Desertification and land degradation: origins, processes and solutions

Table of Contents

1. Authors and acknowledgements
2. Introduction
   1. Aims
   2. Definitions and key concepts
   3. Synthesis of previous and ongoing projects
   4. Key issues and outline
3. Evolution of desertification in the Mediterranean
   1. Climatic fluctuation
   2. Human influence
4. Primary drivers of desertification
   1. Biophysical and socio-economic causes
   2. Pathways of desertification
   3. Driving forces in the Mediterranean
   4. Synthesis of causes for DESIRE hotspots
   5. Conclusions
5. Processes and consequences of desertification in the Mediterranean
   1. Socio-economic and political factors
   2. Biophysical processes
   3. Conclusions
6. Indicators: monitoring desertification
   1. History of monitoring
   2. Indicators
   3. Monitoring and mapping techniques
   4. Concluding remarks
7. Modelling desertification
   1. Definition of modelling
   2. Model types
   3. Biophysical modelling
   4. Socio-economic and participatory modelling
   5. Gaps and progression in modelling
8. Solutions
   1. Biophysical solutions
   2. Political and socio-economic solutions
9. References

Climatic fluctuation

During the successive glaciations of the Pleistocene, the Mediterranean region was covered by open low biomass producing steppe-like vegetation. This was associated with unstable landscapes and low rates of soil development, erosion and formation of colluvial deposits and large alluvial fans during the middle Pleistocene (Sciortino, 2001). The advance of forests during the temperate interglacials, interrupted these periods of land instability. During the last glaciation prior to its maximum (~30,000 - 25,000 years ago), pollen evidence shows that much of southern Europe was covered by Artemisia steppe interspersed by patches of forests and scattered stands of trees (Grove, 1996). In the eastern Mediterranean shoreland a change in the sedimentation regime took place around 14,000 BP: instead of calcareous arenite, a red soil was being formed, indicating an increase in humidity. The area became rich in vegetation and aeolian dust was deposited (Dan and Yaalon, 1971). During the final cool period of the Younger Dryas (c. 12,900 - 11,500 years ago), precipitation was much lower than at present and wind-borne silt from the Sahara was widely deposited while vegetation was of forest-steppe type (Grove, 1996).

Allen (2003) describes a 'route' of vegetation change in the early Holocene, which started in southern Spain and gradually moved northwards (Gulf of Lion). Evidence from southwestern Turkey (Eastwood et al., 1999), Greece and the Balkans suggest that the mountains acted as glacial refugia from where early expansion of deciduous taxa would have occurred (Allen, 2003). The Climatic Optimum (8000 - 6000 years BP) had a more extensive forest cover and a warmer and moister climate than since the Last Interglacial and was an important period for pedogenesis around the Mediterranean (Grove, 1996). Evidence for an eastern trend in vegetation development is recognized by several authors (e.g. Horowitz, 1975; Gat and Magaritz, 1980; Grove, 1996 and Allen, 2003). Fluctuations in climate were at intervals repeated from around 5000 BP until the Little Ice Age (~1550 - 1850 AD), involving vertical movements of the snow- and tree-line through a few hundred metres (Grove, 1996). Such oscillations, however, are likely to have played a less important role in the modification of the Mediterranean ecosystems than variations in human activity (Grove, 1996).