Abstract
An application of Granier method for a long-term measurement of sap flux (u) was discussed. A continuous measurement of u was conducted for over one year for the test stand of Japanese red pine (Pinus densiflora Sieb. et Zucc.). The observation results of the temperature difference between a pair of sensors (ΔT) showed that ΔT was a good indicator of diurnal and long-term variation in u. However, daily maximum of ΔT (ΔTMAX), which is observed at the time of daily minimum of u, had decreasing trend over a long-term period independent of seasonal changes in some environmental factors. If ΔT0, which is ΔT when u is equal to zero, is regarded as the annual maximum value of ΔT, this trend has a possibility to lead some errors in evaluating u. New determination method of ΔT0 was discussed in the present study, and concluded that ΔT0 was determined as ΔTMAX. Sap flux estimated by Granier method based on the new determination of ΔT0 corresponded with that by heat pulse method. Furthermore, the value of daily transpiration of the test stand estimated by the Granier method was good agreement with previous results obtained at the same observation forest. The conclusion of the present study is that Granier method is an efficient and reasonable method for long-term measurement of transpiration of a tree, if the fluctuation of ΔTMAX is considered.
