Intensification of acai palm management largely impoverishes tree assemblages in the Amazon estuarine forest

The exploitation of non-timber forest products has been encouraged in order to reconcile economic uses, biodiversity conservation and the provision of ecosystem services. In this paper we investigate how increments on the acai palm density (Euterpe oleracea) via forest management change tree assemblages across 47 plots in the Amazon estuarine forest (Brazil). Assemblage attributes were confronted to acai clump density, soil fertility, canopy openness and elevation. Both tree species density and richness were negatively affected by acai, but species richness was also affected by tree abundance. Species-accumulation curves also indicated higher alpha and beta diversity across low-intensity forest patches with high-intensity patches lacking half of the tree species. A small set of species dominated forest patches, but acai density did not correlate with the abundance of valuable species. Explanatory variables, including acai density, explained a small fraction of the variation on the functional profile of tree assemblages, but functional richness was reduced by a half across forest stands exceeding 600 acai clumps per ha. Our results suggest that acai intensification alters the structure of woody plant assemblages in estuarine forest. Tree abundance and species richness consistently declines as acai clump density increases, with some forest stands being dominated by acai and almost lacking any tree species. Accordingly, landscapes dominated by high-intensity forest stands are largely impoverished in terms of understory, canopy and emergent tree species. These findings question the current legal regulations and thresholds adopted for acai management, while alert for potential disasters caused by poorly-regulated extractions of NTFPs.