Applicability of the thermal dissipation method (TDM) for sap flow measurement in teak trees
2016
Sato, T. (The University of Tokyo, Aichi (Japan). Graduate School of Agricultural and Life Sciences, The University of Tokyo Forest, Ecohydrology Research Institute) | Tanaka, N. | Tanaka, K. | Igarashi, Y. | Yoshifuji, N. | Suzuki, M. | Tantasirin, C.
To determine the radial distribution of sap flow and to test the applicability of the thermal dissipation method (TDM) for measurements of sap flow velocity in mature, ring-porous teak trees, dye perfusion experiments and simultaneous measurement of water uptake and sap flow using the TDM were conducted. The dye perfusion experiments revealed the sap flow velocity in teak trunks is much larger than in coniferous and diffuse-porous species. According to visual observation of the surface of stained disks, the number of dyed annual rings varied from one to five, and the dye was concentrated around annual ring boundaries. In our absorption experiments, the TDM underestimated the actual water uptake, and the degree of underestimation varied among the sample teak. The extent of underestimation was greatest in a sample with an annual ring density lower than those in two other samples. Thus, the conducting area on the sap flow sensor will change according to the number of annual rings, and the degree of underestimation therefore will vary between individuals. Our dye perfusion and absorption experiments indicated that the large sap flow velocity and non-uniform radial sap flow distribution in teak trunks make it difficult to estimate water uptake by the TDM in teak trees. However we found a linear or hysteretic relationship between the hourly actual and TDM-estimated water uptake. This study indicated that the output of a Granier-type sensor is affected by the anatomical features of the xylem. Exploration of seasonal changes in teak sap flow by the TDM should take into consideration the seasonality of xylem formation.
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