Tree architecture varies with forest succession in evergreen broad-leaved forests in Eastern China

KEY MESSAGE : Vertical and temporal patterns of tree architecture and their relationship with woody plant crown exposure index varied with succession in evergreen broad-leaved forests in eastern China. Linking temporal pattern of tree architecture with changing light conditions through forest succession is important for understanding plant adaptive strategies. We determined vertical (canopy, sub-canopy, and understory species) and temporal (pioneer, mid-successional, and climax species) patterns of tree height, stem basal area, crown area and depth, leaf coverage, leaf convergence (clumped vs. dispersed leaves) and stretch direction of branches (vertical, leaned and horizontal branches) and their relationship with crown exposure index (CEI) for woody plants among three successional series in subtropical evergreen broad-leaved forests in eastern China. The series included three stages: secondary shrub (early-), young (mid-) and climax forests (late-successional stage). Tree height, crown area and depth, stem basal diameter and leaf coverage were the greatest in canopy trees, intermediate in sub-canopy trees, and the smallest in understory plants among the three successional stages; the above parameters and the proportions of dispersed leaves and leaned branches were climax > mid-successional > pioneer species. In contrast, the proportions of clumped leaves and vertical branches were pioneer > mid-successional > climax species. Between canopy and understory species, the patterns of branch stretch direction and leaf convergence were not consistent among the three successional stages. Tree height, crown area and depth, leaf coverage, and stem basal diameter were positively correlated with CEI for both vertically different species and successional species. Tree architectural traits were interactively affected by forest age and CEI (p < 0.01). In conclusion, tree architecture varies with changes in both forest vertical structure and successional status. The large variability of tree architectural traits in relation to CEI and forest age reflects a strong control of light availability that affects biomass allocation strategies of trees. Our study demonstrated that light induced shift in tree architecture may result in species coexistence through divergence of vertical space, as well as species replacement through forest succession.