The Frankfurt biosphere model. A global process orientated model for the seasonal and long-term CO2 exchange between terrestrial ecosystems and the atmosphere. (II) Global results from potential vegetation in an assumed equillibrium state
Climate Research, (1997)DOI: 10.3354/cr008061
Abstract
Regional variability and seasonal courses of atmospheric CO2 provide important clues to the understanding of the carbon exchange fluxes which determine the global carbon budget. We apply the Frankfurt Biosphere Model (FBM) to all 32 vegetation types of a modified global Matthews' vegetation map, simulating seasonal carbon exchange fluxes of the terrestrial ecosystems and their geographical variability on a global scale. For each 0.5° by 0.5° grid element the model calculates gross photosynthesis of the canopy and autotrophic respiration on an hourly time step, and heterotrophic respiration as well as the model-compartment sizes and LAI (leaf area index) on a daily time step. The driving variables temperature, irradiation, and soil moisture are derived from the Cramer and Leemans database. Soil moisture is calculated by an improved bucket model in which the soil properties given by the FAO soil map are combined with the rooting depth of different vegetation types to deduce the available water capacity and the permanent wilting point. Based on mean estimates of ecological variables e.g. net primary production (NPP), biomass and soil carbon and a characteristic seasonal climate, the free parameters of each vegetation type are calibrated. With these parameters, taking the climate variation within the vegetation types into account, the seasonal courses of NPP are calculated, summing up to a global annual integral of 50.3 Gt C yr-1. The results are presented in the form of a world map showing the annual NPP and a table with monthly values of NPP averaged over 5° latitude belts. The latter results are graphically displayed not only for NPP but also for heterotrophic respiration and the resulting seasonal net ecosystem production. Since the FBM keeps track of the seasonal development of leaf biomass, the corresponding seasonal LAI is examined for each grid element. The calculated leaf emergence dates are in good agreement with observations from phenological gardens as well as with NDVI (normalized difference vegitation index) derived phenology.