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1. One sixth of Amazonian tree diversity is dependent on river floodplains

   https://doi.org/10.1038/s41559-024-02364-1  

   Householder, John Ethan; Wittmann, Florian; Schöngart, Jochen; Piedade, Maria_Teresa Fernandez; Junk, Wolfgang J; Latrubesse, Edgardo Manuel; Quaresma, Adriano Costa; Demarchi, Layon O; de_S_Lobo, Guilherme; Aguiar, Daniel_P_P de; et al (May 2024, Nature Ecology & Evolution)

   Abstract Amazonia’s floodplain system is the largest and most biodiverse on Earth. Although forests are crucial to the ecological integrity of floodplains, our understanding of their species composition and how this may differ from surrounding forest types is still far too limited, particularly as changing inundation regimes begin to reshape floodplain tree communities and the critical ecosystem functions they underpin. Here we address this gap by taking a spatially explicit look at Amazonia-wide patterns of tree-species turnover and ecological specialization of the region’s floodplain forests. We show that the majority of Amazonian tree species can inhabit floodplains, and about a sixth of Amazonian tree diversity is ecologically specialized on floodplains. The degree of specialization in floodplain communities is driven by regional flood patterns, with the most compositionally differentiated floodplain forests located centrally within the fluvial network and contingent on the most extraordinary flood magnitudes regionally. Our results provide a spatially explicit view of ecological specialization of floodplain forest communities and expose the need for whole-basin hydrological integrity to protect the Amazon’s tree diversity and its function. 

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2. Mapping density, diversity and species-richness of the Amazon tree flora

   https://doi.org/10.1038/s42003-023-05514-6  

   ter_Steege, Hans; Pitman, Nigel_C A; do_Amaral, Iêda Leão; de_Souza_Coelho, Luiz; de_Almeida_Matos, Francisca Dionízia; de_Andrade_Lima_Filho, Diógenes; Salomão, Rafael P; Wittmann, Florian; Castilho, Carolina V; Guevara, Juan Ernesto; et al (December 2023, Communications Biology)

   Abstract Using 2.046 botanically-inventoried tree plots across the largest tropical forest on Earth, we mapped tree species-diversity and tree species-richness at 0.1-degree resolution, and investigated drivers for diversity and richness. Using only location, stratified by forest type, as predictor, our spatial model, to the best of our knowledge, provides the most accurate map of tree diversity in Amazonia to date, explaining approximately 70% of the tree diversity and species-richness. Large soil-forest combinations determine a significant percentage of the variation in tree species-richness and tree alpha-diversity in Amazonian forest-plots. We suggest that the size and fragmentation of these systems drive their large-scale diversity patterns and hence local diversity. A model not using location but cumulative water deficit, tree density, and temperature seasonality explains 47% of the tree species-richness in the terra-firme forest in Amazonia. Over large areas across Amazonia, residuals of this relationship are small and poorly spatially structured, suggesting that much of the residual variation may be local. The Guyana Shield area has consistently negative residuals, showing that this area has lower tree species-richness than expected by our models. We provide extensive plot meta-data, including tree density, tree alpha-diversity and tree species-richness results and gridded maps at 0.1-degree resolution. 

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3. Geography and ecology shape the phylogenetic composition of Amazonian tree communities

   https://doi.org/10.1111/jbi.14816  

   Luize, Bruno Garcia; Bauman, David; ter_Steege, Hans; Palma‐Silva, Clarisse; do_Amaral, Iêda Leão; de_Souza Coelho, Luiz; de_Almeida Matos, Francisca Dionízia; de_Andrade Lima Filho, Diógenes; Salomão, Rafael P; Wittmann, Florian; et al (July 2024, Journal of Biogeography)

   Abstract AimAmazonia hosts more tree species from numerous evolutionary lineages, both young and ancient, than any other biogeographic region. Previous studies have shown that tree lineages colonized multiple edaphic environments and dispersed widely across Amazonia, leading to a hypothesis, which we test, that lineages should not be strongly associated with either geographic regions or edaphic forest types. LocationAmazonia. TaxonAngiosperms (Magnoliids; Monocots; Eudicots). MethodsData for the abundance of 5082 tree species in 1989 plots were combined with a mega‐phylogeny. We applied evolutionary ordination to assess how phylogenetic composition varies across Amazonia. We used variation partitioning and Moran's eigenvector maps (MEM) to test and quantify the separate and joint contributions of spatial and environmental variables to explain the phylogenetic composition of plots. We tested the indicator value of lineages for geographic regions and edaphic forest types and mapped associations onto the phylogeny. ResultsIn the terra firme and várzea forest types, the phylogenetic composition varies by geographic region, but the igapó and white‐sand forest types retain a unique evolutionary signature regardless of region. Overall, we find that soil chemistry, climate and topography explain 24% of the variation in phylogenetic composition, with 79% of that variation being spatially structured (R² = 19% overall for combined spatial/environmental effects). The phylogenetic composition also shows substantial spatial patterns not related to the environmental variables we quantified (R² = 28%). A greater number of lineages were significant indicators of geographic regions than forest types. Main ConclusionNumerous tree lineages, including some ancient ones (>66 Ma), show strong associations with geographic regions and edaphic forest types of Amazonia. This shows that specialization in specific edaphic environments has played a long‐standing role in the evolutionary assembly of Amazonian forests. Furthermore, many lineages, even those that have dispersed across Amazonia, dominate within a specific region, likely because of phylogenetically conserved niches for environmental conditions that are prevalent within regions. 

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4. Centuries of compounding human influence on Amazonian forests

   https://doi.org/10.1073/pnas.2514040122  

   McMichael, Crystal_N H; Bush, Mark B; ter_Steege, Hans; Piperno, Dolores R; Gosling, William D; Nascimento, Majoi N; Lombardo, Umberto; de_Souza_Coelho, Luiz; Leão_do_Amaral, Iêda; de_Almeida_Matos, Francisca Dionízia; et al (November 2025, Proceedings of the National Academy of Sciences)

   Recent evidence suggests that the ecological footprints of pre-Columbian Indigenous peoples in Amazonia persist in modern forests. Ecological impacts resulting from European colonization c. 1550 CE and the Amazonian Rubber Boom c. 1850 to 1920 CE are largely unexplored but could be important additive influences on forest structure and tree species composition. Using environmental niche models, we show the highest probabilities of pre-Columbian and colonial occupation sites, and hence human-induced ecological influences, occurred in forests along rivers. In many areas, the predicted pre-Columbian and colonial distributions overlap spatially with the potential for superimposed ecological influences. Environmental gradients are known to structure Amazonian vegetation composition, but they are also strong predictors of past human influence, both spatially and temporally. Our comparisons of model outputs with relative abundances of Amazonian tree species suggest that pre-Columbian and colonial-period ecological legacies are associated with modern forest composition. 

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5. Above‐ and below‐ground biodiversity responses to the prolonged flood pulse in central‐western Amazonia, Brazil

   https://doi.org/10.1002/edn3.268  

   Bredin, Yennie K; Hess, Laura L; Scabin, Andressa B; Dunthorn, Micah; Haugaasen, Torbjørn; Peres, Carlos A; Nilsson, Henrik R; Antonelli, Alexandre; Ritter, Camila D (May 2022, Environmental DNA)

   Abstract Amazonia encompasses extensive forests in areas that are periodically inundated by overflowing rivers. The inundation depth and duration vary according to the slope of the terrain and distance to major water bodies. This creates a flooding gradient from the lowest lying seasonally flooded forest up into the unflooded forest, which directly affects the biota. However, the effect of this gradient on soil organisms remains elusive. Here, we use DNA metabarcoding to estimate prokaryote and eukaryote diversity from soil and litter samples along the flooding gradient in central‐western Amazonia using 16S and 18S gene sequences, respectively. We characterize the below‐ground diversity and community composition based on amplicon sequence variants (ASVs). We examine relationships between the soil biota and the flooding gradient, soil properties, and above‐ground woody plant diversity. The flooding gradient does not explain below‐ground biodiversity, nor is below‐ground diversity explained by the above‐ground woody plant diversity. We uncover several taxonomic groups—such as Patescibacteria—not previously reported from Amazonian seasonally flooded forests. The flooding gradient and woody plant diversity partly explain the community composition of soil bacteria. Although the effects of the flooding gradient, soil properties, and above‐ground woody plant diversity are difficult to quantify, our results indicate that flood stress may influence below‐ground bacterial community composition. 

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