Validation of the Integrated Biosphere Simulator over Canadian deciduous and coniferous boreal forest stands

Data collected during the Boreal Ecosystem-Atmosphere Study (BOREAS) at fou r different forest stands were used to test surface energy and carbon fluxe s simulated by the Integrated Biosphere Simulator (IBIS). These stands incl uded deciduous and conifer species and were located in both the BOREAS nort hern and southern study areas. Two runs were made: one using the original I BIS model and the other using a version modified to consider an organic soi l layer (OSL) covering the mineral soil surface. Results show that the incl usion of the OSL substantially improved the simulation of soil heat flux, a s well as of temperature and moisture in the topmost soil layer. Simulation s show that latent and sensible heat fluxes, and net ecosystem exchange of carbon, were not affected appreciably by the presence of a thin (10 cm or l ess) OSL covering the forest floor. With a thick (50 cm) OSL, however, simu lation of latent heat flux and net ecosystem exchange of carbon was substan tially improved. Consideration of the OSL in the model also led to better s imulation of the onsets of soil thawing. Correct estimation of heat diffusi on to deep soil through thick organic layers requires a parameterization th at accounts for the state of the organic material decomposition. Simulation s presented here also show the necessity for using detailed information on soil physical properties for better evaluation of model performance.