Stand age related dissimilarity in radial growth of a moisture-sensitive forest tree species is greater under a lower drought limitation.

• Radial growth of Qinghai spruce differed with stand age. • Stand age effect on radial growth is not consistent. • Stand age effect of growth was lower at drier sites. • Stand age growth concordance was negatively correlated with site moisture. Although stand age has been shown to strongly affect forest ecosystem processes, little is known about the role that forest stand age plays in tree radial growth processes. The knowledge on geographical patterns of the stand age effect on radial growth along climatic gradients is also scarce. Based on dendrological methods and tree-ring cores from 2276 trees at 14 sampling plots, we confirmed that differences in stand age could result in radial growth dissimilarities of Qinghai spruce (Picea crassifolia Kom.), a moisture-sensitive forest tree species endemic to the Tibetan Plateau. However, the effect that stand age has on the radial growth of Qinghai spruce is not consistent. There is evident dissimilarity in the radial growth dynamics of Qinghai spruce from different-aged forest stands in semi-humid regions, but this dissimilarity is minimal in regions under higher drought limitation. Additionally, we observed significant negative correlations in temporal changes of growth concordance of Qinghai spruce from different-aged stands and regional moisture conditions at each study site. It can therefore be concluded that Qinghai spruce will exhibit greater stand age related growth dissimilarities under lower drought limitation. Findings from this study can improve our understanding of biogeographical patterns of moisture-sensitive tree growth that will be necessary to improve future projections of forest dynamics and to guide forest management under a changing climate. [ABSTRACT FROM AUTHOR]