Heat dissipation sensors have been used for decades as a method to determine the rate of xylem sap flux in trees. Errors across growing seasons due to xylem tissue physiological wounding response or sensor malfunction can affect data quality. The process of sensor installation requires drilling into the conducting xylem tissue (i.e., sapwood) to create a pore for the sensor to be placed. The insertion of the sensor may cause both a short-term (embolism) and long-term wounding response over the course of a single or multiple growing seasons. Wounding responses may manifest as changes in the magnitude of actual or measured flux rates or systematic changes in response to environmental drivers. Measurements of sap flux across new and previously established installations within the same tree can be used to directly test for these wounding responses. Grainer-style sap-flux probes were installed in 32 trees of five species (Acer rubrum, Acer saccharum, Betula alleghaniensis, Fraxinus nigra, and Populus tremuloides) across three study locations in northern Minnesota and Michigan’s western Upper Peninsula. Probes were maintained or replaced in situ across multiple growing seasons and compared to newly installed probes within the same trees to determine the effects of tree wounding on sap-flux measurements.
Results/Conclusions
Daily sap flux, kgm2d-1 (Js) relative to newly installed probes and response of Js to daylight-weighted vapor pressure deficit (Dz) were compared across probe ages using a mixed-modelling approach. There were no significant differences across the 0, 1, and 2-year installations or in the response of Js to Dz. These results suggest that any wounding response from probe installation is not systematic within or across species. Our study also suggests no long-term effect of wounding at the installation sites across multiple growing seasons. Wounding effects of sap-flux sensor installation may be negligible across northern hardwood tree species in the upper Midwestern United States.