Geoscience Reference
In-Depth Information
Table 26.2.
Major soil groups in drylands and their susceptibility to various forms
of land degradation. (Compiled by the author, based on his field observations in
Africa, Asia and Australia.)
Natural erosion
status
Desertification
hazards
Parent material
Soil group
Fresh or weathered rock
Cambisols
A1
A2, B1
Leptosols
A1
A2
Regosols
A1
A2
Weathered rock
Ferralsols
A1, B1
A2
Limestone
Calcisols
A1
A2
Sand sheets
Arenosols
C1
A1, B1, C3
Alluvium
Fluvisols
A1, B1
A2, B1, D3
Luvisols
A1, B1
A2, B2, C2, D3
Clays
Vertisols
A1, B1
B2, D2
Sands over clays
Planosols
A1, B1
A2, B3, C1, D2
Clays, silts, sands
Solonchaks
A2, B1, D1
A2, B2, D3
Solonetz
A2, B1
A3, B3, D3
A: sheet erosion; B: gully erosion; C: wind erosion; D: salinization
1: minor; 2: moderate; 3: severe
substances), but it is far more difficult to come to grips with the full complexity
of biodiversity and its operation at the three different levels of ecosystems, species
and genes. The 2005 Millennium Ecosystem Assessment painted a bleak picture of
the global threats to species extinction from habitat destruction, the introduction of
invasive species, pollution, the over-exploitation of biological resources and climate
change. It follows that any actions that are taken to prevent or mitigate deserti-
fication processes will also reduce present-day threats to biodiversity in the desert
world.
26.4 Conserving soil and water in drylands
Water, rather than soil, is almost invariably the limiting factor controlling land use
in dry areas (Williams and Balling,
1996
; Barakat and Hegazy,
1997
). However, the
nature of arid land soils can be extremely variable and needs to be taken into account
when planning different forms of land use, whether irrigation, livestock rearing or
rain-fed cultivation.
Table 26.2
is a qualitative portrayal of the erosion hazards and
susceptibility to different forms of land degradation of arid zone soils in Africa,
Asia and Australia based on the author's field observations over many years. If we
compare the natural erosion status listed for different soils in column three with the
desertification hazards listed in column four, it is clear that these soils are often very
