For millennia humans have left their mark on the world's forests, although it was difficult to see. By the twenty-first century, however, forests that humans once thought were endless are shrinking before their eyes. Forests are not only a source of timber; they perform a wide range of social and ecological functions. They provide a livelihood for forest dwellers, protect and enrich soils, regulate the hydrologic cycle, affect local and regional climate through evaporation, and help stabilize the global climate. Through the process of photosynthesis they absorb carbon dioxide (CO2) and release the oxygen humans and animals breathe. They provide habitat for half of all known plant and animal species, are the main source of wood for industrial and domestic heating, and are widely used for recreation.
Forests are attractive and accessible sources of natural wealth. They are not, however, unlimited. Deforestation is caused by farmers, ranchers, logging and mining companies, and fuel wood collectors. Governments have often encouraged the settlement of land through cheap credit, land grants, and the building of roads and infrastructure. Much of these activities led to the destruction of forests, causing some governments to reverse their policies.
Forests play a particularly crucial role in the global cycling of carbon. The Earth's vegetation contains two trillion tons of carbon, roughly triple the amount stored in the atmosphere. When trees are cleared, the carbon they contain is oxidized and released into the air, adding to the atmospheric store of carbon dioxide. Many scientists believe that carbon dioxide contributes to global warming.
This release happens slowly if the trees are used to manufacture lumber or are allowed to decay naturally. If they are burned as fuel, however, or in order to clear forestland for farming, almost all of their carbon is released rapidly. The clearing for agriculture in North America and Europe has largely stopped, but the burning of tropical forests has taken over the role of producing the bulk of carbon dioxide added to the atmosphere by land use changes.
A 1995 National Oceanic and Atmospheric Administration (NOAA) study found that about half the carbon dioxide emitted by burning fossil fuels is absorbed by plants in the Northern Hemisphere. The finding showed that plants play a role about equal to that of oceans, to which most of the absorption had previously been attributed. The study showed that plants absorb carbon dioxide that is rich in the carbon isotope 12, or C12, while ocean water absorbs C12 and C13 equally. By determining the ratios of the isotopes, scientists can determine the relative effects of oceans and plants on the atmosphere's carbon dioxide concentration.
Rising Pressures on Forests
According to Janet N. Abramovitz in Taking a Stand: Cultivating a New Relationship with the World's Forests (Washington, DC: Worldwatch Institute, 1998), the Worldwatch Institute, an independent, nonprofit environmental research organization, reported that between 1980 and 1995 alone at least 494 million acres of forests vanished—an area larger than Mexico.
According to the United Nations Food and Agriculture Organization (FAO), approximately half the wood cut worldwide is used for fuel and charcoal. Most fuel wood is used in developing countries. In dry countries such as India, the majority of trees cut are for fuel; in moist tropical areas such as Malaysia, most trees are cut for industrial timber.
Tropical Rain Forests
Tropical forests are the most "alive" places on Earth. Although they cover less than 2 percent of the Earth's surface, they are home to as many as 30 million species of plants and animals—more than half of all life forms on the planet. A single acre of tropical rain forest supports 60 to 80 tree species and an enormous number of vines and mosses.
Rain forests also play an essential role in the weather. They absorb solar energy, which affects wind and rainfall worldwide. Regionally, they reduce erosion and act as buffers against flooding. Tropical trees contain huge amounts of carbon which, when they are destroyed, is released into the atmosphere as carbon dioxide.
Of roughly 3,000 plants identified as having cancer-fighting properties, 70 percent grow in the rain forests. One of every three species of birds in the world nest there. In addition to wildlife, more than 1,000 indigenous tribes still survive in tropical forests, just as they have for thousands of years.
The Natural Resources Defense Council (NRDC), a private organization that supports environmental health, reports that nearly half of the forests on the planet have been decimated and every year more than 30 million acres of tropical forests and woodlands are destroyed for agriculture or logging. Exacerbating this problem, global wood consumption is set to double over the next 30 years, according to the NRDC, further stressing the survival of global forests..
In Combined Summaries: Technologies to Sustain Tropical Forest Resources and Biological Diversity (Washington, DC: U.S. Government Printing Office, 1992) the now-defunct U.S. Office of Technology Assessment concluded that the major underlying cause of deforestation and species extinction is the lack of alternative employment for the growing populations of tropical countries. Logging and the conversion of forestland to short-term, usually unsustainable, agricultural use results in destruction of the land, declining fisheries, erosion, and flooding.
Species in tropical rain forests possess a high degree of mutuality, in which two species are completely dependent on one another for survival; for example, a species of wasp and a species of fig tree. Such relationships are believed to evolve as a result of the relatively constant conditions in the tropics. Any species dependent on trees therefore becomes imperiled when a tree is cut down.
THE AMAZON—AN EXAMPLE.
The Amazon rain forests, located in South America, are the most famous of the Earth's tropical forests. They serve as a good example of the controversies surrounding rain forests worldwide. This controversy generally centers on the interest of environmentalists (often from developed countries) in stabilizing the environment and the developing world's basic need to cut down its forests for fuel and livelihood. Most developing nations claim that these needs are too great to be set aside for the sake of the environment. They also resent the industrialized world's disdain of practices the developed countries once followed themselves in building their own nations. These poorer, developing countries also wonder why they are expected to pay for the cleanup of a world that they did not contaminate.
There are also international incentives for continuing to cut down the rain forests. Foreign countries, especially Asian nations, are increasingly eyeing the Amazon forests as a source of ancient trees to make plywood, ornamental moldings, and furniture. Granting logging rights to these nations may seem an appealing option for those South American countries desperate for money.
Based on studies of satellite photographs taken over the Amazon, researchers believe that as much as 10 percent of the original Amazon forest has been destroyed,
Location of protected forest and other forest in the United States, 2001
mainly through "slash and burn" methods of clearing land that are used to convert the land to farming use. The cleared land's productivity usually decreases within a few years, and farmers often have to abandon the fields and move on—slashing and burning a new area.