天山北翼坡向对森林分布的影响

Effect of Slope Aspect on the Distribution of Mountain Forest in the Northern Flank of the Central Tianshan Mountains

坡向对山地森林的空间分布有重要影响,在干旱区尤其如此。天山山地处于西北干旱区,其山地森林的研究过去多集中在南北翼森林的简单对比,而在更详细的中小尺度上,森林沿坡向梯度的连续变化缺乏定量化的分析。以天山北翼中段为研究区,利用1∶5万DEM和SPOT5遥感图像解译,分析山地森林上下限和面积在全坡向的变化规律。结果表明：1.研究区内97.4%的森林分布在海拔1 600-2 690 m;2.森林上限分布在2 691-2 790m,最高值出现在东坡,最低值出现在西南坡,森林上限随坡向变化不明显;森林下限分布在1 371-1 600 m,最高值出现在西南坡,最低值出现在南坡,森林下限的分布和河谷密切相关;3.森林分布面积在北坡最大,阳坡分布面积非常小,在全坡向范围内呈现“U”型分布,西坡森林面积略大于东坡;但在森林分布的上部（〉2 700 m）及下部（〈1 600 m）,森林面积东坡略高于西坡。

Slope aspect has an important effect on spatial distribution of forest especially in arid areas. Tianshan Mountains are located in drought area in northwest of China and previous studies about Tianshan mountain forests mainly focused on the simple comparison of forests between northern flank and southern flank. However,there is little quantitative analysis on the continuous distribution of mountain forests varying with slope aspects on a small scale in northern flank. This paper explores how the upper and lower limits of altitude and the area of mountain coniferous forests vary with slope aspect in the northern flank of the central Tianshan Mountains. The spatial information of mountain coniferous forest and slope aspects are extracted respectively from SPOT5 image and 1 ∶ 50 000 DEM. The results are shown as follows： 1） 97. 4% of coniferous forests distribute from 1 600 to 2 690 meters above sea level. 2） The upper limits of altitude of mountain coniferous forests vary in elevation between 2 691 m at southwest slope and 2 790 m at east slope and there is no significant exposure effect. The lower limits of altitude of mountain coniferous forests vary in elevation between 1 371 m at south slope and 1 600 m at southwest slope and their distributions are affected by valley. 3） The forest area has a U shaped pattern along 0° - 360° slope aspects.The area of forest on the shady slope is largest while on the sunny slope is smallest. The area of forest on the western slope is larger than on the eastern slope. Notably,there is a difference that the area of upper forest near tree line on the eastern slope is larger than on the western slope.