Experimental investigations concerning spruce [Picea abies (L) Karst] water balance

In an eighty-seven-year-old spruce stand of a hydrological catchment area we measured and estimated the atmospheric evapotranspiration capacity, the transpiration of a single tree, water uptake by roots, sap flow and water storage of the tree as well as the brook runoff. All these meteorological, physiological, soil-physical and hydrological variables oscillate periodically in the course of a day with a phase shift increasing in the direction from the atmosphere through the tree to the sail and the brook. This means that the suction of the atmosphere is propagated in the same direction. In this coupled system we can determine the water balance of the tree and especially the transpiration by the measuring of the above variables. The inclusion of runoff allows the areal generalisation of the single tree measurements.