Patterns of tree diversity and composition in Amazonian floodplain paleo‐várzea forest

QUESTION: In a recent re‐classification of Amazonian floodplain types, a new category was established for paleo‐várzea. Although the geological basis for this classification is sound, a key question is whether it can be supported by botanical criteria, where floodplain paleo‐várzea forests contain distinct tree assemblages compared to other major floodplain types. LOCATION: Central Amazonian floodplains, Brazil. METHODS: We used 41 tree inventories from floodplain paleo‐várzea, várzea and igapó forests to perform a meta‐analysis. Diversity and richness estimators were applied at the level of genus and the examination of floristic composition was performed at family and generic levels. Generic composition across the three floodplain types was investigated using GNMDS and cluster analysis. Similarity coefficients and ANOSIM were applied to quantify floristic resemblance at the generic level between forest types. Indicator species analysis (ISA) was used to identify any indicator genera for the forest types evaluated. RESULTS: Alpha diversity and generic richness in paleo‐várzea forest was similar to várzea. Igapó forest was clearly the least diverse. Family composition was similar across the three forest types; Fabaceae was the dominant family on all three floodplains. Pouteria, Licania and Eschweilera presented the highest importance values in paleo‐várzea, but these genera were also important in várzea and igapó. Nevertheless, ANOSIM analyses show that generic composition differed significantly between the three forest types, and a GNMDS ordination and cluster analysis portrays paleo‐várzea tree composition as intermediate between várzea and igapó. ISA revealed that Euterpe, Dipteryx and Goupia were the most important indicator genera of paleo‐várzea. CONCLUSIONS: We conclude that paleo‐várzea floodplain tree assemblages are dissimilar to those of várzea and igapó, but contain components typical of both these floodplain types, explaining their intermediate positioning in our analyses. This floral mix probably allows paleo‐várzea alpha diversity to be similar to that of várzea.