SIMULATION OF EVAPOTRANSPIRATION BY TREES

As a guide to selecting species for lowering water tables in salt-affected drylands in southwestern Australia, a model of plant water consumption was used to simulate seasonal patterns of soil water storage in a forested catchment 200 km south of Perth. Combinations of leaf area index and stomatal sensitivity to humidity were assessed for their impact on water storage levels in two soils with differing water storage capacities. The model predicted that trees with low stomatal sensitivity to water vapour pressure deficit (VPD) or with high leaf area index (LAI) will deplete soil water more rapidly than trees sensitive to VPD or with low LAI. Trees with stomata insensitive to VPD would have to endure longer periods of severe water stress and would be less likely to survive then trees with stomata responsive to VPD. Differences in stomatal sensitivity to humidity resulted in no net annual change in soil water storage when soil moisture holding capacity was small because all water was consumed each year. Assuming plants initially had free access to water, those with stomata insensitive to VPD reduced water table levels more rapidly than species with stomata responsive to VPD. Total water consumption would be the same for both types of plants after a sufficiently long period when a new equilibrium between annual rainfall and evapotranspiration would be reached.