Environmental Issues in the 21st Century - Desertification and Degradation

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  • Created by: nicola
  • Created on: 18-04-11 16:13

Land degradation - a reduction and loss of biological and economic productivity caused by land use change or by a physical process

Desertification - the spread of desert like conditions in arid and semi-arid areas. Processes tend to affect the moisture availability in an area and changes can be seen through a sustained reduction in biological productivity 

Causes can be natural or human or a combination of the two - many issues linked to global warming. Some include:

  • Surface run-off and erosion (usually from extreme rainfall events)
  • Wind erosion (burial and ablation - minimal in Med as not much loose sand, main issue near deserts)
  • Salinization (mainly from over-abstraction of water from irrigation uses but also coastal flooding)
  • Lowering of groundwater  (e.g. in Azrat area - causes reduction in bioproductivity and diversity)

However, causes may vary depending on the area in question

Issues of salinisation - hard to measure as some bedrock contains more salt than others therefore water may have higher sodium content but not necessarily a problem

Thornes (2009) - Sensitivity of Med to Soil Erosion

Highlights the importance of land deg by soil erosion - high in many areas of the Med particularly Spain, Iberia, southern Italy and Greece

Areas of high soil erosion match those with areas that are vulnerable to desertification 

Optimum conditions for erosion - enough rainfall to erode soil but not enough to trigger extensive veg growth to protect soils

  • Low levels of erosion in driest parts e.g. Sahara - low rainfall and low veg growth
  • Low levels in areas with dense veg cover such as forests (UK)

Naveh and Dan (1973) - Seven phases of degradation

  • Phase 1 = Palaeolithic (1 Ma - 100ka) - minimal degradation
    • Humans were hunter gatherers therefore minimal change to ecosystems
  • Phase 2 = <400ka - human use of fire
    • Possibility that fire was used prior to this but no evidence for this and no evidence that fire clearance had an impact on land degradation
  • Phase 3 = Neolithic (8-6ka) - onset of agriculture
    • Clearing of the land i.e. deforestation to make space for agriculture - more sedentary societies
  • Phase 4 = Roman period (4ka) - extensive land clearance 
    • Terracing of hillsides and irrigation
  • Phase 5 = Muslim conquest - variable impact
    • In Spain, well ordered irrigation and terrace systems
    • Levant - return to nomadism
    • Possibility that land deg was minimal due to ordered management therefore impacts vary depending on location
  • Phase 6 = Technological phase (late 19th C)
    • Widespread irrigation and monoculture agriculture i.e. single crops grown on a large scale for cash - caused large amounts of land deg
  • Phase 7 = 20th C industrialised agriculture
    • Reduction of rural pops seen (migration to urban areas) and as a result abandomnent of rural practices - terraces and other formations caused more deg especially to hillsides

Phases 4-7 were times of major population increases causing stress on…

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