Extreme Drought Event Affects Demographic Rates and Functional Groups in Tropical Floodplain Forest Patches

Floodplains exert restrictions on the development of plants, and the structure and composition of alluvial forests reflect those limitations. We aimed to evaluate how contrasting periods of drought and flooding affect the demographic rates of alluvial forest patches and how these effects are related to forest functional traits and diversity. We studied six alluvial forest fragments in the floodplain along the Sapucaí River in Minas Gerais State, Brazil. We carried out forest inventories in two sequential periods (2005–2011, 2011–2017). We also measured functional traits for species with higher densities and evaluated how the diversity index varied over time. We found that the period with drought (2011–2017) presented higher mortality, higher loss of basal area, and lower recruitment than the period with flood (2005–2011). The alluvial forest responded more intensely and negatively to the impacts of drought (second period) than to the impacts of flooding (first period). Lower diversity plots had higher mortality and basal area loss. We found overall degradation of the alluvial forest with a loss of basal area, a decrease in tree density, and an increase in species with acquisitive functional traits related to a strong drought effect. Thus, increasing extreme events like stronger floods but particularly droughts in function of climate change may be especially pernicious for alluvial forest persistence.