remote sensing Article Historic and Simulated Desert-Oasis Ecotone Changes in the Arid Tarim River Basin, China Fan Sun 1,2 , Yi Wang 1,3, *, Yaning Chen 1 , Yupeng Li 1 , Qifei Zhang 1,2 , Jingxiu Qin 1,2 and Patient Mindje Kayumba 1,2   Citation: Sun, F.; Wang, Y.; Chen, Y.; Li, Y.; Zhang, Q.; Qin, J.; Kayumba, P.M. Historic and Simulated Desert-Oasis Ecotone Changes in the Arid Tarim River Basin, China. Remote Sens. 2021, 13, 647. https:// doi.org/10.3390/rs13040647 Academic Editor: Giovanni Chirico Received: 21 January 2021 Accepted: 6 February 2021 Published: 11 February 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences (CAS), Urumqi, Xinjiang 830011, China; sunfan18@mails.ucas.ac.cn (F.S.); chenyn@ms.xjb.ac.cn (Y.C.); liyupeng@ms.xjb.ac.cn (Y.L.); zhangqifei15@mails.ucas.ac.cn (Q.Z.); qinjingxiu17@mails.ucas.ac.cn (J.Q.); patientestime001@mails.ucas.ac.cn (P.M.K.) 2 College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China 3 School of Water Resources and Hydropower Engineering, North China Electric Power University, Beijing 102206, China * Correspondence: 51102473@ncepu.edu.cn; Tel.: +86-991-7823175 Abstract: The desert-oasis ecotone, as a crucial natural barrier, maintains the stability of oasis agricultural production and protects oasis habitat security. This paper investigates the dynamic evolution of the desert-oasis ecotone in the Tarim River Basin and predicts the near-future land- use change in the desert-oasis ecotone using the cellular automata–Markov (CA-Markov) model. Results indicate that the overall area of the desert-oasis ecotone shows a shrinking trend (from 67,642 km 2 in 1990 to 46,613 km 2 in 2015) and the land-use change within the desert-oasis ecotone is mainly manifested by the conversion of a large amount of forest and grass area into arable land. The increasing demand for arable land for groundwater has led to a decline in the groundwater level, which is an important reason for the habitat deterioration in the desert-oasis ecotone. The rising temperature and drought have further exacerbated this trend. Assuming the current trend in development without intervention, the CA-Markov model predicts that by 2030, there will be an additional 1566 km 2 of arable land and a reduction of 1151 km 2 in forested area and grassland within the desert-oasis ecotone, which will inevitably further weaken the ecological barrier role of the desert-oasis ecotone and trigger a growing ecological crisis. Keywords: Tarim River Basin; desert-oasis ecotone; land-use change; CA-Markov model 1. Introduction The spatial interface between two or more ecological regions and their material, energy, and structural and functional systems is called an ecotone or an ecological ecotone [1]. The desert-oasis ecotone is distributed along the periphery of an oasis and is characterized by a zone of desert vegetation that separates the extensive desert from the oasis [2]. The ecotone records the interaction and mutual transformation between the desert and oasis ecosystems [3] and serves as an ecological link connecting the two. A desert-oasis ecotone is a unique ecosystem between a desert and an oasis, usually characterized by low diversity, sparse cover, and dominance by perennial herbaceous grasses and semi-shrubs, such as Phragmites australis, Tamarix ramosissima, Karelinia caspia, and Alhagi sparsifolia. The ecotone can be used for ranching (of both livestock and wild animals); its vegetation can also increase the roughness of the underlying ground surface, thereby hindering the development of desertification and protecting the oasis from wind erosion and sand deposition [4–7]. At the same time, the desert-oasis ecotone is the interface between the oasis ecosystem and the desert ecosystem where energy, material, and information exchange occurs [8], which is highly sensitive to external environmental and human disturbances, affected easily by human activities, including the expansion of cultivated land Remote Sens. 2021, 13, 647. https://doi.org/10.3390/rs13040647 https://www.mdpi.com/journal/remotesensing