Key Laboratory of Desert and Desertification, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, 730000 Lanzhou, China;
Institute of Geography, University of Erlangen-Nürnberg, D-91058 Erlangen, Germany.
Proc Natl Acad Sci U S A. 2017 Jul 3;114(27):6966-6971. doi: 10.1073/pnas.1616608114. Epub 2017 Jun 19.
Phenological responses of vegetation to climate, in particular to the ongoing warming trend, have received much attention. However, divergent results from the analyses of remote sensing data have been obtained for the Tibetan Plateau (TP), the world's largest high-elevation region. This study provides a perspective on vegetation phenology shifts during 1960-2014, gained using an innovative approach based on a well-validated, process-based, tree-ring growth model that is independent of temporal changes in technical properties and image quality of remote sensing products. Twenty composite site chronologies were analyzed, comprising about 3,000 trees from forested areas across the TP. We found that the start of the growing season (SOS) has advanced, on average, by 0.28 d/y over the period 1960-2014. The end of the growing season (EOS) has been delayed, by an estimated 0.33 d/y during 1982-2014. No significant changes in SOS or EOS were observed during 1960-1981. April-June and August-September minimum temperatures are the main climatic drivers for SOS and EOS, respectively. An increase of 1 °C in April-June minimum temperature shifted the dates of xylem phenology by 6 to 7 d, lengthening the period of tree-ring formation. This study extends the chronology of TP phenology farther back in time and reconciles the disparate views on SOS derived from remote sensing data. Scaling up this analysis may improve understanding of climate change effects and related phenological and plant productivity on a global scale.
植被对气候的物候响应，特别是对正在发生的变暖趋势的响应，已经引起了广泛关注。然而，对于世界上最大的高海拔地区——青藏高原（TP），从遥感数据分析中得到的结果却存在分歧。本研究采用一种创新的方法，利用经过充分验证的、基于过程的树木年轮生长模型，提供了 1960-2014 年期间植被物候变化的视角，该模型独立于遥感产品时间变化的技术特性和图像质量。分析了 20 个综合站点年表，这些站点年表由来自 TP 各地森林地区的约 3000 棵树木组成。我们发现，生长季节开始日期（SOS）在 1960-2014 年期间平均提前了 0.28 天/年。生长季节结束日期（EOS）在 1982-2014 年期间平均延迟了 0.33 天/年。在 1960-1981 年期间，SOS 或 EOS 没有观察到显著变化。4 月-6 月和 8 月-9 月的最低温度是 SOS 和 EOS 的主要气候驱动因素。4 月-6 月最低温度升高 1°C，使木质部物候日期提前 6-7 天，延长了树木年轮形成的时间。本研究将 TP 物候的年表回溯得更远，并调和了遥感数据得出的 SOS 不一致的观点。扩大这种分析可能会提高我们对气候变化影响以及相关物候和植物生产力在全球范围内的理解。
