The seed bank dynamics of Cornus controversa and their role in regeneration

Seed-bank dynamics of C. controversa, a common tree in Japanese temperate forests, were investigated at Ogawa Forest Reserve by direct measurement of seed input, soil seed density, and seedling output (germination of soil seeds), together with two field experiments on postdispersal seed mortality. Soil seed density varied from 4 to 233 m^-2 in the site near conspecific adults (<5 m horizontally from crown edge), and 0 to 18 m^-2 in far sites (≤5 m) during the 1988-92 period. Seed input occurred only in 1988 and 1990: 190-740 m^-2 at the sites near conspecific adults, and 4-20 m^-2 at the far sites. Seedling output was observed every year and accounted for 0-15% of the loss from the seed bank, occasionally 30-60%. Seeds buried at 5-cm depth suffered moderate mortality (c. 0.2 year^-1) by fungal pathogens. In contrast, seeds experimentally placed on the ground suffered higher mortality (0.5-1 year^-1) through predation by ground mammals, probably wood mice. In the experiment seeds whose mesocarp was removed survived much better. On the other hand, distance itself did not appear to affect post-dispersal mortality of seeds. Seeds in canopy gaps also tended to suffer higher mortality. Current spatial pattern and mode of seed dispersal should decrease the potential ability of the seed bank of this species to colonize safe sites. Rare and unpredictable events might increase the contribution of the seed-bank strategy to regeneration in this forest.