Spatiotemporal characteristics and natural forces of grassland NDVI changes in Qilian Mountains from a sub-basin perspective

The Qilian Mountains (QLMs) encompass a diverse alpine grassland ecosystem undergoing notable changes due to global climate change. Understanding the driving forces behind these changes is crucial for effective regional vegetation restoration and management, particularly given the contrasting climatic conditions between the eastern and western regions of the QLMs. This study investigated the spatiotemporal evolution of grassland NDVI and the influence of 13 variables on NDVI changes in six distinct QLM sub-basins from 1990 to 2019 using Landsat data and the Geodetector model, respectively. Results revealed a consistent greening trend in all sub-basins, albeit with varying slopes. Notably, the Qinghai Lake basin exhibited a recent slowdown in NDVI, highlighting the need for enhanced vegetation restoration efforts, especially in permafrost-covered areas. Environmental factors affecting NDVI differed among basins. In the western QLMs, sunshine duration and relative humidity emerged as key factors influencing NDVI distribution, while in the eastern basins, altitude and air temperature played significant roles. This study underscored the importance of hydrothermal conditions, both horizontally and vertically, in shaping grassland NDVI. Other factors, such as vegetation types, soil characteristics, and permafrost degradation, also influenced NDVI, while slope and slope aspects had a limited impact. Furthermore, the research identified threshold-dependent responses of NDVI to the interaction of these factors. These findings emphasized the need to customize vegetation restoration strategies based on the specific environmental conditions of each basin within the QLMs. This nuanced understanding of the distinct driving characteristics between the eastern and western QLMs enables more effective and targeted approaches to restoring and managing grassland ecosystems in this region.