UNDERGROUND WATER-USE BY EUCALYPTUS TREES IN AN ARID CLIMATE

Expanding the area of tree plantations in the Negev desert of Israel r equires prior quantification of the water resources in small watershed s. Combined hydrological and physiological measurements were used to s tudy a ''liman'' (floodwater irrigated plot) in the Negev highlands, w here Eucalyptus and other tree species are grown success fully. The am ount of water flowing into the liman, surplus water flowing out of the liman, temporal soil moisture distribution, and water uptake by the t rees were determined. Depending on rainfall intensity and distribution during the season, the liman received 2-3 times the total seasonal ra infall. Although the study was conducted during a year with a negligib le amount of rainfall, the transpiration rate was closely correlated w ith potential transpiration throughout the year. The amount of water e xtracted from the soil was less than the time-integrated transpiration rate from the trees, suggesting that a water source other than soil w ater storage was available to the trees. We suggest that the trees ext racted water from the rock fractures and/or utilized the lateral flows over the rock/soil interface.