Geography Reference
In-Depth Information
and images from the liveliest traditions of
environmentalism, Lovelock predicts a future of
unprecedented and violent environmental
fluctuation (Lovelock 1990). This would be
followed by an abrupt jump to an equilibrium
state, with a very much higher stable planetary
temperature. Lovelock (1990) links the
destabilising influences of deforestation and
accelerated soil erosion together as a planetary
disease, 'exfoliation'. The guru's advice to
environmentalists is to plant trees and to minimise
the release of greenhouse gases to the atmosphere,
even if that means using nuclear energy rather
than burning fossil hydrocarbons (Lovelock 1990).
Indeed, NASA-based Noever and team (1996)
calculate that, to preserve its current temperature
regime, the planetary system already requires more
forest and less desert.
On the smaller landscape scale, where most
geographers work, deforestation affects most of
the issues that concern geographers. It impacts on
both macro- and micro-scale climatic patterns
(Reading
et al
. 1995). It leads to dysfunctions in
landscape systems, which are caused by the
interrelated degradation of its climatic,
hydrological, edaphic and biological components.
Deforestation allows increased soil erosion,
increased landslide activity, sediment pollution,
changes in fluvial geomorphology, and changes in
the hydrological, biogeochemical and climatic
regime (Haigh 1984). Tropical forests are
enormously complex and highly stable systems.
After deforestation, they are replaced with systems
that are much simpler and have much reduced
biodiversity and much lower stability (Reading
et
al
. 1995). These replacements are, in general, much
less efficient in the tasks of self-preservation, they
retain and recycle nutrients less efficiently, but they
may recover more rapidly from disturbances such
as destruction by fire.
Given its significance, current estimates of
deforestation are alarming. Of course, these
estimates, in common with those for similar global
issues—soil erosion, soil degradation, biodiversity
loss and the rate of species going extinct—are
often suspect. Their range is huge and shifts
according to the definition of deforestation
applied, the techniques used for estimation and
their efficiency, the method employed to convert
remotely sensed data into deforestation data, and
the geographical areas selected to 'ground-truth',
that is calibrate empirically the remotely sensed
data (Grainger 1993; Parisi and Glantz 1992;
cf
.
Skole and Tucker 1993). This is quite apart from
any shift caused by the bias and ambitions of those
who would use such data. However, recent years
have seen a convergence of estimates (Downton
1995).
Forest, of some description, covers about 40 per
cent of the Earth's land surface. The FAO Forest
Resource Assessment suggests that the world's
forests cover 3454 million ha (1995), a little more
than half of which lies in developing nations. The
FAO (Food and Agriculture Organisation of the
United Nations) definition includes forests with a
greater than 10 per cent crown canopy cover in
the developing world and 20 per cent cover in the
developed world (World Resources Institute
1996). The FAO (1997) also suggests that 15.4
million ha of tropical forest is lost annually. Myers
(1993) suggests that the loss to the entire biome is
about 2 per cent per year. Murali and Hegde
(1997) prefer 1.8 per cent and that the rate is
greatest in the smaller nations, especially in Africa.
The World Resources Institute (Washington)
suggests that the true rate is 0.8 per cent per year.
It adds that, between 1960 and 1990, Asia lost
nearly a third of its tropical rain forest and Africa
and Latin America a sixth each. However, the rate
of increase in the area deforested declined
everywhere except Latin America, where
agricultural extension continued to accelerate
(World Resources Institute 1994).
Around 50 per cent of the surviving tropical
rain forests are found in the Amazon basin. Skole
and Tucker (1993) used Landsat images to
determine that, between 1978 and 1988, the
deforested area had expanded from 78,000 to
230,000 ha and that threatened or degraded had
increased from 208,000 to 588,000 ha. Elsewhere,
others offer more dramatic figures. For Venezuela,
Centeno (1996) argues that during the 1980s,
deforestation affected 6 million ha and that the
average rate of deforestation (1.2 per cent per year)
