Forests provide lumber for buildings, wood fuel for cooking and heating, and raw materials for making paper, latex rubber, resin, dyes, and essential oils. Forests are also home to millions of plants and animal species and are vital in regulating climate, purifying the air, and controlling water run-off.
A 1993 global assessment by the United Nations Food and Agriculture Organization (FAO) found that three-fourths of the forests in the world still have some tree cover, but less than one-half of these have intact forest ecosystems. Deforestation is occurring at an alarming rate, and management practices are being sought to try to halt this destruction.
Thousands of years ago, forests and woodlands covered almost 15 billion acres of the earth. Approximately 16 percent of the forests have been cleared and converted to pasture, agricultural land, cities, and nonproductive land. The remaining 11.4 billion acres of forests cover about 30 percent of the earth’s land surface.
Clearing forests has severe environmental consequences. It reduces the overall productivity of the land, and nutrients and biomass stored in trees and leaf litter are lost. Soil once covered with plants, leaves, and snags becomes prone to erosion and drying.
When forests are cleared, habitats are destroyed and biodiversity is greatly diminished. Destruction of forests causes water to drain off the land instead of being released into the atmosphere by transpiration or percolation into groundwater.
This can cause major changes in the hydrologic cycle and ultimately in the earth’s climate. Because forests remove a large amount of carbon dioxide from the air, the clearing of forests causes more carbon dioxide to remain, thus up setting the delicate balance of atmospheric gases.
Rain forests provide habitats for at least 50 percent (some estimates are as high as 90 percent) of the total stock of plant, insect, and other animal species on earth. They supply one-half of the world’s annual harvest of hardwood and hundreds of food products, such as chocolate, spices, nuts, coffee, and tropical fruits.
Tropical rain forests also provide the main ingredients in 25 percent of prescription and nonprescription drugs, as well as 75 percent of the three thousand plants identified as containing chemicals that fight cancer. Industrial materials, such as natural latex rubber, resins,dyes, and essential oils, are also harvested from tropical forests.
Tropical forests in Asia, Africa, and Latin America are rapidly being cleared to produce pastureland for large cattle ranches, establish logging operations, construct large plantations, grow narcotic plants, develop mining operations, or build dams to provide power for mining and smelting operations.
In 1985 the FAO’s Committee on Forest Development in the Tropics developed the Tropical Forestry Action Plan to combat these practices, develop sustainable forest methods, and protect precious ecosystems. Fifty nations in Asia, Africa, and Latin America have adopted the plan.
Several management techniques have been successfully applied to slow the destruction of tropical forests. Sustainable logging practices and reforestation programs have been established on lands that allow timber cutting, with complete bans of logging on virgin lands.
Certain regions have set up extractive reserves to protect land for the native people who live in the forest and gather latex rubber and nuts from mature trees. Sections of some tropical forests have been preserved as national reserves, which attract tourists while preserving trees and biodiversity.
Developing countries have been encouraged to protect their tropical forests by using a combination of debt-for-nature swaps and conservation easements. In debt-for-nature swaps, tropical countries act as custodians of the tropical forest in exchange for foreign aid or relief from debt.
Conservation easement involves having another country, private organization, or consortium of countries compensate a tropical country for protecting a specific habitat.
Another management technique involves putting large areas of the forest under the control of indigenous people who use slash-and-burn agriculture (also known as swidden or milpa agriculture). This traditional, productive form of agriculture follows a multiple-year cycle.
Each year farmers clear a forest plot of several acres in size to allow the sun to penetrate to the ground. Leaf litter, branches, and fallen trunks are burned, leaving a rich layer of ashes. Fast-growing crops, such as bananas and papayas, are planted and provide shade for root crops, which are planted to anchor the soil.
Finally, crops such as corn and rice are planted. Crops mature in a staggered sequence, thus providing a continuous supply of food. Use of mixed perennial polyculture helps prevent insect infestations, which can destroy monoculture crops.
After one or two years, the forest begins to take over the agricultural plot. The farmers continue to pick the perennial crops but essentially allow the forest to reclaim the plot for the next ten to fifteen years before clearing and planting the area again.
Slash-and-burn agriculture can, however, post hazards: A drought in Southeast Asia in 1997 caused fires to burn for months when monsoon rains did not materialize, polluting the air and threatening the health of millions of Indonesians. In 1998, previous abuse of the technique resulted in flooding and mudslides in Honduras after the onset of Hurricane Mitch.
U.S. Forest Management
|U.S. Forest Management|
Forest Service provides inexpensive grazing lands for more than three million cattle and sheep every year, supports multimillion-dollar mining operations, and consists of a network of roads eight times longer than the U.S. interstate highway system.
Almost 50 percent of national forest land is open for commercial logging. Nearly 14 percent of the timber harvested in the United States each year comes from national forest lands.
Total wood production in the United States has caused the loss of more than 95 percent of the old-growth forests in the lower forty-eight states. This loss includes not only high-quality wood but also a rich diversity of species not found in early-growth forests.
National forests in the United States are required by law to be managed in accordance with principles of sustainable yield. Congress has mandated that forests be managed for a combination of uses, including grazing, logging, mining, recreation, and protection of watersheds and wildlife.
Healthy forests also require protection from pathogens and insects. Sustainable forestry, which emphasizes biological diversity, provides the best management.
Other management techniques include removing only infected trees and vegetation, cutting infected areas and removing debris, treating trees with antibiotics, developing disease-resistant species of trees, using insecticides and fungicides, and developing integrated pest management plans.
Two basic systems are used to manage trees: even-aged and uneven-aged. Even-aged management involves maintaining trees in a given stand that are about the same age and size. Trees are harvested, then seeds are replanted to provide for a new even-aged stand.
This method, which tends toward the cultivation of a single species or monoculture of trees, emphasizes the mass production of fast-growing, low-quality wood (such as pine) to give a faster economic return on investment. Even-aged management requires close supervision and the application of both fertilizer and pesticides to protect the monoculture species from disease and insects.
Uneven-aged management maintains trees at many ages and sizes to permit a natural regeneration process. This method helps sustain biological diversity, provides for long-term production of high-quality timber, allows for an adequate economic return, and promotes a multiple-use approach to forest management.
Uneven-aged management also relies on selective cutting of mature trees and reserves clear-cutting for small patches of tree species that respond favorably to such logging methods.
The use of a particular tree-harvesting method depends on the tree species involved, the site, and whether even-aged or uneven-aged management is being applied.
Selective cutting is used on intermediate-aged or mature trees in uneven-aged forests. Carefully selected trees are cut in a prescribed stand to provide for a continuous and attractive forest cover that preserves the forest ecosystem.
Shelter wood cutting involves removing all the mature trees in an area over a period of ten years. The first harvest removes dying, defective, or diseased trees.
This allows more sunlight to reach the healthiest trees in the forest, which will then cast seeds and shelter new seedlings. When the seedlings have turned into young trees, a second cutting removes many of the mature trees. Enough mature trees are left to provide protection for the younger trees.
When the young trees become well established, a third cutting harvests the remaining mature trees, leaving an even-aged stand of young trees from the best seed trees to mature. When done correctly, this method leaves a natural-looking forest and helps reduce soil erosion and preserve wildlife habitat.
Seed-tree cutting harvests almost every tree at one site, with the exception of a few high-quality seed-producing and wind-resistant trees, which will function as a seed source to generate new crops. This method allows a variety of species to grow at one time and aids in erosion control and wildlife conservation.
Clear-cutting removes all the trees in a single cutting. The clear-cut may involve a strip, an entire stand, or patches of trees. The area is then replanted with seeds to grow even-aged or tree-farm varieties.
More than two-thirds of the timber produced in the United States, and almost one-third of the timber in national forests, is harvested by clear-cutting. A clear-cut reduces biological diversity by destroying habitat. It can make trees in bordering areas more vulnerable to winds and may take decades to regenerate.
Forest fires can be divided into three types: surface, crown, and ground fires. Surface fires tend to burn only the undergrowth and leaf litter on the forest floor. Most mature trees easily survive, as does wildlife.
These fires occur every five years or so in forests with an abundance of ground litter and help prevent more destructive crown and ground fires. Such fires can release and recycle valuable mineral nutrients, stimulate certain plant seeds, and help eliminate insects and pathogens.
Crown fires are very hot fires that burn both ground cover and tree tops. They normally occur in forests that have not experienced fires for several decades. Strong winds allow these fires to spread from dead wood and ground litter to treetops. They are capable of killing all vegetation and wildlife, leaving the land prone to erosion.
Ground fires are more common in northern bogs. They can begin as surface fires but burn peat or partially decayed leaves below the ground surface. They can smolder for days or weeks before anyone notices them, and they are difficult to douse.
Natural forest fires can be beneficial to some plant species, including the giant sequoia and the jack pine trees, which release seeds for germination only after being exposed to intense heat.
Grassland and coniferous forest ecosystems that depend on fires to regenerate are called fire climax ecosystems. They are managed for optimum productivity with prescribed fires.
The Society of American Foresters has begun advocating a concept called new forestry, in which ecological health and biodiversity, rather than timber production, are themain objectives of forestry.
Advocates of new forestry propose that any given site should be logged only every 350 years, wider buffer zones should be left beside streams to reduce erosion and protect habitat, and logs and snags should be left in forests to help replenish soil fertility. Proponents also wish to involve private landowners in the cooperative management of lands.