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    Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings from three nurseries in the Pacific Northwest United States were lifted on five dates from mid-October through mid-December 2006. Each nursery provided seedlings from a low- and a high-elevation seed lot. Photoperiod and accumulated chilling hours (calculated using two methods) were evaluated throughout the lifting period. Seedlings had typical patterns of fall cold hardiness development, with some indication that the high-elevation lot at each nursery was hardier than the low-elevation lot. Photosynthetic yield measured on seedlings from one of the nurseries decreased with decreasing temperatures, thereby corresponding well to levels of tissue damage at each freezing test temperature over time. Seedlings were either cold- or freezer-stored until February 2007, then tested for physiological quality and planted into a garden plot. Overall, seedlings from earlier lift dates tended to perform poorly in all attributes compared with those from later lift dates. Low-elevation seedlings tended to have lower root growth potential after storage and also reduced survival and longer bud break in the garden plot compared with high-elevation seedlings, although low-elevation seedlings tended to have more height and stem-diameter growth. Freezer-stored seedlings tended to have greater survival compared with cold-stored seedlings, although storage type did not influence growth. This study exemplifies the many influencing factors that growers must consider when determining lift dates. This paper was presented at a joint meeting of the Western Forest and Conservation Nursery Association, the Intermountain Container Seedling Growers Association, and the Intertribal Nursery Council (Boise, ID, September 9-11, 2014).

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    Haase, Diane L.; Khadduri, Nabil; Mason, Euan; Dumroese, R. Kasten. 2016. Relationships among chilling hours, photoperiod, calendar date, cold hardiness, seed source, and storage of Douglas-fir seedlings. Tree Planters' Notes. 59(1): 52-63.


    Douglas-fir, Pseudotsuga menziesii, seedlings, nurseries

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