The functional paradox of dryland plant communities

Nicolas Gross, French National Research Institute for Agriculture, France

Background/Question/Methods
Because the phenotypic characteristics of organisms – functional traits – relate to how species acquire, conserve and release resources, they are increasingly used to infer general patterns in terms of how species assemble within communities and respond to their environment, and how changes in communities feedback on ecosystem functioning. Central to trait-based approach is the environmental filtering hypothesis, which posit that the abiotic environment selects species with similar trait values in a given environment. In dryland, strong environmental constraints such as high aridity conditions, scarce and unpredictable rainfall, and low soil nutrient contents should reduce plant functional diversity, as predicted by the theory. However, dryland ecosystems may contradict these theoretical predictions and exhibit a strikingly high diversity of plant forms and functions; perhaps precisely as a result of plants´ response to such unpredictable conditions, the importance of biotic interactions and the diversity of habitats that composes dryland ecosystems worldwide.
I will present new results gathered from a global trait survey conducted in 335 dryland plant communities in 27 countries worldwide (the DRY database). The DRY survey includes data on plant size, leaf morphology, and chemical traits for ~21000 individuals from > 2000 species measured in situ using trait-transect. This database constitutes a major step forward over existing global trait databases (e.g. TRY), which contain a poor representation of dryland species, and do not have information on intra-specific trait variability, species abundance within communities and their spatial distributions.
Results/Conclusions
Trait diversity observed at the scale of the dryland biome largely overlaps with that observed across the rest of terrestrial ecosystems when comparing with available data from TRY. Moreover, the variance in dryland trait distributions is as large, and sometimes larger, than that observed across other terrestrial ecosystems. These results illustrate what we define as the functional paradox of drylands, i.e. the higher than expected functional diversity in dryland plants compared to those from less environmentally-constrained environments. Remarkably, dryland also exhibit trait distributions characterized by lower kurtosis than communities from the rest of the world. In other words, drylands host a high plant functional diversity of plant species that are more evenly represented than in other biomes. I will discussed both theoretical and applied perspectives for conservation strategies in drylands considering that high trait diversity has been shown to promote high multifunctionality and stability in dryland ecosystems worldwide.