Soil seed bank assembly following secondary succession on abandoned agricultural fields in Nicaragua

Abstract

The composition and density of seeds in soils of secondary forests derived on abandoned fields after 4, 9 and 14 years of abandonment were quantified to examine whether the soil seed bank assembles during secondary succession as the plant communities assemble. A total of 18, 37 and 48 soil samples from 4-, 9- and 14-year old sites, respectively were collected in 15 cm × 15 cm plots up to 9 cm depth. A total of 3, 5 and 9 species were found on sites abandoned 4, 9 and 14 years ago, respectively. Among different life forms, trees were highly represented in the soil seed bank of 9-year (60%) and 14-year (33%) old sites compared to 4-year old site entirely dominated by nonwoody flora. The total number of seeds ranged from 327 in the 4-year old site to 146 in the 14-year old site, and the corresponding density of viable seeds ranged from 141 seeds ·m−2 in the 4-year old site to 26 seeds m−2 in the 14-year old site with a consistent decreasing pattern in the chronosequence. The similarity between the soil seed flora and the standing woody vegetation was low for both 9- and 14-year old sites while complete dissimilarity was found for 4-year old site. We concluded that the species composition of soil seed banks assemble gradually during secondary succession, but the overall seed density is still low for natural regeneration of trees to rely on. To expedite the recovery of secondary forests on such abandoned fields, the seed bank needs to be supplemented by direct seeding, enrichment planting of desired species and installing artificial perches for facilitating seed dispersal.