Radial-Growth Response of Forest-Tundra Trees to Climate in the Western Hudson Bay Lowlands

The effects of climate on radial growth of Larix laricina (Du Roi) K. Koch, Picea glauca (Moench) Voss, and Picea mariana (Mill) BSP were investigated in the Hudson Bay Lowlands of northern Manitoba. The objective was to characterize spatial and temporal variations in growth of trees across the forest-tundra ecotone. Along a 250 km transect, 299 trees were sampled in three zones: northern forest, central tundra, and southern forest. Ring-width indices were compared with climate through correlation- and response-function analyses. Numerous years of suppressed growth at the three locales resulted from cooling that followed major volcanic eruptions at much lower latitudes. Temperatures during July of the current year and autumn of the previous year were most limiting, particularly for L. laricina, which was temperature-sensitive across the region. A weakened growth response to temperature during the 1940-60 period was likely due to atmospheric circulation shifts. Most chronologies were intercorrelated, which suggests common environmental forcing, though environmental influences differed in the southern forest (particularly for P. mariana). The source of this disparity has yet to be determined.