Earth Day, event first observed internationally on April 22, 1970, to emphasize the necessity for the conservation of the world’s natural resources. Starting as a student-led campus movement, initially observed on March 21, Earth Day has become a major educational and media event. Environmentalists use it as an occasion to sum up current environmental problems of the planet: the pollution of air, water, and soils; the destruction of habitats; the decimation of hundreds of thousands of plant and animal species; and the depletion of non-renewable resources. The emphasis is on solutions that will slow and possibly reverse the negative effects of human activities. Such solutions include the recycling of manufactured materials, fuel and energy conservation, banning the use of harmful chemicals, halting the destruction of major habitats such as rainforests, and protecting endangered species.
Conservation, sustainable use of natural resources, such as soils, water, plants, animals, and minerals. In economic terms, the natural resources of any area constitute its basic capital, and wasteful use of those resources constitutes an economic loss. From the aesthetic and moral viewpoint, conservation also includes the maintenance of national parks, wilderness areas, historic sites, and wildlife. In certain cases, conservation may imply the protection of a natural environment from any human economic activity.
Natural resources are of two main types, renewable and non-renewable. Renewable resources include wildlife and natural vegetation of all kinds. The soil itself can be considered a renewable resource, although severe damage is difficult to repair because of the slow rate of soil-forming processes. The natural drainage of waters from the watershed of a region can be maintained indefinitely by careful management of vegetation and soils, and the quality of water can be controlled through pollution control. See Air Pollution; Environment; Reclamation; Sewage Disposal; Water Pollution; Energy Conservation.
Non-renewable resources are those that cannot be replaced or that can be replaced only over extremely long periods of time. Such resources include the fossil fuels (coal, petroleum, and natural gas) and the metallic and other ores. For discussions of conservation problems in this area, see individual entries on the substances concerned.
Although the conservation of natural resources has been recognized as desirable by many peoples since ancient times, frequently the basic principles of sound land use have been ignored, with disastrous results. Major losses—for example, the silting of rivers and the flooding of lowlands—resulted from the destruction of the forests and grasslands that protected watersheds in northern China and the Tigris-Euphrates area. Large areas in North Africa and the Middle East were rendered barren by centuries of uncontrolled livestock grazing, unwise cultivation, and excessive cutting of woody plants for fuel. Similar damage has also occurred in most of the more recently developed regions of the world, sometimes through the unwise introduction of species into new environments. The increasing industrialization of nations around the world continues to present severe conservation problems although international cooperation efforts have also evolved in certain areas, such as the protection of some endangered species. Some basic conservation principles in major areas of concern are discussed below.
III FOREST CONSERVATION
In forests more than any other ecosystem, demand is increasingly being made that conservation should involve preservation from any destructive commercial use, particularly the cutting of trees for timber, which in a virgin forest is known to have harmful consequences far beyond the loss of the actual trees (for example the loss of animal habitats, and soil erosion). Where tracts of virgin forest are given over to timber production, principles of management have evolved in order to minimize the destructiveness of the process and to make it as sustainable as possible. The management of forest trees for timber production involves three fundamental principles. The first is the protection of the growing trees from fire, insects, and disease. However, fire, once regarded as a destroyer of forests, is now recognized as a management tool when carefully employed. Some important timber trees actually require fire for successful regeneration. Insects, such as the gypsy moth, spruce budworm, and pine sawfly, and disease, still take a heavy toll. However, biological control measures and some aerial spraying, proper cutting cycles, and slash disposal are increasingly effective. The second principle concerns proper harvesting methods, ranging from removal of all trees (clear-cutting) to removal of selected mature trees (selection cutting), and provision for reproduction, either naturally from seed trees or artificially by planting. The rate and frequency of any cutting should aim for sustained production over an indefinite period. The third principle of timber management is the complete use of all trees harvested. Technological advances, such as particleboard and gluing, have created uses for branches, defective logs, trees too small to be milled into boards, and so-called inferior trees. As demand for wilderness areas and recreational use of forests increases, management of commercial forests will become more intense. See Forest; Forest Fires; Forest Conservation and Management.
IV CONSERVATION OF GRAZING LANDS
One of the principles of range conservation is the use of only a portion (usually about a half) of the annual forage plant production of a particular range in order to maintain healthy plant growth and reproduction. In addition, each range is stocked with the number of animals that can be nourished properly on the available usable forage and are permitted to graze only during the season suitable for that type of range. The conservation of ranges is based on a programme of grazing designed to keep them productive indefinitely and to improve depleted areas by natural reproduction or by artificial seeding with appropriate forage species. Although these principles are well established, many hundreds of thousands of acres of public grazing lands are still overgrazed.
V WILDLIFE CONSERVATION
One of the basic principles of wildlife conservation involves providing adequate natural food and shelter to maintain populations of each species in a given habitat. A major threat facing wildlife is both the destruction of habitat, through drainage, agriculture and urban expansion, and the fragmentation of habitat into parcels too small for wildlife populations to use. Illegal trade in feathers, horns, ivory, hides, and organs has brought many endangered species to the verge of extinction. Wildlife is an important biological, economic, and recreational resource that can be maintained through careful management. Hunting regulations allow the culling of many species without affecting overall population levels, and can even help control species that have grown too abundant for the region they inhabit.
VI SOIL CONSERVATION
Among the basic measures for soil conservation currently in use is the zoning of land by capability classes. In this system, the more level and stable soils are designated as suitable for annual crops, and other areas are designated for perennials, such as grass and legumes, or for use as grazing or forest lands. Another conservation method involves the use of soil-building plants in crop rotations. Such crops hold and protect the soil during growth and when ploughed under, supply much-needed organic matter to the soil. Cultivation methods that leave a layer of vegetable waste on the surface of the soil represent a major advance in land use. In many areas, these techniques have supplanted the use of the mouldboard plough, associated with the practice known as clean cultivation, which left the soil surface exposed to all the natural erosive forces. Special methods for erosion control include contour farming, in which cultivation follows the contours of sloping lands, and ditches and terraces are constructed to diminish the run-off of water. Another soil conservation method is the use of strip-cropping—that is, alternating strips of crop and fallow land. This method is valuable for control of wind erosion on semi-arid lands that need to lie fallow for efficient crop production. In addition, the maintenance of soil fertility at the maximum level of production often involves the use of inorganic (chemical) fertilizers. See Erosion; Soil; Soil Management.
VII CONSERVATION OF DRAINAGE BASINS
Recent studies have confirmed that extremely dense vegetation prevents the collection of the maximum amount of water in a given drainage basin. Greater yields of water have been obtained from some mountain forest regions by thinning the natural tree stands, but not so much as to increase soil erosion or flood danger. A forest or shrub cover containing numerous small openings has been found to be more effective for capturing water than a dense, continuous cover that intercepts much snow and rain and permits the moisture to be lost by evaporation. Highly important in drainage basin conservation is the preservation of wetlands, which function as filtration systems that stabilize water tables by holding rainfall and discharging the water slowly, and as natural flood-control reservoirs.
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