A millennium-long tree-ring width chronology for the middle Qilian
Mountains in northwestern China has been developed back to A.D. 775. Correlation analysis indicates that the tree-ring width reflects growingseason moisture variability. Our chronology reveals three distinct periods based on the prevailing moisture anomalies: A.D. 775–1101 (wetness persistence), 1101–1831 (dryness persistence) and 1831–2006 (wetness persistence). A 31-year running mean through the tree-ring index series clearly shows seven obvious dry spells and eight wet spells. Compared with the proxies associated with the East Asian monsoon and the westerlies in the past millennium, our moisture-sensitive tree-ring chronology revealed that the East Asian summer monsoon had a strong influence on tree growth before A.D. 1300. From about A.D. 1450–1750, the westerlies strongly affected the Qilian Mountains. After A.D. 1750, a combined influence of both East Asian monsoon and westerlies was apparent. In the past century, the effect of westerlies has become stronger. Our results suggest that tree rings can preserve the information on the advance and retreats of the westerlies and the East Asian summer monsoon. Additionally, this research is helpful for understanding the driving mechanism of the Asian monsoon and the westerlies in northwestern China over the past thousand years.
This article documents the development of a precisely dated and wellreplicated long regional tree-ring width dating chronology for Qilian juniper (Juniperus przewalskii Kom.) from the northeastern Qinghai- Tibetan Plateau. It involves specimens from 22 archeological sites, 24 living tree sites, and 5 standing snags sites in the eastern and northeastern Qaidam Basin, northwestern China. The specimens were cross-dated successfully among different groups of samples and among different sites. Based on a total of 1438 series from 713 trees, the chronology covers 3585 years and is the longest chronology by far in China. Comparisons with chronologies of the same tree species about 200 km apart suggest that this chronology can serve for dating purposes in a region larger than the study area. This study demonstrates the great potential of Qilian juniper for dendrochronological research.