sustainability Article Quantitative Assessment for the Dynamics of the Main Ecosystem Services and their Interactions in the Northwestern Arid Area, China Tingting Kang 1,2, Shuai Yang 1,2, Jingyi Bu 1,2 , Jiahao Chen 1,2 and Yanchun Gao 1,* 1 Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, P.O. Box 9719, Beijing 100101, China;
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[email protected] Received: 21 November 2019; Accepted: 13 January 2020; Published: 21 January 2020 Abstract: Evaluating changes in the spatial–temporal patterns of ecosystem services (ESs) and their interrelationships provide an opportunity to understand the links among them, as well as to inform ecosystem-service-based decision making and governance. To research the development trajectory of ecosystem services over time and space in the northwestern arid area of China, three main ecosystem services (carbon sequestration, soil retention, and sand fixation) and their relationships were analyzed using Pearson’s coefficient and a time-lagged cross-correlation analysis based on the mountain–oasis–desert zonal scale. The results of this study were as follows: (1) The carbon sequestration of most subregions improved, and that of the oasis continuously increased from 1990 to 2015. Sand fixation decreased in the whole region except for in the Alxa Plateau–Hexi Corridor area, which experienced an “increase–decrease” trend before 2000 and after 2000; (2) the synergies and trade-off relationships of the ES pairs varied with time and space, but carbon sequestration and soil retention in the most arid area had a synergistic relationship, and most oases retained their synergies between carbon sequestration and sand fixation over time.