This study aimed to evaluate the floristic composition, diversity, spatial distribution and structure of tree species natural regeneration in Steppe Savannah Park vegetation, located at southwest of Rio Grande do Sul, Brasil. This vegetation tipology is characteristic of this part of the country with endemic and vulnerable species. For analysis, a permanent unit sample of 4ha (200x200m) sub-divided in 400 subunits of 100m² (10x10m) each were installed. These, 60 subunits were randomly selected, where all trees taller than 30cm diameter at soil level (DSL) by ±3m of height, smaller than 9.5cm were sampled. It was found 174 individuals distributed in five botanical families, six genders and six different species. The natural regeneration presented Shannon's diversity index estimated at 0.82, indicating low results for diversity species. The species with highest importance values were Vachellia caven (Molina) Molina (63.96%) and Celtis ehrenbergiana (Klotzsch) Liebm. (30%). These two species presented aggregated behavior, while Prosopis affinis Spreng., characteristically park specie, had no aggregated behavior according to the Payandeh Index. The natural regeneration at the local is not balanced however follows the "J" inverted pattern model, with deficit of individuals at initial diameter class, possible due to current grazing in the area.
phytosociology; Steppe savannah park; Prosopis
