In harsh and treeless environments, shrubs constitute the dominant growth form of woody plants, thus offering the opportunity to extend dendrochronological networks beyond the uppermost and northernmost distribution limits of trees. However, shrub-based dendrochronology has so far resulted in only a few long and climate-responsive ring-width chronologies at such stressful sites, particularly above the alpine tree line. A previous study on an alpine Rhododendron shrub species resulted in <80-year-long ring-width chronologies. Here, we collected Rhododendron agan-niphum var. schizopeplum stems from elevations between 4000 and 4500 m a.s.l. on the SE Tibetan Plateau and built six tree-ring width chronologies. One of them is 401 years long and well replicated from AD 1670 to 2011 (EPS>0.85), thus representing the longest shrub chronology available to date. A principal component analysis (PCA) converted the total variability of all six site chronologies into PCs. Then, the six site chronologies and the PC1, accounting for 65.9% of the total variance of the tree-ring width, were correlated with time series of monthly climate data. Based on this, the year-to-year variability of the ring-width indices was positively correlated with July temperature, which thus turned out to be the dominant factor controlling growth. Accordingly, such long shrub-ring chronologies may act as climatic and ecological proxies in treeless environments of the Tibetan Plateau.
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机译：在恶劣和无树的环境中，灌木构成了木本植物的主要生长形式，因此提供了将树木年代学网络扩展到树木的最高和最北端分布范围之外的机会。然而，迄今为止，基于灌木的树木年代学仅在这种压力较大的地点，特别是在高山林线以上，产生了一些对气候有响应的长环年表。先前对高山杜鹃灌木物种的研究导致<80年的环宽年代学。在这里，我们收集了杜鹃花杜鹃花。裂殖藻起源于海拔4000至4500 m a.s.l.在东南部青藏高原上建立了六个树轮宽度年表。其中之一是401年的历史，可以很好地复制自公元1670年至2011年（EPS> 0.85），因此是迄今为止可用时间最长的灌木年代。主成分分析（PCA）将所有六个站点时间顺序的总变异性转换为PC。然后，将六个地点的年代和PC1（占树轮宽度总变化的65.9％）与每月气候数据的时间序列相关联。基于此，环宽指数的年际变化与7月的温度呈正相关，因此成为控制增长的主要因素。因此，在青藏高原的无树环境中，如此长的灌木环年表可能充当气候和生态的代理。
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