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Abstract
Sap flow calibration is crucial for accurately estimating transpiration in trees; however, we do not understand how different calibration approaches affect sap flow estimates of tree transpiration and most publications rarely apply calibration coefficients. To examine the prevalence of calibration, a review of the past 11 years of tree sap flow publications was conducted. Additionally, we performed an experiment comparing two calibration approaches that use either positive or negative force to move water through stems. Through this research, we confirmed that despite the repeated emphasis on the importance of calibration, it is far from common within the tree sap flow community. Furthermore, we determined that differences in sap flow approaches have significant effects on the calculation of transpiration. Sap flow studies should perform calibration and report results to improve our measurements and understanding of transpiration.