Deforestation is the destruction or clearing of forested lands, usually for the purposes of expanding agricultural land or for timber harvesting. When the process is conducted by clearcutting (removal of most or all of the canopy tree growth, leaving few or no live or dead trees standing) or when mass forest burning occurs, significant losses of habitat and biodiversity may result, including the erosion of biological community structure and the extinction of species. Deforestation is proceeding at a rapid pace in may areas of the world, especially in the tropical and boreal forest regions of the earth, with annual net loss of forests during the 1990s estimated in the range of nine to sixteen million hectares per annum. Large scale deforestation may have adverse impacts on biosequestration of atmospheric carbon dioxide, exacerbating greenhouse gas buildup, through the release of stored carbon in tree biomass and reduced CO2 fixation rates due to loss of trees. Deforested regions are often subject to accelerated rates of soil erosion, increased surface runoff and sedimentation of streams and rivers, reduced infiltration and ground water recharge, with adverse water quality impacts on surface water and ground water resources.
Root causes of deforestation include a broad range of economic and social factors, such as (a) poorly formulated property rights systems, (b) widespread poverty and overpopulation, placing pressure on marginally productive lands for subsistence, (c) expansion of agriculture to feed a dramatically increasing human population, (d) short term view of forest management economics at the expense of long term forest productivity and (e) lax forest management. The impacts of deforestation can include the displacement of indigenous peoples from their historic living areas, or the loss of traditional livelihoods and food production and procurement systems. At the current time there is a strong correlation between widespread deforestation and countries which have a low per capita income, deforestation fom commercial timber harvesting is still a problem in many industrialized countries as well.
Types of deforestation
Chief methods of deforestation are: (a) land clearing to prepare for livestock grazing or expansion of crop planting, (b) commercial logging and timber harvests, (c) slash-and-burn forest cutting for subsistence farming, and (d) natural events such as volcanic eruption, stand windthrow from hurricanes, catastrophic forest fires, or changes in local climate and rainfall regimes. It is important to note that those natural factors which may cause deforestation represent only a small fraction of observered deforestation worldwide during historical time.
Causes of deforestation
See Main Article: Causes of deforestation
The predominant driver for deforestation world wide is the clearing of trees to expand agriculture, according to the United Nations Framework Convention on Climate Change. Subsistence agriculture in poor countries is responsible for 48% of deforestation; with commercial agriculture is responsible for 32% of deforestation; and commerical logging is responsible for only 14% of deforestation; charcoal and other fuel wood removals comprise less than 6% of deforestation, but those uses can generally be assigned to subsistence practises.
The degradation of forest ecosystems has also been traced to economic incentives that make forest conversion appear more profitable than forest conservation. Many important forest functions lack readily visible markets, and hence, are without economic value that is apparent to the forest owners or the communities that depend on forests for their well-being. Considerable deforestation arises from a lack of security of property rights and from the absence of effective enforcement of conservation policies, both factors particularly prominent in developing countries; in some cases, terrorism and governmental corruption are concomitant factors in forestn forest losses.
Small scale deforestation was practiced by some societies tens of thousands of years before the present, with some of the earliest evidence of deforestation appearing in the Mesolithic period. These initial clearings were likely devised to convert closed forests into more open ecosystems favourable to game animals. With the advent of agriculture in the mid-Holocene, greater areas were deforested, and fire becamet an increasing methodl to clear land for crops. In Europe by 7000 BC. Mesolithic hunter-gathers employed fire to create openings for red deer and wild boar. From pollen core records, in Great Britain, shade-tolerant species such as oak and ash were being replaced by hazels, brambles, grasses and nettles. Removal of the forests led to decreased transpiration, resulting in increased formation of raised peat bogs. Widespread decrease in elm pollen across Europe between 8400-8300 BC and 7200-7000 BC, starting in southern Europe and gradually moving north to Great Britain, likely represents land clearing by fire at the onset of Neolithic agriculture.