Abstract
Pruning of live branches is a management option to enhance wood quality in plantation trees. It may also alter whole-tree water use, but little is known about the extent and duration of changes in transpiration. In this study, sap flow sensors were used to measure transpiration for 14 days prior to, and 75 days following the removal, through pruning, of the lower 50% of the live-crown length of 10–11 m tall four-year old Eucalyptus pilularis Sm. and E. cloeziana F. Muell. trees. Pruning had no effect on stem growth, sapwood water content or radial pattern of sap velocity in either species. Pruning reduced mean daily water use by 39% in E. pilularis and 59% in E. cloeziana during the first eight days after pruning. Thirty six days after pruning there were no longer any significant differences in transpiration rates between pruned and unpruned trees in either species. Our results show that pruning of live branches had only a short-term effect on whole-tree transpiration in these sub-tropical eucalypt species.
Highlights
Whole-plant water use is influenced by soil nutrient and moisture conditions [1,2,3,4], humidity of air adjacent to leaves [5,6] and the supply of water from conducting stem tissue [7]
Defoliation through removal of 50% of the live-crown length of E. pilularis and E. cloeziana trees led to an initial reduction in whole-tree water use of 39% and 59%, respectively
Removal of 45% of the leaf area of Eucalyptus globulus trees had no significant effect on transpiration [10]
Summary
Whole-plant water use is influenced by soil nutrient and moisture conditions [1,2,3,4], humidity of air adjacent to leaves [5,6] and the supply of water from conducting stem tissue [7]. Rapid reductions in functional or effective photosynthetic leaf area following shading, disease or defoliation have the potential to dramatically alter whole-plant water use, not necessarily in proportion to the leaf area reduction [8,9]. Tree conductance was immediately reduced following shading of the lower 78% of foliage of a Pinus radiata tree [9]. When tree conductance was normalised with respect to the illuminated foliage area, water use increased by 50%–75%. Pruning 75% of the leaf area of Eucalyptus nitens trees reduced transpiration of the dominant 200 trees ha−1 by about 16%, but increased transpiration per unit leaf area, 2–3 years after pruning [12]
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