Cambial-age related correlations of stable isotopes and tree-ring widths in wood samples of tree-line conifers

Abstract. A recent analysis of stable isotopes of the Alpine Holocene Tree-Ring Dataset, consisting of samples from 192 larch and cembran pine trees, revealed that δD and δ¹⁸O exhibit no trends in adult trees, but evidence trends in the juvenile period of the first 100 years of cambial age. In this work we applied the Spearman statistical analysis on different cambial age classes to verify if these changes were correlated with tree-ring width values, that are known to show age trends. The results prove a significant correlation between tree-ring-width (TRW) and both hydrogen and oxygen stable isotopes before 100 year of cambial age, but not afterwards, in both larch and cembran pine. A trend in the correlation values was also found between the two water isotopes, while no trend was found in correlations involving δ¹³C. We hypothesized the δD and δ¹⁸O values reflect the higher xylogenesis activity of the juvenile period, that is associated with reduced atom exchanges of photosynthates with xylem water. The result indicates that the climate response of δD and δ¹⁸O may differ in the juvenile and mature period of tree life at treeline.