Dispersal and survival of juveniles of dominant tree species in a tropical rain forest of West Sumatra

Abstract

Adult trees of a given species distribute sparsely in tropical rain forests due to high tree species diversity, and dispersal and sur vival of juveniles are impor tant processes to form such a pattern. Dispersal and juvenile survival of seven tree species were studied over 13 years in a 1−ha plot of tropical rain forest in Ulu Gadut, West Sumatra, Indonesia. All individuals of juveniles were marked and examined in 1989, 1998 and 2002. Estimation of dispersal kernel was successful for Calophyllum soulattri having the highest juvenile density among 7 species. Although dispersal kernel was significant in Gonystylus forbesii and Mastixia trichotoma, actual juvenile density was lower than expected in some subplots having high expected sapling density. Significant reduction of the sapling survival rate by neighboring conspecific saplings was detected in Calophyllum soulattri and Hopea dryobalonoides, and that by conspecific trees was detected in Swintonia schwenkii and Cleistanthus glandulosus. The negative ef fect of conspecific plants on juvenile survival was a more important factor than topography, and may be common in tropical rain forest trees. Aggregated distribution of saplings around mother trees might be formed just after seed dispersal; however, such patterns might be obscured by high mortality around mother trees, and relatively uniform tree distribution may be formed. Since regeneration is a rare phenomenon due to gregarious reproduction, we might be able to observe only limited stages of these processes simultaneously.