Water use by contour-planted belts of trees comprised of four Eucalyptus species

Over a 12-month period, soil water content and water use were measured concurrently in a contour-planted belt of trees comprised of Eucalyptus saligna (Smith), E. camaldulensis (Dehnh), E. leucoxylon (F. Muell) and E. platypus (Hook). These data were used to calculate water uptake by the trees from current rainfall, and from sources other than current rainfall (U′), to describe the temporal pattern of switching between these water sources, and to calculate the number and spacing of tree-belts necessary to reduce groundwater recharge to 5 mm per year. The data were also used to quantify competition for water between trees and adjacent crops or pastures. The tree-belt used 595 mm on a projected crown area basis over a 12-month period. Of this, 440 mm was transpiration, 100 mm interception and 55 mm soil evaporation. Rainfall was 445 mm and was all captured by the upper 2 m of the soil profile. U′ was 150 mm. Both soil water measurements and piezometric data from the same site indicated that most of U′ was from groundwater flowing under the trees. This study confirms that where groundwater is accessible, contour-planted belts of trees are an effective means of reducing groundwater recharge with minimal tree-crop competition for water.