The Frankfurt Biosphere Model: a global process-oriented model of seasonal and long-term CO2 exchange between terrestrial ecosystems and the atmosphere. II. Global results for potential vegetation in an assumed equilibrium state

Abstract

Regional variability and seasonal courses of atmospheric CO, 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 LA1 (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 c11-mate, 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-' 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 5Olatitude 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 LA1 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.

Seasonality of ecosystem respiration and gross primary production as derived from FLUXNET measurements

“…From a functional perspective, ecosystems could be grouped by their mass and energy exchange or productivity and respiration rates. Applying a more morphologic view, global models of climate change and productivity employ classification schemes by biome or vegetation type, e.g., evergreen needle-leaf forest, deciduous broad-leaf forest (Warnant et al, 1994;Field et al, 1995;Sellers et al, 1996a,b;Kohlmaier et al, 1997). We analyzed seasonal pattern of F GPP and F RE to test the potential to generalize functional characteristics within currently applied classification schemes.…”

Effects of spatial aggregation on predictions of forest climate change response

“…Some large-scale biogeochemical models have taken a biome-scale approach to calibration. For example, the flux equations of the Frankfurt Biosphere Model (FBM, Kindermann et al 1993, Lüdeke et al 1994, Kohlmaier et al 1997 Melillo et al 1993, Kohlmaier et al 1997. Although FBM uses 0.5°input data to make estimates for each grid cell within a vegetation type, it is not clear where the underlying resolution of the model lies on the continuum between stand-level and biome-level resolution.…”

Impulse response functions of terrestrial carbon cycle models: method and application

“…To account for the effects of herbivory on turnover, some carbon is shunted to the surface metabolic pool in proportion to annual NPP . The biomass turnover times were derived from an analysis by Kohlmaier et al (1997), but autotrophic respiration is not calculated; this is an NPP-referenced model.…”