Historical and current environmental selection on functional traits of trees in the Atlantic Forest biodiversity hotspot

Questions How is community functional composition associated with environmental and historical factors and how is this relationship mediated by spatial and phylogenetic autocorrelation? Location Atlantic Forest of South America. Methods We compiled abundance data of 2,122 species (most trees) distributed across 281 communities, seven functional traits, and 29 environmental and historical predictors. We mapped traits using community-weighted means, and related traits to predictors by combining the fourth-corner and the extended RLQ approaches. Results We found that decreases in rainfall, soil nutrition, biome stability in the last 120 kyr, and the increase in thermal variability were associated with high specific leaf area (SLA) and leaf N content, and reduced leaf thickness. In addition, increased temperature and soil sand content, and low biome stability in the last 21 kyr were associated with high wood density and leaf dry matter content, and reduced maximum plant height. Tree communities rich in taxa with N-rich thin leaves and high SLA were mostly located in semideciduous and deciduous forests (e.g., Fabaceae), while communities rich in taxa with N-poor thick leaves and low SLA were mostly found in rain forests (e.g., Myrtaceae and Lauraceae). Species with short stature, high wood density and heavy leaves were particularly abundant in the northern part of the Atlantic Forest (e.g., Myrtaceae), whereas tall species with light wood and leaves were abundant in the south (e.g., Lauraceae). There was not a particular direction in which seed dry mass increased most in response to predictors. Conclusions Our study reinforces the view that the multifaceted nature of community assembly needs analytical approaches that integrate abundance, functional, phylogenetic, and spatial data to properly understand how environmental and historical factors determine the dominance of functional traits. The observed patterns suggest that different regions of a given biome function in different ways, and probably provide different ecosystem services.