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Forest - is a large area of land covered with trees. But a forest is much more than just trees. It also includes smaller plants, such as mosses, shrubs, and wildflowers. In addition, many kinds of birds, insects, and other animals make their home in the forest. Millions upon millions of living things that can only be seen under a microscope also live in the forest. Climate, soil, and water determine the kinds of plants and animals that can live in a forest. The living things and their environment together make up the forest ecosystem. An ecosystem consists of all the living and nonliving things in a particular area and the relationships among them. The forest ecosystem is highly complicated. The trees and other green plants use sunlight to make their own food from the air and from water and minerals in the soil. The plants themselves serve as food for certain animals. These animals, in turn, are eaten by other animals. After plants and animals die, their remains are broken down by bacteria and other organisms, such as protozoans and fungi. This process returns minerals to the soil, where they can again be used by plants to make food. Although individual members of the ecosystem die, the forest itself lives on. If the forest is wisely managed, it provides us with a continuous source of wood and many other products. Before people began to clear the forests for farms and cities, great stretches of forestland covered about 60 per cent of the earth's land area. Today, forests occupy about 30 per cent of the land. The forests differ greatly from one part of the world to another. For example, the steamy, vine-choked rain forests of central Africa are far different from the cool, towering spruce and fir forests of northern Canada.Forests have always had great importance to people. Prehistoric people got their food mainly by hunting and by gathering wild plants. Many of these people lived in the forest and were a natural part of it. With the development of civilization, people settled in cities. But they still went to the forest to get timber and to hunt. Today, people depend on forests more than ever, especially for their (1) economic value, (2) environmental value, and (3) enjoyment value. The science of forestry is concerned with increasing and preserving these values by careful management of forestland. Economic value.

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Forests supply many products. Wood from forest trees provides lumber, plywood, railroad ties, and shingles. It is also used in making furniture, tool handles, and thousands of other products. In many parts of the world, wood serves as the chief fuel for cooking and heating. Various manufacturing processes change wood into a great number of different products. Paper is one of the most valuable products made from wood. Other processed wood products include cellophane, plastics, and such fibers as rayon and acetate. Forests provide many important products besides wood. Latex, which is used in making rubber, and turpentine come from forest trees. Various fats, gums, oils, and waxes used in manufacturing also come from trees. In some primitive societies, forest plants and animals make up a large part of the people's diet. Unlike most other natural resources, such as coal, oil, and mineral deposits, forest resources are renewable. As long as there are forests, people can count on a steady supply of forest products. Environmental value. Forests help conserve and enrich the environment in several ways. For example, forest soil soaks up large amounts of rainfall. It thus prevents the rapid runoff of water that can cause erosion and flooding. In addition, rain is filtered as it passes through the soil and becomes ground water. This ground water flows through the ground and provides a clean, fresh source of water for streams, lakes, and wells. Forest plants, like all green plants, help renew the atmosphere. As the trees and other green plants make food, they give off oxygen. They also remove carbon dioxide from the air. People and nearly all other living things require oxygen. If green plants did not continuously renew the oxygen supply, almost all life would soon stop. If carbon dioxide increases in the atmosphere, it could severely alter the earth's climate. Forests also provide a home for many plants and animals that can live nowhere else. Without the forest, many kinds of wildlife could not exist. Enjoyment value. The natural beauty and peace of the forest offer a special source of enjoyment. In the United States, Canada, and many other countries, huge forestlands have been set aside for people's enjoyment. Many people use these forests for such activities as camping, hiking, and hunting. Others visit them simply to enjoy the scenery and relax in the quiet beauty.Human activities have had tremendous impact on modern forests. Since agriculture began about 11,000 years ago, large forest areas have been cleared for farms and cities. Beginning in the 1800's, great expanses of forest have also been eliminated because of logging and industrial pollution. The destruction and degrading of forests is called deforestation. Severe deforestation now occurs around the world, even in the most remote rain forests and boreal forests. Until the late 1940's, rain forests covered about 8.7 million square miles (22.5 million square kilometers) of the earth's land. Today, they cover less than half that area. Millions of acres or hectares of rain forests are destroyed each year. Since 1800, huge areas of temperate forests have also been cleared. Many parts of eastern North America, for example, have less than 2 percent of even degraded forests remaining. Industrial pollution is a chief cause of deforestation. Factories often release poisonous gases into the air and dangerous wastes into lakes and rivers. Air pollutants may combine with rain or other precipitation and fall to earth as acid rain. Acid rain and polluted bodies of water can restrict plant growth or even kill most plants in a forest. Massive deforestation has made many remaining forest tracts small, isolated islands. As forests become smaller, their ability to sustain the full variety of plant species decreases. Many forests are so seriously degraded by logging activities that they fail to regenerate replacement forests. Loss of forests has helped create many ecological problems. For example, rain water normally trapped by the forests is causing more floods around the world. In addition, as forest areas decrease or degrade, the production of oxygen from photosynthesis also decreases. Oxygen renewal is vital to the survival of oxygen-breathing organisms. At the same time, as less carbon dioxide is taken up by photosynthesis, the amounts of carbon dioxide released into the air increases. Thus more heat from the sun is trapped near the earth's surface instead of being reflected back into space. Many scientists believe that this greenhouse effect is causing a steady warming that could lead to threatening climatic conditions.
The destruction of forest ecosystems also destroys the habitats of many living creatures. Countless species of animals and plants have been wiped out by deforestation, and more are killed each year at an increasing rate. To combat these problems, people and governments have been seeking out and protecting old growth forests that remain undisturbed by humans. Such protection enables scientists to conduct long-term research on how old growth forests sustain the variety of plants and animals that live there.