Knowledge of the response of grassland phenology towards climatic factors is essential to improve our understanding of ecological processes under global warming. To date, however, it remains unclear how climate change and associated changes in vegetation dynamics might affect autumn phenology of grasslands at the global scale. In this study, the trends in start of growing season (SOS) and end of growing season (EOS) dates were explored using remote sensing data (1981–2014). The responses of EOS to preseason temperature, rainfall, SOS, and net primary productivity (NPP) were then investigated for the mid-latitude (30°N ~ 55°N) grasslands of the Northern Hemisphere. The remotely-sensed SOS/EOS and PhenoCam-based SOS/EOS were first compared and a good correlation was observed. Trend analysis revealed that the time span of SOS/EOS (from the earliest SOS/EOS to the last SOS/EOS) and the growing season length (from SOS to EOS) have extended for the entire study region. Furthermore, a forward shift in all SOS pixels was observed in Central-West Asian grasslands, whereas no such significant trend was observed for North American grasslands and East Asian grasslands. The duration of EOS completion had shortened within North American grasslands but lengthened in Asian grasslands. Next, correlation analysis uncovered a stronger relationship between EOS and previous rainfall than between EOS and temperature, indicating the key role of water availability in controlling autumn phenology. The sensitivity of EOS to both temperature and rainfall was higher in drier and warmer locations. Moreover, a significant negative correlation between EOS and SOS was observed in part of the study region, but no significant relationship between NPP and EOS was observed. Overall, this study highlights the spatially intensified heterogeneity of spring and autumn phenology in northern grasslands and that climatic changes in precipitation might act as key drivers for modifying autumn phenology of grassland vegetation in the Northern Hemisphere.

了解草地物候对气候因素的反应对于增进我们对全球变暖下的生态过程的理解至关重要。然而，迄今为止，尚不清楚气候变化及其相关的植被动态变化如何影响全球范围内草原的秋季物候。在这项研究中，利用遥感数据（1981-2014年）探索了生长期开始（SOS）和生长期结束（EOS）日期的趋势。然后调查了北半球中纬度（30°N〜55°N）草原EOS对季前温度，降雨量，SOS和净初级生产力（NPP）的响应。首先比较了遥感的SOS / EOS和基于PhenoCam的SOS / EOS，并观察到良好的相关性。趋势分析显示，SOS / EOS的时间跨度（从最早的SOS / EOS到最后的SOS / EOS）和生长季节的长度（从SOS到EOS）已扩展到整个研究区域。此外，在中亚西亚草原上观察到所有SOS像素都向前移动，而在北美草原和东亚草原上没有观察到这种显着趋势。在北美草原上，EOS完成的时间缩短了，但在亚洲草原上，则延长了。接下来，相关性分析揭示了EOS与先前的降雨之间的关系比EOS与温度之间的关系更强，这表明了水分可用性在控制秋季物候方面的关键作用。在较干燥和较热的地方，EOS对温度和降雨的敏感性较高。而且，在研究区域的一部分观察到EOS和SOS之间存在显着的负相关，但没有观察到NPP和EOS之间存在显着的关系。总体而言，这项研究强调了北部草原春季和秋季物候空间分布的异质性，并且降水的气候变化可能是改变北半球草原植被秋季物候的关键驱动力。