible fruits and vegetables, and only a few of these have been cultivated for commercial use. With correct management, however, these species might yet provide enough food to feed a hungry world.
During prehistoric times, humans lived in the forest because it offered protection. Those native peoples who still live in the rain forest continue to depend upon it for shelter. Trees provide building materials. Trunks can be 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. However, these names can be confusing because some softwood trees, such as the yew, produce woods that are harder than many hardwoods. And some hardwoods, such as balsa, are softer than most softwoods.
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, which is 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.
Nearly all the hardwoods used commercially come from tropical forests. Countries that cut and sell their wood include Brazil, Burma, Colombia, Indonesia, Malaysia, and Thailand.
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, however, it is abandoned.
Since the earliest times, plants have been used for their healing properties. It is estimated that at least 1,400 tropical plants may contain substances active against cancer. Quinine, from the cinchona tree, and curare, from the bark of a jungle vine and a deadly poison in its natural form, are both used as the basis for important drugs. Many drug companies maintain large tracts of forest as part of their research programs.
Tannins are chemical substances found in the bark, roots, seeds, and leaves of many plants and 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, while 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.
While forests have had a positive effect on human life, human life has had a mostly negative impact on forests. Nearly 2,000,000,000 tons (1,814,000,000 metric tons) of timber are cut from the world's forests each year. Most of the loss of forests have occurred in developing nations where wood is used for fuel and where trees are cleared away for farming. A vast number of trees are also lost each year to commercial use.
In tropical regions, much forest land is being lost as populations grow and want the land for farms and cattle pasture. "Slash and burn" agriculture is practiced in which the trees are cut and burned. Rain forests are disappearing at the rate of 26,923 square miles (70,000 square kilometers) each year. According to some estimates, more than 100 species of plants and animals, most of them insects, become extinct every week as a result. 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—the cutting down of every tree in an area—cheaper and more efficient than selecting only certain trees for harvesting. Unfortunately, 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 its habitat.
Destruction of the forests does not mean just loss of their beauty and the products they provide. Water quality also suffers. Because the trees are gone, rain no longer seeps into the soil but runs off, and underground water reserves are not replaced. Topsoil is eroded away. This soil often ends up in streams and rivers, and 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. Air pollution is also helping to destroy forests, some of which take on a sickly appearance in polluted environments.
With the popularity of the automobile, carbon dioxide and other undesirable gases have built up in the atmosphere. Some scientists believe that these gases are helping to raise the temperature of the Earth's climate (the greenhouse effect). Because forests help remove carbon dioxide from the air, cutting them down may be helping to cause global warming. If the Earth grows warmer, many species of plants and animals could become extinct.
Most rain forests grow in undeveloped countries, which need forest resources for economic reasons. Since 1945, more than 40 percent of the world's rain forests have been cut, and another 10 percent are expected to be lost by the year 2000. However, 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.
True jungle peoples have been found in all the major rain forests of the world, some of whom include the Birhor of central India, the Veddas of India and Sri Lanka, the Senoi Semai and Santu Sakai of Central Malaya, the Tapiros of New Guinea, the Penans of Borneo, the Tasaday of the Philippines, the Xingu of Brazil, the Batak of central Africa, the Bambuti of the Ituri forest of the Congo, the Siriono of Bolivia, and the Yumbri (Ghosts of the Yellow Leaves) of Thailand.
In general, forest dwellers tend to be small in stature, the men no more than 59 inches (150 centimeters) tall and the women even shorter. They are also usually hunter-gatherers who make few changes in the forest environment. However, changes other people are making may destroy their way of life. Before Europeans arrived in South America, for example, about 4,000,000 Indians lived in the Amazon region. Today, fewer than 100,000 survive.
The Bambuti (also called the Twides, the Aka, or the Efe) are the shortest people of Africa, averaging about 54 inches (137 centimeters) in height. They are nomads (wanderers) who live in small family groups of 10 to 25 people. Their huts are made of stick frames covered by leaves, which they live in for about 30 days and then abandon.
The rain forest provides them with all their needs: food, water, wood for fires, and clothing. They hunt with bows and arrows, nets, and spears.
A study of the Bambuti was made by anthropologist Colin Turnbull and is described in his book The Forest People: A Study of the Pygmies of the Congo.
The Siriono of eastern Bolivia live in the rain forest of the Amazon basin in South America. These nomadic people wear no clothing but decorate their bodies with paint and feathers. The men hunt or fish, and their huts are made of poles covered by leaves. Because they have no method of preserving food, starvation is always a threat.
The Yumbri live in the jungles of Thailand near the border of Laos. Until the 1930s, rumors of their existence were not taken seriously, especially since other Thai peoples referred to them as the Pi Tong Luang—Ghosts of the Yellow Leaves. At that time, they numbered only about 300. They never stay more than one night in any location, and they have no weapons with which to defend themselves. With no weapons, they cannot hunt, and the only meat they eat is that left over from the kill of a leopard or tiger. They survive on fruit, root vegetables, berries, nuts, and insects.
Source: "Rain Forest." U·X·L Encyclopedia of Biomes, Vol. 2. U·X·L, Detroit: 2000.