2026 Volume 25 Issue 2 Pages 61-75
Understanding tree hydraulics is becoming increasingly important for adaptation to climate change for the growth and survival of trees in forest ecosystems. Measurement of radial dimensional changes in tree stems has been used to monitor changes in the water status of trees. In this study, long-term (over several months) monitoring was performed on mature coniferous trees with large diameters, by evaluating the capacitive water storage by bark and the pressure potential of sapwood using an improved system of dendrometer. The dendrometer system enabled simultaneous monitoring of tree water deficit (TWD), which was a measure of time-course change of the bark water storage, and the differential pressure potential of sapwood (dPP), which was a measure of time-course change of the sapwood pressure potential. It was concluded that the full of one-growing season was a suitable limit for the longest continuous measurement. The results of the measurement revealed that their responses to the fluctuations in climatic conditions differed diurnally and seasonally: e.g., the diurnal fluctuation of dPP corresponded well with those of vapour pressure deficit and sap flow although that of TWD showed time-lags behind dPP. The responses of trees to changes in climatic conditions differed between individual trees and species: both TWD and dPP were variable along to fluctuating climatic conditions in Larix spp.; changeable TWD and stable dPP were observed in Cryptomeria japonica; and only minimum responses of TWD and dPP were found in Abies sachalinensis. The relationship between the sub-daily fluctuations of TWD and dPP was used to interpret dynamics of water movement in tree stems including the radial movement between sapwood and bark. Those results showed the usefulness of the long-term simultaneous monitoring for further understanding of tree hydraulics.
