Wood production per evapotranspiration was increased by irrigation in plantations of Eucalyptus globulus and E. nitens

Wood volume growth per unit evapotranspiration was calculated from water balance and growth measurements in irrigated and water-limited Eucalyptus globulus and E. nitens plantations in the 3rd, 4th and 5th year of growth. Wood volume growth per unit evapotranspiration (plantation water productivity) was increased by irrigation for both species in the 3rd and 4th growing year but only in E. nitens in the 5th year. Irrigated trees required significantly less water than water-limited trees to produce 1 m3 of wood. At the same site, stomatal conductance was significantly greater in irrigated compared to water stressed trees through spring, summer and early autumn of each year. These data provide indirect evidence that leaf-scale measures of water-use efficiency are not well correlated with stand-scale measures of plantation water productivity. This was probably due to increased proportional allocation of assimilated carbon to stem wood in the irrigated compared to the water-limited stands. These results are consistent with recent studies in Brazil and Australia and suggest that plantation management systems, inclusive of tree breeding, that maximise growth rather than leaf-scale water-use efficiency, will also maximise the amount of wood produced from each unit of water used by the stand.