中文摘要：

林树下线是干旱河谷背景下一种特殊的地理生态现象,针对林树下线的定位和比对研究是揭示山地环境自然变化过程与人类活动环境效应的有效途径之一。选取岷江上游林树下线为研究对象,采用遥感和GIS聚类分析方法,基于1999-2009年两个时期、聚落区和非聚落区两类区域的比对研究,揭示林树下线的空间分异特征及其移动规律。结果表明：①林树下线分布具有集聚性特征,主要分布于海拔1400~3800 m V型河谷谷肩上部,这一特征与山区降水随海拔升高的梯度变化相适应;② 6°~15°坡度是林树下线分布的峰值,林树下线随着坡度递增分布明显减少;③林树下线坡向分异显著,平均高程表现为南坡高于北坡、东坡高于西坡,最小值为西北方向,源于阴坡水分/湿度更适于植被生长;④聚落区林树下线10年间向低海拔空间移动达108.6 m,而非聚落区仅为38 m,这一结果可为定量评估1999年起实施的退耕还林等生态建设工程成效提供科学判据。

英文摘要：

The lower timberline is a special eco-geographic phenomenon in the dry valley background. Research on the positioning and comparison of lower timberline could reveal the relationship between mountain environmental changes and environmental influence from anthropic activities. Based on remote sensing data and cluster analysis of Geographic Information System （GIS）, the research took the lower timberline in the upper reaches of Minjiang River as an investigated object. By comparing the lower timberline in 1999 and 2009, this paper analyzed the lower timberlines of the settlement area and non-settlement area, respectively, and revealed the spatially distributed characters and moving rules of the lower timberline were revealed. The results show that： 1） The lower timberline is characterized by cluster distribution and mainly concentrates in the upper part of V-shaped valley ranged from 1400 m to 3800 m. This character is consistent with distribution of precipitation along altitude. 2） The peak values of lower timberline were observed on the slopes of 6°~15°. Furthermore, the lower timberline values clearly decrease as the increase of slope. 3） The distribution of lower timberline varies significantly with slope. The lower timberline on the southern slope is obviously higher than that on the northern slope, and that in the eastern part is higher than that in the western. The lowest altitude of lower timberline is found in the northwest. The altitude distribution of lower timberline is related to shady slope, which is more suitable for growth of vegetation than sunny slope owing to more moisture. 4） The spatial variation of the lower timberline in the settlement area is different from that in the non-settlement area. The lower timberline in the settlement area spatially moves downward by 108.6 m from 1999 to 2009, but in the non-settlement area by 38 m. The spatially moving downward degree of lower timberline caused by human activities such as the Grain-for-Green Project is larger than that caused by na