Desertification is a type of land degradation in which a relatively dry land region becomes
increasingly arid, typically losing its bodies of water as well as vegetation and wildlife.
It is caused by a variety of factors, such as climate change and human activities. Desertification
is a significant global ecological and environmental problem.
Definitions Considerable controversy exists over the proper
definition of the term "desertification" for which Helmut Geist has identified more than
100 formal definitions.The most widely accepted of these is that of the Princeton University
Dictionary which defines it as "the process of fertile land transforming into desert typically
as a result of deforestation, drought or improper/inappropriate agriculture"
The earliest known discussion of the topic arose soon after the French colonization of
West Africa, when the Comité d'Etudes commissioned a study on desséchement progressif to explore
the prehistoric expansion of the Sahara Desert. History
The world's most noted deserts have been formed by natural processes interacting over long
intervals of time. During most of these times, deserts have grown and shrunk independent
of human activities. Paleodeserts are large sand seas now inactive because they are stabilized
by vegetation, some extending beyond the present margins of core deserts, such as the Sahara,
the largest hot desert. Desertification has played a significant role
in human history, contributing to the collapse of several large empires, such as Carthage,
Greece, and the Roman Empire, as well as causing displacement of local populations.Historical
evidence shows that the serious and extensive land deterioration occurring several centuries
ago in arid regions had three epicenters: the Mediterranean, the Mesopotamian Valley,
and the loessial plateau of China, where population was dense.
Areas affected
Drylands occupy approximately 40–41% of Earth’s land area and are home to more than
2 billion people. It has been estimated that some 10–20% of drylands are already degraded,
the total area affected by desertification being between 6 and 12 million square kilometres,
that about 1–6% of the inhabitants of drylands live in desertified areas, and that a billion
people are under threat from further desertification. As of 1998, the then-current degree of southward
expansion of the Sahara was not well known, due to a lack of recent, measurable expansion
of the desert into the Sahel at the time. Vegetation patterning
As the desertification takes place, the landscape may progress through different stages and
continuously transform in appearance. On gradually sloped terrain, desertification can create
increasingly larger empty spaces over a large strip of land, a phenomenon known as "Brousse
tigrée". A mathematical model of this phenomenon proposed by C. Klausmeier attributes this
patterning to dynamics in plant-water interaction. One outcome of this observation suggests an
optimal planting strategy for agriculture in arid environments.
Causes
The immediate cause is the removal of most vegetation. This is driven by a number of
factors, alone or in combination, such as drought, climatic shifts, tillage for agriculture,
overgrazing and deforestation for fuel or construction materials. Vegetation plays a
major role in determining the biological composition of the soil. Studies have shown that, in many
environments, the rate of erosion and runoff decreases exponentially with increased vegetation
cover. Unprotected, dry soil surfaces blow away with the wind or are washed away by flash
floods, leaving infertile lower soil layers that bake in the sun and become an unproductive
hardpan. Alternatively, recent research has suggested that the movement and migration
of large herds of livestock and wildlife has an integral role in the preservation of vegetation
and soil fertilization, and that the removal of livestock and wildlife has been the main
driver of increasing desertification. Poverty
At least 90% of the inhabitants of drylands live in developing nations, where they also
suffer from poor economic and social conditions. This situation is exacerbated by land degradation
because of the reduction in productivity, the precariousness of living conditions and
the difficulty of access to resources and opportunities.
A downward spiral is created in many underdeveloped countries by overgrazing, land exhaustion
and overdrafting of groundwater in many of the marginally productive world regions due
to overpopulation pressures to exploit marginal drylands for farming. Decision-makers are
understandably averse to invest in arid zones with low potential. This absence of investment
contributes to the marginalisation of these zones. When unfavourable agro-climatic conditions
are combined with an absence of infrastructure and access to markets, as well as poorly adapted
production techniques and an underfed and undereducated population, most such zones
are excluded from development. Desertification often causes rural lands to
become unable to support the same sized populations that previously lived there. This results
in mass migrations out of rural areas and into urban areas, particularly in Africa.
These migrations into the cities often cause large numbers of unemployed people, who end
up living in slums. Countermeasures and prevention
Techniques exist for mitigating or reversing the effects of desertification, however there
are numerous barriers to their implementation. One of these is that the costs of adopting
sustainable agricultural practices sometimes exceed the benefits for individual farmers,
even while they are socially and environmentally beneficial. Another issue is a lack of political
will, and lack of funding to support land reclamation and anti-desertification programs.
Desertification is recognized as a major threat to biodiversity. Some countries have developed
Biodiversity Action Plans to counter its effects, particularly in relation to the protection
of endangered flora and fauna. Reforestation gets at one of the root causes
of desertification and isn't just a treatment of the symptoms. Environmental organizations
work in places where deforestation and desertification are contributing to extreme poverty. There
they focus primarily on educating the local population about the dangers of deforestation
and sometimes employ them to grow seedlings, which they transfer to severely deforested
areas during the rainy season. Techniques focus on two aspects: provisioning
of water, and fixation and hyper-fertilizing soil.
Fixating the soil is often done through the use of shelter belts, woodlots and windbreaks.
Windbreaks are made from trees and bushes and are used to reduce soil erosion and evapotranspiration.
They were widely encouraged by development agencies from the middle of the 1980s in the
Sahel area of Africa. Some soils, due to lack of water can become
consolidated rather than porous. Some techniques as zaï or tillage are then used to still
allow the planting of crops. Another technique that is useful is contour
trenching. This involves the digging of 150m long, 1m deep trenches in the soil. The trenches
are made parallel to the height lines of the landscape, preventing the water of flowing
within the trenches and causing erosion. Stone walls are placed around the trenches to prevent
the trenches of closing up again. The method was invented by Peter Westerveld.
Enriching of the soil and restoration of its fertility is often done by plants. Of these,
the Leguminous plants which extract nitrogen from the air and fixes it in the soil, and
food crops/trees as grains, barley, beans and dates are the most important. Sand fences
can also be used to control drifting of soil and sand erosion.
As there are many different types of deserts, there are also different types of desert reclamation
methodologies. An example for this is the salt-flats in the Rub' al Khali desert in
Saudi-Arabia. These salt-flats are one of the most promising desert areas for seawater
agriculture and could be revitalized without the use of freshwater or much energy.
Farmer-managed natural regeneration is another technique that has produced successful results
for desert reclamation. Since 1980, this method to reforest degraded landscape has been applied
with some success in Niger. This simple and low-cost method has enabled farmers to regenerate
some 30,000 square kilometers in Niger. The process involves enabling native sprouting
tree growth through selective pruning of shrub shoots. The residue from pruned trees can
be used to provide mulching for fields thus increasing soil water retention and reducing
evaporation. Additionally, properly spaced and pruned trees can increase crop yields.
The Humbo Assisted Regeneration Project which uses FMNR techniques in Ethiopia has received
money from The World Bank’s BioCarbon Fund, which supports projects that sequester or
conserve carbon in forests or agricultural ecosystems.
Managed grazing Restoring grasslands store CO2 from the air
into plant material. Grazing livestock, usually not left to wander, would eat the grass and
would minimize any grass growth while grass left alone would eventually grow to cover
its own growing buds, preventing them from photosynthesizing and killing the plant. A
method proposed to restore grasslands uses fences with many small paddocks and moving
herds from one paddock to another after a day a two in order to mimick natural grazers
and allowing the grass to grow optimally. It is estimated that increasing the carbon
content of the soils in the world’s 3.5 billion hectares of agricultural grassland
would offset nearly 12 years of CO2 emissions. Allan Savory, as part of holistic management,
claims that while large herds are often blamed for desertification, prehistoric lands used
to support large or larger herds and areas where herds were removed in the United States
are still desertifying. See also
Aridification Arid Forest Research Institute
Deforestation Oasification
Soil retrogression and degradation Terraforming
Water crisis Mitigation:
Arid Lands Information Network—Kenya Biochar Fertilisation using carbon
United Nations Convention to Combat Desertification Desert greening
Ecological engineering Green Wall of China
Holistic management References
Bibliography
Attribution This article incorporates public domain
material from the United States Government document "http:pubs.usgs.govdeserts".
External links Beyerlin, Ulrich. Desertification, Max Planck
Encyclopedia of Public International Law Bell, Trudy; Phillips, Tony, Dr.. "City-swallowing
Sand Dunes". NASA. Retrieved 2006-04-28. Desert Research Institute in Nevada, United
States Environmental Issues - Desertification in
Africa, The Environmental Blog Eden Foundation article on desertification
FAO Information Portal - Properties and Management of Drylands
UNEP: Global Deserts Outlook UNEP Programme on Success Stories in Land
Degradation/ Desertification Control United Nations Convention to Combat Desertification
- Secretariat Procedural history and related documents on
the United Nations Convention to Combat Desertification in those Countries Experiencing Serious Drought
and/or Dersertification, Particularly in Africa in the Historic Archives of the United Nations
Audiovisual Library of International Law A guide for desert and dryland restoration
by David A. Bainbridge French Scientific Committee on Desertification
Olive Trees May Be The Answer To Desertification The End of Eden on Youtube
News Fighting Desertification Through Conservation
Report on a project to stop the advance of the Sahara in Algeria - IPS, 27 February 2007