Burial and secondary dispersal of small seeds in a tropical forest

Secondary dispersal is an important stage in the life cycle of tree species, determining the fate of a high proportion of all seeds. For small-seeded species both physical and biological processes may influence the secondary fate of seeds, however the relative importance of these processes is not well known. Seeds of the pioneer tree species Cecropia insignis (seed mass 0.5 mg), Trema micrantha (2.5 mg) and Apeiba aspera (14.2 mg) and five types of artificial seed were sown in understorey, treefall-gap and large-gap sites on Barro Colorado Island, Panama, during the wet season of 2005. Sowing areas were excavated after periods up to 26 d and cores divided into depths of 0–5, 5–10, 10–20 and 20–50 mm to allow high-resolution estimation of the rate and amount of burial and displacement of seeds. Over 26 d, 2.8% of artificial seeds were buried to a mean depth of 10.5 mm below the soil surface and 43.9% of unburied seeds displaced laterally >5 cm. Significantly more (87.9% and 80.9%) seeds of Cecropia insignis and Trema micrantha were displaced than artificial seeds of similar mass, size and density. A generalised linear model suggested that burial mostly occurred within 15 d, while displacement occurred continuously up to 26 d. The dominant cause of displacement and burial was probably rainfall, while seed removal by ants may also have contributed to displacement.