Soil seed bank community dynamics in seasonally moist lowland tropical forest, Panama

Seasonal changes in the densities of dormant seeds in the soil around eight pioneer trees in the 50-ha Forest Dynamics Plot, on Barro Colorado Island, Panama were studied, and how seed dispersal and seed dormancy influenced patterns of seed abundance and distribution were examined. Twenty-four, 3-cm-deep soil samples were collected on 30 m transects radiating out from each of the trees in each of four time-intervals through the year, and four 21-cm-deep samples were collected beneath the focal tree crowns. In the surface 0-3 cm of soil, germinable seed densities of all species combined declined from a peak of 1090 seeds m^-2 in the mid-wet season in August, to 330 seeds m^-2 by the end of the wet season in November. In contrast, at soil depths >3 cm, there was little variation in soil seed bank density through the year. Some variation in soil seed bank density for individual species could be accounted for by distance to reproductive conspecifics. Among species, abundance in the soil was negatively correlated with seed size. Seed persistence varied greatly among species at this site; after 1 y of burial in mesh bags, seed germinability of four species was near zero, while four other species showed no consistent decline in seed germinability after >2 y of burial. For at least one species, Trema micrantha, prolonged seed dormancy was also possible under natural conditions. Twenty-five percent of Trema seeds extracted from the soil at a site occupied by an isolated Trema tree that died between 1982 and 1985 were still germinable in 1994.