Highly Simplified Model of Terrestrial Carbon Balance

In order to consider the mechanisms that may be producing a carbon sink in the terrestrial biosphere, it is useful to consider a highly simplified model of terrestrial carbon dynamics. Using just a few equations, we can describe the flow of carbon from the atmosphere into vegetation, litter, and soil carbon pools. Here we use a simplified model based on Foley (1995) (Figure 14.3).

In this highly simplified model, the carbon balance of vegetation can be written as:

dt î=iî i=i t v,i where Cv is the carbon storage within vegetation biomass, NPP is the total net primary productivity of the ecosystem, ai is the allocation coefficient for different vegetation pools (leaves, wood, and roots), Tv is the average residence time of carbon in biomass pools, and D is the removal of biomass through disturbances or land use.

When vegetation biomass is lost (through natural turnover or mortality), it is sent to litter—the amount of "dead" carbon that is beginning to decompose—forming CO2 and soil organic matter. We can represent the carbon balance of the litter pool as:

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