FORESTRY

the management of forested land, together with associated waters and wasteland, primarily for harvesting timber but also for conservation and recreation purposes. About one-third of the world's land surface is classified as forest land, and approximately 1 percent of the standing timber is harvested each year. Almost half of the felled timber is used for fuel, the remainder being made into wood products or pulp for paper and packaging materials. The trees providing the raw materials are grouped into three general classifications: conifers, broadleaves, and monocotyledons. Almost all conifers, which are also called softwood, or gymnosperm (naked-seeded), trees, are evergreen. The most common include species of northern pine (of the genus Pinus), spruce (Picea), Douglas fir (Pseudotsuga), cedar (Cedrus), cypress (Cupressus), redwood (Sequoia), and hemlock (Tsuga). Conifers are characterized by their needle-shaped leaves; they survive well in harsh climates and where soil conditions are relatively poor. Most conifer forests are found in the Northern Hemisphere, the largest concentration occurring in a northern band, called taiga, that cuts a broad swath across North America, northern continental Europe and Scandinavia, Russia, and northern China and Japan. There is also a discontinuous conifer forest in the southern portion of the Northern Hemisphere and small areas of conifer forest in the Southern Hemisphere. Conifers are among the most commercially useful trees and are commonly used for paper, furniture, and building materials. The broadleaves, or hardwood trees, thrive not only in temperate climates but also in sub-tropical and tropical forests. This group includes species of such temperate trees as oak (Quercus), elm (Ulmus), birch (Betula), ash (Fraxinus), maple (Acer), chestnut (Castanea), poplar (Populus), beech (Fagus), and alder (Alnus), as well as such semitropical and tropical evergreens as eucalyptus (Eucalyptus), teak (Tectona grandis), mahogany (Swietenia macrophylla), and balsa (Ochroma pyramidale). Broadleaf trees growing in temperate climates are deciduous; they shed their leaves in autumn and remain leafless through the winter. They are used in a variety of commercial products, including furniture, wood veneers, panelling, and flooring. Monocotyledons, or monocots, include palm and bamboo. Found mainly in tropical and subtropical climates, monocots have less commercial value than the conifers and broadleaves. Palms are economically more important for their fruit (e.g., coconuts, dates, and products fashioned from their leaves) than for their timber. Bamboo, however, has a variety of commercial applications that range from pulp for paper to materials for construction and furniture making. The planned management of forests originated in early medieval Europe. Large tracts of forest land were owned by monarchs and nobles who utilized the woodland resources for their own needs and for trade. Laws and regulations regarding the felling of timber and the use of forests for hunting were set and enforced by the feudal owners. As the value of timber for fuel and wood products increased and the commercial markets for it grew, the owners instituted programs for the replacement of trees that had been removed; this practice was the basis of modern forestry. The science of forestry is built around the principle of multiple-use land management, although the harvesting and replanting of timber are still the primary activities. The main objective is to create a system of sustained yield, i.e., to maintain a continuous supply of timber through carefully planned harvest and replacement. Through legislation and policies, governments define the amount of timber that can be taken and often set aside areas that cannot be touched. Forest managers set strict controls over how trees will be removedsome areas are cleared while others are thinned, for example. The replacement of timber that has been harvested is called silviculture. There are two techniques, each with its advantages and drawbacks: natural and artificial regeneration. Natural regeneration is the method whereby timber is removed in such a way that gaps or swaths are left in the forest. Seeds from neighbouring trees are then naturally distributed and take root. An advantage of natural regeneration is that it involves much less work in terms of cultivation and nurture, but it restricts the renewal process to those trees that are native to the area. Artificial regeneration involves collecting seeds or cuttings and then sowing them in forest nurseries. After their growth reaches a certain stage, the seedlings are planted in the areas that are being reforested. The method's advantages are that it permits the introduction of different kinds of trees into a specific area, that the process can be more scientifically controlled, and that it is generally a quicker way to restock a forest area. Its main disadvantages are the large amount of investment capital needed and the relatively long time required to recoup the investment. Within the concept of multiple-use forest management, however, the forest manager is also responsible for the application of other land controls, which include the protection of wildlife and the implementation of programs to protect the forest from weeds, insects, fungal diseases, erosion, and fire. Forest areas must be preserved and maintained for recreational uses, ranging from scenic pleasures and nature study to such activities as hunting, fishing, camping, and hiking. the management of forested land, together with associated waters and wasteland, primarily for harvesting timber. To a large degree, modern forestry has evolved in parallel with the movement to conserve natural resources. As a consequence, professional foresters have increasingly become involved in activities related to the conservation of soil, water, and wildlife resources and to recreation. This article traces the history of forestry from its origin in ancient practices to its development as a scientific profession in the modern world, and it discusses the kinds and distribution of forests as well as the principal techniques and methods of modern forest management in detail. Additional reading Forestry textbooks usually deal with a specialized aspect of the science, often in one geographic region. William M. Harlow, Ellwood S. Harrar, and Fred M. White, Textbook of Dendrology, Covering Important Forest Trees of the United States and Canada, 6th ed. (1979), provides descriptions of major tree species in the region. Forest ecology is the subject of K.A. Longman and J. Jenk, Tropical Forest and Its Environment, 2nd ed. (1987); J.J. Landsberg, Physiological Ecology of Forest Production (1986); and Herman H. Shugart, A Theory of Forest Dynamics: The Ecological Implications of Forest Succession Models (1984). For a general historical overview of forestry and related fields, see Richard C. Davis (ed.), Encyclopedia of American Forest and Conservation History, 2 vol. (1983).Principles of forest management, worldwide in application, are systematically outlined by William A. Leuschner, Introduction to Forest Resource Management (1984); and Joseph Buongiorno and J. Keith Gilless, Forest Management and Economics: A Primer in Quantitative Methods (1987). Karl F. Wenger (ed.), Forestry Handbook, 2nd ed. (1984), is a reference book of data and methods in all aspects of forestry and allied fields. Grant W. Sharpe, Clare W. Hendee, and Wenonah F. Sharpe, Introduction to Forestry, 5th ed. (1986); and Charles H. Stoddard and Glenn M. Stoddard, Essentials of Forestry Practice, 4th ed. (1987), give a complete overview of modern multiple-use forestry. The requisite elements of forest inventory are detailed in Bertram Husch, Charles I. Miller, and Thomas W. Beers, Forest Mensuration, 3rd ed. (1982). Financial implications are studied in G. Robinson Gregory, Resource Economics for Foresters (1987). The leading international sources of statistics on forestry and timber output are the publications of the Food and Agriculture Organization of the United Nations: World Forest Inventory (irregular), FAO Forestry and Forest Product Studies (irregular); and the special reports Forest Resources of Tropical Africa, 2 vol. (1981), Forest Resources of Tropical Asia (1981), and Forestry in China (1982). Fundamental studies of the physical bases of forest distribution and yield are given in World Resources 1986 (1986), a report prepared by the World Resources Institute and the International Institute for Environment and Development.The theory and practice of raising and tending tree crops are treated in such manuals as Theodore W. Daniel, John A. Helms, and Frederick S. Baker, Principles of Silviculture, 2nd ed. (1979); and David M. Smith, The Practice of Silviculture, 8th ed. (1986), discussing temperate-zone forests. Details of handling seed and young stock are treated in R.L. Willan (comp.), A Guide to Forest Seed Handling: With Special Reference to the Tropics (1985); U.S. Department of Agriculture, Woody-Plant Seed Manual (1948); and Mary L. Duryea and Thomas D. Landis (eds.), Forest Nursery Manual: Production of Bareroot Seedlings (1984). Genetic improvement is discussed in Klaus Stern and Laurence Roche, Genetics of Forest Ecosystems (1974); and M.N. Christiansen and Charles F. Lewis (eds.), Breeding Plants for Less Favorable Environments (1982). The intensive culture of forest plantations is discussed in Bruce J. Zobel, Gerrit Van Wyk, and Per Stahl, Growing Exotic Forests (1987); and W.E. Hillis and A.G. Brown (eds.), Eucalypts for Wood Production (1978, reprinted 1984). Management of forest soils, a primary concern in intensive silviculture, is described in William L. Pritchett and Richard F. Fisher, Properties and Management of Forest Soils, 2nd ed. (1987); and Pedro A. Sanchez, Properties and Management of Soils in the Tropics (1976). Manipulation of soil fertility and study of soil microorganisms are presented in G.D. Bowen and E.K.S. Nambiar (eds.), Nutrition of Plantation Forests (1984); Robert L. Tate, III, and Donald A. Klein (eds.), Soil Reclamation Process: Microbiological Analyses and Applications (1985); and J.C. Gordon and C.T. Wheeler (eds.), Biological Nitrogen Fixation in Forest Ecosystems: Foundations and Applications (1983). The care of tree crops in tropical jungles of both hemispheres is outlined in I.T. Haig, M.A. Huberman, and U. Aung Din, Tropical Silviculture (1958). A wide range of Asiatic conditions is discussed in Harry G. Champion and S.K. Seth, General Silviculture for India (1968).The management of forests as watersheds and the impact of forestry activities on water quantity and quality are discussed in William E. Sopper and Howard W. Lull (eds.), Forest Hydrology: Proceedings of a National Science Foundation Advanced Science Seminar (1967); H.C. Pereira, Land Use and Water Resources in Temperate and Tropical Climates (1973); and K.W.G. Valentine, Soil Resource Surveys for Forestry (1986). Nutrient losses from disturbed watersheds and the potential for accelerated loss attributable to acid deposition are examined in F.E. Clark and T. Rosswall (eds.), Terrestrial Nitrogen Cycles: Processes, Ecosystem Strategies, and Management Impacts (1981); and S. Beilke and A.J. Elshout (eds.), Acid Deposition (1983).Forest protection is treated in textbooks discussing specific hazards. Arthur A. Brown and Kenneth P. Davis, Forest Fire: Control and Use, 2nd ed. (1973), outlines fire dangers and methods of control. T.T. Kozlowski and C.E. Ahlgren (eds.), Fire and Ecosystems (1974); and Henry A. Wright and Arthur W. Bailey, Fire Ecology, United States and Southern Canada (1982), discuss the environmental interactions associated with fire. John S. Boyce, Forest Pathology, 3rd ed. (1961); and Robert O. Blanchard and Terry A. Tattar, Field and Laboratory Guide to Tree Pathology (1981), give details of fungal diseases, climatic dangers, and airborne fume and salt damage. See also Carl F. Jordan (ed.), Amazonian Rain Forests: Ecosystem Disturbance and Recovery (1987). Insect pests are described in Alan A. Berryman, Forest Insects: Principles and Practice of Population Management (1986). Classification and distribution of forests Botanical classification places forest trees into two main groups, Gymnospermae and Angiospermae. The gymnosperms consist exclusively of trees and woody shrubs, whereas the angiosperms are a diverse group of plants that include trees and shrubs as well as grasses and herbaceous plants. The gymnosperms probably gave rise to the angiosperms, although the manner in which this took place is disputed. Gymnosperms The gymnosperms are of very ancient lineage and include the earliest trees on the evolutionary scale. With certain exceptions, the seeds of gymnosperms are borne in cones, where they develop naked or exposed on the upper surface of the cone scales. The wood of these trees has a simple structure. Many species are extinct, such as the tree ferns of the Carboniferous Period (280,000,000 to 345,000,000 years ago), and are known only as fossils. The ginkgo, or maidenhair tree, is the sole survivor of an entire order of gymnosperms, the Ginkgoales. Among the gymnosperms, the most important and numerous forest trees are the conifers, also known as softwoods. This group includes the well-known pines, spruces, firs, cedars, junipers, hemlocks, and sequoias. These species are so dominant in the gymnosperm class that forests of gymnosperm trees are typically called coniferous forests. Except for the ginkgo, larches, and bald cypress, all gymnosperms are evergreen. Purposes and techniques of forest management Multiple-use concept The forests of the world provide numerous amenities in addition to being a source of wood products. The various public, industrial, and private owners of forestland may have quite different objectives for the forest resources they control. Industrial and private owners may be most interested in producing a harvestable product for a processing mill. However, they also may want other benefits, such as forage for grazing animals, watershed protection, recreational use, and wildlife habitat. On public lands the multiple-use land management concept has become the guiding principle for enlightened foresters. This is a complex ecological and sociological concept in contrast to the single-use principle of the past. The challenge, in the words of Gifford Pinchot, is to ensure the greatest good for the most people over the long run. Thus timber production may have top priority in some areas, but in others, such as those near large population centres, recreational values may have high priority. Multiple use calls for exceptional skill on the part of forest managers. Sustained yield Forest management originated in the desire of the large central European landowners to secure dependable income to maintain their castles and retinues of servants. Today forest management is still primarily economic in essence, because modern forest industries, mainly sawmilling and paper manufacture, can be efficient only on a continuous-operation basis. Foresters think in long time scales, in line with the long life of their renewable crop. However, it is possible that a forest can be managed in such a way that a modest timber crop may be harvested indefinitely year after year if annual harvest and the losses due to fire, insects, diseases, and other destructive agents are counterbalanced by annual growth. This is the sustained-yield concept. An important element is the rotation, or age to which each crop can be grown before it is succeeded by the next one. Examples of short rotation periods in the subtropics are seven years for leucaena for fuelwood, 10 years for eucalyptus, and 20 years for pine for pulpwood. Here a sustained yield could in theory be obtained simply by felling one-tenth of the eucalyptus forest each year and replanting it. Rotation periods for pulpwood in northern Europe and North America extend to 50 years. Softwood sawlogs often need 100 years to reach an economic size, while rotation periods for broad-leaved trees, such as oak and beech, in central Europe, may extend to two centuries. Over so long a growing spell only part of the lumber yield is obtained by the clear-cutting of a small fraction of the forest each year. The rest is secured by systematically thinning out the whole forest periodically. Sustained-yield principles are likewise applied to minor forest produce. Turpentine and pitch, also known as naval stores, are obtained by the systematic tapping of the lower trunk of certain subtropical pines. Successive cuts with a chisellike tool every few days during a succession of summers eventually kill the trees. To ensure continued yields, crops of young pines are raised rotationally to replace those felled. A similar system is followed for Para rubber, Hevea brasiliensis, grown in plantations.