EFFECTS OF SOIL-WATER POTENTIAL ON STEM R ADIUS CHANGES OF NORWAY SPRUCE (PICEA-ABIES (L) KARST)

The stem radius of 2 mature Norway spruce trees and the soil water pot ential were continuously measured in situ with dendrometers and tensio meters, respectively. In a period without growth and frost events the stem radius and the soil water potentials correlated closely. A young spruce tree grown under controlled conditions changed its radius in re sponse to the soil water supply likewise. The shrinkage of the stem wa s reversible, even if the soil was very dry (soil water potential << - 1000 hPa). An estimate of the soil water potential seems to be possibl e even beyond -1000 hPa by measurements of stem radius changes.