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Knowledge of natural long-term drought variability is essential for water resource management and planning, especially in arid and sub-arid regions of the world. In the eastern Qilian Mountains of China, long-term drought variability based on high-resolution proxy records such as tree-ring data are still scarce to date. Here we present a new tree-ring chronology from the eastern Qilian Mountains which provides a valuable 1,002-year record (1009-2010 CE) of drought variability. The new reconstruction of June-July 5-month scale standardized precipitation and evapotranspiration index is the first millennium tree-ring estimate of past climate developed in the eastern Qilian Mountains. The record shows that this region has experienced several persistent droughts and pluvials over the past millennium, with significantly drier climate during the fifteenth century and dramatic wetting since the nineteenth century. The low frequency generally agrees with other nearby studies based on both tree-ring data and other proxy data. [ABSTRACT FROM AUTHOR]

Abstract: Tree-line ecotones are strongly climatically limited and serve as potential monitors of climate change. We employed annual growth increment from tree-rings, and tree density and age structure data derived from two Juniperus przewalskii tree-line sites in the eastern part of the Qilian Mountains, northeastern Tibetan Plateau, to detect the responses of tree growth and population dynamics to climate change. High temperature favors tree growth and is associated with increased tree density at tree-line, and an advance in tree-line position. Significantly positive correlations were found between ring-width and mean monthly air temperatures in current and previous June, July and August. Tree recruitment began to increase rapidly at the two sites after the Little Ice Age, but then decreased starting in the 1970s. The number of trees established coincides with temperature changes. The warming trend after the Little Ice Age favors increases of tree density and an advance of tree-line. The majority of trees established during the period of 1931–1970, which coincides well with the rapid radial growth of the trees. [Copyright &y& Elsevier]

While temperature is known to be an important factor determining cambial phenology in cold and humid climates, how it interacts with other factors in determining the onset and end of xylogenesis is still not fully understood. Here, we analyzed phenological traits related to observed cambial phenology and xylogenesis over the course of two extreme hydroclimatic years across six sites that span the spatial distribution of Qilian juniper ( Juniperus przewalskii Kom.) in the northeastern Tibetan Plateau. Cambial phenology and xylogenesis were assessed weekly or biweekly from the microcores of 30 trees. We found that the onset of xylogenesis significantly correlated with annual mean and minimum temperatures, regardless of the moisture conditions, resulting in an advance of the onset of xylogenesis of 10.1 days °C −1 . In contrast, the end of xylogenesis was related to both maximum temperatures and drought conditions. The contrast in drought conditions over the two growing seasons made the importance of the water balance on the end of xylogenesis quite clear. During the extremely dry conditions of 2013, xylogenesis ended up to 30 days earlier than during 2012, a wetter and cooler year. Our results indicate that strong shifts in water availability during the growing season are crucial to the rate of wood production. Also, the significant correlation between the total number of xylem cells and both the duration and rate of wood production, highlights how changes in the timing of xylogenetic processes and the growth rate can have a strong influence on the future growth and performance of J. przewalskii . Our findings indicate that while warming promotes an early growing season and, potentially, a longer growing season, warming and decreased moisture availability has a strong influence on tree growth and productivity in cold and arid regions. [ABSTRACT FROM AUTHOR]