WATER-UPTAKE BY 2 RIVER RED GUM (EUCALYPTUS-CAMALDULENSIS) CLONES IN A DISCHARGE SITE PLANTATION IN THE WESTERN-AUSTRALIAN WHEAT-BELT

The heat-pulse technique was used to estimate year-long water uptake i n a discharge zone plantation of 9-year-old clonal Eucalyptus camaldul ensis Dehnh, near Wubin, Western Australia, Water uptake matched rainf all closely during wetter months but exceeded rainfall as the dry seas on progressed. Average annual water uptake (1148 mm) exceeded rainfall (432 mm) by about 2.7 fold and approached 56% of pan evaporation for the area. The data suggest that at least 37% (i.e. (1/2.7) x 100) of t he lower catchment discharge zone should be planted to prevent the ris e of groundwater. Water uptake varied with soil environment, season an d genotype. Upslope trees used more water than did downslope trees. Wa ter uptake was higher in E. camaldulensis clone M80 than in clone M66 until late spring, The difference reversed as summer progressed, Both clones, however, have the potential to dry out the landscape when pote ntial evapotranspiration exceeds rainfall. This variation in water upt ake within the species indicates the potential for manipulating planta tion uptake by matching tree characteristics to site characteristics, Controlled experiments on the heat-pulse technique indicated accuracy errors of approximately 10%. This, combined with the ability to obtain long-term, continuous data and the superior logistics of use of the h eat-pulse technique, suggests that results obtained by it would be muc h more reliable than those achieved by the ventilated chamber techniqu e. (C) 1997 Elsevier Science B.V.