Abstract

Water use by Eucalyptus tereticornis was studied in two plantations in the Kerala State Forest, India, differing in tree density (1800 stems per hacter at Site I and 1090 stems per hacter at Site II) . At both sites, stomatal conductance, predawn and midday water potentials and microclimate were measured and used to estimate hourly transpiration by the Penman-Monteith equation. Growth in girth was also measured. Stomatal conductance was closely correlated with atmospheric vapour pressure deficit (D)however, stomata did not close completely even at high D (5. 0 kPa) . Midday leaf water potentials did not fall below -2. 0 MPa during any part of the year at either site. Predawn leaf water potentials were greater than -0. 25 MPa during the postmonsoon period, but declined to -0. 7 MPa at Site I during the premonsoon period. Transpiration estimates ranged from 0. 6 to 1. 2 mm per hacter at Site I and from 0. 2 to 0. 6 mm per hacter at Site II. The extrapolated transpiration values