Sex-specific, age-dependent sensitivity of tree-ring growth to climate in the dioecious tree Juniperus thurifera

Tree features may modulate the sensitivity of radial growth to climate, leading to a nonuniform response. Age-related increases in climatic sensitivity have been observed repeatedly. Sex-related climatic sensitivity is also possible because of the long-term differential reproductive cost between the sexes. This study analysed the simultaneous effects of age and sex on the sensitivity of tree-ring growth to climate. Ring widths were measured from 50 female and 50 male Juniperus thurifera trees, 50-350 yr old, growing under a Mediterranean continental climate. Response functions were calculated based on tree-ring chronologies and monthly climatic records. Climatic sensitivity decreased with increasing age. Young trees (50-100 yr) were the most climatically sensitive to June-July precipitation, which affected growth positively. We found a significant interaction between age and sex in the climatic response of J. thurifera, with young females the most sensitive to summer water stress. Our results suggest that age-dependent climatic sensitivity can be determined by site-specific limiting environmental conditions and species-specific architectural and physiological adjustments during ontogeny. This study supports that the different ontogenetic stages of J. thurifera differ in their root structural traits and that sex-related sensitivity to summer drought may be attributable to less efficient water use by females.