A tree ring reconstruction of climatic extreme years since 1427 AD for Western Central Asia

Abstract

Analyses of ring width values of 429 trees from twelve Juniperus sites and three mixed sites (Juniperus, Picea, Pinus) of the northwest Karakorum in Pakistan and seven Juniperus sites of the southern Tien Shan in Kirghizia enable the reconstruction of extreme years since AD1427. Extreme growth reactions are classified as (i) event years- reflecting extreme years of individual trees, (ii) site pointer years- reflecting common extreme years within a site, (iii) regional pointer years- reflecting common extreme years within the Karakorum or Tien Shan, and (iv) inter-regional pointer years- reflecting synchronous extreme years between the Karakorum and Tien Shan. A comparison between the Karakorum and Tien Shan results in eight positive inter-regional pointer years (1916, 1804, 1766, 1703, 1577, 1555, 1514, 1431 AD) and 17 negative inter-regional pointer years (1917, 1877, 1871, 1833, 1806, 1802, 1790, 1742, 1669, 1653, 1611, 1605, 1591, 1572, 1495, 1492, 1483 AD). These years are valid for Western Central Asia. The extreme year reconstructions from the Karakorum and Tien Shan Mountains are dominated by regional pointer years. Regional pointer years result from climatic conditions limiting tree growth independent of site ecology, from the lower, arid, to the upper, humid timberlines, and in different exposures. The seasonal climatic forcing of regional pointer years changes from year-to-year, but temperature variation predominantly limits tree growth. Additional analyses of selected site pointer years, which do not belong to regional pointer years, prove temperature signals from sites near the upper timberline, and precipitation signals from sites near the lower timberlines.