Diurnal changes in branch diameter as indicator of water status of Hinoki cypress Chamaecyparis obtusa

We investigated use of strain gauges for monitoring the water status of trees by measuring changes in the diameter of the largest spreading branch of a 27-year-old Chamaecyparis obtusa tree. The change in xylem diameter in the branch is more closely related than the change in phloem diameter to the change in leaf water potential. Since the diurnal changes in diameter match the diurnal changes in water balance (sap flow velocity – transpiration), measuring the change in xylem diameter using a strain gauge is useful in evaluating the water status of C. obtusa.