Linear trend and climate response of five-needle pines in the western United States related to treeline proximity

Five-needle pines provide some of the world's longest chronologies of paleoclimate interest. We examined 66 five-needle pine growth chronologies from 1896 to their end years using linear trend, correlation, and cluster analyses. Chronologies were categorized based on the sites' proximity to upper treeline. A significant positive trend in ring width over the post-1896 interval was most common in upper treeline chronologies, but positive linear trend was found in all elevational proximity classes and all species. Cluster analysis of climate response patterns identified four groups exhibiting strong associations with (i) positive response to previous autumn, winter, and spring precipitation, (ii) positive response to spring and (or) summer precipitation coupled with an inverse relationship with summer temperature, (iii) positive response to winter and (or) spring precipitation coupled with an inverse relationship with spring temperature, and (iv) positive associations with temperature in all seasons except spring and no appreciative precipitation response. Most chronologies positively associated with temperatures were from sites located near upper treeline and also contain significant positive linear trend. Our results suggest that some five-needle pine treeline chronologies may be reliable predictors of past temperatures, but careful site selection is required.