A Functional Basis for the Assembly of Australian Subtropical Rainforest Tree Communities.

Understanding the role of climate in the assembly of rainforest tree communities is informative for predicting how future climates will impact species and communities. We surveyed rainforest tree communities across the Australian subtropics (spanning 600 to 2500 mm rainfall year) and measured functional traits on 285 (91%) of all recorded species. We used principal component analysis to create axes approximating species' hydraulic strategies, leaf economics and stature and included these as predictors in joint species distribution models, along with traits describing dispersal ability and leaf phenology.

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 hypothesized 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.