Model of forest carbon sequestration incorporating aerial wood radiative budget

The CHANCE model, simulating CO2, energy and water fluxes in a forest ecosystem, is presented. The components of the simulated canopy are the leaves, the branches, the trunks and the soil. The first three are divided into sunny and shaded zones. The model has been calibrated and validated in comparison with measurements performed in the temperate beech forest of Vielsalm (Belgium). For the reproduction of half-hourly net CO2 fluxes, the quality of the CHANCE results is comparable to other models (systematic error of 14%—0.51 μmol m−2 s−1, R2=0.79). The differences between simulated and measured fluxes result essentially from noise in the data, underestimation of the stomatal conductance during very dry days and heterogeneity of the south, southeast sector (presence of conifer patches). Three sensitivity tests have been performed. The first one, neglecting the contribution of aerial wood in the radiation budget, doubles the annual carbon sequestration (Seco). This trend is strengthened in the second test where common radiative and photosynthetic properties are assigned to leaves and branches. The third test induces a 30% reduction of Seco when the calculation of canopy component temperatures using the complete energy balance is replaced by the use of air temperature.