Thermal measurement of sap flow applied to the study of the water withdrawal from trees: literature review and method improvement

Abstract

In this work various thermal methods now available for estimating xylem sap flow are reviewed. A cheap measuring devie involving two thermal sensors (copper-constantan thermocouples), one of which is conected to a constantan heat source, was performed. Sensors are inserted into the xylem to measure temperatura changes into the sap. Subsequent estimation of the volumetric sap flow rate by this method requires no calibration since empirical coefficients are available form the literature. The improved device was tested for estimating the hourly and daily transpiration rate of a birch tree in a field situation. Results show that the thermal sensor provides satisfactory transpiration estimates for individual trees under high and medium flow rate conditions.