Relative low temperature tolerance of lodgepole and ponderosa pine seedlings

摘要: approved: Signature redacted for privacy. Williatn K. Ferreil The hypothesis is explored that lodgepole pine at the seedling emergence period more resistant to low temperatures than ponderosa pine. Differential tolerance between species then related prevalence of in frost pocket areas central Oregon exclusion Tolerance thresholds both were determined in. a controlled environment chamber. chamhey, designed specifically this study, had separate controls air and soil temperatures. With heated 3 2° F., temperature could be lowered, with lights out, minimum about 13 ° F. Controlled chamber treatments consisted exposing groups uniformly reared seedlings each nighttime 30 Seedling varied age by two-week intervals comparisons differences development stages. These experiments showed differential occurred 15°F. 18°F. About twice as manyponderosa killed lodgepole, mortality occa$ionally approaching 100 percent. At warmer up 23 0 continued substantially greater but number deaths was low. Treatments above 230 caused little or no injury either species. During youngest survived better older seedlings. Fall treatment outside planting beds ai1ed show any signs from 15° treatments. results strengthen theory first year occurs during spring. study occurrence field made along transect starting timbered flat continuing through lodgepole-ponderosa transition zone slope. On few occasions period, night minimums near surface compared 20°F. 22°F. slope 80 feet above. This spread five degrees same magnitude laboratorydetermined almost total kill. demonstrated differ ential species, laboratory-determined lethal approximated those recorded 'Tfrost pocketstt. Although only small segment natural complex studied, evidence strongly supports original pine, thus, explaining part "frost pocket" distribution pattern Oregon. Relative Low Temperature Lodgepole Ponderosa Pine Seedlings