Long-term tree-ring variations in Juniperus at the upper timber-line in the Karakorum (Pakistan)

Ring-width series of Juniperus excelsa M. Bieb and Juniperus turkestanica Kom. from six different sites, in the Hunza-Karakorum, were used in reconstructing modes of regional climate over the past 500 years. All reconstructions were derived from trees growing close to the upper timber-line (approx. 4000 m a.s.l.). Standardized site chronologies, derived from ring-width measurements, display common low- and high-frequency variation that is synchronous between all sites. Since the documented increase in atmospheric CO2 loading, roughly 150 years ago, Hunza-Karakorum trees are not growing as well as they were previously. From the mid-nineteenth century to the present, these trees appear to be alternating between states of more extreme favourable and unfavourable growth periods of different amplitude and duration. Maximum (favourable) variations occurred between AD 1579 and 1603, whereas minimum (unfavourable) variations occurred between AD 1825 and 1850.