Abstract:

Objective: This study aimed to verify the applicability of the original Granier formula to calculate the liquid flux density of 107 fast-growing poplar trunks, in order to provide a basis for accurate calculation of tree transpiration. Method: In order to verify the applicability of the original formula of Granier, 107 poplar was taken as the test object, and the liquid flux density was actually measured by in vitro stem segment weighing method and whole-tree container weighing method on the basis of thermal diffusion trunk flow measurement technology. By establishing the statistical relation between the measured liquid flux density and the temperature difference Coefficient (K value) measured by the thermal diffusion method, the correction formula is finally formed. Result: Compared with the actual measurement values of the whole tree container weighing method and the indoor stem weighing method, the fluid flux density calculated by Granier's original formula is seriously underestimated, with error rates of -71.5% and -74.3%, respectively. The correction formulas established based on the real measurement values of the whole tree container weighing method and the indoor stem weighing method are F_d (fluid flux density, cm³·cm^-2 s^-1)=0.010 8K^{0.566 6}(R²=0.812 6) and F_d=0.019 17K^{0.952 8} (R²=0.940 3). According to the data collected on June 23 and 24, compare with the measured value of the whole tree container weighing method in the field under the natural condition, the value of Granier's original formula underestimates by 68.90%, while the whole-tree container weighing method underestimated only 2.95%, and the in vitro stem segment weighing method underestimated by 15.75%. Conclusion: Granier's original formula seriously under estimates the sap flow density of 107 poplar stems, which would cause great error. However, the corrected formula can reflect the relationship between the density of the liquid flux and the K value, and can accurately express the true liquid flow. Therefore, the liquid flux density of 107 poplar stem calculated by the Granier formula corrected based on the whole-tree container weighing method has higher accuracy.

Key words: thermal dissipation method, 107 poplar, weighing method of isolated stem, weighing method of whole-tree, Correction formula