Encyclopedia
The conversion of
forested areas to non-forest. Historically, this meant conversion to grassland or to its artificial counterpart, grainfields; however, the
Industrial Revolution added
urbanization and technological uses. Generally this removal or destruction of significant areas of forest cover has resulted in a degraded environment with reduced
biodiversity. In developing countries, massive deforestation has accompanied mankind's progress since the
Neolithic, and has shaped
climate and
geography.
Deforestation 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 . 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, primarily as an outcome of
slash-and-burn techniques used by shifting cultivators.
Impact on the EnvironmentDeforestation alters the hydrologic cycle, potentially increasing or decreasing the amount of water in the soil and groundwater and the moisture in the atmosphere. Forests support considerable
biodiversity. Forests are valuable habitat for wild
mushrooms and
medicinal conservation and the recharge of
aquifers. With forest bioptopes a major, irreplacable source of new drugs and genetic variations is lost 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; 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 sustainably to maintain both forest cover and provide a biodegrable 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.
Definition of deforestation
Deforestation is the loss or continual degradation of forest habitat due to either natural or human related causes. Agriculture, urban sprawl, unsustainable forestry practices, mining, and petroleum exploration all contribute to human caused deforestation. Natural deforestation can be linked to tsunamis, forest fires, volcanic eruptions, glaciation and desertification. 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.
The term deforestation is often the source of disagreement between various interest groups. Conservation groups often use broad definition while groups seeking to maintain the status quo often use a narrow definition.
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. 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 uses a broad definition of deforestation, while the
Food and Agriculture Organization of the UN uses a narrow definition.
Definitions can also be grouped as those which refer tochanges 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 been used to refer to
fuel wood cutting, commercial
logging and the
slash and burn technique, a component of some shifting cultivation agricultural systems. It is also 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.
The term also has a traditional legal sense of the conversion of Royal forest land into purlieu or other non-forest land.
Causes of deforestation
Present causes
While short-sighted, market-driven
forestry practices are often one of the leading cause of forest degradation, the principal human-related causes of deforestation are agriculture and livestock grazing, urban sprawl, and mining and petroleum extraction. Causes include demand for farm land and fuel wood. Underlining causes include poverty, lack of reform. The causes of deforestation are complex and often differ in each forest and country. Government policies, such as ones in Brazil, make it a priority to resettle some of the country's numerous landless people. The largest cause as of 2006 is
slash-and-burn activity in
tropical forests. Slash-and-burn is a method sometimes used by shifting cultivators to create short term yields from marginal soils. When practiced repeatedly, or without intervening fallow periods, the
nutrient poor soils may be exhausted or eroded to an unproductive state.
Slash-and-burn techniques are used by native populations of over 200 million people worldwide.
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.
History and historical causes
- See timeline of environmental events.
Prehistory
Deforestation has been practiced by humans since the beginnings of civilization.
Fire was 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 7000 BC. Mesolithic foragers used fire to create openings for
red deer and
wild boar. On
Great 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 8400-8300 BC and 7200-7000 BC, starting in southern Europe and gradually moving north to Great Britain, may represent land clearing by fire at the onset of
Neolithic agriculture.
Pre-industrial history
The historic
silting of ports along the southern coasts of
Asia Minor 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, all follow periods of increased settlement growth in the river basins of their hinterlands. In early medieval Riez in upper Provence, alluvial silt from two small rivers raised the riverbeds and widened the floodplain, which slowly buried the Roman settlement in alluvium and gradually moved new construction to higher ground; concurrently the headwater valleys above Riez were being opened to pasturage.
A typical progress trap is that cities are built in a woody area providing wood for some industry which starts consuming it so fast – and without proper replanting – that it becomes impossible to obtain it close enough to remain competitive, leading to the city's abandonment, as happened repeatedly in Ancient Asia Minor. Especially the combination of mining and metallurgy went along this self-destructive path.
Meanwhile most of the population remaining active in the agricultural sector, the main pressure in most areas remained land clearing for crop and cattle farming; fortunately enough wild green was usually left standing for wildlife to remain viable, and the hunting privileges of the elite often protected significant woodlands.
Major parts in the spread of the population were played by monastical 'pioneering' and some feudal lords actively attracting farmers to settle by offering relatively good legal and fiscal conditions – even when they did so to launch or encourage cities, there always was an agricultural belt around and even quite some within the walls.
When on the other hand demography took a real blow by such causes as the
Black Death or devastating warfare this could lead to settlements being abandoned, leaving land to be reclaimed by nature.
The large-scale building of wooden sail ships by European naval owers since the 15th century for exploration, colonization, slave – and other trade on the high seas and naval warfare and piracy meant that whole woody regions were over-harvested, as in Spain, were this contributed to the paradoxical weakening of the domestic economy since Columbus' discovery of America made the colonial activities predominant.
In
Changes in the Land , William Cronon collected 17th century
New England Englishmen's reports of increased seasonal flooding during the time that the forests were initially cleared, though no connection was made at the time.
Industrial pressure
The massive use of
charcoal on an industrial scale was a new acceleration of the onslaught on western forests; even in Stuart England, the relatively primitive production of charcoal has already reached an impressive level.
Deforestation today
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 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 kmē to ca. 120,000 kmē each year. At this rate, all tropical forests may be gone by the year 2090.
Brazil
In Brazil the rate of deforestation is apparently driven by commodity prices. Recent development of a new variety of soybean has lead to displacement of beef ranches and slash and burn farmers which in turn move further into the forest.
Indonesia
There are Large areas of forest in Indonesia that are being lost as native forest is cleared by large multi-national pulp companies and being replaced by plantations.
United States
Upon arrival European-Americans began clearing large areas of forest for wood and agriculture. Beginning in about 1850 farm land began to be abandoned because of soil exhaustion and competition from the mid-west. Also, mechanization allowed land formerly used as pastures for horses to revert to forest. From 1850 to about 1920 the amount of forest land in the United States actually increased. Today the trend in forest cover increase has reversed as
urban sprawl causes conversion of forest as the forest is transformed to suburbs.
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 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 that overnight a stable forest releases exactly the same quantity of carbon dioxide back into the atmosphere. Others state
that mature forests are net sinks of CO
2 .
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.
Numerous countries have developed
Biodiversity Action Plans to limit clearcutting and
slash and burn agricultural practises as deleterious to wildlife, particularly when
endangered species are present.
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 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.
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. 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 .
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 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
Farming
New methods are being developed to farm more food crops on less farm land, such as high-yield
hybrid crops,
greenhouse, autonomous building gardens, and
hydroponics. The reduced farm land is then 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. Selective over farming can also increase the nutrients by releasing such nutrients from the previously inert subsoil. The constant release of nutrients from the constant exposure of subsoil by slow and gentle erosion is a process that has been ongoing for billions of years.
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, whilst during the seventeenth and eighteenth centuries in
Tokugawa Japan 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 . 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.
Afforestation
Today, in
China, where large scale destruction of forests has occurred, the government 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 government claims that at least 1 billion 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 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.
See also
Sources and references
- BBC TV series 2005 on the history of geological factors shaping human history
- A Natural History of Europe - 2005 co-production including BBC and ZDF
- 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 0-521-57658-X
- Williams, Michael. 2003. Deforesting the Earth. University of Chicago Press, Chicago. ISBN 0-226-89926-8
- Wunder, Sven. 2000. The Economics of Deforestation: The Example of Ecuador. Macmillan Press, London. ISBN 0-333-73146-8
- FAO / CIFOR report. Forests and Floods: Drowning in Fiction or Thriving on Facts?
External links
- - Deforestation and its effect on Orchids
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- - CIDA Forestry Advisory Network
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External links: historic deforestation
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- Archaeobotany and siltation at Tell Atchana
- Change in extent of forest and other wooded land 1990-2005
