林分密度对Ⅰ-69杨树冠结构和光能分布的影响

EFFECTS OF STAND DENSITY ON CROWN ARCHITECTURE AND DISTRIBUTION OF LIGHT ENERGY IN POPULUS DELTOIDES CV. 'LUX' I-69/55 PLANTATION

密植的Ⅰ-69杨林分树冠分枝角度小,骨干枝比率低。当叶面积指数达到7.81、冠层最大叶面积密度达0.8～0.9时,是林分最适密度状态。光在冠层内的分布,受叶面积指数和叶片消光系数支配。密植的林分,光强衰减较快。以8%的相对光强作为临界光强,林龄6年时以高密度林分的生产能力最低;中密度林分最高。但林龄7年时,低密度林分的生产能力已经接近中密度林分。

The close spaced Populus deltoides cv. 'Lux' I-69/55 plantations have sharper-angled branches and low percentage of skeleton branches. The optimum stand density appears when the leaf area index, reaches 7.81 and the leaf area density amounts to 0.8~0.9. The light distribution within the canopy is subject to the leaf area index and the extinction coefficient. The light intensity weakens faster in closed plantations. Taking 8 % of the relative light intensity as a criticle light intensity, the close spaced plantation possessed the lowest productivity and the medium density plantation the highest at the sixth year. The widely spaced plantation's productivity approached that of the medium density plantation at the seventh year.