wood, the principal strengthening and nutrient-conducting tissue of trees and other plants and one of the most abundant and versatile natural materials. Produced by many botanical species, including both gymnosperms and angiosperms, wood is available in various colours and grain patterns. It is strong in relation to its weight, is insulating to heat and electricity, and has desirable acoustic properties. Furthermore, it imparts a feeling of “warmth” not possessed by competing materials such as metals or stone, and it is relatively easily worked. As a material, wood has been in service since humans appeared on Earth. Today, in spite of technological advancement and competition from metals, plastics, cement, and other materials, wood maintains a place in most of its traditional roles, and its serviceability is expanding through new uses. In addition to well-known products such as lumber, furniture, and plywood, wood is the raw material for wood-based panels, pulp and paper, and many chemical products. Finally, wood is still an important fuel in much of the world.
Production and consumption of wood
In botanical terms, wood is part of the system that conveys water and dissolved minerals from the roots to the rest of the plant, stores food created by photosynthesis, and furnishes mechanical support. It is produced by an estimated 25,000 to 30,000 species of plants, including herbaceous ones, though only 3,000 to 4,000 species produce wood that is suitable for use as a material. Wood-producing forest trees and other woody plants are of two categories: gymnosperms and angiosperms. Gymnosperms, or cone-bearing trees, produce softwoods, such as pine and spruce, and angiosperms produce temperate and tropical hardwoods, such as oak, beech, teak, and balsa. It should be noted that the distinction implied by hardwood and softwood is not true in all cases. Some hardwoods—e.g., balsa—are softer than some softwoods—e.g., yew.
Wood is a material of great economic importance. It is found throughout the world and can be sustainably managed as a renewable resource—in contrast to coal, ores, and petroleum, which are gradually exhausted. By means of its harvesting in forests, its transportation, its processing in workshops and industries, and its trade and use, wood provides jobs and supports economic development and, in some countries, basic subsistence. Indicative of this importance is the continued high demand for wood and wood products.
On a weight basis, the consumption of wood exceeds by far that of other materials. More than half of roundwood (log) production is consumed as fuel, mainly in less-developed countries. Production of paper and paperboard has shown the most rapid increase among wood products; this trend is expected to continue as consumption per person in the less-developed countries approaches that in the developed nations. Rising world population is the driving force of increasing consumption of wood and consequent deforestation. The depletion of many forests, especially in the tropics, makes uncertain the provision of an adequate wood supply to satisfy the anticipated need. Efforts to stop the reduction of Earth’s forest cover and increase the productivity of existing forests, establishment of extensive reforestation programs and plantations of fast-growing tree species, recycling of paper, and improved utilization of wood through research could ease the problem of wood supply and help to lessen the environmental toll of the lumber industry.
Harvesting of wood
Management
Harvesting of wood differs radically from harvesting of other crops. The yearly growth of each individual tree cannot be detached from the living plant. Rather, new wood is added inseparably to preexisting growth until the entire tree is harvested, after a waiting period that varies widely depending on intended use of the wood—for example, 2–3 years on energy plantations (where biomass is produced as fuel for power generation), 6–8 years for pulpwood (eucalypts), 12–15 years for fast-growing poplar hybrids, 30–50 years for fast-growing pines, and 100 years or more in temperate and tropical forests producing wood of large dimensions.
A prerequisite to harvesting is a management plan, which determines the yearly yield and the method of removal. The harvest method chosen can involve clear-cutting large areas or selective cutting of individual trees or groups of trees. For a forest harvested under the sustained-yield concept, the volume of timber removed at periodic intervals is dependent on the net growth of all trees—as estimated by statistical sampling—during that interval. This concept, combined with natural and artificial seeding and planting, ensures a continuous production of wood and conservation of forests. To promote sustained-yield management, efforts have been made to introduce appropriate ecological labeling (ecolabeling) of marketed wood and wood products. Ecolabeling is intended to ensure that goods offered to the consumer have not been produced in a way detrimental to the environment.
The season of harvest is not determined by the time of ripening, as it is for agricultural crops, but by such factors as the conditions of work for personnel, machines, and animals, such as nesting birds, and the danger of damage to the remaining forest and to the harvested wood. Because felled trees are vulnerable to attack by fungi and insects, the harvest may be timed to avoid conditions favourable for these organisms. Time of harvesting becomes a consideration mainly when the felled trees will not be removed quickly from the forest for processing. Otherwise—for example, in the United States—harvesting is a year-round activity.
