A model for simulating transpiration of Eucalyptus salmonophloia trees

Understanding the water relations of Eucalyptus trees plays an important role in finding solutions to dryland salinity in southern Australia. A model for studying structure-function relationships in isolated tree crowns (radiation absorption, transpiration and photosynthesis, RATP) was parameterized to permit the seasonal transpiration course of a Eucalyptus salmonophloia tree to be quantified. Model responses to different parameterizations were tested in a sensitivity analysis. Predictive quality was mostly affected by the accuracy of information about leaf area density and stomatal responses to air vapor pressure deficit, and to a lesser extend by foliage dispersion. Assuming simple, non-synergistic influences of changes in photosynthetic active radiation and air vapor pressure deficit on stomatal transpiration control, the model was able to simulate the daily water uptake of E salmonophloia trees with reasonable predictive quality during an entire season. In order to more precisely simulate short-term (i.e. diurnal) water use dynamics, the model must be extended to account for hydraulic and chemical controls of stomatal regulation of crown energy balance.