Tree species natural regeneration in a tidal white-water floodplain forest of the Amazon River estuary

The Amazon hosts the worlds most diverse floodplain forests, characterized by tree communities adapted to seasonal flooding. In the estuary, these forests are driven by both fluvial and tidal dynamics, yet remain poorly studied. We assessed natural regeneration in a tidal white-water floodplain forest within the Fazendinha Environmental Protection Area, eastern Amazonia (Brazil). Regenerating individuals (DSH [≤] 5 cm) were sampled in 21 systematically distributed plots, classified into height classes, and analyzed with diversity indices, regeneration parameters, and ordination methods. We recorded 758 individuals from 43 taxa, 35 genera, and 20 families. Fabaceae was the richest and most abundant family, largely due to the oligarch Mora paraensis, which comprised >70% of individuals. Despite this dominance, Shannon diversity was high (H = 5.31), with 53.5% of species occurring as singletons or doubletons. Regeneration density reached 14,438 ind. ha{square}1, concentrated in the smallest classes, with few species spanning all classes. Subtle compositional shifts occurred with river distance, though dominants remained broadly distributed. Our findings highlight the resilience of oligarchic species and the vulnerability of rare taxa, advancing knowledge of estuarine floodplain ecology and providing essential baseline information for conservation and management in this understudied region.