CORRECTION OF SYSTEMATIC-ERRORS IN ESTIMATES OF TRANSPIRATION OBTAINED USING A CONSTANT-TEMPERATURE HEAT-BALANCE TECHNIQUE

Field measurements using 30-month-old grevillea trees indicated that the three main sources of error in sap flow estimation can be overcome by: estimating the temperature bias with the gauge heater switched off or covering the whole trunk with 20 mm thick styrofoam sheet and aluminium foil; or by inserting thermocouples in the stem and accounting for radial and conductive heat losses. These corrections reduce gauge error for tree trunks (50-90 mm diameter) from 10-47% to +/-7%. In the absence of a large lysimeter, a comparison of sap how rates was made by attaching gauges to the trunk and a single terminal branch on the same tree.