Changes in leaf phenology are dependent on tree height in Acer mono, a deciduous broad-leaved tree

Ontogenetic changes in leaf phenology of a hardwood tree, Acer mono, were i nvestigated in individuals in different size classes in a temperate forest. Leaf emergence was earliest in current-year seedlings, and was increasingl y delayed with increasing height of the individual. The shorter the tree, t he longer the duration of leaf emergence. Timing of leaf emergence of the d ominant heterospecific canopy trees was almost identical to that of conspec ific adults; understorey light then gradually decreased with expansion of c anopy leaves. These traits indicate that smaller individuals that receive t he least light in summer can acquire favourable light for a longer period i n spring than taller plants even in a forest understorey, but the advantage decreases with increasing plant height. Changes in the duration of leaf em ergence and leaf longevity in response to environmental light regime [sun ( forest edge) vs. shade (forest understorey)], were greatest for current yea r seedlings but decreased with increasing plant height. These results sugge st that the plastic response of leaf phenology in juvenile stages may reduc e the risk of losing an entire cohort in spatially heterogenous environment s in the understorey of temperate forests. (C) 1999 Annals of Botany Compan y.