A total of 52,467 wind-dispersed seeds from 14 tree and 32 liana species fell into 1720 seed traps in 43 paired light-gap and adjacent forest sites on Barro Colorado Island, Panama. Summed at the community level, many more wind-dispersed seeds were collected from light-gaps (61%) than from forest sites (39%). They accumulated from March through May, 1984 to a density of 328 m-2 in gaps and 207 m-2 in forest sites. In contrast, only 33% of the total of 2782 non-wind-dispersed seeds were collected in gaps. Due to the extreme heterogeneity of the seed rain, these differences between gap and forest sites were not statistically significant at the community-level. Gap sites received more wind-dispersed seeds than adjacent forest sites in only 20 of 43 locations and in 13 of 20 species, especially those with individuals of high fecundity near gap sites. Of the estimated 105 million wind-dispersed seeds contributing to the seed rain of the 50 ha study plot, only 4.1% were dispersed to the rare gap sites that enhance the establishment and growth of seedlings for many of these species.

Seed banks play a crucial role in arid plant communities because they confer stability and long-term persistence. However, seed banks have high temporal and spatial variability, with dramatic changes in density and composition. The aim of this study was to test whether seasonal change affected seed bank community structure and spatial pattern. Moreover, we wanted to know if the effect driven by environmental factors on the seed bank was constant year round. We sampled the seed bank at 188 points along seven parallel transects through a gypsum system in central Spain. Soil samples were taken twice (September and April) in contiguous plots. In each plot we measured environmental parameters, including micro- and macroslope, vegetation band, shrub cover, lichen crust cover and landform. A nearly threefold decrease in seed bank density occurred between September (16,230 seeds m–2) and April (5960 seeds m–2). Seasonal changes in density varied widely among species; however, a seed bank was present for most species at both sampling dates. For several well-studied species (Lepidium subulatum and Helianthemum squamatum), seed losses were within the range of losses by emergence reported in the literature. In both seasons, seed bank composition was controlled mainly by community band and microslope. Sampling season had a significant, but minor effect on seed bank composition. Moreover, a high spatial correlation existed in terms of seed density and richness through the two studied seasons. These results show that the seed bank keeps a constant structure even under substantial variation in density.

Seed density and seed bank species composition were determined by germination trials on soils collected during the initial phase of deforestation in a Mexican tropical deciduous forest. The reference forest, pre-burn, 1-d post-burn, and 1-y post-burn soils contained 700, 1000, 70 and 3500 germinating seeds m−2, of 30, 30, 8 and 13 species, respectively. A total of 43 dicotyledonous species were identified. Percentages of herbs, vines, shrubs and small trees/shrubs were similar in reference forest, pre-burn, and 1-d post-burn soils; herbs were the most common growth form. Pasture conversion greatly altered seed bank species composition; 81% of the species that germinated from the seed bank before burning were absent from the seed bank 1 d after the fires. One-year post-burn soil was dominated by monocots; only 3% of the seedlings were herbs; no vines, small trees/shrubs or trees germinated. The reference forest and the pre-burn soils had 18 dicot species in common and the highest similarity index, 0.43; six of the shared species were herbs. One-day and 1-y post-burn soils had the lowest similarity index, 0.05. Burning the slashed forest and conversion to cattle pasture depleted the original seed bank, replacing it by one dominated by pasture grasses.