The diversity of radial variations of wood properties in European beech (Fagus sylvatica L.) reveals the plastic nature of juvenile wood

Abstract Key message Radial variations in wood quality result from the changes in wood properties with tree age. Here, we show that, at least in beech ( Fagus sylvatica L . ), these patterns of variations are diverse, and reflect a plastic adaptation to changes in the mechanical needs of the trees during their life. Context 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). Aims 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. Methods 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 the slope and curvature of radial profiles. Results For the three parameters, the plot and tree effects were very significant, but within-tree variations were dominating, representing at least 50% of the 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. Conclusion Even if there is some ontogenetic influence in the measured juvenile patterns, their large variability suggests that adaptive juvenility dominates largely.