Efeito da fragmentação na assembléia de herbáceas de uma área de floresta Atlântica do Nordeste do Brasil

Abstract

The conversion of large areas in small forest remnants directs various physical and biological changes that negatively affect the biodiversity of tropical forests, but little is known about the responses of herbaceous plants to human disturbance. Therefore, this study aimed to test the following hypotheses: (1) a fragmented area has less richness, lower diversity and greater density of herbaceous assembly of a continuous environment; (2) there is more accumulated litter, increased soil temperature and soil moisture lower in the fragmented; and (3) the floristic composition and structure of herbaceous areas are distinct from those due to environmental changes provided by forest fragmentation. The study was conducted in the Atlantic forest landscape of the Usina Serra Grande (8°30‟S and 35°50‟O), Alagoas, using the area core a 3500 ha fragment (continuous area) and ten small forest fragments ranging between 7.84 and 83.63 ha (fragmented area). The remnants are dystrophic soils (latosols and ultisols yellow-red), hot and humid tropical climate and vegetation lower montane rain forest and semideciduous. The herbaceous (all non woody plant – including vines and saprophytic) were collected between october 2010 and march 2011, 50 by plotting random plots (5×5 m) in both areas. The plots were established in the area continuously from 200 m from the edge. In the fragmented five plots were plotted near the midpoint of each remaining. We recorded the richness, density, diversity of herbaceous assembly in both areas. In each plot we collected data regarding the amount of litter accumulated, percentage of soil moisture and soil temperature. Differences between environments were evaluated with the following tests: Mann-Whitney (richness); t test of Hutcheson (diversity); t test (density, accumulated litter; soil moisture and temperature). The MDS, ANOSIM with, there a difference in the floristic composition and structure of plots distributed among habitats. Test the correlation species-environmental variable was performed a CCA. Species richness was higher in continuous ambient (97 species) than in fragmented (68), but there was no significant difference in density. The diversity and equability were higher in the continuous ambient (H‟= 3.616 nats/ind.; J‟ = 0.791) than in fragmented (H‟= 2.729 nats/ind.; J‟ = 0.647). In the area fragmented there was a greater amount of accumulated litter, higher soil temperature and lower soil moisture. The MDS showed the segregation of two groups (plots of the area continuous and plots of the area fragmented), and this result is explained by the type of environment. The CCA found that the species are distributed in the areas from a gradient, which involves greater influence of increasing soil temperature and decreased soil moisture in the area fragmented, and the opposite pattern in the area continued, explaining the preference of many species for a certain type of habitat. However, other unmeasured variables may also be acting in the assembly of herbaceous Serra Grande. These results suggest that fragmentation really contributes to the loss of biodiversity of the flora of rain forests, especially of species of herbaceous assembly of the northeastern Atlantic forest, mainly due to environmental changes generated after habitat fragmentation. Thus, it is necessary to perform additional studies in order to broaden the understanding of the factors that control the assembly of herbaceous tropical rain forest areas.