Résumé
The radial variation of wood properties in the young age of the tree can be interpreted as the result of either cambium ageing (ontogenetic juvenility) or adaptation to the changing mechanical constraints during growth (adaptive juvenility). Ring width, specific gravity and specific modulus are important parameters for the mechanical stability of a standing tree. We aim at assessing whether their variations correspond to ontogenetic or adaptive juvenility. These parameters were measured at several positions across diametrical boards from 86 beech trees from 9 high forest stands. Their variance and correlations were analysed globally, between plots and between trees, and variations from pith to bark quantified according to slope and curvature of radial profiles. For the three parameters, the plot and tree effects were very significant, but within-tree variations were dominating, representing at least 50% of total variance. These variations occurred both in the radial and the circumferential direction, as revealed by the frequency of non-symmetric diametral profiles. The patterns of radial variations were very diverse both between plots and within plots, being either increasing, decreasing or non-monotonous. Even if there is some ontogenetic influence in the measured juvenile patterns, their large variability suggests that adaptive juvenility dominates largely.