Saturday, August 4, 2007

Deforestation (From Wikipedia, the free encyclopedia)

This article is about the process of deforestation in the environment. For the program transformation in computer science, see Deforestation (computer science).
Deforestation is the conversion of forested areas to non-forest land use such as arable land, pasture, urban use, logged area, or wasteland.[1][not in citation given] Generally, the removal or destruction of significant areas of forest cover has resulted in a degraded environment with reduced biodiversity. In many countries, massive deforestation is ongoing and is shaping climate and geography

Djouce Mountain, along with most of the island of Ireland, was systematically clearfelled during the 17th and 18th centuries, in order to obtain wood mainly for shipbuilding[2].

Jungle burned for agriculture in southern Mexico.

Deforestation in the United States.Source of 1620, 1850, and 1920 maps: William B. Greeley, The Relation of Geography to Timber Supply, Economic Geography, 1925, vol. 1, p. 1-11.Source of TODAY map: compiled by George Draffan from roadless area map in The Big Outside: A Descriptive Inventory of the Big Wilderness Areas of the United States, by Dave Foreman and Howie Wolke (Harmony Books, 1992)

Orbital photograph of human deforestation in progress in the Tierras Bajas project in eastern Bolivia. Photograph courtesy NASA.

Deforestation for agriculture in Benambra, Australia
Deforestation results from removal of trees without sufficient reforestation, and results in declines in habitat and biodiversity, wood for fuel and industrial use, and quality of life. [3]
Since about the mid-1800s the Earth has experienced an unprecedented rate of change of destruction of forests worldwide.[4] Forests in Europe are adversely affected by acid rain and very large areas of Siberia have been harvested since the collapse of the Soviet Union. In the last two decades, Afghanistan has lost over 70% of its forests throughout the country.[5] However it is in the world's great tropical rainforests where the destruction is most pronounced at the current time and where wholesale felling is having an adverse effect on biodiversity and contributing to the ongoing Holocene mass extinction.[6]
About half of the mature tropical forests, between 750 to 800 million hectares of the original 1.5 to 1.6 billion hectares that once covered the planet have been felled.[7] The forest loss is already acute in Southeast Asia, the second of the world's great biodiversity hot spots. Much of what remains is in the Amazon basin, where the Amazon Rainforest covered more than 600 million hectares. The forests are being destroyed at an accelerating pace tracking the rapid pace of human population growth. Unless significant measures are taken on a world-wide basis to preserve them, by 2030 there will only be ten percent remaining with another ten percent in a degraded condition. 80 percent will have been lost and with them the irreversible loss of hundreds of thousands of species.
Many tropical countries, including Indonesia, Thailand, Malaysia, Bangladesh, China, Sri Lanka, Laos, Nigeria, Liberia, Guinea, Ghana and the Cote d'lvoire have lost large areas of their rainforest. 90% of the forests of the Philippine archipelago have been cut. In 1960 Central America still had 4/5 of its original forest; now it is left with only 2/5 of it. Madagascar has lost 95% of its rainforests. Atlantic coast of Brazil has lost 90-95% of its Mata Atlântica rainforest. Half of the Brazilian state of Rondonia's 24.3 million hectares have been destroyed or severely degraded in recent years. As of 2007, less than 1% of Haiti's forests remain, causing many to call Haiti a Caribbean desert.[8] Between 1990 and 2005, the Nigeria lost a staggering 79% of its old-growth forests.[9] Several countries, notably the Philippines, Thailand and India have declared their deforestation a national emergency.[10][11]

There are many causes, ranging from slow forest degradation to sudden and catastrophic clearcutting, slash-and-burn, urban development, acid rain, and wildfires. Deforestation can be the result of the deliberate removal of forest cover for agriculture or urban development, or it can be a consequence of grazing animals, primarily for agriculture. 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, primarily as an outcome of slash-and-burn techniques used by shifting cultivators. Generally loss of biodiversity is highly correlated with deforestation.

Impact on the environment
Generally, the removal or destruction of significant areas of forest cover has resulted in a degraded environment with reduced biodiversity. In many countries, massive deforestation is ongoing and is shaping climate and geography.
Deforestation affects the amount of water in the soil and groundwater and the moisture in the atmosphere. Forests support considerable biodiversity, providing valuable habitat for wildlife; moreover, forests foster medicinal conservation and the recharge of aquifers. With forest biotopes being a major, irreplaceable source of new drugs (like taxol), deforestation can destroy genetic variations (such as crop resistance) irretrievably.
Shrinking forest cover lessens the landscape's capacity to intercept, retain and transport precipitation. Instead of trapping precipitation, which then percolates to groundwater systems, deforested areas become sources of surface water runoff, which moves much faster than subsurface flows. That quicker transport of surface water can translate into flash flooding and more localized floods than would occur with the forest cover. Deforestation also contributes to decreased evapotranspiration, which lessens atmospheric moisture which in some cases 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. According to one preliminary study, in deforested north and northwest China, the average annual precipitation decreased by one third between the 1950s and the 1980s
Long-term gains can be obtained by managing forest lands sustainable to maintain both forest cover and provide a biodegradable renewable resource. Forests are also important stores of organic carbon, and forests can extract carbon dioxide and pollutants from the air, thus contributing to biosphere stability and probably relevant to the greenhouse effect. Forests are also valued for their aesthetic beauty and as a cultural resource and tourist attraction.

Economic impact
Historically utilization of forest products, including timber and fuel wood, have played a key role in human societies, comparable to the roles of water and cultivable land. Today, developed countries continue to utilize timber for building houses, and wood pulp for paper. In developing countries almost 3 billion people rely on wood for heating and cooking.[12] The forest products industry is a large part of the economy in both developed and developing countries. Short-term economic gains made by conversion of forest to agriculture, or over-exploitation of wood products, often leads to loss of long-term income. Both West Africa and Southeast Asia have experienced lower revenue because of declining timber harvests. Illegal logging causes billions of dollars of losses to national economies annually. [13]

Throughout most of history, humans have considered forest clearing as necessary for most activities besides forestry. In most countries, only after serious shortages of wood and other forest products are polices implemented to ensure forest resources are used in a sustainable manner. Typically in developed countries, as urbanization and economic development increases, land previously used for farming is abandoned and reverted to forests. [14]Today in the developed world, most countries are experiencing forest restoration and most losses in forest land is primary driven by expanding urban areas. [15]
In developing countries, human-caused deforestation and the degradation of forest habitat is primarily due to expansion of agriculture, slash and burn practices, urban sprawl, illegal logging, over harvest of fuel wood, mining, and petroleum exploration.
It has been argued that deforestation trends follow the Kuznets curve [16] however even if true this is problematic in so-called hot-spots because of the risk of irreversible loss of non-economic forest values for example valuable habitat or species loss.
The effects of human related deforestation can be mitigated through environmentally sustainable practices that reduce permanent destruction of forests or even act to preserve and rehabilitate disrupted forestland (see Reforestation and Treeplanting).

Definitions of deforestation
Deforestation defined broadly can include not only conversion 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. BY Narrow definition of deforestation is: 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
It has been argued that the lack of specificity in use of the term deforestation distorts forestry issues.[1] The term deforestation is used to refer to activities that use the forest, for example, fuel wood cutting, commercial logging, as well as activities that cause temporary removal of forest cover such as the slash and burn technique, a component of some shifting cultivation agricultural systems or clearcutting. It is also used to describe forest clearing for annual crops and forest loss from over-grazing. Some definitions of deforestation include activities such as establishment of industrial forest plantations are considered afforestation by others. It has also been argued that the term deforestation is such an emotional term that is used "so ambiguously that it is virtually meaningless" unless it is specified what is meant. [2] More specific terms terms include forest decline, forest fragmentation and forest degradation, loss of forest cover and land use conversion. The term also has a traditional legal sense of the conversion of Royal forest land into purlieu or other non-forest land.

Levels of causation
The causes of deforestation are complex and often differ in each forest and country. It may be difficult to determine the cause of deforestation in a particular forest. For example, a rise in the price of soybeans may result in soybean farmers displacing cattle ranchers in order to expand their farms. This might cause cattle ranchers to shift to land previously used by slash and burn farmers. The farmers in turn shift further into the forest that has been made accessible by roads built by loggers. In this case it may not be clear who "caused" deforestation. In this case it could be claimed that while the loggers caused forest degradation and that the slash and burn farmers were agents of deforestation, the cause was demand for farm land. The underlaying causes may be poverty or the trade in international commodities.

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. Actual data support the first two theories as widespread numerical impacts.

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 much of this stored carbon back to the atmosphere. A.J. Yeomans asserts in Priority One that overnight, as trees consume the sugars that they produced during the day, a stable forest releases exactly the same quantity of carbon dioxide back into the atmosphere. Others state that mature forests are net sinks of CO2 (see Carbon dioxide sink and Carbon cycle). Deforestation caused by humans is estimated to contribute to one-third of all carbon dioxide. The water cycle is also affected by deforestation. Trees extract groundwater through their roots and release it into the atmosphere. When part of a forest is removed, the region can not hold as much water and can result in a much drier climate.

Some forests are rich in biological diversity. Deforestation can cause the destruction of the habitats that support this biological diversity, thus causing contributing to the ongoing Holocene extinction event. Numerous countries have developed Biodiversity Action Plans to limit clearcutting and slash and burn agricultural practices as deleterious to wildlife and vegetation, particularly when endangered species are present.

Loss of research potential
The diverse species within rainforests has long been a useful area for research and learning. Apes and other primates in their natural environment are a source of notable research. Numerous significant medications have been developed from genetic materials within forests, many of which pertain to endangered species. Deforestation can subject some of these genetic materials to irreversible loss.[citation needed]

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 (canopy interception);
their litter, stems and trunks slow down surface runoff;
their roots create macropores - large conduits - in the soil that increase infiltration of water;
they reduce soil moisture via transpiration;
their litter and other 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 functions or human services.
The forest may have little impact on flooding in the case of large rainfall events, which overwhelm the storage capacity of forest soil if the soils are at or close to saturation. And this will result in less fresh air.

Soil erosion
Undisturbed forest has very low rates of soil loss, approximately 0.02 metric tons per hectare. Deforestation generally increases rates of soil erosion, by increasing the amount of runoff and reducing the protection of the soil from tree litter. This can be an advantage in excessively leached tropical rain forest soils. 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 nickname '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.

Tree roots bind soil together, and if the soil is sufficiently shallow they act to keep the soil in place by also binding with underlying bedrock. Tree removal on steep slopes with shallow soil thus increases the risk of landslides, which can threaten people living nearby.

Controlling deforestation

New methods are being developed to farm more intensively, such as high-yield hybrid crops, greenhouse, autonomous building gardens, and hydroponics. These methods are often dependent on massive chemical inputs to maintain necessary yields. In cyclic agriculture, cattle are grazed on farm land that is resting and rejuvenating. Cyclic agriculture actually increases the fertility of the soil. Intensive farming can also decrease soil nutrients by consuming at an accelerated rate the trace minerals needed for crop growth.

Forest management
Efforts to stop or slow deforestation have been attempted for many centuries because it has long been known that deforestation can cause environmental damage sufficient in some cases to cause societies to collapse. In Tonga, paramount rulers developed policies designed to prevent conflicts between short-term gains from converting forest to farmland and long-term problems forest loss would cause,[33] while during the seventeenth and eighteenth centuries in Tokugawa Japan[34] the shoguns developed a highly sophisticated system of long-term planning to stop and even reverse deforestation of the preceding centuries through substituting timber by other products and more efficient use of land that had been farmed for many centuries. In sixteenth century Germany landowners also developed silviculture to deal with the problem of deforestation. However, these policies tend to be limited to environments with good rainfall, no dry season and very young soils (through volcanism or glaciation). This is because on older and less fertile soils trees grow too slowly for silviculture to be economic, whilst in areas with a strong dry season there is always a risk of forest fires destroying a tree crop before it matures.

In the People's Republic of China, where large scale destruction of forests has occurred, the government has in the past 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 government claims that at least 1 billion trees have been planted in China every year since 1982. This is no longer required today, but March 12 of every year in China is the Planting Holiday. 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 locks in the way of life of the primitive tribes living on the forest land. Organizations such as The Nature Conservancy, World Wide Fund for Nature, Conservation International, African Conservation Foundation and Greenpeace also focus on preserving forest habitats.

Forest Plantations
To meet the worlds demand for wood it has been suggested by forestry writers Botkins and Sedjo that high-yielding forest plantations are suitable. It has been calculated that plantations yielding 10 cubic meters per hectare annually could supply all the timber required for international trade on 5 percent of the world's existing forestland. By contrast natural forests produce about 1-2 cubic meters per hectare, therefore 5 to 10 times more forest land would be required to meet demand. Forester Chad Oliver has suggested a forest mosaic with high-yield forest lands interpersed with conservation land.[35]

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