Effects of hydroperiod and substrate properties on tree alpha diversity and composition in Amazonian floodplain forests

It is well established that tree assemblage diversity and composition in Amazonian floodplain forest are influenced by substrate properties and hydroperiod. However, no study to date has tried to disentangle the individual effects of these variables on floodplain tree assemblages. In this study, we investigated the influence of several edaphic variables and hydroperiod on alpha diversity and individual tree species distribution. We carried out floristic inventories in 12 ha of floodplain forests across central-western Amazonia and sampled associated data on substrate properties and hydroperiod. Generalized linear mixed models were used to evaluate the importance of each predictor on the response variables. Flooding was the only variable significantly influencing alpha diversity and also significantly influenced the distribution of the highest number of tree species. Edaphic variables had a lesser effect, and a large number of tree species were not significantly influenced by any of the predictors tested. However, iron had a strong negative influence on several species. We conclude that floristic diversity and composition are more influenced by the hydroperiod than by substrate conditions, and substrate conditions become decreasingly important for increasingly flood-tolerant species. Many floodplain species are generalists occurring across the entire substrate and hydroperiod gradient