Interspecific differences in the hierarchical cluster structure of leaves within tree crowns in Indochina

Abstract

Differences in light capture strategies of tropical monsoon trees were examined with a focus on the function of hierarchical leaf cluster structure. Specifically, morphological differences in leaf clusters were examined among ecological functional groups of tree species. The three-dimensional distribution of leaves within 62 crowns of 21 species in or above the canopy layer was estimated using a terrestrial laser scanner. Leaf clusters with hierarchical structure were identified within each crown, and the thickness and inclination of a leaf cluster were calculated. The light capture property of the crown was examined using the light extinction coefficient and the directional dependency of light capture. An ordination technique was used to organize crown architecture into two axes: one corresponding to the directional dependency of light capture, which separates leaf phenological types, and the other representing the spatial scale contributing to light capture, which separates growth forms. Similar leaf cluster shapes at various spatial levels ranging from small leaf clusters to crowns caused specialization of crown directional dependency, which was clearest in emergent species. In deciduous species, flatter leaf clusters at various spatial levels were specialized to efficiently capture overhead light, whereas rounder leaf clusters at various spatial levels in evergreen species were specialized to uniform light capture from all directions. Different light capture strategies among functional groups in tropical monsoon forest would be related to drought stress response.