Attribution analyses of changes in alpine grasslands on the Qinghai-Tibetan Plateau

Abstract

Alpine grasslands are one of the major ecosystem types on the Qinghai-Tibetan Plateau. In the past decades, the ecological structure and function of alpine grasslands have undergone great changes with intensified climate change and human activities. However, the relative contributions of natural and human factors to such changes are controversial. Based on the optimized residual method, this study evaluated the relative anthropogenic contribution to the changes in alpine grasslands on the Qinghai-Tibetan Plateau in the past twenty years (1990−2013). The Lund-potsdam-jena model (LPJ), Integrated Biosphere Simulator model (IBIS) and Terrestrial ecosystem model (TEM) were selected to simulate grassland productivity driven by climate factors. We found that the temperature on the plateau was on the rise at a rate of about 0.5°C per decade. Precipitation increased slightly, but with a large spatial difference. The population of the Tibetan Plateau increased sharply during the study period. During the two score years (1990−2013), the productivity of alpine grasslands on the Qinghai-Tibetan Plateau increased greatly, mainly (up to 74.0%) contributed by human activities. Where the change was dominated by human activities, the area with increased grassland net primary product (NPP) was greater than that with decreased NPP, indicating that the over-utilization of alpine grasslands has been effectively contained and reversed into moderate protection. For five out of the first ten years (1990−1999), human activities dominated the change of alpine grasslands (relative anthropogenic contribution around 60.1%), the NPP increased for 3 years and decreased for 2 years. After 2000, the impact of human activities increased sharply (up to 84.6%) and the anthropogenic dominating area expanded substantially, indicating that the large ecological restoration project implemented may have increased the productivity of alpine grasslands in the same period (9 out of 13 years for NPP increase). Spatial analyses comparing the two periods showed that 36.7% of areas with changed grassland NPP was dominated first by climate change and then by human activities, among which 10.1% had increased NPP and 26.6% had decreased NPP. In one word, the Qinghai-Tibetan Plateau may be approaching the turning point of the Environmental Kuznets Curve. Therefore, with further strengthened construction of ecological civilization, the ecological function of alpine grasslands would continue to be improved on the Plateau. However, we should also pay attention to the ever larger areas of human activity-induced NPP decrease. Therefore, the restoration and treatment of degraded grasslands is still pivotal to the construction of ecological security barriers and adaptative ecosystem management of grasslands on the Qinghai-Tibetan Plateau.