What role does plant physiology play in limiting species distribution?

To predict vulnerability of tree species to changes in climate, we need to understand what processes are currently limiting their distributions. Although the limits to distribution is among the most fundamental of ecological questions, there are few studies that determine quantitatively which processes can explain observed distributions. Focusing on two contrasting Eucalypt species, a fast-growing coastal species (E. saligna) and a slower-growing inland species (E. sideroxylon), we examined to what extent plant physiological characteristics limit species distributions. The ecophysiology of both species has been extensively characterised in both controlled and field environments. We parameterised an ecosystem model (GDAY, Generic Decomposition and Yield) for both species, using the best available experimental data. We then used the model to predict the spatial distribution of productivity for these species in eastern Australia, and compared these predictions with the actual distributions. The results of this comparison allow us to identify where the distributions of these species are limited by physiological constraints on productivity, and consequently their vulnerability to changes in climate.