11.2.1.4. Drylands
Precipitation is scarce and has a high annual variance in dryland areas. Very
high daily temperature variance is recorded with frequent sand storms, dust
ghost, and intense sunshine. Arid plants usually belong to drought escaper,
drought evader, drought resister, or drought endurer categories. Evaporative
losses and water limitations are the most prominent factors dictating animal
life in arid environments. Low rainfall dictates the formation of shallow or
extremely sallow soils that often are characterized by high content of airborne
particles and small fractions of rock-erosion elements. Most of the soils are
poor in or completely devoid of organic matter, and the nutrient pools of the
soils are low. Apparently, humans not only utilize the ecosystem services of
this region but are also influencing the evolution of some of its important
biotic elements. In Mongolia, for example, while soil fertility has decreased
by about 20% in the past 40 years, about one-third of the pasturage has been
overgrazed and 5 Mha of arid land have constantly been threatened by moving
sands (Khuldorj et al., 1998). Soils exposed to degradation as a result of poor
land management could become infertile as a result of climate change. Temperature
increases would have negative impacts on natural vegetation in desert zones.
Plants with surface root systems, which utilize mostly precipitation moisture,
will be vulnerable. Climate change also would have negative impacts on sheep
breeding and lamb wool productivity.
Just as shifts in vegetation belts are expected in non-drylands, in the drylands
of Asia a shift in dryland types is expected as a result of climate change.
Drylands are ranked along an aridity index, in relation to the ratio of precipitation
to potential evapotranspiration (i.e., to a gradient in soil moisture available
for driving production). Because soil moisture is likely to decline in this
region, the least-dry land type (dry subhumid drylands) are expected to become
semi-arid, and semi-arid land is expected to become arid. It is notable that
population pressure on dryland resources is reduced with increasing aridity,
but resistance to degradation and resilience following degradation also is reduced
with increasing aridity. Therefore, semi-arid drylands, which are intermediate
in aridity as compared to arid drylands and dry subhumid ones, are most susceptible
to becoming further desertified (Safriel, 1995). Because semi-arid drylands
are very common among Asian drylands, large areas will become not only dry but
also desertified as a result of climate change,.
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