Skip to main content
Research article - Peer-reviewed, 2019

Effects of heater wattage on sap flux density estimates using an improved tree-cut experiment

Lopez, Jose Gutierrez; Licata, Julian; Pypker, Thomas; Asbjornsen, Heidi


We assessed the effects of heater wattage on sap flux estimates from heat dissipation sensors and generated calibrated equations for 1-year-old Eucalyptus grandis Hill ex Maiden trees. We used a total of eight trees ranging from 3 to 6 cm in diameter. Our calibration experiment was performed with a modified tree-cut approach, which allowed us to estimate gravimetric water use manually weighing 20 l buckets every 15 min while sap flux was monitored on each tree. Our results indicate that changes the current supplied to the heaters from 0.15 to 0.25 W does not significantly influence sap flux estimates, as long as the maximum temperature (Tmax) is properly determined for each period when wattage is different, and natural temperature gradients are corrected. Using the original parameters developed for this method, sap flux density and sap flow had an average underestimation of 53%, which according to our analysis had a reduced but relevant correlation with tree diameter (R-2 = 0.3, linear regression). These results may allow researchers to supply different currents to heat dissipation sensors to increase sensitivity or to reduce power consumption. They also provide evidence in favor of the correction and use of raw data collected when unwanted changes in wattage occur. The relationship observed between estimation error and tree diameter, while not strongly significant, suggests that diameter plays an important role in the estimation errors that has not been previously considered, and requires further research.


calibration; heat dissipation; heater current; tree-cut method

Published in

Tree Physiology
2019, volume: 39, number: 4, pages: 679-693

Authors' information

University of New Hampshire
Swedish University of Agricultural Sciences, Department of Forest Ecology and Management
Licata, Julian
Bemidji State University
Pypker, Thomas
Thompson Rivers Univ
Asbjornsen, Heidi
University of New Hampshire

UKÄ Subject classification

Forest Science

Publication Identifiers


URI (permanent link to this page)