Foliar high heat contents were determined by standard oxygen bomb calorimetry in jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss), and balsam fir (Abies balsamea (L.) Mill.) from samples collected in central Alberta. New foliage, sampled in mid-July and early September, and foliage 1, 2, and 3 + years old, sampled in late May, mid-July, and early September, were included in these determinations. The heat contents of the new foliage in all four species as well as the heat contents of the old foliage in jack pine, black spruce, and balsam fir consistently increased with each sampling time, while the heat contents of the old foliage in white spruce at first increased and then decreased between the times. The variations of the heat contents attributed to foliar ages lacked consistency in all four species, although the contents of the new foliage were predominantly lower than the contents of the old foliage. The overall heat contents for the combined sampling times and foliar ages in both the new foliage and the old foliage were the lowest in white spruce and the highest in balsam fir, with black spruce having the second highest content in the new foliage and jack pine having the second highest content in the old foliage.© National Research Council of Canada, NRC Research Press. Abstract reproduced by permission.