The Upper Yellow River is the most important area for water conservation and flow production in the Yellow River basin, and the statuses of the ecosystems in this region are related to the ecological stability of the whole Yellow River basin. In this paper, the fractional vegetation cover (FVC), net primary productivity (NPP) of vegetation and water conservation, soil conservation, and windbreak and sand fixation services of the Upper Yellow River ecosystems were analysed from 2000 to 2019 with the trend analysis method. Ecological restoration degree evaluation indices were constructed to comprehensively assess the ecological restoration situation and restoration potential of the ecosystems in the Upper Yellow River region over the past 20 years and to quantitatively determine the contribution rates of climate factors and human activities to these ecosystem changes. The results showed that the settlement ecosystem area exhibited the greatest increase, while the grassland ecosystem area decreased significantly over the study period. In the Upper Yellow River region, the ecosystem quality and ecosystem services generally remained stable or improved. Areas with moderately, strongly and extremely improved ecological restoration degrees accounted for 32.9%, 21.0% and 2.8% of the entire Upper Yellow River region, respectively. Areas with strongly improved and extremely improved ecological restoration degrees were mainly distributed in the Loess Plateau gully areas and on the eastern Hetao Plain. The contribution rates of climatic factors and human activities to the NPP changes measured in the Upper Yellow River were 81.6% and 18.4%, respectively, while the contribution rates of these processes to soil erosion modulus changes were 77.6% and 22.4%, respectively. The restoration potential index of the FVC in the Upper Yellow River was 22.7%; that of the forest vegetation coverage was 14.4%; and that of the grassland vegetation coverage was 23.0%. Over the past 20 years, the ecosystems in the Upper Yellow River region have improved and recovered significantly. This study can provide scientific support for the next stage of ecological projects in the Upper Yellow River region.
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.
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