Fitossociologia, distribuição diamétrica e relações hipsométricas de um fragmento florestal no município de Dois Vizinhos - PR

Abstract

This paper aimed to conduct a phytosociological survey, adjust a model for the diametric distribution and determine hypsometric relations which can represent, in the best way, a forest fragment. The study took place in a fragment of 18.7 hectares, through systematic sampling, where 16 permanent plots of 1,000m² were installed. In which plot, every tree with CAP higher than 15,70m was measured. They were identified in terms of gender and species and, besides CAP, the following information was gathered: bifurcation height, total height, forest layer, tree crown quality, trunk quality, epiphyte presence and tree crown luminosity. A total of 1,484 individuals, in 1,6 hectares, were measured, with an average of 927.5 individuals per hectare, and a basal area average of 26.82m²/ha. There were 110 species, 92 genders and 36 botanical families in the study, and the most representative family was Fabaceae. The species Luehea divaricata, Sebastiania brasiliensis e Parapiptadenia rigida showed the higher values of density, with 110, 56.88 and 53.75 individual/ha, respectively. The species L. divaricata, P. rigida e N. megapotamica got the higher index of importance, 9.94%, 6.66% and 6.11%, respectively. Regarding the forest layer, 68% of the trees were in the understory layer, 29% were under the canopy layer and only 3% were in the canopy layer. Most of the individuals (66%) showed a well vigorous and developed crown, 46% of the trees had an acceptable trunk and 49.46% were shaded by other trees. The functions of probabilistic distribution were tested for the forest and for the three species with higher density, while the models of hypsometric relations were tested for the three species with the highest index of importance. The forest and the species L. divaricata, S. brasiliensis e P. rigida showed diametric distribution as a negative exponential format, reverse-J. The Log-Normal model was the one that represented, in the best way, the diametric distribution for the whole fragment and the species Açoita-cavalo, Branquilho-de-latex and Angico-vermelho. The mathematic model that showed the best performance for the hypsometric relations of L. divaricata, P. rigida e N. megapotamica were the Stoffels model, which got satisfactory results of coefficient of determination, variation coefficient, relative standard error and F calculated value. The forest can be considered in an intermediate to advanced stage of regeneration.