Blowdown disturbance effect on the density, richness and species composition of the seed bank in Central Amazonia

Abstract

Windstorms, known as blowdowns, create large canopy gaps in the tropical rainforest. Despite the occurrence of blowdowns in Central Amazonia, no studies have yet investigated the seed bank in areas altered by blowdown in the Amazon rainforest. The seed bank plays an important role in the regeneration of larger natural gaps, and changes in, or partial loss of, seed bank can modify the successional dynamics locally. In the present study, we compared the density, richness and floristic composition of a seed bank in a post-blowdown secondary forest with approximately six years old and a continuous forest. The seed bank was characterized by collecting 160 soil samples systematically distributed in each forest type at two different times. Samples were collected at a minimum distance of 30 m from each other, sampling the superficial soil 5 cm in depth and 20 cm in diameter. At each sampling point, the slope and canopy openness was also measured. The density and floristic composition of the seed bank was estimated using counts of seedlings that had emerged in a nursery of the collected soil samples. The post-blowdown secondary forest exhibited seed banks 30% denser and 20% richer, on average, than continuous forest. The floristic composition also differed between forest types, with a predominance of Melastomataceae, Urticaceae, and Araceae in the secondary forest, followed by Cyperaceae and Moraceae; however, these did not differ between forest types. In contrast, for other families, greater richness and density were observed in the continuous forest. Higher density and richness of trees, shrubs, epiphytes, and hemiepiphytes were observed in the secondary forest, except for the richness of epiphytes. In general, terrain slope was unrelated to density, richness and floristic composition of the seed bank. Under a disturbance of great magnitude, such as a blowdown, the density and richness of the seed bank were not reduced; on the contrary, its potential for local regeneration was maintained. Despite the limited contribution of the seed bank to the regeneration of climax species, the seed bank was shown to be diverse in species, including different life forms, and may contribute to the regeneration of forest strata, even after severe disturbances. © 2019 Elsevier B.V.