Inter-annual Seed Rain Variability, Dispersal Limitation, Seed/Seedling Mortality in a SE Asian Rainforest: Implications for the Maintenance of Tree Diversity

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This research will test whether mast-fruiting is important to the coexistence of over 800 species of trees in a mega-diverse Southeast Asian rainforest at the Pasoh Research Forest in peninsular Malaysia. Mast-fruiting is the simultaneous seed drop of many tree species in a relatively short time. Periods of mast-fruiting are separated by irregular intervals of 3-9 years with little or no seed production. Mast-fruiting is thought to have evolved as a predator escape response to heavy mammalian seed predators in these forests. This study will be strictly comparable to a 13-year study of the dynamics of seed rain and seedling germination in a neotropical forest on Barro Colorado Island (BCI), Panama, which does not exhibit mast-fruiting. Seed traps and seedling plots will be deployed throughout the Pasoh Forest. Seed rain in the traps will be quantified each week for each tree species over a 5-year period. Species abundances and composition will be compared between adjacent seed traps and seedling plots. This will allow an evaluation of the strength of seed and seedling mortality factors during the seed to seedling transition. Strong density- and frequency-dependent seed and seedling mortality characterized the BCI site. Although these are considered good candidates as primary mechanisms of coexistence, it is unclear if the phenomenon is general or specific to BCI. The proposed research is critical for understanding if tree diversity in different tropical forests is maintained by the same mechanisms. This knowledge is important for managing tropical forests and preserving their biodiversity.