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Theory and Practical Application of Heat Pulse to Measure Sap Flow

Environ. and Risk Manage. Group, HortResearch Inst., Private Bag 11-030, Palmerston North, New Zealand

View larger version (20K): [in a new window]   Fig. 1. Influence of wood moisture content (m3 m-3) on the relationship between measured heat pulse velocity (Vz) and sap flow (JS). This relationship was determined using the numerical model. The temperature probes are Teflon, and the heater is stainless steel.

View larger version (19K): [in a new window]   Fig. 2. Influence of wood moisture content (m3 m-3) on the relationship between measured heat pulse velocity (Vz) and the actual heat pulse velocity (VH). This relationship was determined using the numerical model. The temperature probes are Teflon, and the heater is stainless steel.

View larger version (19K): [in a new window]   Fig. 3. Influence of wound width (mm) on the relationship between measured heat pulse velocity (Vz) and the actual heat pulse velocity (VH). This relationship was determined using a numerical model of heat and mass flow through a 2-d slab of wet wood. The temperature probes are Teflon, and the heater is stainless steel.

View larger version (36K): [in a new window]   Fig. 4. Transpiration rate of a willow tree as measured by the compensation heat pulse method (black line) and calculated by the weight loss from the lysimeter (open circle).

View larger version (17K): [in a new window]   Fig. 5. The influence of sap velocity, JS, on the time for a peak temperature rise to occur, TM, at a distance of xD = 10 mm and 15 mm downstream from the heater probe.

View larger version (17K): [in a new window]   Fig. 6. Temperature rise measured at a downstream distance of 10 mm (data) following the application of a 1-s heat pulse. The measurements are smoothed (LS Fit) to reduce signal noise, and the time for a maximum temperature rise to occur is calculated using the convoluted least-squares procedure of Savitzky and Golay (1964). These are predawn measurements (zero flow) in a mature grape vine.

View larger version (18K): [in a new window]   Fig. 7. Temperature rise measured at a downstream distance of 10 mm (data) following the application of a 1-s heat pulse. The measurements are smoothed (LS Fit) to reduce signal noise, and the time for a maximum temperature rise to occur is calculated using the convoluted least-squares procedure of Savitzky and Golay (1964). These are midday measurements (high flow rate) from a mature grape vine.

View larger version (20K): [in a new window]   Fig. 8. Influence of wound width (mm) on the relationship between measured heat pulse velocity (VM) and the imposed sap flow (JS). The temperature probes are Teflon, and the heater is stainless steel.

View larger version (38K): [in a new window]   Fig. 9. Transpiration rate of a poplar tree as measured by the T-max method (black line) and calculated by the weight loss from the lysimeter (open circle).