Improved Sap Flow Sensor Design for Compensation Heat Pulse and Thermal Dissipation Methodology

Ground-based ET measurements via methods such as flux tower, lysimeter, or sap flow remain relatively expensive and time consuming. This has restricted direct ET measurements to a relatively small number of sites and made it difficult to assess a wide range of vegetative characteristics. Of all the flux measurement methods, sap flow probes offer potential for more widespread, widescale, and remote uses, but costs and power requirements currently limit these applications. The probes are designed for use with the Heat Ratio Method and Thermal Dissipation Method, allowing flexibility for researchers in the field. Empirical laboratory measurements of flow rate through cut branches were used to calibrate Granier’s equation for these probes. Field tests with the Dynamax TDP-30 and traditionally constructed thermocouple-based sap flow probes provided an assessment of accuracy and precision. These inexpensive and easily constructed probes were used to capture a larger variation of physiological and meteorological drivers in plant water use, allowing for more representative estimates when scaled to the stand and watershed level. This work is part of a larger effort to integrate this system into the existing NYS statewide weather station network to provide real-time, web-accessible measurements on tree health and transpiration.