IMPORTANCE OF SEED SIZE FOR THE ESTABLISHMENT OF SEEDLINGS OF 5 DECIDUOUS BROAD-LEAVED TREE SPECIES

Effects of seed size and phenology on the establishment of five decidu ous broad-leaved tree species were examined in deciduous woodland. Tre atments included absence and presence of litter in the forest understo ry, a small gap, and a large gap. Seedling emergence of large-seeded s pecies Quercus mongolica var. grosseserrata and Acer mono was not redu ced by accumulation of litter in the forest understory, but was promot ed in the large gap where litter was less. Seedling emergence of small -seeded species, Alnus hirsuta, Cercidiphyllum japonicum and Betula pl atyphylla var. japonica, was reduced by the litter in almost all of th e sites. Seedlings of large-seeded species avoid shade stress phenolog ically by unfolding all of their large leaves in a short period before canopy closure in the forest understory. These species had little mor tality after seedling emergence. In contrast, small-seeded species hav e a longer duration of leaf emergence, shorter leaf longevity, and rap id leaf turnover in all the sites. These seedlings attained similar he ight to those of the large-seeded species at the end of the second yea r in the large gap, but survival and height growth rate decreased afte r canopy closure in the forest understory. We suggest that the importa nce of seed size in determining seedling establishment largely depends on the relationships between seasonal changes of environmental condit ions and phenological traits of seedlings, which are related to seed s ize.