Influence of leaf size on tree architecture: first branch height and crown dimensions in tropical rain forest trees

Abstract

First branch height is an important attribute of sapling architecture, as it defines the height at which prolonged lateral growth is possible. First branch height, measured on saplings of 70 species in tropical rain forests of Australia, Costa Rica, Panama, and Sabah, Malaysia, was highly correlated with leaf blade and petiole length. The observed relationship, first branch height ∝ blade length × (petiole length)0.5, implies that the ratio of first branch height to blade length increases somewhat with increasing leaf size, among species with a given ratio of petiole to blade length. Orthotropic species, with more or less radially symmetric arrangements of leaves on ascending axes, had a mean first branch height of 7x that observed for plagiotropic species, with planar leaf arrangements. The greater first branch height of orthotropic species was associated with their larger leaves and longer petioles. Plagiotropic species had wider crowns than orthotropic species in the sapling stage, as assessed at the Costa Rican site. Thus, leaf dimensions influence the dynamics of crown construction (or visa versa), as well as affecting leaf energy balance and gas exchange.