Leaf Herbivory and Defenses of Dipterocarp Seedlings in the Pasoh Forest Reserve

Abstract

Leaf herbivores can potentially reduce the growth and survival of individual tree seedlings, thereby influencing the composition and species diversity of plant communities in forests. Plants have developed various defense mechanisms against herbivory. Since the habitat of tree seedlings is highly heterogeneous in tropical rain forests, changes in the environment would affect both plant performance and herbivory. In this study, we demonstrate the relationships between herbivory and the defenses of dipterocarp seedlings under different light regimes in the Pasoh Forest Reserve (Pasoh FR) of Malaysia. In all four species studied, two putative carbon-based defenses (total phenol concentrations in leaves and leaf toughness) were generally higher in plants growing in microsites beneath gaps in the forest canopy. The lack of significant differences in rates of leaf area loss between plants growing beneath canopy gaps and a closed canopy suggests that the potential pressure of leaf herbivory is greater in canopy gaps than beneath a closed canopy. Even though dipterocarp trees are generally regarded as climax shade-tolerant species, the species with the longest leaf lifespan tended to have the greatest concentration of phenols in their leaves and greater leaf toughness than species with the shortest leaf lifespan, irrespective of the light regime. This indicates that the species-specific patterns of leaf defensive traits may reflect evolutionary responses to seedling light requirements.