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

Abstract

The tissue heat-balance method (C ermk) and the heat-dissipation method (Granier) were compared in three Scots pines and two Norway spruces in a forest in central Sweden. The Granier system measured up to 50% lower sapflow than the C ermk system at high flow rates. New coefficients for the Granier system were estimated, based on sapflow density from the C ermk measurements. Without compensation, natural temperature gradients may cause large errors in measurements made by the Granier system. By using a horizontal reference sensor, no compensation was necessary. It was also shown that radial flow patterns must be considered when calculating total tree sapflow. Transpiration of two adjacent stands, one measured by the Granier method and the other by the C ermk method, showed good agreement internally and with total evaporation measured by the eddy-correlation method.