A COMPARATIVE ECOLOGY OF THE SEASONAL SCHEDULES FOR REPRODUCTION BY SEEDS IN A MOIST TALL GRASSLAND COMMUNITY

Seasonal patterns of seedling emergence and seed dispersal as well as their spatial patterns were measured for several dozen component species of a species-rich moist tall grassland community in warm temperate Japan. Although extremely high spatial heterogeneity of seedling emergence was observed for most of the species, which would have resulted from both the spatial heterogeneities of seed rain and "safe-site' distribution, the seasonal pattern of seedling emergence was less varied within a species over space and between years. Yearly seedling emergence in the community started when the accumulated daily air temperature (on a base temperature of 5°C) reached c30 degrees (Kd) and the spring flush of emergence began when daily mean temperatures of warmer days rose >10°C. Emergence seasons in the community were concentrated in spring and early summer. Autumn emergence was recorded for only one species. Mean seed weight significantly and linearly depended on the mean date of emergence of yearly recorded seedlings for individual species, ie the greater the seed mass of the species, the later the seedling emergence season was. Upright annuals had a significantly earlier mean date of emergence than perennials and annual lianas. Since seed dispersal time varied greatly from species to species, ranging from mid-spring to early winter, there was a great variety of relative timings of seed dispersal and seedling emergence among the co-occurring species in the community. -Authors