FLORÍSTICA E FITOSSOCIOLOGIA DE FLORESTAS EM PALEOAMBIENTES FLUVIAIS DE TRÊS BACIAS HIDROGRÁFICAS DA AMAZÔNIA

Abstract

This study contributes to the floristic and phytosociological knowledge of forests that colonize three distinct Amazonian fluvial paleoenvironments: Viruá megafan, in the Branco river basin; paleochannels filled by white-sand sediments in the river Negro basin; and paleochannels filled by sediments of diverse granulation in an abandoned fluvial terrace of the Madeira river. The vegetation analyzes indicate that the drained fluvial paleoenvironments of the Branco and Madeira rivers present high floristic similarity to each other, although they are separated by about 1000 km and occur in tributaries of opposite banks of the Amazonian hydrological system. The main indicator species of the inventoried forests in the Branco and Madeira fluvial paleoenvironments are: Ruizterania retusa, Couma utilis, Licania heteromorpha, Sacoglottis guianensis, Hebepetalum humiriifolium and Humiria balsamifera. The sampled forests in Manaus exhibited a high proportion secondary-growth and long-lived pioneer trees, such as Simarouba amara, Tapirira guianensis, Guatteria procera, Protium heptaphyllum, Protium spruceanum, Myrcia splendens and Goupia glabra, and Oenocapus bacaba. Here we hypothesize that in the hydrologically more stable areas, such as the studied sites in Manaus, the stressing conditions of the soils have been softened after the initial colonization of these areas by trees specialized in white-sand substrates. The enhancement of the edaphic environment allows other long-lived pioneer and secondary-growth tree species to settle in these fluvial paleoenvironments, which gradually may acquire floristic composition closer to those found in the surrounding terra firme forests. Palavras-chave: white-sand, rivers, Amazon, e campinaranas.