Stand Transpiration Estimates from Recalibrated Parameters for the Granier Equation in a Chinese Fir (Cunninghamia lanceolata) Plantation in Southern China.

Chinese fir (<italic>Cunninghamia lanceolata</italic> (Lamb.) Hook) is an important native tree species that is widely distributed in subtropical areas of southern China and cultivated for wood extraction. However, information on water use by Chinese fir plantations is still scarce. In this study, we performed species-specific parameter calibrations for the original Granier equation for sap flow density (<italic>SFD</italic>) estimates. Stand transpiration (<italic>E</italic>_s) was related to environmental inputs, such as rainfall, air temperature (T_a), vapor pressure deficit (VPD), photosynthetically-active radiation (PAR), air relative humidity (RH), and potential evapotranspiration (PET) in order to examine how environmental factors affect the <italic>E</italic>_s of Chinese fir plantations. According to our results, Granier’s original parameters set underestimated <italic>C. lanceolata</italic><italic>SFD</italic> by up to 54% compared to our species-specific calibrated parameters set. A strong positive correlation was found between <italic>SFD</italic>, diameter at breast height (DBH), and tree height among trees populations. The total <italic>E</italic>_s in 2015 was 522.1 mm, with obvious seasonal dynamics and an average of 1.4 mm·day⁻¹. Daily and monthly <italic>E</italic>_s were positively correlated with VPD, PAR, T_a, and PET. A negative relationship between <italic>E</italic>_s and RH was detected only at a daily timescale. Our findings indicate that the original Granier equation requires a parameter calibration when it is applied to species-specific thermal dissipation probe (TDP) estimates, and our findings can also provide novel insights on the water use of Chinese fir in major wood production areas in Southern China. [ABSTRACT FROM AUTHOR]