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[ACG22-P01] Sap flow measurement for Japanese cedar throughout the year with three techniques and related problem
Keywords:Japanese cedar, vapor pressure deficit, deterioration of detecting sap flow
We conducted measurements in a mature stand of Japanese cedar, whose age is 63, within Tsukuba Experimental Watershed located in southern part of Mt. Tsukuba, Japan. We picked up a tree of Japanese cedar whose height is 24.9 m and diameter at breast height is 40.4 cm, and installed sensors of TDP, HRM and HFD. We used handmade sensors for TDM (e.g., Iida et al., 2015b) and sensors for HRM and HFD manufactured by ICT international Pty Ltd (type SFM1 and HFD8, respectively). The length of TDM sensor was 20 mm, and the sap flux density was computed as mean value along the sensor length by the calibration equation proposed by Granier (1985). The width of sapwood was 44 mm, and additional TDM sensor was inserted into the sapwood at the depth from 20 to 40 mm. On the other hand, the length of HRM sensor was 35 mm, and the sap flow movement was detected at the depths of 12.5 and 27.5 mm. For HFD, the sensor length was 96 mm, and the depths of sap flow detected were 20, 30, 40, 50, 60, 70, 80 and 90 mm.
The values of sap flux density by HFD showed high correlation with vapor pressure deficit (VPD). Generally, conifer canopy has large aerodynamic conductance due to the needle leaf, and therefore has high coupling with the ambient air. Thus, the high correlation with VPD is reasonable. Similar trends were confirmed for TDP and HRM. However, the relationships changed with time, and sap flux densities had become gradually smaller since the sensor installation. The clear deterioration was found at 10-months after the installation, in common to TDP, HRM and HFD. This may be induced by wounding or air embolism, which cause disruption in water flow around the sensors (e.g., Moore et al., 2010). Therefore, to obtain the whole-year dataset of sap flow, attentions must be paid for any deteriorations by checking the relationships between sap flow and VPD.
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