Banco de sementes de uma floresta tropical madura e alterada por downburst na Amazônia Central

Abstract

The seed bank constitutes the main reserve of seedlings which will regenerate under anthropogenic and natural changes of great magnitude. It can be defined as a complex system that connects to several factors related to rates of inputs and losses of seeds in soil. The effects of natural disturbances on plant communities result in the formation of gaps. In rain forests, the occurrence of disturbances of great magnitude and very large gaps are rare. Some storms and wind gusts are caused by a phenomenon convective known as downburst and have different magnitudes of severity can totally suppress the tree cover. The present study aimed to characterize the density, richness, diversity, frequency of ecological groups and life habit of seedlings emerged from the seed bank of the mature and altered forest after downburst in different topographic classes and seasons. The average density of seeds was higher in the altered forest (702 seeds m-2) than in the mature forest (447 seeds m-2) independent of the seasons analyzed. In the rainy season there was a higher density of seeds (678 seeds m-2, rainy season; 522 seed m-2, dry season). Density of individuals of Melastomataceae suffered greater influence at the time of collection (U = 13.911,50; p = 0,01). There is no linear relationship between seed density, land slope and canopy openness. A richness and species diversity estimated for number common individuals indicated that the two sampled areas are equally diverse and rich. The high value of evenness indicated a dominance of few species in the seed bank. MRPP analysis showed significant differences in floristic diversity between the two stretches of forest sampled (MRPP, A = 0,124; p = 0,000, rainy; MRPP, A = 0,129; p = 0,000, dry). In the forest changed the floristic similarity analysis indicated differences between the two collection periods (MRPP, A = 0,008; p = 0,028) however mature forest for the differences were not significant (MRPP, A = 0,001; p = 0,351). Ordination detect differences in species richness between two stretches of forest (F = 29,72; p = 0,00, rainy; F = 33,94; p = 0,00, dry) the same was not observed for topographic classes. Of the 120 species present in the seed bank, 68 species do not form transient seed bank, even if present in low density. Melastomatacea, Urticaceae, Araceae e Moraceae configured among the most abundant. Melastomataceae configured as an important component of the seed bank contributing significantly to the number of individuals and species, together with Cecropia spp. these will contribute to the restructuring of the forest cover. The density of tre seedlings was higher than all other life habits identified. Higher density of shrub individuals in the forest changed reflects the successional stange. Irrespective of the severity of the disturbance, the seed bank has a high potential for forest regeneration.