Análise de agrupamento da vegetação de um fragmento de Floresta Estacional Decidual Aluvial, Cachoeira do Sul, RS, Brasil

Abstract

In the state of Rio Grande do Sul, the riparian forests have been altered and fragmented by human activity. The objective of this study was to analyze the structure and floristic composition of these forests, therefore providing information for the re-establishment of these ecosystems. The study site is a 4 ha fragment located in Cachoeira do Sul- RS, low Jacuí River (30o04´36”S; 52o53´09”W). The arboreal and shrubby species and lianas (only life-form) were inventoried using 10 m wide strips that were laid out perpendicular to the river and spaced at 50 m intervals. The strips were divided into 10 x 10 m plots. Within each plot all a individuals with girth at breast height – SBH ³ 15 were identified and their circumference and height measured. Species density data were entered into a matrix (70 x 42) that was used for multivariate analysis. The presence of species clusters at the interior of the fragment was analysed with TWINSPAN (Two-way indicator species analysis), which identified the existence of three forest sub-formations (S-F1, S-F2 e S-F3). S F1 was characterized by a higher influence of flooding and the ground water table was closer to the surface; SF2 occurred in the central part of the fragment, but presented a strong influence of flooding provided by inundation; and S-F3, also in the central part of the fragment, occurred the greatest influence from the ground water table. The indicator species of the three forest sub formations were Sebastiania commersoniana and Eugenia uniflora (S-F1); Gymnanthes concolor, Cupania vernalis and Seguieria aculeata (S-F2); and Casearia sylvestris and Allophylus edulis (S-F3). Therefore, in preservation projects, conservation and reestablishment of these ecosystems, the forest community cannot be treated as riparian only, but environmental and, consequently, floristics variations should be considered.