College of Urban and Environmental Sciences, Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, 100871, P.R. China.
Department of Biology, University of Maryland, College Park, MD, 20742-4415, USA.
Glob Chang Biol. 2015 Oct;21(10):3635-46. doi: 10.1111/gcb.12954. Epub 2015 Jun 19.
Rapid temperature increase and its impacts on alpine ecosystems in the Qinghai-Tibetan Plateau, the world's highest and largest plateau, are a matter of global concern. Satellite observations have revealed distinctly different trend changes and contradicting temperature responses of vegetation green-up dates, leading to broad debate about the Plateau's spring phenology and its climatic attribution. Large uncertainties in remote-sensing estimates of phenology significantly limit efforts to predict the impacts of climate change on vegetation growth and carbon balance in the Qinghai-Tibetan Plateau, which are further exacerbated by a lack of detailed ground observation calibration. Here, we revealed the spatiotemporal variations and climate drivers of ground-based herbaceous plant green-up dates using 72 green-up datasets for 22 herbaceous plant species at 23 phenological stations, and corresponding daily mean air temperature and daily precipitation data from 19 climate stations across eastern and southern parts of the Qinghai-Tibetan Plateau from 1981 to 2011. Results show that neither the continuously advancing trend from 1982 to 2011, nor a turning point in the mid to late 1990s as reported by remote-sensing studies can be verified by most of the green-up time series, and no robust evidence for a warmer winter-induced later green-up dates can be detected. Thus, chilling requirements may not be an important driver influencing green-up responses to spring warming. Moreover, temperature-only control of green-up dates appears mainly at stations with relatively scarce preseason snowfall and lower elevation, while coupled temperature and precipitation controls of green-up dates occur mostly at stations with relatively abundant preseason snowfall and higher elevation. The diversified interactions between snowfall and temperature during late winter to early spring likely determine the spatiotemporal variations of green-up dates. Therefore, prediction of vegetation growth and carbon balance responses to global climate change on the world's roof should integrate both temperature and snowfall variations.
青藏高原是世界上海拔最高、面积最大的高原，其快速升温及其对高山生态系统的影响备受全球关注。卫星观测表明，青藏高原植被返青日期的变化趋势明显不同，温度响应也相互矛盾，这引发了关于高原春季物候及其气候归因的广泛争论。遥感估计物候的不确定性很大，限制了预测气候变化对青藏高原植被生长和碳平衡的影响，而缺乏详细的地面观测校准则进一步加剧了这一问题。在这里，我们使用 23 个物候站的 22 种草本植物的 72 个返青数据集以及来自青藏高原东部和南部 19 个气候站的相应的每日平均气温和日降水量数据（1981 年至 2011 年），揭示了地面草本植物返青日期的时空变化及其气候驱动因素。结果表明，无论是 1982 年至 2011 年的持续推进趋势，还是遥感研究报告的 90 年代中后期的转折点，都无法通过大多数返青时间序列得到验证，也没有发现确凿的证据表明冬季变暖导致返青日期推迟。因此，冷需求可能不是影响返青对春季变暖响应的重要驱动因素。此外，仅温度控制的返青日期主要出现在 preseason积雪较少和海拔较低的站，而耦合温度和降水控制的返青日期主要出现在 preseason积雪较多和海拔较高的站。冬季末到早春期间降雪和温度之间的多样化相互作用可能决定了返青日期的时空变化。因此，预测全球气候变化对世界屋脊上植被生长和碳平衡的响应应综合考虑温度和降雪的变化。
