A Hydrological Study of a Subtropical Semiarid Forest of Acacia harpophylla F. Muell. Ex Benth. (Brigalow)

Abstract

Water input, soil water storage and plant water status were measured at monthly intervals over 2½ years In a mature brigalow (Acacla harpophylla) forest. Redistribution of rainfall by the canopy was slight and stem flow averaged only 1.8%, but the direct loss of intercepted water accounted for 15% of the Annual ramfall In the wettest condltlon the soil stored 890 mm of water to a depth of 3 m The minimum sod water store measured under severe drought conditions was 840 mm when the dawn values of plant water potential were -6.8 MPa The soil water potentials below 1 m were consistently around -3.5 MPa due largely to high salt concentrations The tendency in a drying soil was towards a uniform profile of soil water potentlal, and soil water at depths below 1 m was extracted only when dawn plant water potentials were less than - 3.5 MPa Over monthly Intervals the maximum and minimum rates of evapotransplratlon were 3.3 and 0 .46 mm/d respectively, and the pattern of community water use was related to rainfall and not to potentlal evaporation. To survive in such an environment the plants develop and withstand extremely low water potentials associated wlth the low availability of water and the high evaporative demand.