An unstable tree-growth response to climate in two 500 year chronologies, North Eastern Qinghai-Tibetan Plateau

Abstract Two new Juniper tree-ring-width (TRW) chronologies spanning more than 500 years were developed in the Yellow Riversource area, North Eastern Qinghai-Tibetan Plateau (NE-QTP). For the two studied sites, located approximately 50km apart,split correlation and coherence analysis reveal unstable tree-growth responses to local moisture availability. While signifi-cant correlations are obtained with April–June local precipitation, Palmer Drought Severity Index (PDSI) and river flow from1948/1954 to 1998 and from 1948/1954 to 1970s, these correlations vanish for the time period 1970s-1998. The local instru-mental climate data (precipitation, PDSI and river flow) exhibit opposite correlations with large scale modes of variability (ElNino Southern Oscillation, ENSO, and Pacific Decadal Oscillation, PDO) before and after the 1977 PDO shift. One tree-ring˜chronology is coherent and anti-phased with instrumental ENSO/PDO indices at 5.2-year frequency. On the longer time span,this TRW chronology is compared with PDO reconstructed from historical Chinese data. This comparison also exhibits unstablemulti-decadal relationships, notably in the mid 19th century. Altogether, the comparison between our two chronologies, localinstrumental climate records, and ENSO/PDO indices suggest a cautious use of local TRW records for paleoclimate reconstruc-tions. Further studies are needed to explore both the spatial coherency of tree-ring records and the temporal stability of theirresponse to local and large scale climate variability.© 2010 Istituto Italiano di Dendrocronologia. Published by Elsevier GmbH. All rights reserved.