Respostas da vegetação do sub-bosque em floresta ombrófila e estacional no Nordeste do Brasil

Abstract

The understorey is a stratum of the forest that contributes fundamentally to the biodiversity of the tropical forests, being of extreme importance for the establishment and development of the species that will compose the other strata of the forest. Thus, the present study sought to evaluate the floristic and structural responses of the understorey in response to environmental heterogeneity in two forest fragments, one of which is an ombrophilous forest and the other semideciduous forest, located in lowland and similar temperatures. In each forest, 25 plots of 20x20m, equidistant from 25m, were distributed in five transects. In each plot were sampled all the individuals of the understorey, measuring the canopy opening and light incidence and collected soil samples. The vegetation data and the environmental factors were submitted to statistical analysis to quote: Covariance Analysis (ANCOVA); non-metric multidimensional scaling analysis (NMDS); similarity analysis (ANOSIM) with 999 permutations; Principal Component Analysis (PCA); Hill number analysis; analysis of indicator species and non-metric multidimensional scaling in conjunction with the envfit analysis, all implemented in the statistical program R 3.3.2. The ombrophilous forest presented greater diversity and equability than the semideciduous, while the most abundant populations occurred in the latter. The species richness among the evaluated forests did not show a significant difference. The two forests have a quite distinct floristic composition of the understorey, which indeed varied according to the type of forest and the variables of soil and light. The herbaceous diversity among the forests did not present a significant difference. For each forest (ombrophilous and semideciduous) a group of indicator species was formed associated with the forest type. In both forests, the richness of herbaceous species and abundance were significantly related to edaphic factors, and these factors can determine the occurrence of these species. In general, this study contributed to increasing knowledge about the natural dynamics of the understorey by demonstrating how this forest stratum varies according to spatial heterogeneity, indicating implicit causes of its behavior. Thus, this knowledge comes to collaborate with the optimization of actions aimed at the conservation of fragments of tropical forests, since the responses of understory vegetation (herbs and shrubs) to an environmental heterogeneity of the ecosystem may indicate the basic conditions required for the growth, development, and composition of this component in specific locations.