长白山阔叶红松林冠层透射率的定点观测研究

根据长白山阔叶红松林林上和林地太阳辐射的定点观测结果 ,计算了 5月 2 2日— 10月 14日的林冠透射率 ,发现林冠定点透射率与天空状况有关 ,阴天时透射率的日变程曲线比较平稳 ,少云天波动增加 ,晴天条件下波动最为剧烈 ,这种差别是由林窗和太阳辐射中直接辐射的比率不同而产生的。然而通过 2d定点测定与游走测定的比较发现 ,两种方法测定的透射率日平均值差异不大 ,定点测定的日平均值能较好地代表林冠的透射率特征。定点透射率的日变程曲线还随着生长季进程而变化 ,不仅透射率大小发生变化 ,透射率峰值的出现时间也发生更迭。在观测期间内 ,定点透射率日平均值的季节变程曲线呈U形 ,5月底和 10月上旬较高 ,7— 8月较低且平稳 ,随日期 (季节 )的动态变化符合四次多项式函数 ,反映了冠层叶面积的季节变化特征。

Fixed Point Measurements of Crown Transmissivity of the Broad-leaved Korean Pine Forest in Changbai Mountain

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.