Seed distributions of dominant tree species in a tropical forest in Taiwan

Background/Question/Methods

Spatial distributions of seeds at the forest level represent the initial spatial template of the entire tree populations and determine spatial relationships among individuals.  These spatial relationships impact neighbor interactions, thus critically influencing population and community dynamics.  The aim of this study was to investigate seed distributions of thirteen dominant tree species in the seed rain at the forest level and examine the extent to which factors at individual tree level influenced seed distributions at the forest level in a tropical forest in Taiwan.  We hypothesized that spatial distributions of seeds at the forest level reflected their limitation in dispersal, aggregation of parent trees, and dispersal traits, including seed mass and dispersal mode.  This study was carried out in a 10 ha permanent plot (400 m x 250 m) from August 2006 to August 2007 in Kenting, Taiwan.  Eighteen seed traps were placed along each of four east-west transects at a 20-m interval within the plot.  These transects were 340 m in length and 50/60 m apart.  Seed traps were checked weekly.  All reproductive parts of woody plants greater than 1 mm were collected, dried, weighted and identified by species.  Seed distributions were evaluated by standardized Morista’s index and Green’s Coefficient.  In addition, potential parent trees to the seeds were tagged and mapped. 

Results/Conclusions

Our result indicated that seeds of each of the thirteen target species in the Kenting forest were aggregated at the forest level.  Such aggregations were likely to arise from short dispersal distances and the aggregation of potential parent trees.  Seed traps receiving seeds of a given species were significantly closer to their potential parent trees than traps with no seeds of such species.  Furthermore, seed mass was negatively correlated with the proportion of traps receiving seeds, indicating that heavier seeds reached fewer traps than lighter seeds. This study provided a link to the distributions of seeds at two different spatial scales.  In the future, we plan to evaluate the impact of seed aggregation on seedling establishment.