Geography Reference
In-Depth Information
14
Deforestation
Martin Haigh
radiation. The rain from these clouds helps to
sustain more forest in areas that would otherwise
be too dry (Dickinson 1987).
Deforestation may deprive the Earth of 2.5
Mg×10
9
(Gigatonnes) of above-ground biomass
each year (World Resources Institute 1994). In the
1980s, tropical deforestation was thought to add
4.6 Mg×10
9
of carbon dioxide to the atmosphere,
equivalent to more than 90 per cent of US
emissions from energy and cement production
and perhaps 20 per cent (±10 per cent) of global
emissions from fossil fuel
(ibid.).
Fearnside (1997),
argues that although 90 per cent of the planets
forest biomass remains, continued losses of forest
and
cerrado
savannah could dump 275 Mg×10
6
of
carbon dioxide into the atmosphere through the
next century. Deforestation is also reducing the
planet's ability to cool itself by removing carbon
dioxide from the atmosphere. Using satellite data,
Jang
et al
. (1996) estimate the impact of
deforestation on the decline of global net primary
productivity (NPP). Between 1986 and 1993,
approximately 19 per cent (2,600,000 km
2
) of the
high-NPP regions (>2000 g m
-2
yr
-1
), mainly
tropical rain forests, were reduced to
intermediate-NPP regions (500-1500 g m
-2
yr
-1
)
mainly savannah and cultivated land (Jang
et al
1996).
Lovelock (1991) warns that the loss of the
tropical forests could contribute to a sudden and
dramatic failure of the planet's current system of
climatic regulation, regarded as already being close
to the margins of its stability. Using analyses based
on the mathematics of dynamic systems theory,
INTRODUCTION
Deforestation is an environmental problem that
threatens the survival of the entire current
biosphere. It is counted among the most important
environmental crises facing our planet, not least
because of its role in reducing biodiversity,
increasing global warming and expanding deserts.
However, most humans live in degraded forest
landscapes, agricultural and urban landscapes.
These landscapes, like those of most long-settled
areas, both within and outside the tropics, have
been claimed from forest. They demonstrate that
when the trauma of forest conversion is past,
many—but not all—former forest lands may be
managed sustainably and productively. Forest
conversion is not, inherently, a bad thing for
human society or even for the biosphere. Excessive
forest conversion is another matter.
DEFORESTATION AS
ENVIRONMENTAL CRISIS
The world's forests, especially the tropical forest
belt, have been conceived as part of the planet's
cooling system (Lovelock 1990). Although less
significant than the oceans, (estuaries and) tropical
forests are key regulators. The forests remove
atmospheric carbon dioxide and transform it into
wood, soil, perhaps eventually peat, coal, etc.
Forests also pump water into the atmosphere. The
moisture produced creates clouds, which cool
both the forests and the planet by reflecting solar
