Banco de sementes do solo em ecossistemas sucessionais de floresta na Amazônia oriental.

Abstract

The seed bank is the main way of regeneration after a disturbance in a forest ecosystem, either by anthropic or natural action, besides being an indicator of succession. Thus the objective of the present study was to evaluate the soil seed bank in areas originally covered by Ombrophylous Dense Forest in Belém – PA, Brazil. The collection was carried out in three successional ecosystems: E1 consisting of a primary forest; E2 consisting of an initial secondary forest and; E3 characterizing itself as being a late secondary forest. For the collection, 5 plots of 25 x 25 m were implanted where 5 random samples were collected in each plot, totaling 25 samples per ecosystem, with the aid of a 0.50 x 0.50 m casting template, for a total of 75 Samples. Afterwards, the samples were transferred to plastic trays arranged in 1m high benches kept in an isolated environment of possible contaminations by external propagules. The irrigation was by sprinkling and performed daily for a period of five months. The experimental design was completely randomized with 25 replicates. During the five months of study of the seed bank in a greenhouse, 1,559 individuals emerged, being 49 species and 26 families. The highest number of germinated seeds per m² occurred in the primary forest (94 seeds), followed by the initial secondary forest (66 seeds) and by the late secondary forest with 58 seeds. According to the Shannon and Pielou index, the ecosystem that presented the highest diversity and species equability was the primary forest. As for the dispersion syndrome, 1041 zoocoric, 348 autocoric, 113 barocoric and 57 anemocoric emerged at the individual level. There was significant difference only for the "zoocoria" dispersion form. In the E1 and E3 ecosystems the predominant life form was tree, followed by shrub, although in E2 the predominant life form consisted of shrub, followed by arboreal, grass, cipó, grassy and finally indeterminate. There was a significant difference between treatments only for the "bush" lifestyle. As for the succession of the species, the seed bank presented the highest number of pioneer individuals in the three ecosystems, consisting of 289 individuals (93.2%) in ecosystem 1, Followed by ecosystem 3 with 288 individuals (88.7%) and finally the ecosystem E2 with 188 (75.06%). The "Initial Secondary" individuals obtained a greater amount in E1 with 89 (23.12%), while climaxes had a lower percentage of individuals in the three ecosystems under study. The highest number of pioneer individuals found themselves in the initial secondary forest, indicating a more persistent seed bank. As for the seed bank, the primary forest presented a denser bank, a result that refutes the hypothesis presented in this study. The primary forest was also the most diverse, mainly the species of arboreal habit, with predominantly zoocoric dispersion syndrome.