Growth and water use of Eucalyptus globulus and E. nitens in irrigated and rainfed plantations

Early patterns of growth and water use of Eucalyptus globulus subsp. globulus and Eucalyptus nitens were measured for the first four years in a plantation established on a low rainfall site in SE Tasmania, Australia. Half the plantation was irrigated to maintain soil water deficits at levels where available water did not limit growth, and the other half was subjected to a series of water stress cycles which were interrupted by rainfall or terminated by supplementary irrigation to end severe drought stress. Height growth of E. globulus was greater than that of E. nitens irrespective of water status. For both height and diameter, differences due to levels of available water remained insignificant until the third year of growth. Increments in volume were significantly greater in E. globulus than E. nitens in the third and fourth year of growth and these differences were more apparent in the rainfed than the irrigated treatment. However, there were no differences in water use between species for either treatment in the second, third or fourth year of growth. Maximum rates of growth were associated with total water use just above pan evaporation. The ratio of water use (mm water) to volume increment (m) was always lower for E. globulus than E. nitens. It was concluded that E. globulus was more suited to sites where moderate water stress is experienced as part of the normal annual growing cycle.