Page 166 - Encyclopedia Of World History

516 berkshire encyclopedia of world history

All our knowledge—past, present, and future—is nothing compared
to what we will never know. • Tsiolkovsky (1857–1935)

fluctuations in vegetation production may take place Experts have debated whether desertification is irre-
from year to year. Meteorological satellite observations of versible. In many cases where ecological conditions are
green biomass production levels on the southern margins favorable because of the existence of such factors as deep,
of the Sahara Desert have revealed such fluctuations. sandy soils, vegetation recovers after excess pressures are
The International Soil Reference Center in the Nether- eliminated. The speed of recovery depends on how
lands conducted a global assessment by soil degradation advanced deterioration is, the size of the area that is de-
(GLASOD) on behalf of UNEP during the late 1980s graded, the nature of the soils and moisture resources,
and early 1990s. The center used a Geographical Infor- and the nature of local vegetation. Much desert vegeta-
mation System to analyze data collected through a clearly tion is adapted to drought and to harsh conditions and
defined, but largely qualitative, methodology. Despite its often has inbuilt adaptations that enable a rapid response
flaws, the GLASOD provided a database through which to improved circumstances.
experts could assess susceptible dry land soil degradation Nonetheless, elsewhere long-term monitoring tends to
in terms of spatial distribution, contributory degradation reveal that in certain circumstances recovery is so slow
processes, and relationships to land use. and so limited that it may be appropriate to talk of “irre-
The GLASOD estimated that during the late 1980s versible desertification.” For example, in southern Tunisia
and early 1990s approximately 1 billion hectares, equiv- tracks made by tanks and wheeled vehicles during World
alent to 20 percent of the susceptible dry lands, had expe- War II are still apparent on the ground and in the dev-
rienced accelerated soil degradation caused by human astated and unregenerated vegetation.
activities.Water erosion was identified as the major phys-
ical process of degradation in 48 percent of this area and Causes of Desertification
wind erosion in 39 percent. Chemical degradation (in- The causes of desertification remain controversial. Experts
cluding salinization) was dominant in just 10 percent of have asked whether it is the result of temporary serious
the area, and physical changes such as compaction and droughts, long-term climatic change, or human actions
crusting in just 4 percent.The severity of degradation was degrading the biological environments in arid zones. No
described by the GLASOD as strong or extreme in 4 per- doubt severe droughts do take place, and their effects
cent of the susceptible dry lands. This figure relates to become worse as human and domestic animal popula-
lands that have had their original biotic (relating to living tions increase.The devastating drought in the Sahel (the
organisms) functions of the soil destroyed and that are semidesert southern fringe of the Sahara Desert) from
irreclaimable without major restorative measures. the mid-1960s caused greater ecological stress than the
The spatial character of desertification is also the sub- droughts of 1910–1915 and 1944–1948, largely be-
ject of controversy.The spread of desert-like conditions is cause of increasing anthropogenic pressures.
not, as popularly supposed, an advance over a broad Experts have discredited the concept that climate is
front in the way that a wave overwhelms a beach. Rather, deteriorating through postglacial progressive desiccation.
it is like a “rash” that tends to be localized around settle- However, numerous studies of meteorological data
ments. Fundamentally, as Mabbutt has explained, “the (which in some cases date back as far as 130–150 years)
extension of desert-like conditions tends to be achieved do not allow experts to reach any firm conclusions on
through a process of accretion from without, rather than systematic long-term changes in rainfall, and the case for
through expansionary forces acting from within the climatic deterioration—whether natural or aggravated by
deserts” (Mabbutt 1985, 2).This distinction is important humans—is not proven. Indeed, Rapp wrote that after
because it influences perceptions of appropriate remedial consideration of the evidence for the role of climatic
or combative strategies. change in desertification his conclusion was “that the