Tropical rainforests are broad-leafed evergreen woodlands that receive at least 100 inches of rain annually. Rainforests once covered about 5 billion acres in the tropics. As a result of human interference, only half of the original rainforests exist today. Nevertheless, they are home to at least 5 to 10 million species of plants and animals approximately one half of Earth's life forms. Remaining rainforests are disappearing at a rate of 100 acres per minute an area the size of Kansas every year.
Many natural resources and much of our food come from tropical rainforests. Rainforests serve as a genetic pool for many fruits and vegetables, and new varieties continue to be discovered. Only 1 percent of the tropical rainforest plants that have been identified have been scientifically analyzed, yet they are the source of more than a quarter of the medical compounds sold on the market today.
Nearly the entire acreage of tropical rainforests lies within the borders of developing countries. Often the governments of these countries are encouraged to exploit the resources of their forests to pay off foreign loans. External financial pressures have forced them to sacrifice long-term sustainability to service short-term national debt. Population growth and inequitable distribution of land have further contributed to the problem.
Each year millions of acres of tropical rainforests are burned to make way for agriculture, much of it for export. The nutrients of the rainforest are stored in its multi-layered canopy. When forests are burned, these nutrients mix with the barren topsoil, where they are quickly eroded by rain. When the land is depleted of nutrients, the farmer moves on and clears more rainforest.
In Central America the primary motive for clearing rainforest is to make way for cattle ranching. Most of the beef, however, is produced for export to developed countries to be used by fast food restaurants. Over 120 million pounds of beef are imported by the United States from Central America annually.
According to the World Bank and the United Nations Development Programme, at least 12.5 million acres of tropical rainforest are logged every year. Much of this lumber is exported for use in furniture and other hardwood products. Teak, mahogany, rosewood, purpleheart and ramin are some of the more common tropical hardwoods imported by developed countries. The United States imports about 15 percent of the world's hardwood products.
Many acres of rainforest are flooded each year as a result of large hydroelectric projects built to provide energy for large metropolitan areas and for multinational industrial projects. As a result of these hydroelectric projects, thousands of indigenous peoples who have relied upon the sustenance of the rainforests for thousands of years have been relocated, and their cultures destroyed.
Clearing tropical rainforests means destruction of habitat for the millions of species of plants and animals that live in these regions. Furthermore, forests act as a natural sink for carbon dioxide the major "greenhouse" gas responsible for global warming. As rainforests are destroyed, carbon dioxide is released into the atmosphere, leading to higher global temperatures. Scientists predict that as global temperatures rise we will face an increase in crop failure, oceans will rise and flood coastal areas, and many species of plants and animals will become extinct.
Two-thirds of the world's fresh water, excluding that which is locked in the polar ice caps, is cycled within tropical rainforest systems. Rainforests absorb this large amount of water, releasing it slowly and evenly through the process of evapotranspiration. But as rainforests are cleared, soils become exposed to heavy rain, leading to flooding and erosion. It is often impossible to re-establish a rainforest once it has been cleared.
STS Actions.
• Provide students with a map of the world and ask them to identify the location of at least one tropical rainforest. Tell them that about 50 acres of rain forest are destroyed each minute (almost 27 million acres per year, equal in size to the state of Pennsylvania). What impact could this deforestation have on:
1. Earth's temperature2. Animal and plant extinction
3. Amount of carbon dioxide in the atmosphere
4. Quality of life for people in the tropics.
• Engage students in a debate regarding this statement made by Randy Hayes, Executive Director, Rainforest Action Network: "We believe that tropical rainforests are one of the most important global ecological issues of our time. These forests are a vital part of the life support systems of the planet. To ensure their survival is to ensure our own survival. If we don't act now they could be gone by the year 2050. We may be the last generation that will have a chance to save the rainforests."