Genetic Variation in Some Phenological Characteristics of Forest Trees

Abstract

During the night between June 9 and 10, 1972, the temperature at Rhinelander dropped to — 3.5°C. Severe frost damage of new shoot growth of both conifers and hardwoods resulted (Plate 1). Since that dismal June night we have been evaluating the damage to different spruce species, populations within species, and progencies of individual parent trees within populations. At all levels there are significant differences in the amounts of damage. Some differences are caused by actual resistance to frost; the actively growing tissues can withstand freezing temperatures without showing damage (Kiellander, 1953, 1962), but much of the variation is due to frost avoidance. Seasonal development differs among types, and since the phenophases differ in susceptibility to frost, the differences in damage can be seen. Thus frost damage is closely related to the time of the initiation of growth.