Upscaling the effect of traits in response to drought: The relative importance of safety-efficiency and acquisitive-conservation functional axes.

We tested the idea that functional trade-offs that underlie species tolerance to drought-driven shifts in community composition via their effects on demographic processes and subsequently on shifts in species' abundance. Using data from 298 tree species from tropical dry forests during the extreme ENSO-2015, we scaled-up the effects of trait trade-offs from individuals to communities. Conservative wood and leaf traits favoured slow tree growth, increased tree survival and positively impacted species abundance and dominance at the community-level. Safe hydraulic traits, on the other hand, were related to demography but did not affect species abundance and communities. The persistent effects of the conservative-acquisitive trade-off across organizational levels is promising for generalization and predictability of tree communities. However, the safety-efficient trade-off showed more intricate effects on performance. Our results demonstrated the complex pathways in which traits scale up to communities, highlighting the importance of considering a wide range of traits and performance processes.

Diverging functional strategies but high sensitivity to an extreme drought in tropical dry forests.

Extreme drought events have negative effects on forest diversity and functioning. At the species level, however, these effects are still unclear, as species vary in their response to drought through specific functional trait combinations. We used long-term demographic records of 21,821 trees and extensive databases of traits to understand the responses of 338 tropical dry forests tree species to ENSO2015 , the driest event in decades in Northern South America. Functional differences between species were related to the hydraulic safety-efficiency trade-off, but unexpectedly, dominant species were characterised by high investment in leaf and wood tissues regardless of their leaf phenological habit. Despite broad functional trait combinations, tree mortality was more widespread in the functional space than tree growth, where less adapted species showed more negative net biomass balances. Our results suggest that if dry conditions increase in this ecosystem, ecological functionality and biomass gain would be reduced.

Phylogenetic classification of the world's tropical forests.

Knowledge about the biogeographic affinities of the world's tropical forests helps to better understand regional differences in forest structure, diversity, composition, and dynamics. Such understanding will enable anticipation of region-specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present a classification of the world's tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. Our results do not support the traditional neo- versus paleotropical forest division but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar, and India. Additionally, a northern-hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern-hemisphere forests.