Age-related climate sensitivity in Pinus Edulis at Dinosaur National Monument, Colorado, USA

Abstract

The influence of tree age on climate sensitivity is of central importance in dendrochronology. Recent research has highlighted the disparate nature of age-dependent growth responses across species and geographic locations. We compared growth sensitivity and the influence of climate in Pinus edulis (Piñon) of varying ages at Dinosaur National Monument (DINO, northwestern Colorado, USA. Piñon is a particularly good species for this study because of its long life-span and climate sensitivity, and the DINO site is at the northern extreme of the current distribution. We evaluated changes in climate-growth relationships in piñon using total ring-width measurements and running averages of chronology statistics, mean sensitivity (MS) and coefficient of variation (CV), and we investigated growth response to climate variability as trees age. These measures indicated initial low growth sensitivity, increasing as trees reached mid-life stages, approximately 200–250 years, then relatively constant sensitivity from 250-800+ years. First order partial auto correlation (PAC1) declined throughout the life stages of piñon at DINO. The trend in declining autocorrelation leads to higher MS values in the older age classes. Greater year to year variation indicates less persistence in the study population, hence lower autocorrelation.We investigated the degree to which this relationship could be explained by the summer Palmer Drought Severity Index (PDSI) and whether this relationship varied with tree age. The strength of the tree-ring growth response to PDSI was at a maximum during the first two centuries of growth (R2 = 0.54). between two and six centuries (R2 = 0.48), after which we detected a decline in the sensitivity of tree growth to PDSI with increasing age (R2 = 0.41). This study adds to the literature on age-related climate sensitivity in trees; our findings indicate that age-related changes in climate-tree-ring growth responses should be considered when climate variables are reconstructed from tree-ring width chronologies, and specifically from Pinus edulis.