Aggregated seed dispersal in a Neotropical coastal thicket vegetation: The role of microhabitat, dispersal syndrome and growth form

Coastal thicket vegetation in Brazil (restinga) is characterized by three distinct microhabitats - thicket center, thicket edge, and open area - and the spatial pattern of seed dispersal varies among them. The objectives of this study were to differentiate microhabitats, considering dispersal syndromes and growth forms, and to determine the existence of seasonality in the seed dispersal for this ecosystem where the climate is seasonal. Seeds were monthly captured by seed traps during 24 months. They were counted, identified and dispersal syndromes and growth forms were determined. Number of seeds was low and most species were underrepresented in the seed rain. Abundance, richness, and diversity of seed rain were substantially higher in both thicket microhabitats than in the open area, probably due to the combined effects of seed production and seed retention in thickets, resulting in a non-random aggregated pattern of seed dispersal. Anemochory and zoochory were high in both thicket microhabitats, but in the open area anemochory was predominant. Herbs and shrubs contributed the greatest number of seeds and species in all three microhabitats. Our results showed a general aseasonal seed rain pattern at the community level, in contrast to the seasonal climate in this region. We conclude that seed dispersal face limitations in the plant community, natural regeneration potential is restricted, and degraded thicket vegetation will not be able to naturally regenerate the original biodiversity. Our findings considerably increase knowledge on the seed rain process at the community level and may contribute to the conservation and restoration in sandy coastal ecosystems.