Radial sap flux profiles and beyond: an easy software analysis tool

Sap flow measurements are nowadays used worldwide to validate forest-ecosystem estimates of water use and storage. Tall trees with large radial variability in sap flux across their sapwood still present a challenge in scaling single point sap flux measurements to whole-tree sap flow. Assessment of the radial sap flux profile is, hence, necessary to make a precise scaling possible. A sensor useful for assessing the radial sap flux profile in trees is the heat field deformation (HFD) sensor. This sensor records changes in the heat field around a linear heater at different radial positions in the xylem and links the heat field deformation to sap flow. The technical construction of the HFD-sensor, however, requires the configuration of multiple channels on the data logger (usually 8 to 12 channels per sensor or 48 to 72 channels per one “cross section” of the tree trunk when using 6 sensors in one cross section). Logging each channel with a small scan rate (e.g. 5 min) quickly results in a massive amount of data. The task of analysing these large data sets can become difficult and cumbersome with spreadsheet programs and the large file sizes often prevent efficient data interpretation. The objective of this paper was therefore to develop a software tool for easy analysis of HFD-data sets, including very large ones. Its primary use is to visualise in a fast way the measured radial sap flux profile in both 2D and 3D. The computed results can be saved in a compact form, drastically reducing the resulting file size in comparison to the output generated using classical spreadsheet programs. But the features of the software tool go beyond the analysis of radial sap flux profiles. Due to easy determination, K-values inherent to the sap flux density calculations can now be used to derive stem specific properties (e.g. relative water content) or raw signals can be used to quantify the sap flow index