Geoscience Reference
In-Depth Information
A century later, the geographer A.T. Grove pointed out that 'nomadic flexibility is
an advantage to people living in fluctuating, marginal environments, and nomadic
mobility allows good use to be made of variable grazing' (Grove,
1974
, p. 151). He
went on to observe that unfortunately the traditional systems of pastoral nomads 'do
not fit neatly into the framework of a modern state' (op. cit., p. 151). The problem
is exacerbated in times of severe drought when nomadic pastoralists move into land
that has been cultivated by sedentary farmers during the dry season , especially when
traditional modes of conflict resolution have been taken over by a remote central
government. The roots of the current violence in Darfur in arid western Sudan stem
from these causes. Friction between herder and cultivator is nothing new, as shown
by the recurrent nineteenth-century conflicts between cowboys and sodbusters in the
drylands of the North American Southwest.
A tricky problem in many degraded rangelands is how to separate out the effects of
climatic fluctuations such as drought from those of overgrazing and indirect human
modification of the vegetation communities (Nicholson,
2011
). One useful approach
to this complex issue, tested in both Australia and Botswana, is to monitor changes
in land cover along selected transects, starting near the main watering points where
overgrazing pressure is likely to be greatest, and to see whether plant recovery fol-
lowing the end of a drought returns to the same condition as in areas deemed to be
the least degraded (Pickup,
1998
; Dube and Pickup,
2001
). In an effort to assess plant
cover across six types of terrain common in semi-arid south-east Botswana, Dube
(
1998
) used different wave bands of SPOT and Landsat imagery but found that the
variance in vegetation within a given landscape exceeded the variance in vegetation
cover between different landscapes. She later developed a more precise method of
estimating plant cover, in this instance woody plant density in communal and lease-
hold land tenure systems in semi-arid north-west Botswana, using aerial photographs
and a carefully devised set of protocols (Dube,
2008
). These studies show the diffi-
culties involved in gauging changes in plant cover, and also highlight the importance
of taking into account differences in spatial scale.
Although there is far less in the way of both biomass and biodiversity in the desert
world than in the tropical rainforests, the harsh conditions in deserts have led to a wide
variety of adaptations to hot, dry environments that may prove to have great survival
value should severe and prolonged droughts become more common in the future (see
Chapter 25
). In public discourse, biodiversity is consistently undervalued, not least
because of the conflict between economic development and habitat conservation, as
Aldo Leopold noted in 1949. Capitalism and free-market enterprise are not best-fitted
to place an appropriate value on what have been termed ecosystem services, such as
the provision of oxygen to the air we breathe as a by-product of photosynthesis. It is
relatively easy to understand the significance of, say, ozone depletion (hence the rapid
international agreement to sign the Montreal Protocol phasing out ozone-depleting
