Evolution and driving forces of ecological quality in the Three Mountains of Ningxia

The "Three Mountains" of Ningxia-Helan Mountain, Liupan Mountain, and Luo Mountain-are three nationally protected nature reserves and serve as vital ecological security barriers in northwest China. Their ecological quality plays a significant role in promoting ecological civilization in the region. However, previous studies have largely focused on individual mountain ecosystems, lacking a comprehensive analysis of the Three Mountains as a whole. This study systematically analyzed the spatiotemporal evolution of ecological quality in the Three Mountains from 1993 to 2022 and its driving factors, based on the Remote Sensing-Based Ecological Index (RSEI) and the Boosted Regression Tree (BRT) model. The results reveal distinct gradient differences in ecological quality among the mountains, with varying evolutionary trends: Liupan Mountain exhibited the greatest improvement, and Luo Mountain showed a steady upward trend, whereas Helan Mountain experienced notable fluctuations. Precipitation and soil moisture were the main driving factors behind ecological quality evolution and regional variation, with 440 mm of total annual precipitation was recognized as the threshold for rapid ecological quality improvement. Human activities, such as land use/cover change (LUCC) and gross domestic product (GDP), played a secondary role. This study provides valuable insights into the mechanisms governing ecological change in arid and semi-arid regions and offers scientific basis for ecological management and environmental policy-making in the Three Mountains of Ningxia.