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

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 domes