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

Human influence

Human impact on Mediterranean landscape modification occurred very early. The first hominid site in the Levant was dated at 1.4 million years ago (Conacher and Sala, 1998). The impact of people through hunting and food gathering was, however, insignificant. The use of fire initiates another phase of human impact around 400,000 BP. Since the Neolithic Age (7000 - 4000 years BC), human actions started to having marked effects on European natural ecosystems, becoming prominent during the Bronze Age (Sciortino, 2001). In the former, the beginning of agriculture and pastoral livestock husbandry is considered to have been a major revolution in human technological development (Conacher and Sala, 1998). The Mediterranean areas in Israel, Lebanon, Syria and Turkey were probably the first sites of domestication and cereal cultivation. In the lowlands, extensive clearing by fire and the introduction of the plough led to increased rates of soil erosion (Conacher and Sala, 1998). This corresponds with indications of forest degradation around 6500 BP in southern France and eastern Spain (Vernet and Thiébault, 1987). A time lag of about 1000 years between the beginning of the Neolithic and its consequences in forest degradation is observed by these authors. Another phase of cultivation started around 5000 BP with, according to Conacher and Sala (1998), the domestication of fruit trees and lasted until the end of the Roman period in the 7^th century AD. Land clearance was extensive, affecting the mountainous areas. Terraces were built to minimize erosion and gain agricultural land, soil and water conservation methods were applied and the population grew to the highest numbers in historical time until the present. Roman imperialism caused extensive pressure on Mediterranean resources. Growth of cities and of the large rural and urban populations and extensive engineering works all contributed to increasing pressure on Mediterranean ecosystems. In the 6^th century AD populations decreased, partly as a consequence of conflict between Roman and northern peoples and partly as a result of disease such as the Great Plague of 542 AD (Hodges and Whitehouse, 1983, in Grove, 1996). Trade between east and west diminished, rural estates and towns were abandoned and hydraulic works fell into disrepair (Grove, 1996).

In the eastern Mediterranean, the fifth phase of human influence (Conacher and Sala, 1998), started with the Muslim conquest of the region and the decline of its economy and agriculture. Pastoral nomadism replaced irrigated hill lands and irrigation ditches. The geomorphic effect was increased erosion, loss of soil in the uplands and the creation of swamps in the lowlands due to river siltation (Conacher and Sala, 1998). The Black Death of the mid-14^th century emptied the Mediterranean countryside and a renewed plague in 1376 killed half the remaining people (Grove, 1996). In the course of the 16^th century, climatic fluctuations caused harvests to diminish in some years. These mark the onset of the Little Ice Age, characterized as a cooler and more humid though highly variable climatic period (Puigdefábregas and Mendizabal, 1998), with its maximum in the second half of the 17^th century being around 0.5(C colder than at present. This coincided with social changes, such as religious wars, recurrent famines and plague, resulting in extensive land use changes. An example from Spain where land use changes in the 16^th and 17^th century occurred as a result of the establishment of Christian rule and colonization in America. This caused a southwards expansion of the dryland agriculture that prevailed on the inner Iberian high plains and a high demand for wool and wood products to meet the needs of American settlers (Puigdefábregas and Mendizabal, 1998). The land use changes led to increased erosion, shown by sedimentological, archaeological and ecological evidence (Puigdefábregas and Mendizabal, 1998). The consequences are, among others, increased sedimentation rates, higher flood frequencies and the conversion of forest to grassland in the subalpine belts. This latter conversion caused a downward extension of the solifluction limit with an increase in mudflows and a possible doubling of specific runoff and an increase by 16 times of specific sediment yield (Puigdefábregas and Mendizabal, 1998). In the late 17^th and early 18^th century signs of land shortage, overgrazing, deforestation and erosion became apparent in the rural areas of southern France, northern Italy and Sicily (Grove, 1996). Recent historical changes in the Mediterranean differ between countries. In southern Spain and Portugal, population was sparse due to continued war between the two countries; deforestation as a result of charcoal burning occurred and soils were barren. Crete seems to have been reasonably prosperous in the 18^th century, trading in olive oil and wine (Grove, 1996). Population declined as a result of plague and the Greek War of Independence (1821-28) against Turkey (Grove, 1996) and terraces were probably abandoned during these times. In France, unlike the countries mentioned so far, population increased from 1730 to 1850 by 50% (Price, 1981 in Grove, 1996). The nobles had retained their land and woods, smallholdings were subdivided, marginal lands were cultivated and people depended on their common rights in the forests (Grove, 1996). In the mid-19^th century, arable land declined and populations in the cities grew at the expense of rural communities. In Spain, overpopulation in rural areas is associated with the encroachment of agriculture on rangelands and the increase of stock densities, which was followed by grassland exhaustion and soil loss by erosion (Puigdefábregas and Mendizabal, 1998). In Conacher and Mala (1998), the sixth phase of human influence on the environment consists of the last 100 years, called the technological phase including changes such as land reclamation, monoculture in agriculture and forestry, introduction of exotic plants and animals, mechanization and the use of pesticides and fertilizers. According to these authors, impacts on the environment differed between developed and under-developed regions. In the first, industrialization accelerated and the number of grazing animals declined, reservation of protected areas increased and reforestation occurred. In developing countries, on the other hand, large population growth increased the pressure on natural areas, causing vegetation decrease. According to Coccossis (1991), migration in the 1950s and 1960s was generally out of disadvantaged areas (islands, mountainous areas) and from rural to urban centres. As a result, marginal areas were abandoned, leading to increased erosion. Agricultural production increased due to mechanization and irrigation, intensifying agriculture in some areas but at the same time increasing pressure on local resources (Coccossis, 1991). One of the most important contributors to economic growth in the Mediterranean area, however, was tourism, which increased by 150% in a decade. Additionally, urbanization and growing tourism increased the pressure on coastal areas, where this activity is concentrated.