Age-related tree-ring sensitivity at the dry forest-steppe boundary in northwestern Patagonia

Key message The association between growth and climate in the forests ofAustrocedrus chilensisplaced at the forest-steppe ecotone was found to be age dependent, with ring widths from the oldest trees providing a better expression of climate variability. Over the course of their lives, trees may undergo changes in sensitivity to climate during their ontogenetic development, i.e., from seedling to maturity. Identifying these age-dependent responses is relevant to minimize under or over estimations of the climatic signal in dendroclimatic reconstructions. It also provides important clues in predicting the reactions of different age-class trees to ongoing climate changes. In this context, the main goal of this study was to determine the sensitivity of radial growth of Austrocedrus chilensis (Cipres de la Cordillera) to climate variability as a function of tree age. Wood cores from 90 trees growing in the forest-steppe ecotone of northwestern Patagonia in Argentina, were sampled. By analyzing their growth rings, trees were classified in two age classes: young (< 93 years) and mature (>= 93 years). Pearson's and moving correlations revealed that spring-early-summer total precipitation positively correlated with growth regardless of age, particularly during the previous growing season. Mean temperature and standardized precipitation-evapotranspiration index (SPEI-1 month), however, showed a stronger association with the growth of mature trees than with young trees, especially in relation to the previous growing season. The moving correlation analysis showed, moreover, that the associations between climatic variables and radial growth of A. chilensis varied between age classes during the last century. The obtained results could help to improve our understanding of the ecology of A. chilensis and provide a better interpretation of how Patagonian forests could be influenced by climate change processes.