## 5 Conclusions  
This study selected seven sets of Landsat remote sensing image data from 1990 to 2020, utilizing the GEE platform to construct an RSEI to analyze the changes in ecological environment quality of the Qinling region over 30 years. The conclusions are as follows:  
1. From 1990 to 2020, the overall quality of the ecological environment in the study area showed an upward trend, with characteristics of different stages. From 1990 to 2005, it was a phase of ecological degradation, with the changes in ecological grade being light and significant degradation, accounting for 10.86% of the total area, which was higher than the 7.43% of the area that showed improvement. From 2005 to 2020, it was a phase of ecological improvement, with changes in ecological grade mostly reflecting light improvements. The area of improvement increased to 51.86%, while the areas of light and significant degradation decreased by 97.24%. 2. The ecological environmental quality of the study area exhibits significant spatial heterogeneity. Areas with altitudes below 1200 m and slopes less than 10\({}^{\circ}\) have the poorest ecological quality, which mainly transitioned from moderate to good over 30 years. In contrast, areas above 1600 m in altitude within the key and core protected areas have the best ecological quality, primarily transitioning from good to excellent. Regions where ecological grades have degraded were mainly located in Ankang, Hanzhong, Shangluo, and Weinan cities. These cities should place a high priority on ecological environmental protection and high-quality development. 3. The spatiotemporal changes in the ecological environmental quality of the study area are influenced by multiple factors, among which NDVI, DEM, land use, and protected areas were key driving factors. The coupled and coordinated effects of the Qinling ecological protection policies and socioeconomic factors have created an enhancing effect on the differentiation of ecological environmental quality. 4. This study has delineated the trends of ecological environmental quality in the Qinling region across three decades, highlighting the significant effects of ecological protection measures and the expansion of vegetation cover on the region's ecological quality. Continuous monitoring is essential for the sustainable development of this critical ecological zone. This study's insights can offer a scientific foundation for the protection of the ecological environment and the promotion of high-quality development of the Qinling area. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/su16083251/s1](https://www.mdpi.com/article/10.3390/su16083251/s1)]([https://www.mdpi.com/article/10.3390/su16083251/s1](https://www.mdpi.com/article/10.3390/su16083251/s1)): Egological protection areas in the Qinling region (downloaded and briefly translated from the government website ([[http://www.shaanxi.gov.cn/zfoxgk/zfgb/2020/d17q/202009/t20200921_1728563.html](http://www.shaanxi.gov.cn/zfoxgk/zfgb/2020/d17q/202009/t20200921_1728563.html)]([http://www.shaanxi.gov.cn/zfoxgk/zfgb/2020/d17q/202009/t20200921_1728563.html](http://www.shaanxi.gov.cn/zfoxgk/zfgb/2020/d17q/202009/t20200921_1728563.html))). Figure S2: Ecological function area in the Qinling region; Table S1: Validation of RSEI results based on field ecological environment surveys. Conceptualization, J.L. and T.X. ; methodology, J.L. and T.X. ; software, J.L. ; validation, D.L., L.C. and Q.L. ; formal analysis, D.L. and L.C. ; investigation, J.L. and T.X. ; resources, T.X. ; data curation, D.L., L.C. and Q.L. ; writing--original draft preparation, J.L. ; writing--review and editing, T.X. and D.L. ; visualization, J.L. ; supervision, T.X. ; project administration, D.L. and L.C. ; funding acquisition, T.X. All authors have read and agreed to the published version of the manuscript.