Infra-red images of heat field around a linear heater and sap flow in stems of lime trees under natural and experimental conditions

The heat field deformation method, HFD, for sap flow measurements was applied under field conditions simultaneously with the infra-red imaging of the smoothed stem surface in two lime (Tilia cordata Mill.) trees. Deformation of the heat field generated in the stems by the linear heater was measured by thermocouples, installed in axial and tangential directions around the heater in different xylem depths. The frontal and radial views of the heat field were visualized at the same time by the infra-red, IR, camera under conditions of zero-flow and moving sap. The IR-technique basically underlines the established interpretation of sap flow dynamics, but contributes by a more complex and visualized picture. The IR also shows directly the xylem anisotropy. The ability of HFD-method for measurements of bi-directional sap flow rates and flows approaching zero was confirmed by simultaneous comparing with IR-images. Fast responding and capabilities of HFD-method for studying tree architecture and function were demonstrated.