川西云杉为我国西南地区特有种，耐寒耐旱，是高海拔森林的优势树种。研究表明，显著的气候变暖使川西云杉森林面临日益严重的干旱胁迫，威胁其生态屏障功能的可持续性。为了准确评估未来的川西云杉森林动态，亟需了解当前气候变暖对树木生长影响的程度和空间特征。本项目将围绕“全球变暖带来的干旱胁迫加剧是否会导致青藏高原东部川西云杉径向生长衰退？”这一科学问题，拟沿着西藏东部天然的区域水分梯度，选取三条林线和相应中、下海拔的川西云杉森林进行树轮年代学调查，获取树轮宽度与树轮δ13C数据。计算树轮的内在水分利用效率（iWUE），用于定量指示树木生长的干旱胁迫历史。通过分析水分梯度和海拔梯度上的树木径向生长与干旱指数的相关关系，以及树轮宽度和iWUE的耦合规律，归纳气候变暖背景下干旱胁迫对树木生长影响的时空特征。研究结果可以为准确预测川西云杉森林动态提供数据支持，为制定针对性的森林管理政策提供依据。

Balfour spruce [Picea likiangensis var. balfouriana (Rehd. et Wils.)], an endemic tree species to the southwestern China and characterized by both cold- and drought- enduring, is a keystone species in alpine forests. According to recent studies, the persistence of the Balfour spruce forests functioning as an ecological security barrier might be compromised by the warming-related drought stress increase. There is thus an urgent need to understand whether and how drought stress will affect tree growth under a warming scenario. Here, the current program is focused on the scientific question that “If warming caused drought stress increase will trigger tree radial growth declines of the Balfour spruce forests on the Eastern Qinghai-Tibetan Plateau?”. We plan to investigate three altitudinal transects consists of upper (treeline), middle, and lower altitudes of alpine forests along a regional moisture gradient in the Eastern Tibet using dendrochronological techniques. Tree-ring widths and tree-ring δ13C would be determined. Then intrinsic water use efficiency (iWUE) would be calculated based on the tree-ring δ13C sequences to indicate severity of drought stress to trees. Tree growth-climate relationships and patterns of the coupling between tree-ring width and iWUE would be compared in both spatial and temporal aspects to get the patterns of drought stress on tree radial growth along both altitudinal and moisture gradients in the region of interest. Our results would help to improve the ability in prediction of future alpine forest dynamics and to benchmark the developing of differential managing policies on the Balfour spruce forests under the global warming background.