Efeito de distúrbios antrópicos na diversidade taxonômica e funcional em fragmentos secundários de Mata Atlântica

Abstract

The Atlantic Forest is one of the most biodiverse and ecosystem-rich biomes in the world, but it has suffered negative impacts due to uncontrolled urbanization, agriculture, livestock farming, and mining. As a result of these impacts, only 28% of its original vegetation remains today. The Doce River basin, completely encompassed within the Atlantic Forest biome, has faced various pressures and human disturbances that have driven its degradation and fragmentation. It was also the scene of one of the country's largest environmental crimes, the rupture of the Fundão dam located in Mariana – MG. In order to mitigate the impacts caused by the dam breach, the Forest Restoration and Sustainable Development Project of the Doce River Basin was created, a partnership between the MST and the Renova Foundation, aiming to restore 1960 hectares of permanent preservation areas and water recharge in agrarian reform settlements in the region. This study was conducted in 11 secondary vegetation fragments, among those to be restored by the project, with the objective of characterizing and evaluating how human disturbances influence the taxonomic and functional diversity of secondary forest fragments. Sampling was carried out by implementing 5 plots of 25mx4m, totaling 100m², in each fragment. Within the plots, data on height and diameter of trees with DBH>15.70 were obtained, and the presence of degradation factors such as fire, invasive grasses, erosion, presence of domestic animals, and exotic tree species was surveyed. Functional attribute data were collected through literature review, and landscape metrics were calculated using QGis software. The influence of environmental variables on taxonomic and functional diversity was calculated through model testing using R software. Nineteen families, 32 genera, and 40 species were sampled. The fragments showed Shannon diversity indices (H') ranging from 0.41 to 2.34 and Pielou's evenness (J') between 0.37 and 0.82. Mean DBH values ranged from 7.82cm to 11.56cm. The average height varied from 5.44m to 6.91m. Basal area values ranged from 6.55m²/ha to 16.62m²/ha. Eighteen species were classified as pioneers, 14 as early secondary, and 8 as late secondary. Sixteen are anemochoric, 13 are zoochoric, and 11 are autochoric. Thirteen species have fleshy fruit, and 27 have dry fruit. Thirty-two species were classified as heliophytes, and 3 as sciophytes. Seed length ranged from 1mm to 40mm, and fruit length ranged from 4mm to 300mm. Wood density ranged from 0.50 g/cm³ to 1.19 g/cm³. The results demonstrate that the fragments are in the early stage of succession, and indicate functional homogenization. Among the evaluated human disturbances, forest cover percentage had the greatest influence on taxonomic and functional richness, indicating that higher forest cover leads to greater diversity. Although not significantly influential, fire was an important factor in reducing diversity in areas with high forest cover. Small forest fragments should not be overlooked in biodiversity conservation, as these areas can form functionally connected mosaics and respond positively to a good restoration strategy. Agrarian reform settlements provide excellent conditions for restoring these small fragments because, in addition to the possibility of establishing connected areas, the support of an organized community committed to sustainability is relevant.