The Frankfurt Biosphere Model: a global process-oriented model of seasonal and long-term CO2 exchange between terrestrial ecosystems and the atmosphere. I. Model description and illustrative results for cold deciduous and boreal forests

Abstract

Within the global carbon cycle the world's ecosystenls are most sensitive to environmental change.We present a global model for calculating the seasonal pattern of uptake and release of CO, by vegetation and soil in a steady-state climate simulation as well as the long-term development in a changing environment.Within the terrestrial ecosystems 32 vegetation types are distinguished and combined with 7 distinct soil types with respect to their water-holding capacities.Within each vegetation type the llving b~omass is divided into 2 compartments, one with a short (seasonal) turnover containing the photosynthesizing tissue, feeder roots, and assinl~late store, and the other with a long turnover mainly consisting of structural plant material.The mathematical description is based on 2 hypotheses: (1) vegetation tends to maximize photosynthesizing tissue; and (2) a minimum amount of structural tissue is needed to support and maintain the product~ve parts, described by an allometric relation.The fluxes are modeled using standard equations for gross photosynthesis of the canopy, autotrophic respiration, and decomposition of dead organic matter depending on surface temperature, soil moisture, and irradiation.Within the system of differential equations the free parameters for each vegetation type are calibrated on the basis of a characteristic seasonal climate.In this paper the results of steady-state chmate experiments for the 2 vegetation types 'cold deciduous forest' and 'boreal forest' are compared with ecological measurements It was shown that the model yields satisfactory results with respect to phenology, gradients in net primary production, and standing b~omass and thus holds the promise to also yield good global results.