ABSTRACT
The floristic and structure alterations were studied in an Ombrophyllous Mixed Forest located in São João do Triunfo (Paraná State - Brazil). Nine plots of 1ha, first evaluated in 1979, were recovered and, measured in 2000. In 1979, all the trees with dbh ≥ 20 cm were identified and tagged, and they had their commercial height and diameter measured. In 2000, based on the same criteria described before, the trees which had not been counted in 1979 were considered as ingrowth, and the missing ones were considered mortality. In 1979, 2133 individuals, 51 species and 29 families were found and in the 2000 survey, 2202 Aquifoliaceae, Lauraceae, Sapindaceae, Myrtaceae and Canellaceae were the most represented in terms of quantity of individuals. Although in both times more than 50 species were counted, in 1979 only 7 species (Araucaria angustifolia, Ilex dumosa, Matayba elaeagnoides, Ocotea porous, Capsicodendron dinisii, Nectandra grandiflora and Campomanesia xanthocarpa) represented 80.4% of the individuals and, in 2000, the same 7 species plus Ocotea corymbosa covered 80.9% of the total number of individuals. Hovenia dulcis, exotic specie, based on the number of adult and regeneration individuals, became to be seen as a threat to the autocnons species. All the structural indicators which were analyzed showed that the community has become more mature during the studied period and that the Araucaria angustifolia increased its dominance. There was a sensible increase of the occupancy grade, indicated by the absolutely dominance that changes from 23.52 m2/ha in 1979, to 28.53 m2/ha, in 2000, an increase of 21.3%. These results indicate that this community is still in development, and has not yet found its equilibrium. It also demonstrates that the Araucaria dominance increased in this period, suggesting that this profile can even increase future in the future. Regarding to the diversity, it was observed that the indices that consider, the amount of species (richness) and the homogeneity of the density distribution (the indexes of Simpson, U and D of McIntosh) are the ones that best represent the alterations of the period.
Keywords:
araucaria forest; phytosociology; forest dynamic; floristic diversity; richness indexes