Ontogenetic changes in crown architecture and leaf arrangement: effects on light capture efficiency in three tree species differing in leaf longevity

Pronounced strategy shifts along ontogeny have been observed in several tree species, mainly because of the trend to maximize growth during the seedling stage, which constitutes the most vulnerable part of the tree’s life cycle. Our aim here was to analyze the ontogenetic changes in crown characteristics and light capture patterns in three Quercus species: the evergreens Quercus ilex and Quercus suber and the deciduous Quercus faginea co-occurring in a Mediterranean open woodland. The seedlings were distributed in the large clearings among the adults and received full sunlight. We constructed three-dimensional models of the aerial parts of seedlings and mature trees of the three species, using the YplantQMC program. Large differences between growth stages were observed for all variables. The seedlings exhibited smaller branch sizes and crown densities than those observed in the adult trees. Leaf angles to horizontal also tended to increase during ontogeny, whereas leaf dispersion and the observed distances between leaves tended to decrease. The amount of photosynthetic radiation absorbed per unit leaf area throughout the growing season was lower in adult specimens than in young specimens. Changes in absorption efficiency during ontogeny were more intense for the species with longer leaf life span at maturity. We conclude that more intense ontogenetic shifts in species with longer leaf life span reflect the priority change from the maximization of short-term productivity at the seedling stage to maximizing leaf longevity during the adult stage.