The Nam Co, situated within the south-central Tibetan Plateau (30°–35°N), is located at the transitional region between the Indian summer monsoon and westerlies in the growing season. This area with an elevation above 4700 m a.s.l. is characterized by extremely cold and dry treeless environment. Trees are absent in this area, where patches of alpine shrub species can survive. However, very few alpine shrub species there provide a rare opportunity to retrieve changes of alpine ecosystem by shrub-ring analysis. Among alpine shrubs, Wilson juniper (Juniperus pingii var. wilsonii) is widespread throughout the south-central Tibetan Plateau.

 

 

Figure 1. Close-up view of Wilson juniper shrub patches around the Nam Co Lake and hydroclimate (Standardized Moisture Anomaly Index) reconstruction in 1605–2010.

 

Team of alpine ecological pattern and process (CAS Key Laboratory of Alpine Ecology, Institute of Tibetan Plateau Research, Chinese Academy of Sciences), CAS Center for Excellence in Tibetan Plateau Earth Sciences established a 537-year standard shrub ring chronology by cross-dating living and dead Wilson juniper shrubs sampled above 4740 m a.s.l. on the central Tibetan Plateau. It is, to date, one of the world’s longest shrub-ring chronologies. Shrub-ring chronology from 1605 to 2010 was then used to reconstruct mean May-June drought severity (Standardized Moisture Anomaly Index). That two long-term dry spring periods (1637–1683 and 1708–1785) occurred during the Little Ice Age (LIA) implies that cold temperature may slow down the hydrological cycle. This study highlights the importance of alpine juniper shrubs in understanding the hydrological cycle in dry, continental alpine treeless areas.

 

The first author is Dr. Lu Xiaoming, and the corresponding author is Prof. Liang Eryuan. This work was supported by the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (2019QZKK0301) and the National Natural Science Foundation of China (41807444, 41525001). We thank the Nam Co Station for Multisphere Observation and Research, Chinese Academy of Sciences for the fieldwork support and Qi-Bin Zhang for providing May–June PDSI reconstructions on the Tibetan Plateau.

 

The shrub-ring chronology and reconstructed SZI series data are available at National Tibetan Plateau Data Center: https://data.tpdc.ac.cn/en/data/7ff4fcde-4c6a-4e04-bd95-dae4d0d0cbe1/

 

Online link: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL087707