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The World Resources Institute estimates that more than 50 percent of the earth's natural forests have already been destroyed (Hermosilla 2000). The United Nations Environment Programme (2009) states that "forests cover 30 per cent of the planet's total land area. The total forested area in 2005 was just under 4 billion hectares" As a result a United Nations report has stated that "deforestation and forest degradation are widely recognized as one of the most critical environmental problems facing human society, with serious long-term economic, social and ecological consequences" (UN 1999).
The causes of deforestation are widely debated and are attributed to many causes such as over population and urbanisation such as new settlements and transport extensions (Geist and Lambin, 2002). However one of the main causes of deforestation is attributed to agriculture.
The 'arc of deforestation' along the southern and eastern extent of the Brazilian Amazon is the most active land-use frontier in the world in terms of total forest loss" (Morton et al, 2006) and "Globally, the main forest conversion process in the humid tropics was the transformation of closed, open, or fragmented forests to agriculture" (Achard et al 2002).
Deforestation originally occurred on a small scale level due to subsistence farming or timber collection. However the Amazon rain forest has seen a recent increase in industrial agriculture "intensive mechanized agriculture in the Brazilian Amazon grew by >3.6 million hectares during 2001-2004" (Morton et al, 2006) and this has been a significant source of deforestation in recent years. "In 2010 cattle are projected to be grazing on some 24million hectares of Neotropical land that was once forest in 2000" (Wassenaar et al, 2006).
Figure 1 shows the causes of Amazonian deforestation from 2000- 2005. The pie chart shows that cattle ranching, a part of agriculture is the main cause of deforestation. Cattle ranching accounts for 65-70% of deforestation; vast areas of land are cleared by commercial farmers to raise cattle (for meat and dairy) and to provide pasture land for the cattle to graze. Moreover another major cause of deforestation is small scale agriculture by subsistence farmers. Subsistence farmers are causing deforestation because of poor practices (Butler 2008). Farmers burn the trees to clear them, and then over-exploit the land causing the soil quality to decline which results in the farmers having to find new land (shifting cultivation) and thus destroy more trees. In addition government policies can lead to deforestation. In Brazil the government allows farmers to claim a piece of unclaimed public land which they must use for over a year; and after 5 years they become the official owners of the land and so can sell it and claim new land (Butler 2008). In addition population growth and subsequent food demand is also a cause for expanding agriculture.
Figure 1. (Butler, 2008)
However research has also shown that agriculture is not the main cause or contributor to deforestation. Instead the main cause of deforestation if attributed to population growth, and its subsequent need to find new land for settlements to be built on. Myers, 1984 says that the main reason for deforestation "in the tropics is human population growth. In the African and Asian tropics, it is generally associated with high rates of natural increase (i.e., high net rates of population growth due to high fertility) and, in the Amazon, it is assumed to be the high rates of in-migrationâ€¦ followed by subsequent intergenerational high rates of natural increase".
In addition another primary cause of deforestation, particularly Indonesia is the logging industry. The World Bank (2000) and WRI (2000) state that "the leading cause of Indonesian deforestation in the 1990s has been large-scale commercial logging" (Palmer 2001). Palmer (2001) continues to say that logging causes areas of forest to be cleared, "allowing access to new areas of forest and as a result previously unexploited forest, thus allowing other economic activities such as agricultural conversion and shifting cultivation to take place". Consequently the logging industry can be seen as a major, if not the major contributor to deforestation and not agriculture.
Agriculture has been linked to being a cause of desertification, however a variety of other factors are also causes of desertification and a combination or interaction of processes leads to desertification. The United Nations Conference on Environment and Development defines desertification as "land degradation in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities" (UNCCD, 1992)
The UNCCD states that "Desertification does not refer to the expansion of existing deserts. It occurs because dryland ecosystems, which cover over one third of the world's land area, are extremely vulnerable to over-exploitation and inappropriate land use. Poverty, political instability, deforestation, overgrazing and bad irrigation practices can all undermine the productivity of the land" (UNCCD 2005).
Agriculture plays a large role in desertification, the over grazing of land by animals particularly damaging to the soil and is a major factor contributing to desertification; "overgrazing is by all measures the principal cause of rangeland degradation (Dregne and Chou, 1992).Â Over grazing can occur by having too many animals, or by not managing and controlling the animals grazing activities (Rayburn, 2000). "Overgrazing reduces plant leaf areas, which reduces interception of sunlight and plant growth.Â Plants become weakened and have reduced root length, and the pasture sod weakensâ€¦ Overgrazing can increase soil erosion.Â Reduced soil depth, soil organic matter, and soil fertility hurt the land's future productivity" (Rayburn 2000). Darkoh (2006) highlights that overgrazing in North Africa has led to the desertification of land "led to moderate to severe desertification of rangelands in arid and semiarid zones of Algeria, Libya, Morocco and Tunisia"
Moreover it is not just overgrazing that can lead to soil degradation and desertification. Poor farming techniques such as over exploitation, and constant crop growing without a fallow field can lead to degradation. "Arid and semi-arid regions may initially support agriculture, but repeated cultivation frequently leads to a loss of a soil's nutrients and water-holding capacity. (Global environmental Governance Project, 2009). Over cultivation removes nutrients from the soil which can lead to the soil becoming derogated and infertile, therefore nothing can grow on it which can lead to soil erosion. In addition to this, poor irrigation systems can lead to salinzation of the soil due to groundwater dissolving salts in the soil. When evaporation takes place, this leaves concentrated amounts of salts in the soil which are toxic to plants and thus the land becomes barren.
However agriculture may not be a direct cause of desertification, it can be caused due to knock on effects of population growth and the subsequent increased demand for food.
"In Africa, a leading cause of desertification is human population pressure which leads to overexploitation and intensified stresses on the natural environment. Africa's population has doubled in the past three decades to about 708 million (1994) and continues to expand at a rate of some 3 per cent a year. This means that Africa's farmers must feed an additional 21 million people every year" (Darkoh, 1998).
Moreover population increase can lead to urbanization and more resources being demanded, such as fuel wood which is a common fuel in third world countries; deforestation is also a primary cause of desertification as tree roots bind the soil together, preventing erosion. As a result population pressure has lead to the need for intensive agriculture which can lead to desertification "Increased population pressure on the fragile and vulnerable soils of Africa's dryland regions, leads to overexploitation of water, land, forest and pasture resources through over cultivation, overgrazing and deforestation. These practices therefore constitute the principal threats to the livelihood of millions of people. These are the foremost causes of soil erosion, the rates of which in Africa are among the highest in the world." (Darkoh,1998).
Agriculture plays a large role in deforestation and desertification, but it may not be the main causes of both. Shifting cultivation leads to deforestation as farmers move to new areas of land, often forests which need to be cut down so that the land can be used for agriculture. In addition over grazing and cultivation as well as as poor farming techniques and can lead to desertification. However the real cause of deforestation and desertification can be attributed to government policies and government mismanagement. If governments encourage farmers to seek out new land in the Amazon rain forest, and also do not stop practices of illegal logging. In addition if governments act in their own economic interests and issue policies that lead to environmental harm such as deforestation and desertification then it is not the practices of its people and their techniques (farmers) that cause the damage to the planet, it is the consequence of poor, and often myopic, government policies seeking economic gain; instead of addressing the real causes of the problems of desertification and deforestation. In addition many LEDC's rely on agriculture for economic growth; therefore a balance needs to be met between economic development and sustainability.