SOIL ACIDIFICATION UNDER THE CROWN OF OAK TREES .1. SPATIAL-DISTRIBUTION

Thirty oak trees (Quercus robur L. sensu lato) growing on the same site were selected on the basis of their stem diameter (D(bh) greater-than-or-equal-to 0.625 m) and their effect on soil properties was assessed. Litterfall, old litter accumulation, acidity and buffering capacity of the A1 horizon were measured at three distances from the trunk (0.4, 1.4 and 2.4 m) and in four directions (N, E, S, W). Results led to the conclusion that on average more acidification and litter accumulation occurred near the trunk base and in the north direction, but this general trend was far from being followed by every tree. The clay content of the soil was inversely related to acidification and litter accumulation. Interrelationships between soil organisms, crown leaching, bark substances and the parent rock are proposed as working hypotheses for the future of this study.