AN INTEGRATED BIOSPHERE MODEL OF LAND-SURFACE PROCESSES, TERRESTRIAL CARBON BALANCE, AND VEGETATION DYNAMICS

Here we present a new terrestrial biosphere model (the Integrated BIos phere Simulator - IBIS) which demonstrates how land surface biophysics , terrestrial carbon fluxes, and global vegetation dynamics can be rep resented in a single, physically consistent modeling framework. In ord er to integrate a wide range of biophysical, physiological, and ecolog ical processes, the model is designed around a hierarchical, modular s tructure and uses a common state description throughout. First, a coup led simulation of the surface water, energy, and carbon fluxes is perf ormed on hourly timesteps and is integrated over the year to estimate the annual water and carbon balance. Next, the annual carbon balance i s used to predict changes in the leaf area index and biomass for each of nine plant functional types, which compete for light and water usin g different ecological strategies. The resulting patterns of annual ev apotranspiration, runoff, and net primary productivity are in good agr eement with observations. In addition, the model simulates patterns of vegetation dynamics that qualitatively agree with features of the nat ural process of secondary succession. Comparison of the model's inferr ed near-equilibrium vegetation categories with a potential natural veg etation map shows a fair degree of agreement. This integrated modeling framework provides a means of simulating both rapid biophysical proce sses and long-term ecosystem dynamics that can be directly incorporate d within atmospheric models.