Root cold hardiness and native distribution of subalpine conifers

COLEMAN, M.D., HINCKLEY, T.M., MCNAUGHTON, G., and SMIT, B.A. 1992. Root cold hardiness and native distribution of subalpine conifers. Can. J. For. Res. 22: 932-938. Root and needle cold hardiness were compared in seedlings of subalpine conifers to determine if differences existed among species originating from either cold continental climates or mild maritime climates. Ahies amabilis (Dougl.) Carr. and Tsuga mertensiana (Bong.) Carr. are exclusively distributed in maritime environments, while Abies lusiocarpa (Hook.) Nutt. and Pinus confortu Dougl. are more generally distributed in both continental and maritime environments. Because of the differing winter soil conditions of these two climatic types, special emphasis was placed on root cold hardiness. Cold hardiness for root samples, as measured by a decrease in the electrolyte leakage, was much greater for A. amubilis and A. lusiocurpa than for P. contortu and T. merfensiuna (-I 1.4, -1 1.5, -7.5, and -7.5”C. respectively). Thus, subalpine conifer species distribution was not found to be influenced by root cold hardiness. Root cold hardiness of field-grown seedlings paralleled changes in soil temperature through February. Under constant temperature conditions (3°C) the maximum cold hardiness achieved in 6 weeks was not subsequently maintained in A. amabilis and A. lusiocurpu. Injury in unhardened roots was coincident with bulk freezing, whereas hardened roots were able to tolerate bulk freezing. Needles had more than three times the level of cold hardiness of roots when measured in December. All species except P. contorta reached needle cold hardiness levels below -40°C.