Change in leaf structure in relation to crown position and size class for tree species within a Sri Lankan tropical rain forest

Abstract

The purpose of our study was to examine change in leaf structure (anatomy and morphology) through different phases of tree size and crown position within a Sri Lankan rain forest. We selected four late-successional canopy species that represented dominant genera ( Shorea , Mesua ) within an Asian tropical rain forest. All are considered shade-tolerant and capable of growing to maturity beneath closed-canopy late-successional forests. Species within each genus were either restricted to seepages and bottom slopes (valley species) or to upper slopes and ridges (ridge species). The size classes represented (i) seedlings, (ii) saplings, (iii) poles growing beneath closed-canopy conditions, and (iv) trees of the rain forest canopy. Between size classes, leaves were thicker and with higher stomatal densities for canopy trees than for seedling, sapling, and pole size classes. Plasticities for measures of leaf structure were greater for ridge species than valley species; except for cuticle thickness, which showed the opposite trend (valley > ridge). Area, length, and width of leaves attained maxima for the sapling size class for all species. Drip-tip lengths were greatest for seedlings of all species, and least for canopy trees. Trends in leaf structure and morphology dimensions across size classes for late-successional canopy tree species are the same as those trends reported between rain forest species of different habitat strata (e.g., understory shrubs versus upper canopy trees). Our results suggest leaf dimensions could provide robust measures of environment, irrespective of species, or size class of tree.