Geoscience Reference
In-Depth Information
4.1.1
Causes of Desertification
Desertification is mainly caused by climate variation and human factors. Human
factors are the major elements involved in accelerated land degradation including
population growth, unsustainable economic development, poor environmental and
ecological awareness, over-cultivation and improper conversion of rangelands for
cropping, mis-management of water resources, overgrazing, unsustainable exploita-
tion of fuel wood and uncontrolled collection of herbal medicines, deforestation
and shifting cultivation, terrace cropping on slopes and hilly areas, salinization/
alkalization, oil exploration and mineral mining.
Desertification does not refer to the expansion of existing deserts (Squires 2003 ).
It occurs because dry land ecosystems, which cover over one third of the world's
land area, are extremely vulnerable to over-exploitation and inappropriate land
use practices. Poverty, political instability, deforestation, overgrazing and poor
irrigation practices can all undermine the land's productivities. Climate change is
now believed to contribute also (Reynolds and Stafford Smith 2002 ).
4.1.2
The Processes of Land Degradation
Desertification often results from the degradation of the vegetation cover by
overgrazing, over trampling, fuelwood collection, repeated burning, or inappropriate
agricultural practices. It leads to a general decrease in productivity of the land and
in accelerated degradation of the soil resource due to soil erosion (both by wind
and water), siltation, salinization and alkalinization of irrigated lands, or dryland
salting. The excessive loss of soil nutrients, and sometimes depletion of the soil
seed bank, affects the capacity of the vegetation to recover and constitutes the
principal mechanism of irreversible damage to the environment (Squires 2010a , b ).
The impact of grazing on pastoral rangelands is explained more fully in Li ( 2010 ).
4.2
Consequences of Desertification
China has been severely hit by persistent drought and desertification. Related natural
catastrophes, such as sand-dust storms are increasingly becoming a matter for
national and international concern (Yang et al. 2002 ). Hazards of desertification
in China are serious.
Desertification is generally conceived as a much wider concept than drought, in-
volving not only water availability issues, but also various forms of soil degradation,
loss of biological productivity, and a host of human impacts. Desertification must
be distinguished from drought. The combination of progressive desertification and
drought can be severely crippling to the environment, as the stress created by human
overexploitation of the land becomes especially visible during severe drought.
Droughts and desertification can amplify each other's impacts and the resulting
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