Der Bodenwasserhaushalt an einem Fichtenstandort im Hochschwarzwald – Messung und Modellierung zur Deutung der montanen Nadelvergilbung

The occurrence of high-altitude needle tip-yellowing in spruce was repeatedly related to dry years and in general explained as a Consequence of magnesium deficiency. To test this hypothesis the Soil water regime of the mountain site Schluchsee (southern Black Forest) was analysed. No apparent drought stress was expected from the climatic situation and the soil physical properties in order to get a high resolution of the soil water content in space and time, a soil water model was fitted with-soil water data from an 8 years measurement period (1987-1995):She model-enables retrospective simulations of daily soil water balance with climatic data from neighbouring meteorological stations 25 years before measurement starred at this Site. In the markedly dry years 1976 and 1983 the organic layer showed parching of the soil up to the permanent wilting point. In contrast to the dry situations in 1991 and 1992, the dry periods in 1976 and 1983 commenced shortly after the start of the growing season. Additionally,in 1983 the dryness of the organic layer lasted for more than 6 weeks. In times of high nutrient demand (period of spring flush in early summer) the shallow rooting pattern of spruce is likely to cause drought induced bottle-necks in the supply of nutrient elements. Especially magnesium is latently deficient at this site because it-is mainly supplied through litter decomposition. In the magnesium-poor mineral soil normally matric potentials will not be reached that may limit seriously transpiration, so: that water supply to the roots in dry periods is not hampered. Therefore, the appearance of high-altitude tip-yellowing is Likely to be associated with an extreme climatic condition of an early summer drought inducing nutritional disturbances.