We observed seed (or diaspore) dispersal of six species (4 species of Betulaceae, 2 species of Aceraceae) for 5 years in a species-rich deciduous broad-leaved forest (Ogawa Forest Reserve, central Japan), and explained the observed patterns with a mechanistic model of dispersal. The model involves three parameters which can be biologically interpreted; terminal seed velocity (F), tree height (H), and amount öf dispersed seed per reproductive individual (Q).The relationship between dispersed seed density and distance from a single seed source were explained well by the model. Two dimensional distribution of seed density dispersed from multiple seed sources was approximated by the model. We evaluated the dispersal success in reaching safe sites as the gap area covered by a given seed density, and discussed the adaptive meaning of the dispersal traits based on the model and empirical data. While Fdid not vary greatly among the species, Qshowed greater variation among the species in this forest. The species with large Qdescended more slowly (H/F)in this forest. The traits which were related to the enlargement of dispersal area tended to compensate for the low survival-of seedlings.
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