The Natural Fix?

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.

carbon stored in the vegetation is considerably lower, with typical quantities being around 2–30 tonnes of carbon per ha in total.

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

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.

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.

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