Is phylogenetic and functional trait diversity a driver or a consequence of grassland community assembly?

1. Community assembly changes fundamentally in response to disturbance following habitat destruction due to extreme events and human activities. There are several important aspects of community assembly that can be measured in response to disturbance or during species establishment. Of these measurable outcomes, metrics of taxonomic or species diversity (SD) are perhaps the most common and logistically the easiest to evaluate. 2. It is increasingly evident that measurements of phylogenetic (PD) and functional trait (FD) diversity can provide more information than traditional measures of diversity and desirable and informative metrics to measure restoration outcomes. However, it is unclear whether FD and PD are drivers or a consequence of community assembly. 3. This Special Feature highlights eight field studies and a review that have investigated how PD diversity and functional trait diversity can be used to better understand grassland community assembly following disturbance or during restoration, and how as potential drivers they can be manipulated experimentally or incorporated into evolutionary models. Topics include: colonizing species as a function of FD and PD; dominant species origin impacts on subordinate species FD; impacts of environmental gradients such as seed mix richness, first-year precipitation and restoration age on FD and taxonomic diversity; impacts of drought and resource availability; and a synthesis of studies that measured FD and PD to determine if they provide similar or incongruent inferences for ecological and functional processes. 4. The work in this Special Feature indicates that SD, FD and PD can act as drivers and passengers of community assembly, and often yield different insights. Environmental gradients such as soil nutrients, precipitation and environmental drivers like drought can influence FD and PD of assembling communities in predicted and unexpected ways. 5. Synthesis. Results from the studies in this Special Feature highlight the importance of considering a multitude of ecological and evolutionary drivers of community assembly in grassland ecosystems. Studies pushing this field forward will be those that incorporate or study higher trophic levels, realistically incorporate climate change and disentangle the impacts of FD and PD.