NOAA/WDS Paleoclimatology - Tibetan Plateau 55 Year Phenology Data

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 1C 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.

植被物候对气候变化——尤其是当前持续的增温趋势——的响应，已受到学界广泛关注。然而针对全球面积最大的高海拔区域——青藏高原（Tibetan Plateau, TP），基于遥感数据的分析却得到了不一致的结果。本研究采用一种基于经过充分验证的过程性树木年轮生长模型的创新分析方法——该模型不受遥感产品技术属性与图像质量随时间变化的影响——，探究了1960-2014年间的植被物候变化规律。本研究共分析了20组复合样点年表，涵盖青藏高原林区内约3000株树木。研究结果表明，1960-2014年，植被生长季始期（Start of Growing Season, SOS）平均以每年0.28天的速率提前；1982-2014年，生长季末期（End of Growing Season, EOS）平均以每年0.33天的速率延后。1960-1981年间，未观测到SOS或EOS出现显著变化。4-6月与8-9月的最低气温分别是调控SOS与EOS变化的主要气候驱动因子。4-6月最低气温每升高1℃，会使木质部物候期提前6至7天，延长树木年轮形成的持续时长。本研究将青藏高原物候年表的时间范围进一步向前拓展，并调和了此前基于遥感数据得到的关于SOS的分歧结论。将本研究的分析方法推广至全球尺度，或可增进人们对气候变化影响及其相关的物候变化与植物生产力的认知。