THE VARIABILITY OF VESSEL SIZE IN BEECH (FAGUS-SYLVATICA L) AND ITS ECOPHYSIOLOGICAL INTERPRETATION

The vessel areas of ten beech trees growing on a dry site were measure d separately for all tree rings using automatic image analysis. These data were correlated with the monthly amount of precipitation from the July prior to the growing season until the August of the current grow ing season. It is evident that vessel formation at the beginning of ca mbial activity is mainly controlled by internal factors. The rainfall in the previous summer and autumn and in the contemporary May had only a slight influence, Vessel formation towards the end of the cambial a ctivity is strongly influenced by the July rainfall and is thus determ ined to a greater degree by external factors. These results are discus sed on the basis of hypotheses of tree physiology.