Deforestation
From Biocrawler, the free encyclopedia.
Deforestation is the conversion of forested areas to non-forest. Generally this involves the removal or destruction of significant areas of forest cover. Deforestation is an important aspect of habitat destruction and is invariably accompanied by some degree of desiccation, the gradual reduction of water resources in a deforested region; desertification is an extreme result. Historiically, deforestation has accompanied mankind's progress since the Neolithic, and has shaped climate and geography.
Deforestation (whether deliberate or unintended) is the result of the removal of trees without sufficient reforestation. There are many causes, ranging from extremely slow forest degradation to sudden and catastrophic wildfires. Deforestation can be the result of the deliberate removal of forest cover for agriculture or urban development, or it can be an unintentional consequence of uncontrolled grazing (which can prevent the natural regeneration of young trees). The combined effect of grazing and fires can be a major cause of deforestation in dry areas. In addition to the direct effects brought about by forest removal, indirect effects caused by edge effects and habitat fragmentation can greatly magnify the effects of deforestation.
While tropical rainforest deforestation has attracted most attention, tropical dry forests are being lost at a substantially higher rate.
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Effect of deforestation
Forests support considerable biodiversity. Forests are valuable habitat for wildlife. Direct economic benefits accrue from the harvest of forest resources such as wildlife, non-wood products like wild mushrooms and medicinal herbs and from the sale of hunting and camping equipment. Forests also play an important role in watershed protection, soil conservation and the recharge of aquifers. They can also be the source of new drugs (like taxol).
The effect of deforestation is more fundamental than its mere human factor. Shrinking forest cover lessens the landscape's capacity to intercept and retain precipitation. Instead of trapping precipitation, which then percolates into the soil, deforested areas become sources of surface water runoff, increasing potential for flooding. Deforestation also contributes to decreased evapotranspiration, which lessens atmospheric moisture and precipitation levels, and affects precipitation levels downwind from the deforested area, as water is not recycled to downwind forests, but is lost in runoff and returns directly to the oceans; in deforested north and northwest China, the average annual precipitation decreased by one third between the 1950s and the 1980s [1] (http://www.library.utoronto.ca/pcs/state/chinaeco/forest.htm).
Although timber production can be an important cause of deforestation, higher long-term gains can be obtained by managing forest lands to maintain forest cover. Forests are also important stores of organic carbon, and forests can extract carbon dioxide and pollutants from the air. Forests are also valued as a thing of aesthetic beauty and as a cultural resource. Deforestation results in the loss of these benefits.
Definition of deforestation
There is no universally accepted definition of deforestation. Various governments and organizations use different definitions. The replacement of natural forests by plantations may be classified as reforestation by government agencies, but classified as deforestation by conservation groups. Deforestation can be defined broadly to include not only converstion to non-forest, but also degradation that reduces forest quality - the density and structure of the trees, the ecological services supplied, the biomass of plants and animals, the species diversity and the genetic diversity. Narrow definitions of deforestation define deforestation as the removal of forest cover to an extent that allows for alternative land use. The United Nations Research Institute for Social Development (UNRISD) uses a broad definition of deforestation, while the Food and Agriculture Organization of the UN (FAO) uses a narrow definition.
Definitions can also be grouped as those which refer to changes in land cover and those which refer to changes in land use.
Land cover measurements often use a percent of cover to determine deforestation. This type of definition has the advantage in that large areas can be easily measured, for example from satellite photos. A forest cover removal of 90% may still be considered forest in some cases. Under this definition areas that may have few values of a natural forest such as plantations and even urban or suburban areas may be considered forest.
Land use definitions measure deforestation by a change in land use. This definition may consider areas to be forest that are not commonly considered as such. An area can be lacking trees but still considered a forest. It may be a land designated for afforestation or an area designated administratively as forest.
Use of the term deforestation
The term deforestation has ben used to refer to fuel wood cutting, commercial logging, slash and burn cultivation. It also is used to describe forest clearing for annual crops, for grazing, and establishment of industrial forest plantations. The meaning of the term is ambiguous enough and so charged with emotion that the use of a more precise term might be better suited in specific cases. Related terms are forest decline, forest fragmentation and forest degradation, loss of forest cover and land use conversion.
Causes of deforestation
Agents
Agents of deforestation can be individuals or groups of individuals that are clearing the forest. Commercial farmers, slash and burn farmers, cattle ranches and loggers are all agents of deforestation. Agents are usually acting in their own self interest.
Causes
Causes include demand for farm land and fuel wood. Underlining causes include poverty, lack of land reform. The causes of deforestation are complex and change over time. Deforestation can be most easily be understood by studying the causes for each forest and country separately.
Theories of deforestation
Three schools of thought exist with regards to the causes of deforestation - the Impoverishment school, which believes that the major cause of deforestation is "the growing number of poor", the Neoclassical school which believes that the major cause is "open-access property rights" and the Political-ecology school which believes that the major cause of deforestation is that the "capitalist investors crowd out peasants". The Impoverishment school sees smallholders as the principal agents of deforestation, the Neoclassical school sees various agents, and the Political-ecology school sees capitalist entrepreneurs as the major agents of deforestation.
History
Deforestation has been practiced by humans for thousands of years. Fire was probably the first tool that allowed humans to modify the landscape. The first evidence of deforestation shows up in the Mesolithic. Fire was probably used to drive game into more accessible areas. With the advent of agriculture fire became the prime tool to clear land for crops. In Europe there is little solid evidence before 5000 BP. Mesolithic foragers used fire to create openings for red deer and wild boar. In Britain shade tolerant species like oak and ash are replaced in the pollen record by hazels, brambles, grasses and nettles. Removal of the forests led to decreased transpiration resulting in the formation of upland peat bogs. Widespread decreased in elm pollen across Europe between 6400-6300 BP and 5200-5000 BP, starting in southern Europe and gradually moving north to Britain, may represent land clearing by fire at the onset of Neolithic agriculture.
The historic silting of ports along the southern coasts of Asia Minor (e.g. Clarus) and in coastal Syria during the last centuries BC, and the famous silting up of the harbor for Bruges, which moved port commerce to Antwerp, follow periods of increased settlement growth (and apparently of deforestation) in the river basins of their hinterlands.
In 17th century New England, William Cronon (Changes in the Land 1983) collected Englishmen's reports of increased seasonal flooding during the time that the forests were initially cleared, though no connection was made at the time.
Recent change
The rate of clearance increased during the second half of the 19th century due to agricultural expansion in Europe. Deforestation rates peaked in New England about 1900 and in the Great Lakes region of the United States in the late 19th century. Rates of tropical deforestation have increased substantially into the post-war period as logging operations became mechanised.
Growing worldwide demand for wood to be used for fire wood or in construction, paper and furniture - as well as clearing land for commercial and industrial development (including road construction) have combined with growing local populations and their demands for agricultural expansion and wood fuel to endanger ever larger forest areas.
Agricultural development schemes in Mexico, Brazil and Indonesia moved large populations into the rainforest zone, further increasing deforestation rates. One fifth of the world's tropical rainforest was destroyed between 1960 and 1990. Estimates of deforestation of tropical forest for the 1990s range from ca. 55,630 km² to ca. 120,000 km² each year. At this rate, all tropical forests may be gone by the year 2090.
Environmental effects
Atmospheric pollution
Deforestation is often cited as one of the major causes of the enhanced greenhouse effect. Trees and other plants remove carbon (in the form of carbon dioxide) from the atmosphere during the process of photosynthesis. Both the decay and burning of wood releases this stored carbon back to the atmosphere.
Wildlife
Some forests are rich in biological diversity. Deforestation can cause the destruction of the habitats that support this biological diversity - thus causing population shifts and extinctions.
Hydrologic cycle and water resources
Trees, and plants in general, affect the hydrological cycle in a number of significant ways:
- their canopies intercept precipitation, some of which evaporates back to the atmosphere;
- their litter, stems and trunks slow down runoff;
- their roots create macropores - large conduits - in the soil that increase infiltration;
- they transport water from the soil to the atmosphere via transpiration;
- their litter and organic residue change soil properties that affect the capacity of soil to store water.
As a result, the presence or absence of trees can change the quantity of water on the surface, in the soil or groundwater, or in the atmosphere. This in turn changes erosion rates and the availability of water for either ecosystem function or human services.
Soil erosion
Deforestation generally increases rates of soil erosion, by increasing the amount of runoff and reducing the protection of the soil from tree litter. Forestry operations themselves also increase erosion through the development of roads and the use of mechanized equipment.
China's Loess Plateau was cleared of forest millennia ago. Since then it has been eroding, creating dramatic incised valleys, and providing the sediment that gives the Yellow River its yellow color and that causes the flooding of the river in the lower reaches (hence the river's nick-name 'China's sorrow').
Removal of trees does not always increase erosion rates. In certain regions of southwest US, shrubs and trees have been encroaching on grassland. The trees themselves enhance the loss of grass between tree canopies. The bare intercanopy areas become highly erodible. The US Forest Service, in Bandelier National Monument for example, is studying how to restore the former ecosystem, and reduce erosion, by removing the trees.
Landslides
Tree roots bind soil together and act to keep the soil in place. Tree removal on steep slopes increases the risk of landslides.
Alternatives
An alternative deforestation for the purpose of timber is to build houses out of non-wood materials, such as brick, stone, concrete, and fiberglass. These materials have the additional benefits of being fireproof, waterproof, and pest-proof. Furthermore, paper products can be made of hemp fiber instead of wood - although there are strong arguments stating that farming trees may create more forests than farming hemp.
Recycling paper reduces the number of trees cut down. E-mails and web pages may also reduce the amount of wood paper used. Some lumber companies are planting trees to replace the trees taken. Hay, dry weeds, trash, garbage, husks, and stalks can be burned for energy instead of wood, although this still causes air pollution.
Farming
New methods are being developed to farm more food crops on less farm land, such as high-yield hybrid crops, greenhouses, autonomous building gardens, and hydroponics. The reduced farm land means less land is cleared for growing crops. In cyclical agriculture, cattle are grazed on farm land that is resting and rejuvenating. Cyclical agriculture prevents the soil from being overfarmed and stripped of its nutrients - reducing the need for slash-and-burn methods.
Grass is allowed to grow on the resting farm land. The cows eat the grass and leave behind their dung, which is also a source of fertilizer. This process also reduces deforestation by using farmland to graze instead of using forest land.
Social change
Some societies are making efforts to stop or slow deforestation. In China, where large scale destruction of forests has occurred, the goverment has required that every able-bodied citizen between the ages of 11 and 60 plant three to five trees per year or do the equivalent amount of work in other forest services. The goverment claims that at least 1000 million trees have been planted in China every year since 1982. In western countries, increasing consumer demand for wood products that have been produced and harvested in a sustainable manner are causing forest landowners and forest industries to become increasingly accountable for their forest management and timber harvesting practices.
The Arbor Day Foundation's Rain Forest Rescue program is a charity that helps to prevent deforestation. The charity uses donated money to buy up and preserve rainforest land before the lumber companies can buy it. The Arbor Day Foundation then protects the land from deforestation. This also preserves the way of life of the primitive tribes living on the forest land.
See also
References
- Whitney, Gordon G. 1996. From Coastal Wilderness to Fruited Plain : A History of Environmental Change in Temperate North America from 1500 to the Present. Cambridge University Press. ISBN 052157658X
- Williams, Michael. 2003. Deforesting the Earth. University of Chicago Press, Chicago. ISBN 0226899268
- Wunder, Sven. 2000. The Economics of Deforestation: The Example of Ecuador. Macmillan Press, London. ISBN 0333731468
External links
- FAO Forestry (http://www.fao.org/forestry/index.jsp)
- CFAN (http://www.rcfa-cfan.org/english/index.issues.html) - CIDA Forestry Advisory Network
- Mongabay.com (http://www.mongabay.com/home.htm)
- University of Wisconsin: Natural Hazrds: deforestation (http://dmc.engr.wisc.edu/courses/hazards/BB02-09.html)
External links:historic deforestation
- Wang Hongchang, "Deforestation and Desiccation in China :A Preliminary Study" (http://www.library.utoronto.ca/pcs/state/chinaeco/forest.htm)es:Deforestación
fr:Déforestation ja:森林破壊 pl:Wylesianie
