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 measurem ents of pressure heads and time-integrated chloride concentrations whe n only throughfall parameters were calibrated. However, the applicabil ity of pressure head and chloride concentration measurements for valid ating the simulation results is very limited. Objective criteria to se lect specific statistical fit-measures are lacking and measures are so metimes contradicting when using either pressure heads or pF-values. T he water holding capacity and the capillary redistribution of water to the root zone appear to be sufficient to fulfil the transpiration dem and in most years although the spruce has a very shallow rooting depth . Therefore, the calculated transpiration is almost entirely determine d by the calculated potential transpiration. Any error in parametrisat ion of the root profile or the physical soil characteristics only caus es changes in the calculated profiles of water uptake or vertical flux es, but not in the total water balance components.