西双版纳片断化望天树林小气候边缘效应比较研究

MICROCLIMATE EDGE EFFECTS WITHIN AND BETWEEN SHOREA CHINENSIS FOREST FRAGMENTS IN XISHUANGBANNA

对西双版纳片断望天树 (Shorea chinensis)林林缘小气候的季节、水平变化进行了观测研究 ,对比分析了 4个不同大小雨林斑块 (30 hm2 、2 5 hm2 、2 0 hm2 、3 hm2 )的小气候边缘效应。结果表明 :各雨林斑块林缘均存在明显的小气候边缘效应 ,其中在干季晴天最为明显 ,且在两个较小斑块林缘出现最高气温及气温日较差高于林外的现象 ;干季 ,部分林缘小气候要素 (最高气温、总辐射、净辐射、最小相对湿度 )林缘与林内的差值均是高于或大于雨季的相应值 ,而地表最高温林缘与林内的差值则是雨季强于干季 ;各斑块相比 ,小气候边缘效应波及林内的深度在最大斑块达到最浅 (2 5 m ) ,而在最小斑块达到最深 (35 m) ,呈现出小气候边缘效应及其影响深度随片断雨林斑块面积减小而增强及向林内进一步延伸的趋势。

Small tropical rainforest remnants are the primary landscape elements in the Xishuangbanna region of southwest China. Microclimate data on this forest landscape is useful both for ecological research and resources management purposes. In this paper, seasonal and horizontal variation in microclimatic elements were recorded in transects passing from the open to the interior of four different sized forest patches (30 hm 2, 25 hm 2, 20 hm 2, and 3 hm 2). The tropical rainforest of these fragments was dominated by Shorea chinensis, an important Dipterocarpus of the region. In each transect the following variables were measured: total radiation, net radiation, light intensity, air temperature, soil temperature, air relative humidity, and wind velocity. Under both clear and cloudy sky conditions and in both dry and rainy seasons, daily differences of all variables were consistently lower in forest interiors than those in the edge and open, with the most obvious differences found in the largest fragments. Variation in air temperature just inside edges was complex. Higher values were in edges than in the open under dry season clear skies in the two smaller fragments, while lower values where found under cloudy sky conditions at all times in the bigger fragments. This study has shown that microclimatic edge effects, including elevated air and soil temperatures, increased light intensity and decreased air relative humidity, can penetrate 25 m and 35 m into forest patches from edges in both the biggest (30 hm 2) and smallest (3 hm 2) fragments under dry and rainy seasons, respectively. A strong trend for increased edge effects with decreasing size of forest fragments was also clear.