Diferen?as florísticas e estruturais entre fitofisionomias do cerrado em Assis, SP, Brasil

摘要

Classification of physiognomies is a challenge for many cerrado vegetation researches either because there are no clear floristic and quantitative criteria for its classification and because the changes it had over come over the years. The objective of this study was to charactherize three phytophysiognomies types in the cerradovegetation (Brazilian savannah) in the Esta??o Ecológica de Assis as well as to verify if they are floristically or structurally disticnts searching for better variables to classify them. The sample consisted of 30 permanent plots with 20 × 50 m, being 10 plots for each one of the physiognomy types: typical cerrado, dense cerrado and cerrad?o, where trees with diameter at breast height > 5 cm. The three studied phytophysiognomies were structuraly distintics in terms of basal area, canopy cover, and average height and diameter of the tallest trees. Basal area (m2 ha-1) was considered the best descriptor to classify the physiognomies of the cerrado vegetation because it is to easy measure and less variable with the inclusion criteria. In terms of floristic composition, savannah phytophysiognomies (typical cerrado and woodland cerrado) are not different from each other either by analyzing only the presence and absence of species or by analyzing the relative importance of the species in the community. Briefily, there are three distinct phytophysiognomies but the flora is different only between woodland cerrado and savannah phytophysiognomies. By analyzing the exclusive species of each physiognomy in relation to tolerance shade tolerance, it was suggested based in the literature that the low light availability under the canopies in the woodland cerrado might have been the conditioning factor of the differentiation between it and the other cerrado physiognomies.