Models of biogeochemical cycles

With the premise that terrestrial ecosystems play a central role in regulating global biogeochemical and climate systems, a suite of models concerned with biogeochemical cycles, particularly carbon and nitrogen (Melillo et al., 1993), have been developed. Such models commonly use a series of mass balance equations to obtain values for given biogeochemical components and rates of fluxes. The relationship between biosphere carbon stocks and [C02]atm during glacial to interglacial cycles may help us understand the mechanisms that drive change during the 21st century and beyond. How tropical vegetation contributes to the global carbon budget is an area of continued discrepancy and hence research activity (Lewis et al., 2004). With rising atmospheric carbon derived from human activities a focus on investigating changes in the global carbon cycle has resulted in dozens of models to simulate atmosphere-biosphere C02 exchange processes. For example, the terrestrial biosphere model "Carbon Assimilation in the Biosphere'' (CARAIB), now in its fourth incarnation, records a slight increase in the extent of tropical rainforest linked to the colonization of exposed continental shelf, such as Sunda. Carbon stocks are commonly calculated from biosphere models that use standing stock and NPP. Efforts can be divided into models orientated towards global simulations and those orientated towards plot-scale simulations that generally have a complex structure and require a large number of parameters. Indeed, there remain many challenges to scale up the single leaf process, and to parameterize respiration, allocation, deposition, and sequestration (Ito and 0ikawa, 2002).

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