THE VERIFICATION OF THE HEAT PULSE VELOCITY TECHNIQUE FOR ESTIMATING SAP FLOW IN EUCALYPTUS-GRANDIS

The heat pulse velocity technique was verified on a diffuse porous hardwood, Eucalyptus grandis Hill ex. Maiden, using the cut-tree method. The heat pulse velocity apparatus accurately reflected sap flow in the stems of 3-year-old trees and of a 16-year-old tree. Measured sap flow was found to be particularly sensitive to errors in the estimation of the wound size and probe separation. Four probes, each providing a point estimate of heat pulse velocity, were sufficient to estimate sap flow in young trees, but a minimum of eight was needed for trees larger than about 20 cm in diameter. For the successful field application of the heat pulse velocity technique on standing E. grandis trees, it is necessary to wait 5 days after implanting the probes to enable tyloses to form, which facilitates wound size measurement. This technique is recommended for the accurate and rapid measurement of water use by E. grandis and other similar plantation tree species.