Structure of a global and seasonal carbon exchange model for the terrestrial biosphere the frankfurt biosphere model (FBM)

Carbon exchange fluxes of terrestrial ecosystems are expected to depend on the internal dynamics of C stocks in vegetation and soils, on nutrient availability, and on the local climatic conditions / weather. The model structure which we present focuses on the internal dynamics in the living vegetation. The mathematical description is derived from two basic hypotheses: 1) vegetation tends to maximize photosynthesizing tissue, and 2) the relative amounts of C in pools with relatively short and long turnover times are given by allometric relations. The model can be calibrated for any vegetation type in a typical climate under the condition to meet mean ecological estimates of e.g. biomass and NPP. For C cycle modeling the FBM yields the net CO2 flux between the grid elements and the atmosphere in a daily resolution. It is demonstrated that simulations with a 1°x1° spatial resolution reproduce the response of the time course of C fluxes to local climates.