Desertification in the Mediterranean Europe: A case in Greece

Desertification, as defined by the 1994 Convention of the United Nations, has affected large areas in the European Mediterranean and is threatening even larger territories. The vulnerability of the land to severe degradation that leads to desertification is attributed to several factors, including: large moisture deficits, climatic variability with frequent extreme events, steep terrain, geologic formations favouring desertification processes, out of phase climatic and vegetative periods, shallow soils and long periods of intensive human interference. Under the existing natural conditions lands have inertia and resilience, and resist extreme degradation. Desertification processes have been triggered and accelerated only by human action.

Process of desertification are either physical or chemical. The dominant physical process is soil erosion, which is activated by the destruction of the vegetative cover and affects marginal sloping lands. Soil salinization and natrification is the dominant chemical process. It is localized but affects valuable low lands and is the result of irrational irrigation practices.

In this paper, we present an example of range land desertification in the island of Lesvos in the North-eastern Aegean Sea. Three distinct climatic zones exist in the 167,000 hectares island: semiarid, subhumid and a transitional zone. Desertification has affected continuous territories in the semiarid zone and shows a fragmental pattern in the transitional zone. Sequential land use changes that lead to acute soil degradation were: destruction of the original oak forest, cultivation of rain-fed cereals
grazing, land abandonment, dominance of unpalatable thorny small plants (economic desertification), burning of thorny vegatation followed by overgrazing resulting in irreversible physical desertification. Interactions among climate, geology, physiography, soils, vegetation and animals are discussed.