Abstract:

The sap flow of Larix principi-rupprechtii, which is one of the most principal species for afforestation in northwestern China, was researched by means of heat pulse method. The results indicated that the sap flow changed regularly from day to night in later growth season. In the night, it was very slow and the value was usually below 0.000 08 m³·h^-1,and became stronger with increasing of solar radiation intensity and atmosphere temperature in daytime, and the maximum could reach 0.001 079 m³·h^-1. The results also showed that the sap velocity of points of stem section from outer to inner accorded with the law that the velocity is slow-quick-slow. The daily transpiration of individual tree was estimated on the basis of calculation of daily cumulative sap flow, at the same time, the cut tree experiment was done to validate the value. The study showed that the results were not different significantly using two methods, and the later value (0.003 17 m³·d^-1) was 8.2% higher than the former, because the logger was not enough sensitive to record low sap flow. And the stand daily water use for transpiration was estimated by applying to DBH and sapwood area as two scalars to scale up based on individual tree measurement respectively. And the former value was 0.64 mm·d^-1, which was 0.051 mm lower than the later. At last, the relationship between daily transpiration and environment factors was studied by correlation analysis. The result showed that solar radiation intensity, atmosphere temperature and relative humidity were three significant environmental factors to determine daily transpiration water use, and the regression equation was constructed accordingly.

Key words: Forest hydrology, Transpiration, Scaling up, Environmental factors, Larix principi-rupprechtii plantation