IBIS Vol. 3.0

IBIS (massively parallelized version 2) is a comprehensive model of terrestrial biospheric processes, and includes land surface physics, canopy physiology, plant phenology, vegetation dynamics and competition, and carbon cycling. The land surface module simulates the energy, water, carbon and momentum balance of soil/vegetation/atmospheric system on a short time step consistent with general circulation models (20-60 minutes). The module includes two vegetation layers (trees, and grasses and shrubs) and six soil layers to simulate soil temperature, soil water, and soil ice content over a total depth of 4 m. Physiologically-based formulations of C3 and C4 photosynthesis (Farquhar. et al., 1980), stomatal conductance (Collatz, et al., 1992; Collatz, et al., 1991) and respiration (Amthor, 1984) are used to simulate canopy gas exchange processes. Budburst and senescence depend on climatic factors following the empirical algorithm presented by Botta, et al. (2000). The annual carbon balance allows the vegetation dynamics submodel to predict the maximum leaf area index and biomass for 12 plant functional types, which compete for light and water. IBIS represents vegetation dynamics using very simple competition rules. The relative abundance of the 12 plant functional types in each grid cell changes in time according to their ability to photosynthesize and use water, IBIS simulates carbon cycling through vegetation, litter and soil organic matter. The soil biogeochemistry model of Verbene, et al. (1990). The total below-ground carbon in the first meter of soil is divided into pools characterized by their residence time: from a few hours for the microbal biomass to more than 1000 years for stabilized organic matter. Decomposition rates of litter and soil carbon depend on soil temperature and soil moisture.