|Manderscheid, B; Matzner, E: Auswirkungen unterschiedlicher Feinwurzelverteilungen und -biomassen auf das Risiko für Trockenstreß und Nadelverluste in Fichtenbeständen - Ergebnisse von Simulationsrechnungen zum Wasserhaushalt, Forstwissenschaftliches Centralblatt, 115, 350-362 (1996)|
Chronic needle and leaf losses of major tree species, called "novel forest damage", are widespread in Central Europe. Air pollutants are often blamed for this kind of damage. The influence of air pollutant deposMon, soil chemical changes and the increasing nitrogen availability may cause a shallowing of the root system and decreasing fine root blomass. We hypothesize that the changes in the root system cause decreasing drought susceptability of the trees and needle or leaf losses. Using computer models for the watercycle in a mature Norway spruce stand over a period of 18 years we quantified the influence of different rooting patterns on the transpiration and the risk of drought stress. Here we compared the dry year 1976 with the wet year 198t. In 1976 the simulated xylem water potenuals indicate severe drought stress under conditions of shallow rooting and low root biomass. Under these rooting conditions the drought stress in 1976 would have been avoided, if the trees had lost about 30% of the needle mass. During the wet year 1981 rooting patterns also influenced xylem water potentials, but severe drought stress did not occur.