ArticleWidth Identification and Spatiotemporal Change in the Landscape Ecotones in the Poyang Lake Sandy Land Based on an Advanced Remote Sensing Ecological IndexWangyang Wu 1,2, Junwen Tian 2, Lihui Tian 1,*, Dengshan Zhang 1, Peng Fan 2 and Shuyu Yang 21 State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China ;2 School of Earth and Planetary Sciences, East China University of Technology, Nanchang 330013, China;* Correspondence: lhtian@qhu.edu.cn; Tel.: +86-155-2830-2040