Page 76 - Soil Degradation, Conservation and Remediation

62 2 Physical Deterioration of Soil

these ecosystems that can be measured by reduced productivity of desirable plants,
undesirable alterations in the biomass and the diversity of the micro and macro fl ora
and fauna, accelerated soil deterioration, and increased hazards for human occu-

pancy.” The formal definition of desertification adopted by the United Nations
Convention on Desertification (UNCCD) in 1994 is, “Land degradation in arid,

semi-arid, and dry sub-humid areas resulting from various factors, including
climatic variations and human activities.” Due to desertification, forests, grasslands,

shrublands, and croplands are converted to desert-like lands. Desertifi cation has
gained growing attention of the international community since the 1970s about its
devastating and destabilizing potential on the natural environment and the human
society. Based on United Nations estimates, the phenomenon has interested nearby
70 % of arid lands, amounting to about 30 % of the world cultivable land. The prob-
lem is particularly severe in Africa and in several developing countries in Asia,
South America, and the Caribbean, but it interests also the USA, Australia, and
Southern Europe (especially Greece, Spain, Portugal, and also Italy) (Eswaran and
Reich 1998 ; Perini et al. 2009 ). According to OECD, the main processes of soil
degradation are due to erosion, submersion, acidification, salinization, soil compac-

tion, surface crusts and compact layers along the profile, loss of organic matter,

deterioration of the soil structure, accumulation of toxic substances, as well as loss
of nutrients (Perini et al. 2009 ). Desertification affects over 2 billion people and

around 100 countries across all 5 continents (Bied-Charreton 2008 ). Ten million ha
productive land with 24 billion tons of topsoil is lost every year due to desertifi ca-
tion. The principal worldwide problems caused by desertification are loss of biologi-

cal productivity, loss of economic productivity, and loss of complexity in the
landscape (UNCCD 1994 ).

2.6.1 Natural Versus Human-Induced Desertifi cation

Causes of desertification are complex, frequently local, and vary from one part of
the world to another. The severity of impact also varies with less-developed coun-
tries experiencing greater human misery. The causes and processes of desertifi ca-
tion are much debated among the experts of many different disciplines such as
geography, ecology, environmental science, economics and sociology. According to

some scientists, desertification is a natural phenomenon occurring due to irregular
fluctuation of short- and long-term drought, as experienced in African Sahel (Hill

and Peter 1996 ). Other scientists believe that desertification is a human-induced

phenomenon resulting from pressures on land resources, unwise development poli-
cies, and misuse of land (Graetz 1996 ). Regions vulnerable to desertifi cation are
undeveloped, poverty stricken, and poor in biomass resources. Soil and vegetation
in the arid and semiarid regions are naturally fragile. Still, human pressure on veg-
etation and land is enormous, but the support of technology, soil, and climate is
inadequate. Culet ( 2002 ) suggested that overgrazing, deforestation, and other agri-
cultural activities may respectively contribute 35, 30, and 28 % to desertifi cation.