Palm community structure in relation to topography, hydrography, and forest structure in the Iriri River Valley, eastern Amazon

The distribution of palm (Arecaceae) species distribution is closely associated with topography, hydrology, and forest architecture, but site- and species-specific studies remain scarce in the Amazon. Here, we describe patterns of palm community structure and their associations with environmental gradients in a remote area of the eastern Amazon, helping fill an approximately 500-km geographic knowledge gap. We hypothesized that local environmental heterogeneity, particularly hydrographic conditions, topography, and forest structure, would promote spatial variation in palm community structure, with species richness and composition varying along these gradients and dominant species showing species-specific associations with local environmental conditions. A field survey across a 5-km transect, subdivided into 100 plots in the Riozinho do Anfrísio Extractive Reserve, Pará, Brazil, identified palm species and collected environmental data, including NDVI, altitude, terrain characteristics, and proximity to permanent and intermittent streams. We assessed associations between species richness, community composition, and environmental variables using multivariate and regression-based analyses. Eighteen palm species were recorded, with the palm community overwhelmingly dominated by Attalea speciosa , which reached exceptionally high local abundance, followed by Geonoma baculifera and Euterpe longibracteata . Variation in species composition was significantly associated with NDVI, altitude, and distance to streams, whereas species richness showed stronger associations with the presence of igarapés and terrain shape. A. speciosa was associated with lower NDVI values and areas away from igarapés, whereas Euterpe oleracea and G. baculifera were positively associated with the presence of igarapés. The observed patterns partially support the hypothesis that local environmental heterogeneity promotes spatial variation in palm community structure by creating habitats differing in environmental suitability for palm species. These findings provide a baseline characterization of palm communities in a poorly documented region of the Eastern Amazon and contribute to understanding how local environmental gradients shape palm community structure and species distribution.