西双版纳雾凉季次生林林窗光照特征初步分析

A PRELIMINARY STUDY ON THE SUN-SHINE CHARACTERISTICS OF THE SECONDARY FOREST GAP IN XISHUANGBANNA IN FOGGY-COOL SAESON

利用西双版纳雾凉季次生林林窗光照观测资料，探讨了林窗光照的时空变化特征。结果表明：由于天气现象（浓雾）和林窗树木的共同影响，林窗区域光强存在明显的差异；受浓雾影响的上午，光强的时间变化及水平梯度均不明显；11时后雾散日出，在太阳辐射的影响下，各测点光强均迅速上升，尤以林窗偏东侧林缘最为突出；中午的平均光强最大区域由林窗中心向东北侧林缘移动；但在林窗偏西侧，受树木遮蔽影响，光强增加较小，形成平均光强的低值区，使得中午林窗区域光照强度呈现显著的不对称性，同时造成光强水平梯度增大；下午由于太阳西进，林窗区域均受到树木遮蔽影响，光强降低，水平梯度变化趋于和缓。研究结果可为探讨林窗演替、更新机制及林窗生物多样性研究提供参考。

Light intensity measurements in the tropical secondary forest canopy gap were conducted in Xishuangbanna, Yunnan, in January 1999（foggy-cool season）. On the basis of this measurement, spatial-temporal variations of light intensity on 8 azimuth in the secondary forest canopy gap were discussed. The results indicated that: Because of the influence of Condition of foggy environment and the tree, the light intensity is significant different in the gap, showing that temporal and spatial-temporal variation of light intensity is not significant in the morning in the study site; after the fog lifting, due to the influence of radiation, the light intensity significantly increase on all sites, the second-east edge of gap is dominant; the maximum mean value of light intensity was shifted to the North-east edge, on the other hand, because of the influence of shade of the edge-arbor, second-west sites light intensity mildly increase, becoming source of low light intensity. Asymmetry of light is significant in the gap at noon. At the same time, horizontal gradient becomes significant. With the sun moved west-ward, because of the influence of the shade of tree at the edge of gap, spatial variation of light intensity is not significant in the study site. This result will provide references of studying forest dynamic and bio-diversity.