Effects of tree diameter at breast height and soil moisture on transpiration of Schima superba based on sap flow pattern and normalization

The eigenvalues of continuous sap flow pattern, i. e. , skewness and kurtosis, were used to investigate the water usage of Schima superba with different diameter at breast height (DBH), and the method of normalization was firstly applied to eliminate the effects of strong affecting factor (photosynthetic active radiation, PAR) to explore the possible relationship between weak affecting factor (soil moisture) and sap flow. Generally, the trees with larger DBH had smaller skewness of sap flux density and later-appeared but larger peak values, suggesting that much more water was transpired, and the larger trees showed smaller skewness and later-appeared larger peak values in wet season than in dry season, suggesting that more water was transpired in wet season. On the other hand, smaller trees had lesser differences in the skewness between dry and wet seasons, suggesting that there was no significant difference in the transpiration between the two seasons. The relationship between individual tree's transpiration