Fitossociologia de espécies arbóreas em dique marginal de floresta ribeirinha no Rio Grande do Sul, Brasil, e compara??o com ambientes aluviais e n?o aluviais

摘要

The riverine forests have an important role in reducing erosion, contribute in maintaining the quality of water resources and are important biodiversity corridors. In Rio Grande do Sul these forests were largely modified or removed. In the municipality of Restinga Seca, RS, a phytosociological study was conducted in the River Vacacaí, in order to characterize the forest vegetation and to compare with other surveys in riparian forest, alluvial and not alluvial forest. The method used was point-centered quarter. Individuals with DAP 3 5 cm were sampled in 50 points arranged in a line parallel to the river course. The sampled individuals were identified, had their diameter measured and height estimated. The richness, diversity and phytosociological estimates of horizontal structure: density, frequency, dominance and importance value (IV) were determinated. The distribution of the diameters was determined and a floristic comparison was conducted with other research by cluster analysis. A total of 28 species belonging to 12 families was sampled. Euphorbiaceae and Myrtaceae had the highest species richness. The species with the highest VI was Sebastiania commersoniana (Baill.) Smith et Downs. The total density corresponded to 1,918 ind./ha and the Shannon index to 2.54 nats. The average height of the trees were estimated at 5.47 m and most individuals had diameters between 5 and 9.9 cm. The low species richness and relatively small diversity can be attributed to periodic flooding environment and anthropogenic impact that was submitted in the past. The study showed the highest floristic similarity with a survey conducted in the same watershed.