A diversidade arbórea em uma paisagem florestal urbana : efeitos dos estágios sucessionais e de perturbações antrópicas crônicas

Abstract

Globally, tropical forests are under threat, due to anthropogenic disturbances, which not only reduce forests to fragments of different successional stages but also affect richness and diversity of tree assemblages. This study aimed at testing the hypothesis that age of forest regeneration and chronic anthropogenic disturbances affect the structure and diversity of tree assemblages on two forest strata (sub-canopy, 10 cm > DBH ≥ 5 cm; and canopy, DAP ≥ 10 cm) in an urban forest landscape. The study was carried out at the Dois Irmãos State Park (PEDI), in which PPBio (Research Program on Biodiversity) site is set up, as part of the Atlantic Forest Network. Data collection followed the RAPELD method and protocols for the inventory of tree assemblages, comprising a total sample of approximately 10 hectares. We used the chronosequence previous determined for the PEDI (three forest ages: mature, late regenerating and initial regenerating) and date on anthropogenic disturbances collected from plots and trails, based on pre-selected indicators. For analyses, we applied: rarefaction and Hill’s numbers, for analyses of richness and diversity between ages. Data on disturbances were analyzed through Principal Component Analysis (PCA); we used dbMEMs (distance-based Moran's eigenvector maps) in order to control the effect of spatial autocorrelation, adding them as covariables to the analytical model for Redundancy Analysis (RDA). In order to understand the effect of the spatial structure on species composition, we carried out variance partitioning. We used analysis of beta diversity in order to verify (dis)similarities between ages. We sampled 6,092 individuals in total, 3,524 on the sub-canopy and 2,568 in the canopy. Total richness was of 265 plant species in 52 families. Rarefied richness and diversity did not differ between ages. Hill’s numbers for both strata revealed that most species in the assemblages are rare. Species composition was different only between mature forests and regeneration sites, with no difference between late and initial regeneration. We recorded 2534 disturbances, of which wood exploitation, invasive species and informal recreation were the most impact-inducing ones. Forest age only did not explain species richness. Variance partitioning indicates that for both strata disturbances and age are spatially related and contribute to the variation on species richness and diversity. The influence of anthropogenic disturbances on the forest demands urgent measures for effective forest conservation, mainly because of the pressure posed by the urban communities surrounding the forest.