Environmental Engineering Reference
In-Depth Information
links cannot be ignored. They clearly need
additional investigation.
The problem of the destruction of woodland
will also have to be addressed if desertification
is to be prevented. Trees and shrubs protect the
land against erosion, yet they are being cleared
at an alarming rate. One hundred years ago in
Ethiopia, 40 per cent of the land could be
classified as wooded; today only 3 per cent can
be designated in that way (Mackenzie 1987b).
Good land-use planning would recognize that
certain areas are best left as woodland, and
would prevent the clearing of that land for the
expansion of cultivation or the provision of fuel
wood. The latter problem is particularly serious
in most of sub-Saharan Africa where wood is
the only source of energy for most of the
inhabitants. It also has ramifications which
reach beyond fuel supply. Experience has
shown that where wood is not available animal
dung is burned as a fuel, and although that may
supply the energy required, it also represents a
loss of nutrients which would normally have
been returned to the soil. Any planning
involving the conservation of fuelwood must
consider these factors, and make provision for
an alternative supply of energy or another
source of fertilizer.
Many of the techniques which could be
employed to prevent desertification are also
considered capable of reversing the process.
Certainly there are areas where the destruction
of the land is probably irreversible, but there have
also been some successes. In parts of North
America, land apparently destroyed in the 1930s
has been successfully rehabilitated through land-
use planning and direct soil conservation
techniques such as contour ploughing, strip
cropping and the provision of windbreaks.
Irrigation has also become common, and methods
of weather modification, mainly rain making,
have been attempted, although with inconclusive
results (Rosenberg 1978). Many of these methods
could be applied with little modification in areas,
such as Africa, where desertification is rampant.
Dry-farming techniques have been introduced
into the Sudan (CIDA 1985); in Ethiopia, new
forms of cultivation similar to contour ploughing
have been developed to conserve water and
prevent erosion (Cross 1985b); in Mali and other
parts of West Africa, reforestation is being
attempted to try to stem the southward creep of
the desert (CIDA 1985). Most observers consider
the success rate of such ventures to be limited
(Pearce 1992f). Problems arise from the
introduction of inappropriate technology, from
the unwillingness of farmers or pastoralists to
adopt the new methods and from a variety of
economic factors, including, for example,
fertilizer costs and the availability of labour
(Nelson 1990). There is clearly no universal
panacea for desertification. Solutions will have
to continue to be specific to the issue and the
location, but even then there can be no guarantee
that solutions which appear ideal in the short-
term will not ultimately exacerbate the problem.
The lack of moisture has been tackled directly in
many areas, for example, by the drilling of
boreholes to provide access to groundwater.
Logical as this may seem, without strict control,
it may not be the best approach. Extra water
encourages larger flocks and herds which
overgraze the area around the borehole. Le
Houerou (1977) has pointed out that around
some of the boreholes drilled at the time of the
Sahelian drought, the pasture was completely
destroyed within a radius of 15-30 km around
the bore. Subsequent investigation, however, has
suggested that this was primarily a local problem
at only a few wells, and its impact was therefore
much less than originally estimated (Pearce
1992f).
All of these developments deal directly with
the physical symptoms of desertification, but it
has been argued that many studies have over-
looked economic and social constraints (Hekstra
and Liveman 1986). Ware (1977) has suggested,
for example, that insufficient development of
markets, transportation and welfare systems
made a major contribution to the problems in
the Sahel, and future planning must give these
factors due consideration. The profit motive is
also an important factor in some areas. In Kenya,
experience in agroforestry schemes indicates that
