n Southern African Forestry Journal - Water use efficiency : what are the implications for plantation forestry? : evidence for sustainable plantation forestry




Water use efficiency (WUE) is the ratio of some measure of growth or carbon assimilation to water utilization. It can be considered at the level of the leaf, whole plant or stand, and can be expressed in terms of total plant biomass or that of harvestable stems. It is a ratio and will be influenced by changes in either or both of the components. WUE is extremely variable with climatic and local weather conditions, soil type and plant age. Increases in yield of harvestable stem would increase WUE, but breeding practices have probably already maximised stem yield. Reductions in transpiration are considered unlikely to be achievable in plants growing in well-watered soils, and any such reductions would probably also bring about reductions in productivity. 'Water conservation' strategies are also unlikely in plants in water-limited soils, as competing neighbours would utilise the conserved water. It is not known whether there are differences among genotypes in intrinsic WUE, but if there are, these are more likely to become apparent under conditions of low, rather than high water availability. However, high WUE may not be a good selection criterion for plants suitable for water-limited conditions; the ability to acquire water and the ability to survive periods without water may be more important than the efficiency with which water is utilised.


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