Size-related changes in leaf, wood, and bark traits in even-aged Falcataria falcata trees

Revealing the size-dependency of traits (physiological and morphological properties) not only provides insights into species' life history strategies but also contributes to the accurate prediction of changes in tree- and forest-level growth and responses to environments. We investigated the size-dependency of 18 leaf, wood, and bark traits related to resource use strategies and wood quality, using twenty 23-year-old Falcataria falcata trees with variable sizes (14.6-53.0 cm and 9.4-21.9 m in diameter at breast height [DBH] and height, respectively) in Okinawa, Japan. The radial variation in the wood density from the pith was also investigated. No leaf traits were correlated with DBH and height, whereas several wood and bark traits changed significantly with size. Larger trees produced dense wood with high water content and thick inner and outer bark, possibly reflecting the greater mechanical loads at the stem and greater translocation of carbon from the larger canopy. The radial gradients in wood density were steeper for small-sized trees, suggesting that age partially controlled xylem formation. We also found that fast growth did not compromise stem stiffness. Our results reveal the size-dependency differ between leaf and stem traits, possibly reflecting their different functional requirements. The size-related changes in traits observed here will be utilized for model parameterizations to predict changes in growth, carbon stocks, responses to environments, and wood quality in F. falcata plantations during the stand development.