Global decoupling of functional and phylogenetic diversity in plant communities

Plant communities are composed of species that differ both in functional traits and evolutionary histories. Understanding how species’ traits and histories interact with the environmental conditions of a site and drive the assembly of ecological communities is the basis for predicting the impacts of climate change on biodiversity and ecosystem functioning. As species’ functional traits partly result from their individual evolutionary history, the functional diversity (FD) of communities is expected, on average, to covary positively with their phylogenetic diversity (PD). However, this expectation has only been tested at local scales, for specific growth forms or specific habitat types, e.g. grasslands. Here, we compared the standardized effect sizes of FD and PD for 1,781,836 vegetation plots using the global sPlot database. In contrast to our expectations, the correlation between FD and PD was weak, not positive but negative, and these two facets of diversity were more often decoupled than coupled. While PD reflected recent climatic conditions and vegetation type, being higher in forests, FD depended on recent (1981-2010) and past climatic conditions (21,000 years ago).The independent nature of functional and phylogenetic diversity makes it crucial to consider both aspects of diversity when analyzing ecosystem functioning or prioritizing conservation efforts.