Woody plant subregions of the Amazon forest

The Amazon forest covers 7.5 million km(2) in nine countries, hosts 25% of the global biodiversity and is a major contributor to the biogeochemical and climatic functioning of the Earth system. Despite its global importance, a regionalization of the Amazon tree flora is still lacking. Clear and data-driven delimitation of subregions is important for macroecological studies, to the identification of metacommunities and is a requisite for conservation planning. We aimed at identifying and mapping plant species subregions and investigated their relationships with environmental, historical and human correlates. We provide the first woody plant regionalization of the entire Amazon forest using a data-driven approach based on assemblage composition patterns. We compiled data on woody species composition from 301 assemblages based on species occurrences. We then used unconstrained ordination, interpolation and clustering techniques to identify and map discrete woody subregions. Hierarchical clustering analysis was conducted in order to investigate the relationships between the identified subregions. We used multinomial logistic regression model and deviance partitioning to investigate the influence of environmental, historical and human factors on subregions distribution. We identified 13 woody subregions in the entire Amazon forest. The hierarchical subregion classification showed a broad Andean-Cratonic east-west division. Variation in subregions was explained jointly by human factors and spatial structure followed by environmental factors and spatial structure combined. Synthesis. Our woody plant subregions differed from World Wildlife Fund ecoregions and physiognomic-based maps, highlighting the importance of basing regionalizations on taxon-specific groups and confirming that vegetation maps should not be used as proxies to plant diversity subregions. Our findings also confirm the need for multiple and extensive protected areas in the Amazon forest. The relevance of current climate factors in our study alerts to a profound impact that climate change could have on the spatial organization of the Amazon flora.