Land Use and Geo-Engineering - Introduction to Carbon Capture and Sequestration - page 526

• Deserts and dry shrublands : Due to low or very seasonal precipitation,

the amount of biomass per unit area in these regions is very small.
The total amount of carbon in these desert areas is 178 Gt.

• Tropical and subtropical grasslands, savannas and shrublands :

Savannas are the largest component of the earth's vegetation. The
total amount of carbon in this biome is 285.3 Gt.

• Tropical and subtropical forests : This biome contains 547.8 Gt of

carbon and thus contains the largest amount of carbon. The high
temperatures enable rapid growth. Most of the carbon is in biomass.

Tundras

The tundras are mainly found in the arctic (see Figure 11.2.3 ). The very
low temperatures cause the plants to grow very slowly during a short
period of the year. The cold temperatures also make the decomposition
process even slower, resulting in a large amount of carbon that has accu-
mulated over the years. The total carbon pool in the tundra is twice as
much as in the atmosphere.
The tundras have been affected very little by land use and have little
potential to gain more carbon. The permafrost associated with tundras,
however, is predicted to be a major contributor to climate change.
Increasing global temperatures can cause the permafrost to decompose,
yielding large additional emissions of CO 2 and CH 4 . This positive feed-
back loop could give rise to signifi cantly higher future temperatures than
are currently predicted by the climate models.

Forests

The boreal, temperate, and tropical forests are important sinks for car-
bon. The boreal forest has the second highest reservoir of carbon,
mainly because modest temperatures prevent decomposition. This low
decomposition rate and the continuous growth make these forests a
net, albeit small, carbon sink.
In the temperate forest, the decomposition rate is much larger, which
also yields very fertile soil. This fertile soil is attractive for conversion into
cropland. In many regions, this conversion process has stopped; in a few
cases, it has even been reverted. Returning croplands back to temperate
forests will return these biomes to carbon sinks.