Up to 400‐year‐old Rhododendron shrubs on the southeastern Tibetan Plateau: prospects for shrub‐based dendrochronology

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 aganniphum 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.