Análise da estrutura, diversidade florística e variações espaciais do componente arbóreo de corredores de vegetação na região do Alto Rio Grande, MG

Abstract

The constant human occupation of natural systems, the indiscriminate use of resources, as well as the agricultural expansion, results in forest fragmentation. In this context, a new landscape model, in mosaic, appears, composed by habitat portions surrounded by a matrix and vegetation corridors. The corridors, being linear vegetation structures, are able to connect isolated vegetation remains and decrease the negative effects of the fragmentation. Therefore, this study had as objectives the evaluation of the structure, floristic diversity, pattems of tree species distribution in fragments and associated vegetation corridors in the Upper Rio Grande region, Minas Gerais. These corridors are very narrow (more or less 4 m) and resulted from the native tree species colonization of ditches, used for land division purposes. The studied corridors and fragments are located in the municipality of Lavras, Upper Rio Grande region, south of Minas Gerais State, between the coordinates 21°19'25"S and 44o59'53"W, 21°17'15"S and 44°58'59"W. The vegetation is defined as a disjunction of savanna biome (cerrado) inserted within an area of distribution of semideciduous estational forest in Southeastem Brazil. The analyses included eight fragments connected to a vegetation corridor formed by a main axis and four ramifications. The total sample area (fragments and corridors) was 1.08 ha. The system fragments-corridors has equability and diversity similar to the fragments of the region. Some species prefer one of the two different habitats, corridors or fragments, although these habitats are pretty similar in terms of floristic composition. Possibly, the environmental variables that most strongly contribute to the differential species distribution between corridors and fragments are light and soil humidity. Corridors are denser, have larger basal area and trees are concentrated in the upper diameter classes and lower height classes. In the corridors, the species have preference for the sectional ditch sectors (bottom, wall and border), probably because of differences in terms of luminosity, phosphorus levels and soil humidity. The sectors are also different in terms of tree distribution by diameter classes, where has the bottom the largest trees. Besides me historical importance of these ditches in the region, the associated vegetation corridors are considered essential for conservation purposes, because of their considerable floristic diversity and the occurrence of exclusive species in these habitats. Therefore, the corridors can be indicated as complementation for the remaining habitat portions in the region, acting on behalf of the conservation of the diversity less represented in fragments and establishing connections among them.