Climate warming is expected to increase growth and expansion of evergreen vegetation in many cold regions, with substantial influences on ecological and atmospheric processes. Nevertheless, the direction and magnitude of changes in productivity (greenness) of evergreen vegetation, as well as their potential drivers, remain unclear in many parts of the world. The woody evergreen vegetation on the Tibetan Plateau influences ecosystems and land surface processes, affecting regional and continental weather and climate through regulating land-air interactions. Here, we show that the remotely-sensed winter greenness of evergreen vegetation increased by 9.8% over 2000–2021 on the Tibetan Plateau, with significant ( < 0.05) greening across 55.8% of the areas with evergreen vegetation, which is more widespread than the increase of summer peak greenness, suggesting upslope shifts in treelines and shrublines and encroachment by evergreen woody plants. While our results show that warming was the principal climate driver of greening, the spatial pattern of greening was more related to the temperature sensitivity of greenness rather than temperature trends. Positive impacts of increasing precipitation on greenness were observed in a few areas classified as grasslands. Moreover, the magnitude of winter greening on the plateau was larger than that of the greening in the Arctic, where warming was faster, which indicates higher level of sensitivity of greenness to temperature of evergreen vegetation on the Tibetan Plateau. Our results highlight the high sensitivity of evergreen vegetation to climate warming and provide a new foundation for improving the understanding the responses and feedbacks of the Tibetan Plateau ecosystem to climate change.

中文翻译：

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2000-2021年气候变暖导致青藏高原冬季绿化

气候变暖预计将促进许多寒冷地区常绿植被的生长和扩张，对生态和大气过程产生重大影响。然而，在世界许多地区，常绿植被生产力（绿色度）变化的方向和幅度及其潜在驱动因素仍不清楚。青藏高原的木本常绿植被影响生态系统和地表过程，通过调节陆气相互作用影响区域和大陆天气和气候。在这里，我们发现青藏高原常绿植被的遥感冬季绿度在2000年至2021年期间增加了9.8%，55.8%的常绿植被地区显着绿化（<0.05），这比青藏高原的常绿植被覆盖范围更广。夏季峰值绿度增加，表明林线和灌木丛向上倾斜，以及常绿木本植物的侵占。虽然我们的结果表明变暖是绿化的主要气候驱动因素，但绿化的空间格局更多地与绿化的温度敏感性相关，而不是与温度趋势相关。在一些被归类为草原的地区观察到降水量增加对绿化的积极影响。而且，青藏高原冬季绿化程度大于变暖较快的北极地区绿化程度，这表明青藏高原常绿植被绿度对温度的敏感性较高。我们的研究结果凸显了常绿植被对气候变暖的高度敏感性，为提高青藏高原生态系统对气候变化的响应和反馈的认识提供了新的基础。