Little is known about seed bank dynamics in Neotropical savannas. We studied temporal variation in seed density, species richness, species composition, seed mass, and seed number in the topsoil seed bank of a savanna on “La Iguana” Experimental Station, Guárico State, Venezuela. Total soil surface sampled was 57,600 cm2, in 400 cm2 units, at four times of the year. Seeds from 124 plants from 20 families were encountered. Species composition varied seasonally, but grass seeds dominated almost all the year, both numerically and in species number. Seed density and species richness were highest in the dry season and declined to a minimum in early wet season. Mean density was 1702 seeds/m2, with a range of temporal variation from 235 to 4624 seeds/m2. Average seed mass across species by date ranged from 0.97 to 2.53 mg, but because tiny seeds were most numerous throughout the year, the abundance-weighted averages only varied from 0.8 to 1.19 mg. We found a high spatial variability in the seed distribution in the soil throughout the year. There were also substantial changes in the topsoil seed bank among seasons, as a consequence of herbaceous plant phenology and germination strategies, which are tightly coupled with hydroperiodism in Venezuelan savannas. Based on the species-area curves, we concluded that the minimal sampling effort needed to adequately estimate the species richness in the topsoil of this savanna is 11 fold higher than that used in most seed bank studies in tropical environments.
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Vol. 33 • No. 3