Amazonian forests are recognized as harboring the most diverse tree communities on the planet, yet we still understand relatively little about how tree communities are structured across geographic and environmental gradients. Here we address the relative contributions of geographic distance and soil and climate dissimilarity in structuring tree communities in lowand Amazonian forests.
We established a plot network with a replicated design across three common lowland habitat types on opposite side of Amazonia terra firme clay forests, white sand forests, and seasonally-flooded forests. We have standardized data from 74 0.5ha plots across the region by comparing project morphotype vouchers at the Missouri Botanic Gardens herbarium and by integrating DNA barcoding for difficult and speciose genera.
Results/Conclusions:
Overall, we found more than 2300 distinct morphospecies among more than 20,000 sampled trees. Alpha diversity varied markedly among habitats, with lowest values (Hill Numbers below 45) in white sand forests in both regions, and the highest values (Hill numbers above 140) in terra firme clay forests, especially in Peru.
Beta-diversity, or species turnover across habitats and regions, was pervasive. More than a third of the observed species were found to be significantly associated with one of the three habitat types. Overall, less than 7% of the taxa observed, only 160 morphospecies, were shared between the two regions. This finding is unprecedented given the inclusion of all unidentified morphospecies standardized in the analyses.
Our results provide insights into the origin and maintenance of one of the most diverse floras in the world, with strong contributions of both geographic and environmental distance to tree community assembly. Our study also underlines the urgent need for continued floristic descriptions in understudied habitats and regions and particularly for the intensive collections work necessary to standardize taxonomic inventories.