Land Use and Geo-Engineering - Introduction to Carbon Capture and Sequestration - page 523

in land use have resulted in net carbon sinks. Unfortunately, the positive
effects in these countries are more than compensated by emissions asso-
ciated with changes in land use in other parts of the world.
In Chapter 3 (The Carbon Cycle), we stated that 2,100 Gt of carbon
is stored in the biosphere and soil (in living organisms and organic matter
in soil), which is about twice the amount of carbon we fi nd in the atmos-
phere. This organic matter is not uniformly distributed over the planet; in
each part of the world the organic matter is stored in a different form.
Changes in the land use will be dependent on this [11.2].
Figure 11.2.2 shows the distribution of terrestrial carbon over the
planet. We see that most of the terrestrial carbon is stored in the tropics
and in the high altitude regions. In the tropical regions the carbon is
mainly biomass, while in the high altitude regions it is in the form of per-
mafrost (permanently frozen layers of soil).
Managing land use in a permafrost region will be very different from
managing land use in a tropical forest. We can consider the terrestrial
world as being comprised of seven distinct biomes, each of which stores
carbon in a very different format. Figure 11.2.3 summarizes the relative
amounts of carbon in the seven biomes.

The different biomes are:

• Tundras : Tundras contain 155.4 Gt carbon. Only slow growing, sturdy

plants can survive this harsh climate. Cold temperatures prevent plant
decomposition and the soil contains a large amount of frozen dead
plant materials (permafrost).

• Boreal forests : Boreal forests contain 384.2 Gt. Because of the low

temperatures the decomposition is very slow and most of the carbon
is in the soil.

• Temperate forests : In a temperate forest, the temperatures are higher,

resulting in rapid decomposition of organic material. The total amount
of carbon is 314.9 Gt.

• Temperate grasslands, savannas and shrublands : The typical vegeta-

tion in these parts of the world is too dry for forests, yet these regions
get more rain than forests. Grazing animals are an essential part of
grassland ecosystems. Often these lands can be successfully con-
verted to crop production with little impact on the carbon balance.
These areas contain less biomass per unit surface than forests. The
total amount of carbon in this biome is 183.7 Gt.