An ecophysiological basis for the assembly of Australian rainforest tree communities

Abstract Understanding how past climate has filtered different tree strategies into communities is crucial for predicting how future climates will impact species and communities, yet few studies have used physiologically interpretable traits to explain the assembly of entire tree communities across large, continuous climatic gradients. To address this gap, we systematically surveyed rainforest tree communities across the Australian subtropics (spanning 600 to 2,500 mm rainfall yr− 1) and measured functional traits on 285 (91%) of the recorded tree species, including detailed measurements of xylem anatomy to describe species’ hydraulic strategies. The direction and shape of species’ occurrence trends across the regional moisture gradient were strongly related to their hydraulic strategies. Evergreen species with efficient hydraulics were more prevalent in mesic locations, while those with safer hydraulics favoured drier climates. Despite having extremely efficient hydraulics, deciduous species declined along the moisture gradient. At the dry end of the gradient, lower soil fertility increased the prevalence of very safe evergreen strategies and decreased the prevalence of deciduous species, relative to high-fertility sites. Overall, we reveal how climate, soil and biogeography have jointly filtered tree strategies into communities across the Australian subtropics, providing a general foundation for prediction under ongoing climate change.