Forest structure, tree species composition and diversity in Amazonian black-water floodplains in relation to hydro-chemical gradients

Summary

Quantitative scientific information about the influence of the flooding regime and soil chemistry on the black-water floodplain forest along the Rio Negro (Igapó) in central Amazonia is scarce. This study is based on the Flood Pulse Concept which explains that annual, predictable and long duration inundation are the most important factors affecting the vegetation; plants as reaction respond with a set of morphological, anatomical and physiological adaptations to the flood stress. Inundation is thus a powerful factor which determines the occurrence, growth and floristic variations in floodplain forests. The nutrient-poor status that characterizes the Rio Negro is conditioned by the geologic conditions of their catchment area and may indicate the regional edaphic conditions which at the same time might determine floristic variations. However, no scientific evidence is available.

This study, therefore, aims to understand how the forest changes locally and along the course of the river. In particular, a fundamental aspect is to understand and to systematically determine how the abiotic aspects as flooding regime (height and duration of inundation) and the chemistry of alluvial soil determine and condition the composition and distribution of species as well as diversity patterns and forest structure. Three sampling sites along the Rio Negro have been selected: in the upper, middle and lower Rio Negro. In each site two plots 2x1-ha will be randomly placed at different positions along the flooding gradient (low, intermediate, and highly flooded). Each plot will be subdivided in sixteen 25x25m subplots, which not necessarily have to be established close to another. A total of 6 ha will be inventoried. In each plots, all trees >10 cm dbh will be registered recording the following information: 1) local names (if available), 2) DBH (diameter at breast height in cm) and 3) total height. When necessary, voucher specimen of trees will be collected, identified (to species or morphospecies) and deposited in the herbarium of the Instituto Nacional de Pesquisas da Amazonia (INPA). Soil samples will be collected from the sampling sites, and data on height and duration of inundation in each plot will be registered.

In general, this study will contribute floristic inventories to a region in which there is a lack of quantitative scientific information and knowledge is limited about the vegetation. This basic information will also contribute to the classification of wetland in the Amazon region, which is an ongoing initiative lead by the research consortium INPA/Max Planck Institute. More specific, this study will provide scientific insights about the evolutionary patterns and diversification of the Amazonian landscape, especially the floodplain forests. The study can also give important answers to understand the floristic evolution of the Amazonian forests especially during younger geologic eras (e.g. Pleistocene, Holocene and the savanification history). These insights can be also used to formulate climate change scenarios in the future.