The thermal environment of northern red oak terminal growth

Includes bibliographical references.Includes illustrations and map.Northern red oak (Quercus rubra L.) is probably the most important and widespread of the northern oaks in North America. Although past research has addressed shoot growth responses to different environmental variables, generalizations for the species or any of its races cannot yet be made, partly because these studies focused on terminal growth patterns of seedlings in greenhouses or of trees at specific locations with no uniformity of experimental design among them. The research reported here was directed toward the goal of identifying consistent correlations of wildling terminal growth with environmental parameters over the latitudinal range of the species. Particular attention was given to thermal parameters since previous studies suggest their importance in humid climates which dictate a general adequacy of soil moisture. Study sites chosen for intensive investigations were the Upper Peninsula, Michigan, northern Illinois, and southern Illinois, thus spanning the majority of the commercial range of the species or approximately 10° latitude. Sites and replicate saplings in all three locations met the same selection criteria as closely as possible. The length of terminal shoots was measured daily when possible, and sometimes twice daily. The internal and external environmental variables monitored were air temperature, bud temperature, shoot epidermis temperature, soil temperature, and shoot moisture content. Terminal growth is later and more concentrated from south to north. In the Upper Peninsula, 90% of the growth is confined to a 7 to 8 day period. Onset of terminal growth at all sites coincided with rapid soil temperature increases up to a range of 12°C to 15°C; soil temperatures during growth were comparable at all sites. Rapid growth took place in accord with daily maximum temperatures of 13°C or higher, but within this range, growth rates declined and some buds set when high epidermal temperatures persisted for more than one day. Slow growth was associated with daily minimum air temperatures of 8°C or lower and early morning epidermal temperatures below 12°C. These cool episodes are identified as a second mechanism for instigating bud-set.M.S. (Master of Science