SOIL-WATER DYNAMICS OF THE SOLLING SPRUCE STAND, CALCULATED WITH THE FORHYD SIMULATION PACKAGE

The FORHYD Simulation package was applied to the Selling spruce stand to calculate the water balance and soil water dynamics in the context of a comparison of 16 models which simulate water, carbon and nutrient cycles in forests. The simulated results appeared to fit the measurements of pressure heads and time-integrated chloride concentrations when only throughfall parameters were calibrated. However, the applicability of pressure head and chloride concentration measurements for validating the simulation results is very limited. Objective criteria to select specific statistical fit-measures are lacking and measures are sometimes contradicting when using either pressure heads or pF-values. The water holding capacity and the capillary redistribution of water to the root zone appear to be sufficient to fulfil the transpiration demand in most years although the spruce has a very shallow rooting depth. Therefore, the calculated transpiration is almost entirely determined by the calculated potential transpiration. Any error in parametrisation of the root profile or the physical soil characteristics only causes changes in the calculated profiles of water uptake or vertical fluxes, but not in the total water balance components.