Aside from the direct effects of reduced vegetation
cover, especially from overgrazing, wood
collection and deforestation, human-induced land
degradation does not appear to be a serious issue
over the greater part of the global desert area.
Salinization can be an important problem in some
oases, but in true, open deserts, natural vegetation
cover is nearly always sparse, there is no soil
structure, and little or no soil organic matter to
degrade. As will be seen in more detail in Chapter
6, most of the human-induced pressures on the
desert biome tend to concentrate on the deserts'
edges, that is, the transitional ecotones between
deserts and non-desert regions where some
productivity can be derived from the land, and in
the more humid environments inside the desert
biome, such as oases and desert mountains, or
sky-islands. The true deserts, however, which
cover the vast majority of the biome, are normally
too arid and too inhospitable to be the direct target
of large-scale development.
Some impact, however, does occur, and at a
global scale its cumulative effect can be significant.
The deterioration of vegetative cover mostly
increases the amount of dust particles suspended
in the atmosphere. Populations with more direct
exposure to this phenomenon are more likely to
develop allergies and other respiratory ailments.
Sources of dust are largely restricted to severely
disturbed areas, as well as some natural sources
such as lake beds and ephemeral stream channels.
Newly remobilized dunes become an issue for
humans when they advance over settlements and
Military activities and off-road vehicles do
cause extensive, lasting damage to the fragile
desert cover. The Mesopotamian shrub desert
is fascinating from the ecological and cultural
perspectives. Located in the Tigris and Euphrates
River valleys, it is also an important winter stopover
for migrating Eurasian birds and a refuge for the
endangered and sparse populations of wolves,
hyenas, leopards, oryxes, gazelles and wild boars.
This desert, considered a cradle of civilization, has
been greatly impacted by the recent Iraq wars.
Grazing pressure on the desert, and especially on
the desert margin, is the most extensive agent of
land degradation. For example, the Chihuahuan
Desert in Mexico is in a vulnerable conservation
status because cattle grazing and browsing have
damaged sensitive desert scrubs and riparian
habitats. The degradation of these riparian habitats,
coupled with the loss of springs as a result of
aquifer depletion and the diversion of streams for
irrigation, have had a great impact on wildlife that
depends on water sources.
Although mining activities affect small areas directly,
they have significant impacts on surrounding areas.
When the mine reaches the end of its life, the site
is normally abandoned and remains a mixture of
deteriorated materials, mining by-products, and
unproductive rubble, usually coarse, and often of
extremely toxic chemical composition, which is
unfavourable to colonization by plants and animals.
These sites have left a legacy of polluted land
and groundwater, with wide impacts through the
redistribution of toxic elements by wind and flash
floods, in many deserts.
Chile and Argentina have abandoned mines
of copper, lead, and nitrate in the Puna that
are potential sources of contamination due to
inadequate rehabilitation after their closure and
the risk of chemical spillage (Romero and others
2003). The mining centres located at high altitude
in the Dry Andean Puna, a mountain desert, near
the source of rivers that feed irrigation systems
or provide populated areas with drinking water,
are particularly dangerous and require special
consideration. The Rio Grande in the Quebrada
of Humahuaca receives water from the Yacoraite
River that drains from the eastern face of the
Aguilar Mountain, which is currently being mined.
The water of the Yacoraite has high levels of lead,
iron, manganese, and molybdenum unsuitable
for both llama grazing near the mines and the
inhabitants of the Quebrada downstream (Figure
4.9). At the same time, this area has been declared
by UNESCO as a World Heritage Site and is also
an important tourist destination. The freshwater of
the Rio Grande is used for irrigation of orchards
(early season vegetables) that are commercialized
in large urban centres whose population is put at
risk by the metal discharges (Box 4.2).
Mining and salt extraction of sulphates, borates
and others may also contribute to desert wetland
pollution and consequently affect principal sources
of water. Modern mining methods are very
water-intensive. In addition, mining companies
often excavate beneath the water-table and
must pump and remove the groundwater, in the
so-called practice of "dewatering." Dewatering
can cause failures of springs and wells, land
subsidence, and also threatens oases, wetlands
Oil spills on land and in freshwater bodies are
frequent in some Palearctic deserts, and very
damaging to the environment. Spilled oil affects
surface resources and a wide range of subsurface
organisms that are linked in a complex food chain
that includes human food sources. Additionally,
they can harm the environment by direct physical
damage, that is, through the lethal coating of
animals and plants, and by the toxicity of oil itself.