Measurement of diurnal changes in stem and branch diameters using strain gauges

The applicability of a strain gauge for monitoring the diurnal changes of tree stem diameters and the differences in diurnal shrinkages between a stem and branches were investigated. Estimates of stem diameter changes obtained by a strain gauge were compared with changes obtained by a differential transformer. Patterns of strain changes obtained by a strain gauge were remarkably similar to the changes in the tree trunk diameter. This results demonstrated that a strain gauge is an effective technique for examining the behavior of changes in tree trunk diameter. Diurnal changes of diameter at various parts of the a tree were also measured with the help of several strain gauges. Diurnal strain changes of a stem and branches showed similar patterns of shrink-age during the day and swelling at night. However, the precise times at which the branches had their maximum and minimum strains differed from those observed in the stem, and the maximum rates of the strain changes lagged behind the stems in a day. These results lead us to believe that there is a time lag in the supply of water, which is required for compensating the water deficit between the stem and its branches.