EFFECT OF POPULATION, ENVIRONMENT, AND MATURATION ON THE FROST HARDINESS OF YELLOW-CEDAR (CHAMAECYPARIS-NOOTKATENSIS)

Three 2-year-old experimental plantations of yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach.) seedlings and stecklings (rooted cuttings) from 4- and 12-year-old hedges were analyzed periodically for frost hardiness between September 1991 and May 1992. The plantations were at different elevations and latitudes, and seedlings and stecklings of three geographically diverse populations were represented. Frost hardiness was assessed using the freeze-induced electrolyte leakage method on upper, primary branches. Air temperature at the low elevation sites was monitored. Frost hardiness of all plants increased from September to the end of January, and then decreased. Plants grown at high elevation were consistently more hardy than those grown at low elevation; however, no obvious differences in hardiness between the two latitudes were evident. Seedlings and stecklings of parents from certain families and populations developed greater hardiness than stock of parents from other areas, showing that frost hardiness of yellow-cedar plants has a genetic component. The three stock types did not show any consistent, significant differences in hardiness; however, stecklings from 12- and 4-year-old hedges were, on average, slightly more hardy than seedlings.