EFFECTS OF DIFFERENT FINE-ROOT DISTRIBUTI ONS AND FINE-ROOT BIOMASS ON DROUGHT STRESS AND NEEDLE LOSS IN SPRUCE STANDS - RESULTS FROM SIMULATION CALCULATIONS ON WATER UTILIZATION
B. Manderscheid et E. Matzner, EFFECTS OF DIFFERENT FINE-ROOT DISTRIBUTI ONS AND FINE-ROOT BIOMASS ON DROUGHT STRESS AND NEEDLE LOSS IN SPRUCE STANDS - RESULTS FROM SIMULATION CALCULATIONS ON WATER UTILIZATION, Forstwissenschaftliches Centralblatt, 115(6), 1996, pp. 350-362
Chronic needle and leaf losses of major tree species, called ''novel f
orest damage'', are widespread in Central Europe. Air pollutants are o
ften blamed for this kind of damage. The influence of air pollutant de
position, soil chemical changes and the increasing nitrogen availabili
ty may cause a shallowing of the root system and decreasing fine root
biomass. We hypothesize chat the changes in the root system cause decr
easing drought susceptability of the trees and needle or leaf losses.
Using computer models for the watercycle in a mature Norway spruce sta
nd over a period of 18 years we quantified the influence of different
rooting patterns on the transpiration and the risk of drought stress.
Here me compared the dry year 1976 with the wet year 1981. Ln 1976 the
simulated xylem water potentials indicate severe drought stress under
conditions of shallow rooting and low root. biomass. Under these root
ing 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 1
981 rooting patterns also influenced xylem mater potentials, but sever
e drought stress did not occur.