Forest Management and Harvesting Trees

When forests are managed, their species composi­tion and other characteristics are altered. Specific varieties of trees are planted, not only to conserve the forest in areas where trees have been removed by fire or commercial harvest, but to prevent soil erosion and preserve watersheds. Forest manage­ment also includes thinning out or removing tree' that are not as commercially desirable.

Forest management often results in low-diversity forests. In the southeastern United States, for example, forests of young pine that are grown for timber and paper production are all the same age and are planted in rows a fixed distance apart. These forests are essentially monocul­tures—areas covered by one crop, like a field of corn. One of the disadvantages of monocultures is that they are more prone to damage by insect pests | and disease-causing microorganisms. Consequently, I pests and diseases must be controlled in managed forests, usually by applying pesticides.

Trees are harvested in several ways—by selec­tive cutting, shelter wood cutting, seed tree cutting, clear cutting, and whole-tree harvesting. Selective cutting, in which mature trees arc cat individually or in small clusters while the rest of the forest remains intact, allows the forest to regen­erate naturally. The trees left by selective cutting produce seeds that germinate to fill the void. Selec­tive cutting has fewer negative effects on the forest environment than other methods of tree harvest, but it is not as profitable because timber is not re­moved in great enough quantities.

The removal of all mature trees in an area over a period of time is known as shelter wood cutting. In the first year of harvest, undesirable tree species and dead or diseased trees are removed. The forest is then left alone for perhaps a decade, during which the remaining trees continue to grow and new seedlings become established. During the sec­ond harvest, many mature trees are removed. The forest is then allowed to regenerate on its own for perhaps another decade. A third harvest removes the remaining mature trees, but by this time a healthy stand of younger trees is replacing the ma­ture ones. Little soil erosion occurs with this method of tree removal, even though more trees are removed than in selective cutting.

In seed tree cutting, almost all trees are har­vested from an area; a scattering of desirable trees is left behind to provide seeds for the regeneration of the forest. Clear cutting is the removal of all trees from an area. After the trees have been removed by clear cutting, the area is either allowed to reseed and regenerate itself naturally or is planted with specific varieties of forest trees. Timber companies prefer clear cutting because it is the most cost-effec­tive way to harvest trees; also, very little road building has to be done to harvest a large number of trees. However, clear cutting is ecologically un­sound. It destroys wildlife habitat that takes many years to restore it. On sloping land, clear cutting increases soil erosion. Obviously, the recreational benefits of forests arc lost when clear cutting occurs.

A special type of clear cutting is whole-tree harvest, in which machines harvest the entire tree, including roots and small branches, and cut it into small chips, which are processed for paper products or fuel. Whole-tree harvest has the short-term eco­nomic benefit of making maximum use of all parts of every tree in the forest. However, over time, the nutrients in soils where whole-tree harvest has oc­curred become depleted because no part of the tree remains to decompose and recycle essential nutri­ents back to the soil.

U.S. Forests

The U.S. Forest Service, an agency in the Depart­ment of Agriculture, manages approximately 10 percent of the land in the United States. Forest Service lands have multiple uses, including timber harvest, livestock forage, water resources, recrea­tion, and providing habitat for fish and wildlife. The Bureau of Land Management (BLM), an agency in the Department of the Interior, oversees some public forest lands, two-thirds of which lie in Alaska. Outside Alaska there are approximately 2 million hectares (5 million acres) of public forest, which require intensive management to produce.

Tropical Forests and Deforestation

There arc two types of tropical forests: tropical rain forests and tropical dry forests. In places where the climate is very moist throughout the year—on the order of 200 to 450 cm (79 to 177 inches) of pre­cipitation annually—tropical rain forests prevail. Tropical rain forests are found in Central and South America, Africa, and Southeast Asia, bur almost half of them are in just three countries: Bra­zil in Smith America, Zaire in Africa, and Indonesia in Southeast Asia.

In other tropical areas where annual precipita­tion is less but is still enough to support trees— including regions subjected to a wet season and a prolonged dry season—tropical dry forests occur. During the dry season, tropical trees shed their leaves and remain dormant, much as temperate trees do during the winter. India, Kenya, Zim­babwe, Egypt, and Brazil are a few of the countries that have tropical dry forests.

The importance of tropical forests, particularly tropical rain forests, as the repositories of most of the world's biological diversity was discussed in the previous contents. Tropical forests also provide such im­portant environmental services as forming and holding the soil, cleansing the water and air, and providing shelter and food for countless animals and humans. When a forest is intact, it regulates surface water and thereby controls floods and droughts. In addition, tropical forests have a pro­found effect on the global carbon cycle, because much of the world's photosynthesis occurs there.

What Happens When Tropical Forests Disappear?

The destruction of all tree cover in an area is defor­estation. When tropical forests are harvested or destroyed, they no longer make valuable contribu­tions to the environment or to the people who de­pend upon them. Tropical forest destruction partic­ularly threatens native people whose cultural and physical survival depends upon the forests. When these people come into conflict with developers and colonizers of forests, they have little political strength or legal recourse and are usually forced off their land. Even beyond their right to exist, when indigenous tribes disappear, fields as diverse as anthropology and botany suffer the loss. Deforestation results in decreased soil fertility and increased soil erosion. Because poor rural peo­ple, both natives and colonizers, depend upon the soil for their livelihood, tropical deforestation con­tributes to the downward spiral of poverty in which many of these people find themselves. Uncon­trolled soil erosion, particularly on steep deforested slopes, can affect the production of hydroelectric power if silt builds up behind dams. Increased sedimentation of waterways caused by soil erosion can also harm fisheries. In drier areas, deforestation can lead to the formation of deserts.

When forest is removed, the total amount of surface water that flows into rivers and streams ac­tually increases. However, because this water flow is no longer regulated by forest, the affected region experiences alternating periods of flood and drought.

Deforestation causes the extinction of plant and animal species. Many tropical species, in par­ticular, have very limited ranges within a forest, so they are especially vulnerable to habitat modifica­tion and destruction. Migratory species based in temperate areas, including birds and butterflies, also suffer from tropical deforestation.

Deforestation induces regional and global climate changes. Trees release substantial amounts of moisture into the air; about 97 percent of water that a plant's roots absorb from the soil is evaporated directly into the atmosphere. This moisture falls back to the Earth in the hydrologic cycle. When forest is removed, rainfall de­clines and droughts become common in that re­gion. Tropical deforestation contributes to an increase in global temperature by causing a release of stored carbon into the atmos­phere as carbon dioxide, which in turn enables the air to retain solar heat.

Where and Why Are Tropical Forests Disappearing?

In the past thousand years, forests in temperate areas were largely cleared for housing and agricul­ture. Today, however, deforestation in the tropics is occurring much more rapidly and over a much larger area.

Most of the remaining undisturbed tropical forest, which lies in the Amazon and Congo River basins of South America and Africa, is being; cleared and burned at a rate that is unprece­dented in human history. Tropical forests are also being destroyed at an extremely rapid rate in south­ern /Via, Indonesia, Central America, and the Philippines. Ton countries account for 76 percent of tropical deforestation: Brazil, Indonesia, Zaire, Burma, Colombia, India, Malaysia, Mexico, Nige­ria, and Thailand.

Although exact figures on rates of forest de­struction are unavailable, the Food and Agriculture Organization (FAO) of the United Nations re­leased in late 1991 its second global assessment of worldwide tropical deforestation. A total of 87 tropical countries were evaluated in this study. The FAO estimated an annual rate of change in forest cover of -0.9 percent per year from 1981 to 1990, and some areas, such as West Africa, experienced a loss of forest estimated at greater than 2 percent per year. If this rate of deforestation—which represents a worldwide annual loss of 16.9 million hectares (41.8 million acres) of forest—continues, tropical forests will he all hut gone within the next several decades.

The three main causes of tropical deforestation art: subsistence agriculture, commercial logging, fin by the FAO shows that deforest and citric ranching. Subsistence agriculture, in which enough food is produced by a family to feed itself, is by far the most important cause, accounting for 60 percent of tropical defor­estation. Other reasons for the destruction of tropi­cal forests include mining and the development of hydroelectric dams.

Subsistence Agriculture: In many developing countries where tropical rain forests occur, the ma­jority of people do not own the land on which they live and work. Land ownership (and therefore profit) is in the hands of a few; for example, in Brazil 5 percent of the farmers own 70 percent of the land. Most subsistence farmers were displaced from traditional farmlands because of the inequita­ble distribution of land ownership. They have no place to go except into the forest, which they clear to grow food. Tropical deforestation by subsistence farmers is also affected by population pressures (re­call that these countries have some of the highest fertility rates in the world) and pervasive poverty. Land reform would make the land owned by a few available to everyone, thereby easing the pressure on tropical forests by subsistence farmers. This sce­nario is unlikely, however, because wealthy land­owners have more economic and political clout than landless peasants.

Subsistence farmers often follow loggers' access roads until they find a suitable spot. They first cut down the forest and allow it to dry, then they burn the area and plant crops immediately after burning; this is known as slash-and-burn agriculture. The yield from the first crop is often quite high because the nutrients that were in the burned trees are now available in the soil. However, soil productivity declines at a rapid rate and subsequent crops are poor. In a very short time, the people farming the land must move to a new part of the forest and repeat the process. Cattle ranchers often claim the abandoned land for grazing, because land that is not rich enough to support crops can still support livestock.

Slash-and-burn agriculture done on a small scale with periods of 20 to 100 years between cycles is actually sustainable. But when several hundred million people try to obtain a living in this way, the land is not allowed to lie uncultivated long enough to recover, and disaster results.

Commercial Logging: Twenty-one percent of trop­ical deforestation is the result of commercial log­ging; vast tracts of tropical rain forests are being harvested for export abroad. Most tropical countries allow commercial logging to proceed at a much faster rate than is sustainable.

For example, in Sabah and Sarawak (both part of Malaysia), log­ging is currently removing the forest at almost twice the sustainable race. If this continues, Malay­sia will soon experience shortages of timber and will have to start importing logs and other forest products, losing the potential revenues from its own newly vanished forests. In the final analysis, tropical deforestation does not lead to economic development; rather, it destroys a valuable re­source.

Cattle Ranching and Agriculture for Export

Ap­proximately 12 percent of tropical forest destruc­tion is carried out to provide open rangeland for cattle. After the forests are cleared, cattle can graze on the land for six to ten years, after which time shrubby plants, known as scrub savannah, take over the range. Much of the beef raised on these ranches, which are often owned by foreign companies, is exported to fast-food restau­rant chains.

A considerable portion of the land cleared for plantation-style agriculture produces crops such as citrus fruits and bananas for export. Because cash crops are usually grown on land owned by a few wealthy landowners, who rely on foreign companies for shipping and processing, this type of agri­culture does little to alleviate the poverty of the local people.

Why Are Dry Tropical Forests Disappearing?

Dry tropical forests are also being destroyed at an alarm­ing rate, primarily for fuel. Wood—perhaps half of the wood consumed worldwide—is used as heating and cooking fuel by much of the developing world.

Often the wood cut for fuel is converted to charcoal, which is then used to power steel, brick, and cement factories. Charcoal production is ex­tremely wasteful: 3.6 metric tons (4 tons) of wood produce enough charcoal to fuel an average-sized iron smelter for only 5 minutes.