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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.
DESERT AND DRY SHRUBLANDS
The large surface area of drylands gives dryland carbon sequestration a global signifi-
cance, despite their relatively low carbon density. The fact that many dryland soils have
been degraded means that they are currently far from saturated with carbon and their
potential to sequester carbon can be high.
Deserts and dry shrublands occupy regions of very low or
highly seasonal precipitation and can be found in numerous
regions including many parts of Africa, southern USA and
Mexico, parts of Asia and over large areas of Australia. The slow
growing vegetation consists mainly of woody shrubs and short
plants and is highly adapted to minimise water loss. Like plant
diversity, animal diversity is generally low.
The lack of moisture determines the way in which these ecosys-
tems process carbon. Plant growth tends to be highly sporadic
and plants invest heavily in protecting themselves against water
loss and herbivores by making their tissues tough and resistant
to decomposition. Lack of water also slows decomposition rates,
leading to the accumulation of carbon-rich dead plant material
in the soil. Amundson (2001) estimates carbon content of desert
soils as between 14 and 100 tonnes per ha, while estimates for dry
shrublands are as much as 270 tonnes per ha (Grace 2004). The
carbon stored in the vegetation is considerably lower, with typical
quantities being around 2–30 tonnes of carbon per ha in total.
Some recent studies have suggested that carbon uptake by des-
erts is much higher than previously thought and that it con-
tributes significantly to the terrestrial carbon sink (Wohlfahrt
et al.
2008). However, considerable uncertainties remain and
there is need for further research to verify these results, for ex-
ample by quantifying above- and below-ground carbon pools
over time (Schlesinger
et al.
2009).
HUMAN IMPACTS AND IMPLICATIONS FOR
CARBON MANAGEMENT
As these ecosystems are generally nutrient poor, they tend to
make poor farmland and food production on these lands is
often at a subsistence level. Land degradation, resulting from
inappropriate land uses, leads to carbon loss from the soil.