IS THERE A TEMPERATURE OR HYDROCLIMATE SIGNAL IN TREE-RING WIDTH OF QINGHAI SPRUCE AND QILIAN JUNIPER IN THE WULAN REGION,QINGHAI PROVINCE?
The northeastern Tibetan Plateau is highly vulnerable to global climate change.Due to the arid and semi-arid conditions,hydroclimate is widely considered to be the factor dominating the radial growth of trees in this region.However,studies have revealed that tree-ring width(TRW)in Wulan and its eastern regions show more complicated climatic responses,to both temperature and hydroclimate variables.In order to investigate the potential of TRW for reconstructing the regional climate,this study analyzed climatic responses of TRW of Qinghai spruce(90 cores)and Qilian juniper(141 cores)in the Wulan region,Qinghai Province.We further compared these chronologies with one composite TRW series developed in the Delingha region which clearly exhibits a robust hydroclimate signal.The results suggest that:(1)Between 1956 and 2010 A.D.,the Qinghai spruce TRW recorded a significant signal of July temperatures of the growing year,while the Qilian juniper TRW responded strongly to July temperatures,precipitations from May to June and Palmer Drought Severity Index(PDSI)from May to July.(2)The climatic responses of TRW of the two species appeared to have been shifted around 1970～1980 A.D.The effect of growing season temperatures on the radial growth of Qinghai spruce and Qilian juniper gradually increased,while the responses to hydroclimate gradually weakened through time,with a U-shaped response to precipitations from previous July to current June for TRW of Qilian juniper.(3)Over a longer period of 1789～2010 A.D.,both species were highly correlated with a hydroclimate-sensitive TRW chronology of Qilian juniper developed from the Delingha region.These findings suggest that the recent warming and humidification may have been a major cause of the increasing temperature control on the radial growth of Qinghai spruce and Qilian juniper in the Wulan region.In contrast to a temperature signal,TRW variations of the two species are more likely dominated by hydroclimatic factors in earlier periods not covered by instrumental records.Future studies are needed to account for growth-climate response at different time spans,especially in regions where this relationship may have been potentially shifted,to better understand the potential of long tree-ring series for climate reconstructions.
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