Revisiting the role of mean annual precipitation in shaping functional trait distributions at a continental scale

Mean annual precipitation (MAP) varies substantially across the globe, impacting the spatial distribution and structure of vegetation. However, evidence for consistent relationships between MAP and the functional traits of the organisms in these ecosystems is equivocal. Indeed, while some early global-scale analyses reported MAP as a key predictor of plant traits, more recent analyses have found relatively weak relationships between traits and MAP (among other broad-scale climatic variables), seemingly at odds with the important role that water availability is predicted to play in determining plant success from first principles. The independent contribution of MAP in shaping the spatial distribution of species traits, at least at the global scale, has therefore remained unclear.