Estrutura e composição florística de uma floresta de baixio de terra firme da reserva Adolpho Ducke, Amazônia central

Abstract

The Forest Reserve Adolpho Ducke (RFAD) is an terra firme forest that has an area of 100 square kilometers in the urban area of Manaus. Is in the watershed between two river basins in the east the Amazon River and west the Negro River. In the Reserve are found four types of environments, plateau, slope, campinarana and baixio. These forest types are defined by the type of topography and soil. In the clay soil, the species are adapted to sandy soils with poorly drained soils to hydromorphic or with morphological structures adapted to the conditions of episodic hypoxia as anchors and adventitious roots, and many surface roots. On terra firme, the baixio is the one with environmental conditions similar to those of flooded forests. Therefore, it was found that many species of floodplain would form pre-adaptations in baixio environments and species that migrate to the terra firme areas periodically flooded, as the Igapó and várzea, because in the baixios and swamps they would create preadaptations to stress periodic flooding. We investigated the composition in 2 acres of a baixio of Barro Branco stream in the reserve and its comparison with some studies in environments plateau and slope the terra firme, the Igapó and floodplain forests in plains. The main focus was on the occurrence of species among the different environments, as well as aspects phytosociological and ecological. A total of 1378 individuals with DBH ≥ 10 cm were sampled in two acres, belonging to 38 families and 246 species. The index of evenness (J') was 0.83 suggesting a heterogeneity in the proportions individuals/species within the plant community. The mixing coefficient, which expresses the average number of individuals per species in the community was 1/6, ie, for every six individuals in its general composition, there is a different species. The average index of floristic similarity between plots was 18.44% with maximum of 45.07%. The average species richness of plots was 37.2 ± 8.8. The VIF (value of importance of family), family Fabaceae, Arecaceae, Myristicaceae, Sapotaceae, Lecythidaceae, Moraceae, Chrysobalanaceae, Malvaceae, Euphorbiaceae, Burseraceae Annonaceae and was above 10. The species with the highest levels of value of importance were Oenocarpus bataua Mart. (Arecaceae), Virola Pavonis (A.DC.) A.C.Sm. and Iryanthera juruensis Warb. (Myristicaceae), Bellucia dichotoma Cogn. (Melastomataceae), Protium hebetatum Daly (Burseraceae), and Allantoma lineata (Mart. ex Berg) Miers (Lecythidaceae). The diameter structure showed that more than 61.68% of the total number of individuals are distributed in smaller diameter classes, showing a typical curve in the form of "inverted J". The basal area per individual ranged between 0.8 and 0.008 meters in the 20 plots surveyed. The value of basal area of each hectare was respectively 30.9 and 28.9 meters. The similarity analysis performed was concluded that the flora of floodplain and terra firme are very different, with low similarity. The similarity values between inventories compared to várzea found 19.35%. While considering the baixio near the Igapó, the floristic similarity did not maintain the same relationship, as it showed the lowest similarities. The greatest similarity in land occurred between the slope and the plateau (84.33%). And the greatest similarity between the inventories in the baixios recorded 51.57%. Among the inventory there were a clear tendency to cluster both the geographical proximity and the distinctions between these ecosystems.