Spatial and temporal variation in Nothofagus pumilio growth at tree line along its latitudinal range (35°40′-55° S) in the Chilean Andes

Aim To identify the dominant spatial and temporal patterns of Nothofagus pumilio radial growth over its entire latitudinal range in Chile, and to find how these patterns relate to temperature and precipitation variation from instrumental records. Location This study comprises 48 tree line or high elevation N. pumilio sites in the Chilean Andes between 35 degrees 36' and 55 degrees S. Nothofagus pumilio is a deciduous tree species that dominates the upper tree line of the Chilean and Argentinean Andes in this latitudinal range. Methods At each of the sampled sites, two cores from 15 to 40 living trees were collected using increment borers. Cores were processed, tree rings were measured and cross-dated, using standard dendrochronological procedures. Radii from nearby sites were grouped into 13 study regions. A composite tree-ring width chronology was developed for each region in order to capture and integrate the common growth patterns. For the identification of the dominant patterns of growth, as well as temperature and precipitation variation, we used principal components (PCs) analysis. Correlation analysis was used for the study of the relationship of N. pumilio tree-ring growth with temperature and precipitation records. Results Nothofagus pumilio tree line elevation is 1600 m in the northernmost region and gradually decreases to 400 m in the southernmost region. Despite local differences along the transect, the decrease in tree line elevation is fairly constant, averaging c. 60 m per degree of latitude (111 km). Tree growth at the northernmost regions shows a positive correlation with annual precipitation (PC1-prec) and negative correlation with mean annual temperature (PC2-temp), under a Mediterranean-type climate where water availability is a major limiting factor. Conversely, tree growth is positively correlated with mean annual temperature (PC1-temp) in the southern portion of the gradient, under a relatively cooler climate with little seasonality in precipitation. Main conclusions Our findings indicate that temperature has a spatially larger control of N. pumilio growth than precipitation, as indicated by a significant (P < 0.05) either positive or negative correlation of tree growth and PC1-temp and/or PC2-temp for nine of the 13 regional chronologies (69.2% of the total), whereas precipitation is significantly correlated with only two chronologies (15.4% of the total). Temporal patterns of N. pumilio tree growth reflected in PC1-growth for the period between 1778 and 1996 indicate an increasing trend with above the mean values after 1963, showing high loadings in the southern part of the gradient. This trend may be explained by a well-documented increase in temperature in southern Patagonia. Ongoing and future research on N. pumilio growth patterns and their relationship to climate covering the Chilean and Argentinean Andes will improve the understanding of long-term climate fluctuations of the last three to four centuries, and their relationship to global change at a wide range of spatial and temporal scales.