Evaluation of heat balance and heat dissipation methods for sapflow measurements in pine and spruce

The tissue heat-balance method (Cermak) and the heat-dissipation method (Gr anier) were compared in three Scots pines and two Norway spruces in a fores t in central Sweden. The Granier system measured up to 50% lower sapflow th an the Cermak system at high flow rates. New coefficients for the Granier s ystem were estimated, based on sapflow density from the Cermak measurements . Without compensation, natural temperature gradients may cause large error s in measurements made by the Granier system. By using a horizontal referen ce sensor, no compensation was necessary. It was also shown that radial flo w patterns must be considered when calculating total tree sapflow. Transpir ation of two adjacent stands, one measured by the Granier method and the ot her by the Cermak method, showed good agreement internally and with total e vaporation measured by the eddy-correlation method.