Deforestation
Deforestation, clearance or clearing is the removal of a forest or stand of trees where the land is thereafter converted to a non-forest use.[1] Examples of deforestation include conversion of forestland to farms, ranches, or urban use.
About half of the world's original forests had been destroyed by 2011, the majority during the previous 50 years.[citation needed] Since 1990 half of the world's rain forests have been destroyed.[citation needed] More than half of the animal and plant species in the world live in tropical forests.
The term deforestation is often misused to describe any activity where all trees in an area are removed.[not in citation given][neutrality is disputed] However in temperate climates, the removal of all trees in an area[not in citation given]—in conformance with sustainable forestry practices—is correctly described as regeneration harvest.[3] In temperate mesic climates, natural regeneration of forest stands often will not occur in the absence of disturbance, whether natural or anthropogenic.[4] Furthermore, biodiversity after regeneration harvest often mimics that found after natural disturbance, including biodiversity loss after naturally occurring rainforest destruction.[5][6]
Deforestation occurs for many reasons: trees are cut down to be used or sold as fuel (sometimes in the form of charcoal) or timber, while cleared land is used as pasture for livestock, plantations of commodities and settlements. The removal of trees without sufficient reforestation has resulted in damage to habitat, biodiversity loss and aridity. It has adverse impacts on biosequestration of atmospheric carbon dioxide. Deforestation has also been used in war to deprive an enemy of cover for its forces and also vital resources. A modern example of this was the use of Agent Orange by the United States military in Vietnam during the Vietnam War. Deforested regions typically incur significant adverse soil erosion and frequently degrade into wasteland.
Disregard or ignorance of intrinsic value, lack of ascribed value, lax forest management and deficient environmental laws are some of the factors that allow deforestation to occur on a large scale. In many countries, deforestation, both naturally occurring and human induced, is an ongoing issue. Deforestation causes extinction, changes to climatic conditions, desertification, and displacement of populations as observed by current conditions and in the past through the fossil record.[5]
Among countries with a per capita GDP of at least US$4,600, net deforestation rates have ceased to increase.[when?][7][8]
Causes
About half of the world's original forests had been destroyed by 2011, the majority during the previous 50 years.[citation needed] Since 1990 half of the world's rain forests have been destroyed.[citation needed] More than half of the animal and plant species in the world live in tropical forests.
The term deforestation is often misused to describe any activity where all trees in an area are removed.[not in citation given][neutrality is disputed] However in temperate climates, the removal of all trees in an area[not in citation given]—in conformance with sustainable forestry practices—is correctly described as regeneration harvest.[3] In temperate mesic climates, natural regeneration of forest stands often will not occur in the absence of disturbance, whether natural or anthropogenic.[4] Furthermore, biodiversity after regeneration harvest often mimics that found after natural disturbance, including biodiversity loss after naturally occurring rainforest destruction.[5][6]
Deforestation occurs for many reasons: trees are cut down to be used or sold as fuel (sometimes in the form of charcoal) or timber, while cleared land is used as pasture for livestock, plantations of commodities and settlements. The removal of trees without sufficient reforestation has resulted in damage to habitat, biodiversity loss and aridity. It has adverse impacts on biosequestration of atmospheric carbon dioxide. Deforestation has also been used in war to deprive an enemy of cover for its forces and also vital resources. A modern example of this was the use of Agent Orange by the United States military in Vietnam during the Vietnam War. Deforested regions typically incur significant adverse soil erosion and frequently degrade into wasteland.
Disregard or ignorance of intrinsic value, lack of ascribed value, lax forest management and deficient environmental laws are some of the factors that allow deforestation to occur on a large scale. In many countries, deforestation, both naturally occurring and human induced, is an ongoing issue. Deforestation causes extinction, changes to climatic conditions, desertification, and displacement of populations as observed by current conditions and in the past through the fossil record.[5]
Among countries with a per capita GDP of at least US$4,600, net deforestation rates have ceased to increase.[when?][7][8]
Causes
Causes According to the United Nations Framework Convention on Climate Change (UNFCCC) secretariat, the overwhelming direct cause of deforestation is agriculture. Subsistence farming is responsible for 48% of deforestation; commercial agriculture is responsible for 32% of deforestation; logging is responsible for 14% of deforestation and fuel wood removals make up 5% of deforestation.[9]
Experts do not agree on whether industrial logging is an important contributor to global deforestation.[10][11] Some argue that poor people are more likely to clear forest because they have no alternatives, others that the poor lack the ability to pay for the materials and labour needed to clear forest.[10] One study found that population increases due to high fertility rates were a primary driver of tropical deforestation in only 8% of cases.[12]
Other causes of contemporary deforestation may include corruption of government institutions,[13][14] the inequitable distribution of wealth and power,[15] population growth[16] and overpopulation,[17][18] and urbanization.[19] Globalization is often viewed as another root cause of deforestation,[20][21] though there are cases in which the impacts of globalization (new flows of labor, capital, commodities, and ideas) have promoted localized forest recovery.[22]
The last batch of sawn wood from the peat forest in Indragiri Hulu, Sumatra,Indonesia. Deforestation for oil palm plantation.
In 2000 the United Nations Food and Agriculture Organization (F A O) found that "the role of population dynamics in a local setting may vary from decisive to negligible," and that deforestation can result from "a combination of population pressure and stagnating economic, social and technological conditions."[16]
Experts do not agree on whether industrial logging is an important contributor to global deforestation.[10][11] Some argue that poor people are more likely to clear forest because they have no alternatives, others that the poor lack the ability to pay for the materials and labour needed to clear forest.[10] One study found that population increases due to high fertility rates were a primary driver of tropical deforestation in only 8% of cases.[12]
Other causes of contemporary deforestation may include corruption of government institutions,[13][14] the inequitable distribution of wealth and power,[15] population growth[16] and overpopulation,[17][18] and urbanization.[19] Globalization is often viewed as another root cause of deforestation,[20][21] though there are cases in which the impacts of globalization (new flows of labor, capital, commodities, and ideas) have promoted localized forest recovery.[22]
The last batch of sawn wood from the peat forest in Indragiri Hulu, Sumatra,Indonesia. Deforestation for oil palm plantation.
In 2000 the United Nations Food and Agriculture Organization (F A O) found that "the role of population dynamics in a local setting may vary from decisive to negligible," and that deforestation can result from "a combination of population pressure and stagnating economic, social and technological conditions."[16]
Environmental problems
Atmospheric
Illegal slash and burn practice inMadagascar, 2010
Deforestation is ongoing and is shaping climate and geography.[27][28][29][30]
Deforestation is a contributor to global warming,[31][32] and is often cited as one of the major causes of the enhanced greenhouse effect. Tropical deforestation is responsible for approximately 20% of world greenhouse gas emissions.[33] According to theIntergovernmental Panel on Climate Change deforestation, mainly in tropical areas, could account for up to one-third of total anthropogenic carbon dioxide emissions.[34] But recent calculations suggest that carbon dioxide emissions from deforestation and forest degradation (excluding peatland emissions) contribute about 12% of total anthropogenic carbon dioxide emissions with a range from 6 to 17%.[35] Deforestation causes carbon dioxide to linger in the atmosphere. As carbon dioxide accrues, it produces a layer in the atmosphere that traps radiation from the sun. The radiation converts to heat which causes global warming, which is better known as the greenhouse effect.[36] Other plants removecarbon (in the form of carbon dioxide) from the atmosphere during the process of photosynthesis and release oxygen back into the atmosphere during normal respiration. Only when actively growing can a tree or forest remove carbon over an annual or longer timeframe. Both the decay and burning of wood releases much of this stored carbon back to the atmosphere. In order for forests to take up carbon, the wood must be harvested and turned into long-lived products and trees must be re-planted.[37] Deforestation may cause carbon stores held in soil to be released. Forests are stores of carbon and can be either sinks or sources depending upon environmental circumstances. Mature forests alternate between being net sinks and net sources of carbon dioxide (see carbon dioxide sink and carbon cycle). In deforested areas, the land heats up faster and reaches a higher temperature, leading to localized upward motions that enhance the formation of clouds and ultimately produce more rainfall.[38] However, according to the Geophysical Fluid Dynamics Laboratory, the models used to investigate remote responses to tropical deforestation showed a broad but mild temperature increase all through the tropical atmosphere. The model predicted <0.2°C warming for upper air at 700 mb and 500 mb. However, the model shows no significant changes in other areas besides the Tropics. Though the model showed no significant changes to the climate in areas other than the Tropics, this may not be the case since the model has possible errors and the results are never absolutely definite.[39]
Illegal slash and burn practice inMadagascar, 2010
Deforestation is ongoing and is shaping climate and geography.[27][28][29][30]
Deforestation is a contributor to global warming,[31][32] and is often cited as one of the major causes of the enhanced greenhouse effect. Tropical deforestation is responsible for approximately 20% of world greenhouse gas emissions.[33] According to theIntergovernmental Panel on Climate Change deforestation, mainly in tropical areas, could account for up to one-third of total anthropogenic carbon dioxide emissions.[34] But recent calculations suggest that carbon dioxide emissions from deforestation and forest degradation (excluding peatland emissions) contribute about 12% of total anthropogenic carbon dioxide emissions with a range from 6 to 17%.[35] Deforestation causes carbon dioxide to linger in the atmosphere. As carbon dioxide accrues, it produces a layer in the atmosphere that traps radiation from the sun. The radiation converts to heat which causes global warming, which is better known as the greenhouse effect.[36] Other plants removecarbon (in the form of carbon dioxide) from the atmosphere during the process of photosynthesis and release oxygen back into the atmosphere during normal respiration. Only when actively growing can a tree or forest remove carbon over an annual or longer timeframe. Both the decay and burning of wood releases much of this stored carbon back to the atmosphere. In order for forests to take up carbon, the wood must be harvested and turned into long-lived products and trees must be re-planted.[37] Deforestation may cause carbon stores held in soil to be released. Forests are stores of carbon and can be either sinks or sources depending upon environmental circumstances. Mature forests alternate between being net sinks and net sources of carbon dioxide (see carbon dioxide sink and carbon cycle). In deforested areas, the land heats up faster and reaches a higher temperature, leading to localized upward motions that enhance the formation of clouds and ultimately produce more rainfall.[38] However, according to the Geophysical Fluid Dynamics Laboratory, the models used to investigate remote responses to tropical deforestation showed a broad but mild temperature increase all through the tropical atmosphere. The model predicted <0.2°C warming for upper air at 700 mb and 500 mb. However, the model shows no significant changes in other areas besides the Tropics. Though the model showed no significant changes to the climate in areas other than the Tropics, this may not be the case since the model has possible errors and the results are never absolutely definite.[39]
Hydrological
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 trees no longer transpire this water, resulting in a much drier climate. Deforestation reduces the content of water in the soil and groundwater as well as atmospheric moisture. The dry soil leads to lower water intake for the trees to extract.[45] Deforestation reduces soil cohesion, so that erosion, flooding and landslides ensue.[46][47]
Shrinking forest cover lessens the landscape's capacity to intercept, retain and transpire 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 study, in deforested north and northwest China, the average annual precipitation decreased by one third between the 1950s and the 1980s.[citation needed]
Trees, and plants in general, affect the water cycle significantly:
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.
Tropical rainforests produce about 30% of our planet's fresh water.[41]
Shrinking forest cover lessens the landscape's capacity to intercept, retain and transpire 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 study, in deforested north and northwest China, the average annual precipitation decreased by one third between the 1950s and the 1980s.[citation needed]
Trees, and plants in general, affect the water cycle significantly:
- their canopies intercept a proportion of precipitation, which is then evaporated 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 contribute to terrestrial evaporation and reduce soil moisture via transpiration;
- their litter and other organic residue change soil properties that affect the capacity of soil to store water.
- their leaves control the humidity of the atmosphere by transpiring. 99% of the water absorbed by the roots moves up to the leaves and is transpired.[48]
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.
Tropical rainforests produce about 30% of our planet's fresh water.[41]
Soil
About soil
Soil is a natural body consisting of layers (soil horizons) that are primarily composed ofminerals which differ from their parent materials in their texture, structure, consistency, color, chemical, biological and other characteristics. It is the unconsolidated or loose covering of fine rock particles that covers the surface of the earth.[1] Soil is the end product of the influence of the climate (temperature, precipitation), relief (slope), organisms (flora and fauna), parent materials (original minerals), and time. In engineering terms, soil is referred to as regolith, or loose rock material that lies above the 'solid geology'.[citation needed] In horticulture, the terms 'soil' is defined as the layer that contains organic material that influences and has been influenced by plant roots and may range in depth from centimetres to many metres.
Soil is composed of particles of broken rock (parent materials) which have been altered by physical, chemical and biological processes that include weathering (disintegration) with associated erosion (movement). Soil is altered from its parent material by the interactions between the lithosphere, hydrosphere, atmosphere, and biosphere.[2] It is a mixture of mineral and organic materials in the form of solids, gases and liquids.[3][4] Soil is commonly referred to as "earth" or "dirt"; technically, the term "dirt" should be restricted to displaced soil.[5]
Soil forms a structure filled with pore spaces and can be thought of as a mixture of solids, water, and gases.[6] Accordingly, soils are often treated as a three-state system.[7] Most soils have a density between 1 and 2 g/cm³.[8] Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic,[9] although fossilised soils are preserved from as far back as the Archean.[10]
Soil is a natural body consisting of layers (soil horizons) that are primarily composed ofminerals which differ from their parent materials in their texture, structure, consistency, color, chemical, biological and other characteristics. It is the unconsolidated or loose covering of fine rock particles that covers the surface of the earth.[1] Soil is the end product of the influence of the climate (temperature, precipitation), relief (slope), organisms (flora and fauna), parent materials (original minerals), and time. In engineering terms, soil is referred to as regolith, or loose rock material that lies above the 'solid geology'.[citation needed] In horticulture, the terms 'soil' is defined as the layer that contains organic material that influences and has been influenced by plant roots and may range in depth from centimetres to many metres.
Soil is composed of particles of broken rock (parent materials) which have been altered by physical, chemical and biological processes that include weathering (disintegration) with associated erosion (movement). Soil is altered from its parent material by the interactions between the lithosphere, hydrosphere, atmosphere, and biosphere.[2] It is a mixture of mineral and organic materials in the form of solids, gases and liquids.[3][4] Soil is commonly referred to as "earth" or "dirt"; technically, the term "dirt" should be restricted to displaced soil.[5]
Soil forms a structure filled with pore spaces and can be thought of as a mixture of solids, water, and gases.[6] Accordingly, soils are often treated as a three-state system.[7] Most soils have a density between 1 and 2 g/cm³.[8] Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic,[9] although fossilised soils are preserved from as far back as the Archean.[10]
Deforestion Affecting Soil
Undisturbed forests have a very low rate of soil loss, approximately 2 metric tons per square kilometer (6 short tons per square mile).[citation needed] Deforestation generally increases rates of soilerosion, 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 underlyingbedrock. Tree removal on steep slopes with shallow soil thus increases the risk of landslides, which can threaten people livin
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 underlyingbedrock. Tree removal on steep slopes with shallow soil thus increases the risk of landslides, which can threaten people livin
Biodiversity
Deforestation on a human scale results in decline in biodiversity.[49] and on a natural global scale is known to cause the extinction of many species.[5] The removal or destruction of areas of forest cover has resulted in a degraded environment with reducedbiodiversity.[50] Forests support biodiversity, providing habitat for wildlife;[51] moreover, forests foster medicinal conservation.[52] With forest biotopes being irreplaceable source of new drugs (such as taxol), deforestation can destroy genetic variations (such as crop resistance) irretrievably.[53]
Illegal logging in Madagascar. In 2009, the vast majority of the illegally obtained rosewood was exported to China.
Since the tropical rainforests are the most diverse ecosystems on Earth[54][55] and about 80% of the world's known biodiversity could be found in tropical rainforests,[56][57] removal or destruction of significant areas of forest cover has resulted in a degraded[58] environment with reduced biodiversity.[5][59]
It has been estimated that we are losing 137 plant, animal and insect species every single day due to rainforest deforestation, which equates to 50,000 species a year.[60] Others state that tropical rainforest deforestation is contributing to the ongoing Holocene mass extinction.[61][62] The known extinction rates from deforestation rates are very low, approximately 1 species per year from mammals and birds which extrapolates to approximately 23,000 species per year for all species. Predictions have been made that more than 40% of the animal and plant species in Southeast Asia could be wiped out in the 21st century.[63] Such predictions were called into question by 1995 data that show that within regions of Southeast Asia much of the original forest has been converted to monospecific plantations, but that potentially endangered species are few and tree flora remains widespread and stable.[64]
Scientific understanding of the process of extinction is insufficient to accurately make predictions about the impact of deforestation on biodiversity.[65] Most predictions of forestry related biodiversity loss are based on species-area models, with an underlying assumption that as the forest declines species diversity will decline similarly.[66] However, many such models have been proven to be wrong and loss of habitat does not necessarily lead to large scale loss of species.[66] Species-area models are known to overpredict the number of species known to be threatened in areas where actual deforestation is ongoing, and greatly overpredict the number of threatened species that are widespread.[64]
A recent study of the Brazilian Amazon predicts that despite a lack of extinctions thus far, up to 90 percent of predicted extinctions will finally occur in the next 40 years.[67]
Illegal logging in Madagascar. In 2009, the vast majority of the illegally obtained rosewood was exported to China.
Since the tropical rainforests are the most diverse ecosystems on Earth[54][55] and about 80% of the world's known biodiversity could be found in tropical rainforests,[56][57] removal or destruction of significant areas of forest cover has resulted in a degraded[58] environment with reduced biodiversity.[5][59]
It has been estimated that we are losing 137 plant, animal and insect species every single day due to rainforest deforestation, which equates to 50,000 species a year.[60] Others state that tropical rainforest deforestation is contributing to the ongoing Holocene mass extinction.[61][62] The known extinction rates from deforestation rates are very low, approximately 1 species per year from mammals and birds which extrapolates to approximately 23,000 species per year for all species. Predictions have been made that more than 40% of the animal and plant species in Southeast Asia could be wiped out in the 21st century.[63] Such predictions were called into question by 1995 data that show that within regions of Southeast Asia much of the original forest has been converted to monospecific plantations, but that potentially endangered species are few and tree flora remains widespread and stable.[64]
Scientific understanding of the process of extinction is insufficient to accurately make predictions about the impact of deforestation on biodiversity.[65] Most predictions of forestry related biodiversity loss are based on species-area models, with an underlying assumption that as the forest declines species diversity will decline similarly.[66] However, many such models have been proven to be wrong and loss of habitat does not necessarily lead to large scale loss of species.[66] Species-area models are known to overpredict the number of species known to be threatened in areas where actual deforestation is ongoing, and greatly overpredict the number of threatened species that are widespread.[64]
A recent study of the Brazilian Amazon predicts that despite a lack of extinctions thus far, up to 90 percent of predicted extinctions will finally occur in the next 40 years.[67]