Abstract:

The transmissivity of the broad-leaved Korean Pine forest was calculated according to the fixed-point automatic measurements of global radiation above the forest and the transmission on the floor, from May 22 to October 14. The results showed that the transmissivity was correlated to sky conditions. The diurnal variation curve of the transmissivity was flatter under overcast and fluctuant under scattered sky. The violent fluctuation of the curves appeared in clear sky. These phenomena were due to the gaps of the crown and the percentage of direct ray in the global radiation. However, the comparison of fixed-point and wandering measurements showed that the difference of daily averaged transmissivities between the two methods was little. So the daily averaged transmissivities were reasonable to represent the characteristics of the crown. The transmissivity also varied with the growing stage not only in the values, but also the appearing times of the peak of the diurnal curves. Seasonal variation curve of the transmissivity (daily averaged) was took U shape during the measured period. The transmissivity was higher in late May and early October, lower and stable in July and August. The relationship between the transmissivity and days' number fitted quartic polynomial. This reflected the seasonal variation of leaf area index of the forest.

Key words: Transmissivity, Broad-leaved Korean Pine forest, Seasonal variation, Diurnal variation