Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, 100081, Beijing, China; Freie Universität Berlin, Institute of Biology, Theoretical Ecology, 14195, Berlin, Germany.
Lhasa National Ecological Research Station, Key Laboratory of Ecosystem Network Observation and Modelling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 100101, Beijing, China; School of Geographic Sciences, Nantong University, 226007, Nantong, Jiangsu Province, China.
J Environ Manage. 2021 Mar 1;281:111875. doi: 10.1016/j.jenvman.2020.111875. Epub 2020 Dec 28.
Alpine grasslands on the Qinghai-Tibetan Plateau are sensitive and vulnerable to climate change and human activities. Climate warming and overgrazing have already caused degradation in a large fraction of alpine grasslands on this plateau. However, it remains unclear how human activities (mainly livestock grazing) regulates vegetation dynamics under climate change. Here, alpine grassland productivity (substituted with the normalized difference vegetation index, NDVI) is hypothesized to vary in a nonlinear trajectory to follow climate fluctuations and human disturbances. With generalized additive mixed modelling (GAMM) and residual-trend (RESTREND) analysis together, both magnitude and direction of climatic (in terms of temperature, precipitation, and radiation) and anthropogenic impacts on NDVI variation were examined across alpine meadows, steppes, and desert-steppes on the Qinghai-Tibetan Plateau. The results revealed that accelerating warming and greening, respectively, took place in 76.2% and 78.8% of alpine grasslands on the Qinghai-Tibetan Plateau. The relative importance of temperature, precipitation, and radiation impacts was comparable, between 20.4% and 24.8%, and combined to explain 66.2% of NDVI variance at the pixel scale. The human influence was strengthening and weakening, respectively, in 15.5% and 14.3% of grassland pixels, being slightly larger than any sole climatic variable across the entire plateau. Anthropogenic and climatic factors can be in opposite ways to affect alpine grasslands, even within the same grassland type, likely regulated by plant community assembly and species functional traits. Therefore, the underlying mechanisms of how plant functional diversity regulates nonlinear ecosystem response to climatic and anthropogenic stresses should be carefully explored in the future.
青藏高原高山草原对气候变化和人类活动敏感且脆弱。气候变暖及过度放牧已经导致高原上很大一部分高山草原退化。然而，人类活动（主要是牲畜放牧）如何在气候变化下调节植被动态仍不清楚。在这里，高山草原生产力（用归一化差异植被指数（NDVI）替代）被假设为随气候波动和人类干扰呈非线性轨迹变化。通过广义加性混合模型（GAMM）和剩余趋势（RESTREND）分析，一起研究了青藏高原高寒草甸、草原和荒漠草原的气候（温度、降水和辐射）和人为因素对 NDVI 变化的幅度和方向的影响。结果表明，青藏高原高山草原分别有 76.2%和 78.8%的地区加速变暖并变绿。温度、降水和辐射影响的相对重要性相当，在 20.4%至 24.8%之间，在像素尺度上共同解释了 66.2%的 NDVI 方差。人类的影响分别在 15.5%和 14.3%的草原像素中增强和减弱，略高于整个高原上任何单一气候变量。人为和气候因素可以以相反的方式影响高山草原，即使在同一草原类型内，这可能受到植物群落组装和物种功能特征的调节。因此，未来应该仔细探讨植物功能多样性如何调节非线性生态系统对气候和人为压力的响应的潜在机制。
