Changes in trait covariance along an orographic moisture gradient reveal the relative importance of light- and moisture-driven trade-offs in subtropical rainforest communities

• A range of functional trait-based approaches have been developed to investigate community assembly processes, but most ignore how traits covary within communities. 
• We combined existing approaches (community-weighted means [CWMs] and functional dispersion [FDis]) with a metric of trait covariance to examine assembly processes in five angiosperm assemblages along a moisture gradient in Australia’s subtropics. In addition to testing hypotheses about habitat filtering along the gradient, we hypothesised that trait covariance would be strongest at both ends of the moisture gradient and weakest in the middle, reflecting trade-offs associated with light capture in productive sites and moisture stress in dry sites.
• CWMs revealed evidence of climatic filtering, but FDis patterns were less clear. As hypothesised, trait covariance was weakest in the middle of the gradient, but unexpectedly peaked at the second driest site due to the emergence of a clear drought tolerance – drought avoidance...