Fjölrit RALA - 05.12.1999, Síða 29

RALA Reportno. 200
Desertification in the Mediterranean Europe.
A case in Greece
Nicholas J. Yassoglou and C. Kosmas
Agricultural Universitv of Athens, Athens, Greece
Tel/Fax: 301 804 1 793:E-maiI: nyassog@hol.gr
ABSTRACT
Desertification, as defined by the 1994 Convention of the United Nations, has affected Iarge 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 mois-
ture deficits, climatic variability with frequent extreme events, steep terrain, geologic formations fa-
vouring 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 acceler-
ated 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-eastem Aegean Sea. Three distinct climatic zones exist in the 167,000 hectares island: semi-
arid, subhumid and a transitional zone. Desertification has affected continuous territories in the semi-
arid zone and shows a fragmental pattem 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 cere-
als grazing, land abandonment, dominance of unpalatable thorny small plants (economic desertifica-
tion), buming of thomy vegatation followed by overgrazing resulting in irreversible physical deserti-
fication. Interactions among climate, geology, physiography, soils, vegetation and animals are dis-
cussed.
Key words: desertification, grazing, land abandonment, Lesvos, Mediterranean, soil erosion.
INTRODUCTION
Desertification, or “land degradation in arid, semi-arid and dry subhumid areas, re-
sulting from climatic variations and human activities” (UN-CCD 1994) has been
known to the people of the Mediterranean Europe and has been of concem since an-
cient times. Writers such as Solon, Plato, Theophrastus, Cicero, Pliny and Lucretius
described land degradation and were aware of its consequences, but the degree of
awareness has been uneven through the historical periods (Rubio 1995).
The phenomenon must be distinguished from the classical concept of desert as e.g.
in Sahara Kalahari. where the aridity of the climate is a single and sufficient factor to
cause desert like conditions regardless of the state of other environmental factors.
In Mediterranean Europe, desertification processes are activated and accelerated
only when, in addition to climatic limitations, other land parameters are driven beyond
critical thresholds by human action (e.g. Archer and Stokes 2000). Therefore, the phe-
nomenon is spatially and temporally discontinuous.
VULNERABILITY OF THE LAND
Irrational human action can easily trigger desertification in the semi-arid and in the
dry subhumid zones of Mediterranean Europe, because several land parameters are
unfavourable and/or sensitive to such an action.