DENDROCLIMATIC RECONSTRUCTION OF SUMMER TEMPERATURES IN NORTHWESTERN CANADA SINCE AD 1638 BASED ON AGE-DEPENDENT MODELING

Ring widths from five Picea glauca stands at the alpine treeline in no rthwestern Canada are used to investigate climate-growth responses and to develop a long reconstruction of summer temperatures, Response fun ction and linear regression analyses indicate that the radial growth r esponse of these trees to climate varies with age and site, At most si tes, the period of significant positive response to growing season tem peratures declines with tree age, Age-dependent and standard (age inde pendent) models are then used to develop two reconstructions of June-J uly temperatures for northwestern Canada extending back to A,D, 1638, Calibration statistics were similar for both models, but the standard model performed poorly during verification. The reconstruction produce d using age-dependent modeling suggests June-July temperatures were co oler than present throughout most of the past 350 years, with the exce ption of the late 18th century, Particularly cool periods occurred at similar to 1700 and in the mid-19th century, In constast, the standard model suggests that temperatures were similar to or warmer than prese nt during the last 350 years, The age-dependent reconstruction compare s favorably with other proxy climate records from northern North Ameri ca. Age-dependent dendroclimatic modeling can provide a sensitive reco rd of recent climatic change that allows the inclusion of previously r ejected sites into dendroclimatic analyses. (C) 1995 University of Was hington.