Resumo. This study aimed to describe the floristic composition of the regenerative component and to relate it with the adult component of an Araucaria Forest fragment, in South Brazil, in order to infer about the process of tree species community assemblage. To do so, five 10 x 20 m transection were allocated, in a forest fragment located at municipality of Lages, SC state. Each transect was made up by five plots, 20 m from each other, subdivided in different sizes, according to the sampled size class. The adult and regenerative components were compared each other for floristic-structural organization (Permutational Multivariate Analysis of Variance and Indicator Species Analysis), richness (rarefaction), population, individual spatial distribution (Standardized Morisita Index), and pattern of species coexistence or segregation in the studied plots (C-score Index). The results demonstrated significant differences between adults and regenerating components in relation to floristic-structural similarity and to richness. The adult component presented a greater proportion of populations with a random spatial distribution; and a smaller coexistence of species in plots than the regenerative component. We infer that the tree community assemblage is under influence of different ecological process, which intensity is ontogenetic dependent.