Effects of seed size and emergence time on tree seedling establishment: importance of developmental constraints.

To evaluate the importance of developmental constraints in the determination of the relative importance of seed size and emergence time, early seedling performance of two woody species with contrasting growth phenology were observed under competitive conditions with tall herbs in an early successional habitat. The oak, Quercus mongolica var. grosseserrata, with determinate shoot development (a single leaf flush), showed a marked influence of seed size on subsequent seedling height growth and survival. Because of determinate growth, emergence time had negligible effects. The walnut, Juglans ailanthifolia, which continued to produce new leaves throughout the growing season (indeterminate development), showed a marked influence of time of emergence on seedling performance, because it affected the amount of growth that could be achieved; seed size, however, had negligible effects as the seedlings grew. These results suggest that relative importance of seed size and emergence time for early seedling performance is closely associated with developmental constraints (growth phenology).