新疆叶尔羌河流域胡杨林时空格局特征

Analysis of spatio-temporal characteristics of Populus euphratica forests in the Yarkand River Basin, Xinjiang

叶尔羌河流域胡杨林对保障我国新疆南疆地区生态安全有着重要的功能,到目前对该区胡杨林时空格局特征规律的研究极少。基于1995-2015年Landsat TM/OLI长时间序列遥感监测数据,通过土地利用程度变化指数、转移矩阵以及景观指数对叶尔羌河流域胡杨林时空格局变化进行动态监测与分析。结果表明:(1)胡杨林面积从1995年的1916.15 km^2减少到2015年的1652.25 km^2,面积减少了263.90 km^2。永安坝至夏河林场段,耕地向河道扩张,胡杨林转为耕地;而夏河林场至三河口段,水资源匮乏,胡杨林被迫向河道收缩,转为未利用地。(2)胡杨林动态度和空间动态度降低,而胡杨林变化状态指数、斑块密度、最大斑块指数和散布与并列指数增加,斑块结合度指数高,胡杨林空间分布逐渐集中、破碎度降低、连通性增加。流域景观要素连接性逐渐减弱,破碎化程度较高,优势度斑块类型比例逐渐下降,景观类型向复杂化方向发展。(3)1995-2005年胡杨林受气候变化和人类活动的干扰,胡杨林面积减少较快,景观格局变化剧烈,而2005-2015年胡杨林保护措施的实施、区域产业结构的调整以及生态安全输水区域的扩大等,胡杨林面积减少速度减缓,但形势仍较为严峻。在叶尔羌河流域合理利用水资源,统筹协调生活、生产和生态用水、强化水资源管理力度,以及调整产业结构、控制人口增长速度等是该区胡杨林生态系统恢复的有效手段和途径。研究可以为叶尔羌河流域生态系统恢复以及胡杨林保护提供参考。

The Populus euphratica forests, located in the Yarkant River Basin of Xinjiang, play an important role in guaranteeing this area′s ecological security, whereas there are by far few in-depth studies about their spatio-temporal pattern and dynamic law. In this paper, based on the time series data of Landsat TM/OLI from 1995 to 2015, we investigated the spatial and temporal dynamics and trends of the Populuse uphratica forests during this period by using the Land Use Degree Indices, Transfer Matrix, and Landscape Indices. The results showed that:(1) the total area of the Populus euphratica forests decreased with a value of 263.90 km^2 from 1916.15 km^2 in 1995 to 1652.25 km^2 in 2015, where the cultivated land was expanding towards the river channel in the section from Yong′an dam to Xiahe forest farm along the Yarkant river while the riparian Populus euphratica forests were converted into cultivated land areas;from Xiahe forest farm to Sanhekou section, the Populus euphratica forests were shrinking towards the river channel and partly being converted into unused land areas due to scarcity of water sources.(2) The dynamic degree and spatial dynamic degree values of the Populus euphratica forests decreased, while their change state index, patch density, largest patch index, and interspersion and juxtaposition index values increased with high values of their patch adhesion index, and thus, the spatial distribution situation of the Populus euphratica forests was gradually clustering with the corresponding decreases of their fragmentation degree and increases of their connectivity. However, the landscape types in the basin were becoming more complex, which shows up as gradually weakened connectivity of its landscape elements, decreasing proportion of its dominant patch types, and relatively high degree of its fragmentation.(3) The total area of the Populus euphratica forests decreased rapidly and their landscape pattern changed dramatically due to climatic changes and human activities from 1995 to 2005;contrastively, benefitting from the implementation of Populus euphratica forest protection measures, the adjustment of regional industrial structure, and the expansion of ecological safe water delivery areas, the area decrease trend of the Populus euphratica forests in this basin had slowed down since 2005, whilst its situation still remains grim. Therefore, reasonable utilization of water resources, e.g., overall planning and coordinating the water use for domestic, production, and ecological conservation, strengthening the management of water resources, adjusting the industrial structure, and controlling the population growth rate, are available means and approaches to restore the ecosystem of Populus euphratica forests in this region. This study provides useful reference for the ecological restoration and Populus euphratica forests protection in the Yarkant River Basin.