Carbon (C) content in several forest ecosystem pools, including trees, understory species, downed logs, litter, soil organic and mineral layers, and fine roots, and tree growth were compared in balsam fir (Abies balsamea) and black spruce (Picea mariana) ecosystems located along a climatic gradient in eastern Canada spanning regions that differed by 4 °C in mean annual temperature. A total of 19 experimental sites were established, 12 in balsam fir ecosystems and 7 in black spruce ecosystems. Diameter at breast height (dbh), height growth rate, and C contents in trees, understory species, downed logs, litter, and soil organic and mineral layers did not differ significantly between northern and southern experimental sites (P < 0.05). The only C pool that differed significantly among the regions was fine roots. Tree ring data collected on trees greater than 5 cm in dbh at all the sites were related to monthly climatic data between April and October, the active physiological season at the latitudes of the study. The relationships derived indicated that the differential effects of significant climatic variables along the climatic gradient were more important for black spruce than balsam fir. These results suggest that the changes in climatic conditions in the next 100 y may have a relatively small effect on the productivity and C allocation of both forest types when located within a range of climatic conditions similar to those of this study.