Abstract
We reviewed the applicability of a strain gauge for monitoring the diurnal diameter changes in tree stems and branches and the relationships between water status of trees and diurnal diameter changes. We summarized differences of diurnal changes in stem diameters between healthy and declining trees of hinoki cypress. The diurnal changes in xylem diameters (ε) are more closely related than the changes in phloem diameters to the changes in leaf water potential, because the diurnal change rates (Rε) in xylem diameters match the diurnal changes in water balance (sap flow velocity-transpiration rate). The diurnal patterns of Re can be divided into seven types (from type I to type VII) in relation to the soil water condition and water status of a tree. In declining trees, diurnal patterns of Re shift from the type I to VI rapidly as dry condition is continued. Therefore, the maximums and minimums of ε in declining trees tend to decrease more rapidly than those of healthy trees during the long dry period. Last, we discussed wide range of application of measurement of diameter change by strain gauges.
