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Tundra
Boreal forest
Temperate forest
Temperate grasslands, savannas and shrublands
Desert and dry shrublands
Tropical and subtropical forests
Tropical and subtropical grasslands, savannas and shrublands
Source: adapted from Olson
et al
., 2001.
SAVANNAS AND TROPICAL GRASSLANDS
Savannas cover large areas of Africa and South America and can store significant amounts
of carbon, especially in their soils. Activities such as cropping, heavy grazing and in-
creased frequency or intensity of fires can reduce carbon stored in these systems.
Savannas are a major component of the Earth’s vegetation and
occupy large areas in Sub-Saharan Africa and South America.
The savanna biome is characterised by the co-dominance of
trees and grasses, but ranges from grasslands where trees are
virtually absent to more forest-like ecosystems where trees are
dominant. Most of the savanna areas are natural ecosystems;
however, they can also be formed by the degradation of tropi-
cal forests from burning, grazing and deforestation. In Africa
savanna areas support a charismatic fauna of large mammals
and opportunities for eco-tourism are significant.
The amount of carbon stored above ground depends on how
much tree cover there is, and can range from less than 2 tonnes
of carbon per ha for tropical grasslands to over 30 tonnes per
hectare for woodland savannas. Root carbon stocks tend to be
slightly higher, with estimates of 7–54 tonnes of carbon per ha.
Soil carbon stocks are high compared to those of the vegetation
(~174 t C per ha, Grace
et al.
2006). Savannas and tropical grass-
lands are naturally subject to frequent fires, which are an im-
portant component in the functioning of these ecosystems. Fire
events in savannas can release huge amounts of carbon to the at-
mosphere (estimated at 0.5–4.2 Gt C per year globally). However,
the carbon lost is mostly regained during the subsequent period
of plant regrowth, unless the area is converted to pasture or graz-
ing land for cattle (Grace
et al.
2006) and these ecosystems are
considered currently to act overall as carbon sinks, taking up an
estimated 0.5 Gt C per year (Scurlock and Hall 1998).
HUMAN IMPACTS AND IMPLICATIONS FOR
CARBON MANAGEMENT
Human pressure on these ecosystems is still increasing and
it is estimated that more than one percent of global savanna
is lost annually to anthropogenic fires, cattle raising and agri-
cultural activities.