Patterns, Trends, and Causes of Vegetation Change in the Three Rivers Headwaters Region

Abstract

The Three Rivers Headwaters Region (TRHR), situated in the high-altitude region of the Tibetan Plateau, represents a critical ecological security barrier for both China and Southeast Asia. In addition to providing a vital freshwater supply for China, it is also one of the most biodiverse areas in the world. However, the region is characterized by a fragile and sensitive ecosystem, which makes it particularly vulnerable to environmental disturbances. Given the role of vegetation as a reliable indicator of ecosystem changes, investigating the patterns and drivers of vegetation change in the TRHR can provide valuable insights into the state and trajectory of its ecological system. To assess the spatiotemporal dynamics of vegetation changes in TRHR, this study constructed a comprehensive vegetation index (CVI) based on leaf area index (LAI), fractional vegetation cover (FVC), and net primary productivity (NPP). Trend analysis and significance testing were employed to detect and quantify the magnitude and direction of vegetation changes over the past two decades. Moreover, correlation analysis, spatial overlay, and statistical modeling techniques were applied to examine the relative contributions of climate, land use/cover changes, and slope altitude to CVI changes. The results showed the following: (1) the CVI in the TRHR showed an overall increasing trend from 2000 to 2019, with an average annual increase of 0.6%, indicating a positive development trend of vegetation, but with obvious spatial differences. (2) The vegetation in the TRHR has shown a marked increase over the past two decades, with significant increase accounting for 19% of the total area, mainly concentrated in the Yellow River Basin. Conversely, a significant decline in vegetation was observed in 3% of the total area, predominantly in the Yangtze River Basin. (3) Both temperature and precipitation had a positive impact on vegetation restoration in the TRHR, but the area affected by temperature was larger than that affected by precipitation. (4) The land-use regime had a discernible impact on vegetation increase, with the conversion of land use to ecological land promoting vegetation restoration. However, the efficacy of restoration efforts might have varied depending on natural resource endowments in certain regions. (5) With increasing altitude, vegetation conditions initially improved before eventually deteriorating. Conversely, as the slope increased, vegetation experienced an initial improvement before ultimately stabilizing. This study helps to understand the overall changes and driving mechanisms of vegetation in the TRHR and provides a scientific basis and decision-making reference for the dynamic adjustment of vegetation restoration and ecological engineering in the region in the future.