Effects of cold temperatures on breakage of lodgepole pine and white spruce twigs

Twigs from lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) and white spruce (Picea glauca (Moench) Voss) trees were bent at a range of temperatures below 0°C using a two-point bending test. This was done to determine how cold temperatures might affect twig breakage and potential shoot and foliage loss in maturing conifer stands. The bending angle necessary to cause 50% twig breakage decreased linearly with decreasing temperatures for both species. No difference in the relationship between temperature and twig breakage was evident among species. Below -13°C, all breakage was on the tension side; at warmer temperatures there was compression damage to many twigs.