Tikhova G. P., Pavlov A. G., Pridacha V. B., Sazonova T. A. The New Hybrid Method for Measuring Transpiration Sap Flows in Trees

Sap flow measurements have become relevant in many physiological and ecological investigations. A variety of methods are used to estimate sap flow in trees in modern studies. However the determination of accuracy of commonly used techniques often presents a challenge. We analyzed advantages, pitfalls and restrictions of up-to-date methods that were implemented in commercially available devices. We proposed a new hybrid method for measuring linear sap flow velocity, which was designed on the base of different variants of heat-pulse velocity (HPV) technique and thermal dissipation (TD) technique developed by Granier. The method was created in order to increase accuracy and precision of sap flow velocity measurements. The mathematical model of the proposed method was developed. It allows determination of accuracy of measurements and potential limits of applying the new technique in the field studies. The model is based on the description of heat process dynamics in the volume of 1 cubic decimeter of sap tissue. The obtained relationships were used in developed software that allows modelling of reverse heat pulses distribution under the condition of shortened interval between their generations. The proposed algorithm enables verification of zero sap flow velocity measurement in tree trunk with given accuracy. The computer program was developed. It allows defining of maximum acceptable time interval for a given accuracy of determined values when the velocity is close to zero as well as to demonstrate the shape of the heat signal depending of time in the given point of trunk. The model calculations showed that the new method improves the accuracy of sap flow velocity measurements at low and high flow rates when conventional techniques suffer from significant errors. The applying of the new method allows detection of zero sap flow without using any additional measuring procedures and devices.