Deep drainage and water use of forests and pastures grown on deep sands in a Mediterranean environment

Abstract

The neutron scattering technique was used to measure soil-moisture storage beneath native hardwood forests, plantations of softwood forests, perennial pastures and winter annual pastures growing in deep sands of the southwest of Western Australia. The seasonal patterns of water use and of deep drainage to groundwater were calculated using measured soil-moisture characteristics. Fourteen-year-old Pinus pinaster (Ait.) plantations, containing ∼1200 trees per hectare, transpired more water than the native forest they replaced. The pines depleted the soil water faster, and to a greater degree. Deep drainage beyond 6 m was much less in the soil below the pine plantations, indicating a decrease in recharge of shallow groundwaters. The perennial pastures showed a pattern of water use, soil-water depletion and deep drainage similar to the native forests. The winter annual pastures, however, used less water than the native forest, and deep drainage was increased.