Learning Unit 5: Desertification

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Learning Outcomes Define the term "desertification" Classify and explain the causes of desertification Locate the countries within the Sahel Region on a map of Africa Analyse how population growth in the Sahel results in desertification

Definition of desertification The UNCCD defined desertification as land degradation in arid, semi-arid and dry subhumid areas resulting from various factors, including climatic variations and human activities.

Causes of desertification Pages 95-105 in Middleton Five physical processes contributing to desertification: Intensive grazing Overcultivation Overexploitation of vegetation Salinization Drought

Causes of desertification Intensive grazing Overuse of pastures by allowing too many animals or inappropriate types of animals grazing on pastures Removal of biomass by grazing animals and livestock trampling cause soil compaction Decreased vegetation cover increases soil erosion Invasion of desert shrubs contribute to formation of desert pavement Examples: commercial ranches in North America and Australia; Sahel (southern Somalia region in particular)

Causes of desertification Overcultivation Short fallow periods cause nutrient depletion and reduced crop yields Mechanisation causes decreases in soil stability Use of soils in marginal areas, which are more prone to droughts All of the above activities decreases soil organic matter and increases soil erosion Examples: US Great Plains (1930s), Former USSR’s Virgin Lands (1950s) and Niger (1950s and 1960s)

Causes of desertification Overexploitation of vegetation Expansion of grazing or cultivation (agriculture) Provision of firewood Soil is deprived of nutrients and organic matter from decomposing leaf litter Decline in soil structure and fertility May affect water tables Chacoan forests in Argentina example: Use of wood for railways Agricultural expansion Harvesting firewood and fodder Making charcoal

Causes of desertification Salinization of irrigated land The potential evaporation rate of water from soil exceeding the input of water, which allows salts to accumulate near the surface as the soil dries. Salt build-up can occur in the root zone of plants or create saline water tables under irrigated fields Irrigation techniques which lead to salinization are: Water leaks from supply canals Overapplication of water Poor drainage Insufficient application of water to leach salts away Examples: Indus irrigation system in Pakistan, Aral Sea tragedy

Causes of desertification Drought A temporary dry period when precipitation is significantly below normal recorded levels. Three types of drought (meteorological, agricultural, hydrological) Drought and its effects on people vary depending on their coping capabilities. The impact of drought is more severe in some developing countries as in developed countries Examples: Botswana; Niger; Kenya; Ethiopia; Eritrea and Djibouti

Positive changes: Case Study Page 101 in Middleton Reforestation in southern Niger The low-cost method of tree regeneration Amendment of laws in Niger to transfer ownership of trees to farmers Benefits from trees: reducing wind speeds, evaporation and limiting soil and moisture losses Falling leaves used as natural fertilizer Trees producing firewood, fruit and bark Improvement of food security and reducing poverty during a time of rapid population growth Highest tree densities found in areas of high rural population density