Delayed greening, leaf expansion, and damage to sympatric Shorea species in a lowland rain forest.

The function of delayed greening in the seedlings of canopy tree species in a lowland tropical rain forest was examined in terms of its potential defensive value against herbivory. To explore the ecological and evolutionary backgrounds for delayed greening, we chose eight sympatric congeneric (Shorea) dipterocarp species that were either normal-greening or delayed-greening species. Expansion and toughening of leaves took approximately 30 days for all species, and did not differ between the normal- and delayed-greening species. The main factors that affected leaf damage during expansion were insect herbivory and fungal infection. Levels of leaf damage were significantly lower for delayed-greening species than for normal-greening species, but proportions of heavily damaged leaves and leaf abscission during expansion did not differ. In addition, no significant difference was found in damage levels on leaves (aged 1-2 months) of naturally occurring seedlings between normal- and delayed-greening species. Therefore, delayed greening may effectively reduce the level of leaf damage in young expanding leaves, but may not necessarily reduce leaf abscission and damage to mature leaves. The existence of delayed greening could not be simply explained by the phylogenetic and ecological backgrounds of the trees. Consequently, delayed greening may have a function in reducing damage during expansion, but more information (such as knowledge of the secondary metabolites involved in this phenomenon) is needed to explain fully why these species exhibit delayed greening.