Vegetation carbon sequestration, usually expressed by net primary production (NPP), is an important ecosystem service (ES) to mitigate global warming. Multiple soil and water conservation projects (SWCPs) have been implemented to restore disturbed ecosystems on the Loess Plateau (LP), as one of the most eroded areas in the world.However, responses of NPP to the conservation projects are unclear due to trade-offs between NPP and other ESs. Herein, we quantified NPP and other key ESs (i.e., water yield, soil conservation, and crop production) and the spatio-temporal trade-offs among them, using RS/GIS techniques and ecosystem modelling in the Yanhe basin of the LP from 1990 to 2020. Furthermore, the structural equation model was used to quantify the impact of ecological restoration projects and programmes such as check dams, terraces, and the Grain-for-Green (GFG) on NPP. As shown by our results, NPP reached 457 t ha À1 in 2020, which was twice what it was in 1990. Moreover, we found increasing trade-offs between NPP and other ESs at sub-basin scale. Specifically, 63% of NPP changes were explained by ESs and SWCPs. The combined action of check dams and GFG can promote NPP and balance trade-offs between NPP and other ESs, while terracing decreases NPP indirectly according to its specific soil and climate conditions. Overall, the main findings provide a better understanding of the interacting processes of multi-projects that influence vegetation carbon sequestration and the sustainable utilization of ESs in hill and gully regions of the LP.
High altitude areas play an essential role in the global climate system, and their fragile ecosystems sensitively respond to climate change and human activities. An improved understanding of the influences of multiple factors on the spatiotemporal dynamics of vegetation is needed. This study aimed to understand further the impacts of climate, geography, and human on vegetation and disentangle the contributions of climate and humans to vegetation changes using the MOD13Q1 enhanced vegetation index (EVI, 2000(EVI, -2019. Greening was detected for 70% of the Tibetan Plateau under increased warming and wetting in the 21st century. A rise in temperature of up to 0.66 ± 0.49 C decade À1 occurred over 2/3 of the Tibetan Plateau, while precipitation increased slightly. In particular, significant greening covered 1/4 of the Tibetan Plateau and occurred within the steppe and desert on the northern due to wetting and ecological protection. Browning depended on urbanization, overgrazing, and lake expansion in 1.9% of the total area. Orbicular browning around lakes accounted for 18.4% of significant browning, and significant browning trends were also detected in densely populated cities situated at low-altitude and flat areas. The EVI was more strongly positively correlated with the annual mean minimum temperature than the annual mean temperature and maximum temperature and was sensitive to extreme low precipitation events. Residual analysis showed that the relative contribution of climate change was 34%, and that of human activities was 66%. A comprehensive description of the vegetation changes on the Tibetan Plateau will help humans to cope with climate change and ecosystem evolution in high altitude.
The cold and hypoxic environment of the Tibetan Plateau was a major challenge for its prehistoric human occupants. The earliest known hominin occupation (or visitation) of the Tibetan Plateau was at ~200 ka, in the middle Pleistocene, and these hominins must have had survival strategies for this harsh environment. We report the discovery of 5 handprints and 17 footprints on the travertine near the outlet of the Quesang hot spring, a well-documented archeological site with well-studied hominin hand and footprints on the Tibetan Plateau. Based on ichnological analysis and U-Th dating, we found that these intentional and unintentional traces were impressed during the early to middle Holocene. Combined with the 19 previously-dated hand and footprints from around the hot spring, we conclude that this site was attractive to ancient humans who made repeated visits over a long period. The strengthened monsoon in the early and middle Holocene may have promoted the expansion of prehistoric human activity onto the central Tibetan Plateau. The frequent human activities near the Quesang hot spring imply that the widespread hot springs on the Tibetan Plateau provided resources that facilitated human survival in this cold and dry plateau region.
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