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Picea schrenkiana is the dominant tree species in Ili River Basin located in the western Tianshan Mountains of Xinjiang. We investigated the growth decline characteristics of P. schrenkiana at different altitudes (1800, 2300 and 2800 m) based on tree-ring index (TRI) and percentage growth change (GC), aiming to understand the growth response of P. schrenkiana to drought events at different altitudes and the impacts of altitude on tree growth decline in this region. The results showed that P. schrenkiana experienced multiple decline events at low-altitude (1800 m). TRI and GC identified inconsistent occurrence time of the decline events. The variations of TRI indicated that P. schrenkiana at low-altitude experienced two large-scale declines during 1927-1933 and 2017-2014, respectively. The variations of GC identified four decline events, including 1891-1893, 1924-1926, 1973-1975, and 2004-2009. The radial growth of P. schrenkiana across altitudes from low to high was significantly affected by the Palmer drought severity index (PDSI) of the previous growing season. The impact of current PDSI on P. schrenkiana during the growing season initially enhanced but later decreased with increasing altitude. In the extreme drought year 1917, the magnitude of growth decline increased with altitude. At low-altitude (1800 m), the TRI was 0.65, which was 35% lower than the normal level. At mid-altitude (2300 m) and high-altitude (2800 m), it was 0.56 and 0.54, respectively, being 40% lower than the average level. The drought event in 1917 had a 2-year legacy effect on the growth of P. schrenkiana at all the altitudes, with the TRI in 1920 recovered to exceeding 0.9, being close to the normal level. The impact of altitude on drought-induced forest decline was significant. Tree growth in low-altitude areas was more vulnerable to drought events due to the relatively poorer water and temperature conditions at low-altitude, which could lead to multiple large-scale decline events. In mid- and high-altitude areas, where hydrothermal conditions were more favorable, trees could experience even more severe decline during extreme droughts.

ABSTRACT A July-May precipitation reconstruction for the period AD 1816-2010 was developed from a tree-ring width chronology of Picea wilsonii for the Xinglong Mountains area of Lanzhou. The reconstruction explains 55.8% of the actual precipitation variance during the calibration period from 1951 to 2010. Wet conditions prevailed during the periods 1822-1835, 1843-1858, 1870-1877, 1884-1891, 1911-1921, 1933-1938, 1944-1979 and 2009-2010. Dry episodes occurred during 1816-1821, 1836-1842, 1859-1869, 1878-1883, 1892-1910, 1922-1932, 1939-1943 and 1980-2008. Multi-taper method spectral analysis indicates the existence of some significant peaks at 2.8, 3.0 and 3.5 years. Spatial correlations with gridded land surface precipitation data revealed that our reconstruction represents regional precipitation signal for a large area of North China linked to the East Asian summer monsoon (EASM). Comparison with other tree-ring-based precipitation/drought reconstructions from surrounding areas implies a high degree of confidence for our reconstruction. Precipitation variations in the study area are significantly correlated with sea surface temperatures in eastern equatorial Pacific Ocean and tropical western Pacific Ocean, suggesting a possible connection of regional precipitation variations to the EASM and the El Niño-Southern Oscillation (ENSO). [ABSTRACT FROM AUTHOR]

A tree-ring width chronology developed from a site of Larix sibirica at the eastern end of Tien Shan was employed to study the drought variability of east Xinjiang. The drought reconstruction spanning 1785–2009 was developed by calibrating tree-ring data with standardized precipitation-evapotranspiration index (SPEI), an index indicating regional moisture conditions. The SPEI reconstruction accounted for 45.8% of actual October–August SPEI variance during their common period (1957–2009). Wet periods with SPEI above the 225–year mean occurred around 1785–1799, 1821–1833, 1842–1858, 1864–1873, 1887–1898, 1905–1925, 1937–1948, 1954–1962, 1969–1983 and 1991–1993, while dry periods (SPEI below the mean) occurred in 1800–1820, 1834–1841, 1859–1863, 1874–1886, 1899–1904, 1926–1936, 1949–1953, 1963–1968, 1984–1990 and 1994–2009. There was an aridity aggravation trend since the mid-1980s in east Xinjiang. Our results also suggest that east Xinjiang was influenced by the interactions between the Asian monsoon and the Westerlies circulations. [ABSTRACT FROM AUTHOR]