OVER CULTIVATION
Other commonly quoted ways in which human mismanagement causes desertification include “over cultivation”, in which soil is exhausted by nutrient loss and erosion, the excessive clearance of vegetation, often for fuel wood, and poor management of irrigation schemes which results in salinization of soils. Over cultivation occurs due to the shortening of periods when the land is left free from cultivation (“fallow”), or from the use of mechanical techniques, which cause widespread loss of soil. A classic case of over cultivation leading to large-scale wind erosion of soils occurred in the infamous Dust Bowl of the Great Plains of the United States in the 1930s.
DEFORESTATION
Forest and woodland is cleared for a variety of motives, to create agricultural and pasture land for example, but the most serious cause of desertification in this respect is the so-called “fuel wood crisis” which is characteristic of many dry lands in the developing world. The collection of fuel wood from urban hinterlands in the Sahel, the most severely affected region, has resulted in the almost total loss of trees around major cities. Examples include Ouagadougou (Burkina Faso) and Dakar (Senegal), while the radius of the treeless zone around Khartoum in Sudan is 90 km (56 mi).
SALINIZATION
Salinization is one of the clearest examples of human-induced desertification, affecting about one-fifth of all irrigated cropland in Australia and the United States, and one-third in countries such as Egypt, Pakistan, and Syria. The proportion is one-half in Iraq. Excessive concentrations of salts in irrigated soils adversely affect crop yields and can ultimately kill plants.
SAHEL
Sahel a region in western Africa, forming a transition zone between the arid Sahara on the north and the wetter tropical areas to the south.
The Sahel runs from Senegal in the west to Sudan in the east. A relatively sparse savannah vegetation of grasses and shrubs predominates. Rainfall averages between 102 and 203 mm (4 and 8 in) a year and falls mostly from June to September; periods of low rainfall and drought are common, however. An extended drought in the Sahel, lasting from the late 1960s until the early 1980s, the worst in 150 years, suggested an increasingly arid regional climate and increased desertification, bringing the Sahara further south.
EFFECTS
Desertification reduces the ability of land to support life, affecting wild species, domestic animals, agricultural crops and people. The reduction in plant cover that accompanies desertification leads to accelerated soil erosion by wind and water. South Africa losing approximately 300-400 million tonnes of topsoil every year. As vegetation cover and soil layer are reduced, rain drop impact and run-off increases.
Water is lost off the land instead of soaking into the soil to provide moisture for plants. Even long-lived plants that would normally survive droughts die. A reduction in plant cover also results in a reduction in the quantity of humus and plant nutrients in the soil, and plant production drops further. As protective plant cover disappears, floods become more frequent and more severe. Desertification is self-reinforcing, i.e. once the process has started, conditions are set for continual deterioration.
STEPS TO COMBAT DESERTIFICATION
Many organizations have been formed to try and combat desertification. One project is the Eden Project, by the Eden Foundation. The Eden Foundation has a field station loca ted in Niger (North Western Africa), which is researching different ways of revegetating land. Two ways The Eden Foundation has found of revegetating land are direct seeding and natural revegetation.
Desertification is becoming a problem that is drawing a lot of attention. One of the larger responses to it seems to be the United Nations Convention to Combat Desertification (CCD), which has been joined by many countries. Although it is extremely lengthy in description, it is very vague and general.
