Comparison between sensors for sap flux density measurement based on Granier method

Abstract

Sap flux density was observed at a tree of Pinus densiflora by two commercial sensors, which are based on Granier method. One is Sapflow Meter (SFM) from UP Gmbh and the other is Thermal Dissipation Probe (TDP-30) from Dynamax Inc. The observation result showed 10% underestimate in sap flux density measured by TDP-30. A pair of thermocouple temperature sensors composes Granier sensor. One temperature sensor X includes the heater to trace the sap flux density, and the other sensor Y, which measures the reference temperature of sapwood without the thermal effect by the heater, dose not include the heater. We concluded that the underestimation by TDP-30 resulted from the increase of temperature at the sensor Y, and argued that this increase of temperature was caused by the thermal conductance of the heater due to the lack of distance between the sensors of TDP-30.