لطفا منتظر باشید ...
Forestry
I INTRODUCTION
Forestry, management of forestlands for maximum sustained yield of forest resources and benefits. Although forestry originally concerned mainly timber production, it now also involves the management of grazing areas for domestic livestock, the preservation of wildlife habitats, watershed protection, and the development of recreational opportunities. The management of forestlands therefore helps to ensure that wooded areas are used for maximum benefit according to their nature.
II HISTORY
Attempts to regulate and manage forestlands occurred well before the 19th century in Rome, the Middle East, China, and Western Europe. Wars and political instability invariably interfered with these efforts; so destructive use of forests was common in the more densely populated countries. Early settlers in the U.S., for example, regarded forests as impediments to cultivation and sought to remove them as quickly as possible. This attitude fostered a “cut and get out” philosophy among timber operators, and exploitative logging persisted well into the 20th century. Scientific forestry was initiated in the U.S. at the end of the 19th century largely through the influence of the federal government, with measures including the establishment of the Division of Forestry in 1885 and authorization of forest reserves in 1897. The latter became known as the National Forests in 1905, when the jurisdiction of reserves was transferred from the Department of the Interior to the Department of Agriculture, and the Division of Forestry became the Forest Service. Since that time, forest management has been practiced on state and private lands as well as on federal holdings.
Education in technical forestry began in Western Europe about 1825 with private schools in France and Germany; these were later replaced by state institutions. Until World War II, Western Europe was the world leader in scientific forestry, and many famous schools and institutes were established there. In the U.S. the first forestry curriculum was established in 1898. Forestry education is now offered in many universities throughout the country and elsewhere in the world.
III PRACTICE
Forestry comprises such specialties as dendrology, silviculture, forest protection, mensuration, engineering, utilization, and management. Dendrology concerns tree identification, distribution, age determination, and species characteristics. Silviculture studies the relationship of a forest to its environment and involves the development, care, and reproduction of stands of timber. Forest protection examines sources of injury, including disease, erosion, insect and animal destruction, and fire. The science of measuring forest stands, including rate of growth and potential yield of standing timber, is called mensuration. Forest engineering concerns the mechanics of cutting and transportation involved in modern timber growing and harvesting. Forest utilization considers the properties of wood and its conversion into lumber and wood products. Forest management applies business methods and the principles of technical forestry to the overall operation of forestlands.
The practice of technical forestry includes many operations, from tree planting to harvesting. Central to the operation is the cycle of cutting and replenishment. Four major methods have been developed for this purpose: clear-cutting, selection, seed tree, and shelterwood. In clear-cutting all trees in a given area are cut, and reproduction is obtained by artificial planting or by natural seeding from trees bordering the cleared areas. This method, adapted to light-demanding species, produces even-aged stands, allows control of stand composition, and is conducive to mechanized harvesting and disposal of slash, or logging debris. Selection cutting maintains a forest of mixed ages from which the largest and most mature trees are harvested periodically. Although this method is expensive and may cause injury to younger trees during logging, it provides continuous cover and an attractive forest and involves sounder ecological practices. In the seed tree method, about 10 percent of the trees in the cutting area are left in an evenly spaced pattern as a natural seed source. The shelterwood method, which involves the removal of the mature trees in cuttings over a 10- to 15-year period, promotes natural reproduction and produces relatively even-aged stands.
Other practices contribute to the development of commercial forestry. These include artificial planting by direct seeding or transplants, especially in conjunction with clear-cutting; treatment with fertilizers to increase production; and the selection and breeding of timber trees, producing strains that excel in growth, disease resistance, or other desirable characteristics. These measures fit into the pattern of an intensive forestry in which greater production is obtained through technical knowledge and increased mechanization.
Contributed By:
David L. Adams
Edwin W. Tisdale
The Role of Forests
Forests provide habitat for a wide variety of plants and animals and perform many other important functions that affect humans. Photosynthesis is the chemical process in the leaves that uses sunlight and carbon dioxide to produce energy-supplying sugars for the tree. In the process the foliage gives off pure oxygen for breathing. The forest canopy (the treetops) and root systems provide natural filters for the water we use from lakes and rivers. When it rains the forest canopy intercepts and re-distributes precipitation that can cause flooding and erosion, the wearing away of topsoil. Some of the precipitation flows down the trunks as stemflow, the rest percolates through the branches and foliage as throughfall. The canopy is also able to capture fog, which it distributes into the vegetation and soil. Forests also increase the ability of the land to store water. The forest floor can hold as much as five times its weight in water and a tree contains water in its roots, trunk, stems, and leaves. Because of all this stored moisture, forests help to maintain an even flow of water in rivers and streams in times of flood or drought. The roots of the trees and other vegetation hold the soil in place and control erosion from wind and rain, preventing flooding and clouding of streams and rivers.
Microsoft Corporation. All Rights Reserved.
