Phytosociology of the arboreal and natural regeneration strata in a black-wattle (Acacia mearnsii De Wild.) plantation in the region of Semideciduis Seasonal Forests of Rio Grande do Sul

This study analyzes the structure and floristic composition of the regeneration of native forest species under black-wattle plantation, established 16 years ago Ill a riparian area, and it verifies the possibility of the black-wattle be considered all invasive species of this environment. The tree stratum (circumference at breast height (CBH) >= 15 cm) was evaluated in 12 plots of 100 m(2), established In four blocks. The natural regeneration stratum (0.3 m height to <15 cm CBH) was evaluated In two Subplots of 9 m(2). established in opposite vertexes of each plot. The tree stratum was composed by 26 species of 14 families and the natural regeneration stratum by 49 species of 23 families. The Shannon diversity index for species, considering all plots, was 2.60 and 3.06 to the tree and natural regeneration strata, respectively. The native species, Casearia sylvestris, Myrsine lorentziana and Zanthoxylum petiolare presented the larger importance value in the tree stratum and Faramea marginata, Myrsine lorentziana and Myrcia glabra the biggest density in the natural regeneration stratum. The ecological characteristics of the species found ill several height strata indicated that the forest succession process is in evolution. The black-wattle did not regenerate in this area and the planted trees of this species are in the senescence phase. Only 100 tree/ha of black-wattle were found, which represents 4.5% of the original population. Thus, black-wattle is not all invasive species for this environment.