Açaí palm management and the multidimensional erosion of beta diversity across tree assemblages in the Amazon estuarine forest

Abstract

Non-timber forest products persist as an opportunity to conciliate tropical forest integrity and better life for traditional communities, but sustainability must be continuously evaluated. This paper examines diversity-related impacts from increments on the açaí palm density for fruit production (i.e., açaí intensification) on the tree assemblages of the Amazon estuarine forest. By examining 43 forest stands covering 20–1260 açaí clump.ha⁻¹, we documented a decline on taxonomic, phylogenetic and functional beta diversity, which resulted from species loss along the intensification gradient. Such an impoverished community assembly resulted from the fact that forest stands with <400 açaí clump.ha⁻¹ exhibited higher scores of species accumulation or beta diversity, while no species responded positively to increments on açaí clump density and 17 species did negatively. The community-level threshold for species loss was 180 clump.ha⁻¹, and after the 400-clumps threshold (as posed by current regulation) almost half of the tree species was already lost. Our results suggest that the açaí intensification represents a driver of tree species assembly and a tangible threat for integrity of the Amazon estuarine forest by promoting a multidimensional community impoverishment at regional scale. Threat magnitude depends on which extension managed, high-density açaí stands replace forest patches supporting açaí natural densities. The açaí case demonstrated how fragile or ephemeral the sustainable production of non-timber forest products can be, since markets pose a demand beyond the threshold represented by the yields supported by natural populations, while it offers additional revenue from traditional communities coming from such a “industrial production and harvesting”.