Graduate Thesis Or Dissertation
 

Evaluating the quality of Douglas-fir (Pseudotsuga menziessii (Mirb.) Franco) seedlings : a comparison of some current and proposed evaluation methods

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  • The physiological condition of tree seedlings at the time they are planted can have a profound impact on their subsequent field performance. Damaged or low vigor seedlings have a much greater chance of dying in the field, or at best, of growing slowly during their initial establishment period. Several methods of evaluating the physiological quality of seedlings are currently used to try to predict how seedlings will perform after outplanting. The root growth potential (RGP) approach measures the ability of seedlings to initiate and elongate roots when placed in an environment favorable to root growth. The vigor method, or test, monitors the survival and bud burst of potted seedlings in a growthstimulating environment. While both methods reportedly provide a general indication of seedling health or vigor, the effectiveness of these techniques in actually predicting field survival and height growth of Douglas-fir [Pseudotsuqa menziesii (Mirb.) Franca] seedlings has either not been sufficiently documented, or there have been inconsistent results. A primary goal of this research was to evaluate and compare how well these methods predict growth and survival of Douglasfir seedlings. Another goal was to examine two new, more rapid, methods of evaluating seedling quality and determine how effective they are. The first of these, called the PMS method, monitors changes in plant moisture stress (PMS) of potted seedlings during a one-week interval in the growth room. The second method measures the root respiration rate of seedlings to determine if changes in seedling quality are reflected in altered root respiratory activities. Results from these studies indicated that measurements from both the RGP and vigor method were significantly correlated with first- and second-year survival and height growth for two Douglas-fir seed sources planted on a variety of sites. For RGP, the best predictor of field performance was the number of new roots greater than 0.5 cm produced during 28 days in the growth room. For the vigor method, the survival of both stressed and unstressed seedlings after 6 weeks in the growth room were the best predictors. Seedlings from lots that produced more new roots, or had higher growth room survival, also had higher field survival and greater growth. The RGP procedure was the best predictor of seedling terminal height growth, while the vigor method was the best predictor of field survival. When these procedures were used in conjunction, correlations with field performance variables improved slightly, but not enough to justify the time and expense of using both. Measurements of plant moisture stress were found to reliably predict damage to seedlings caused by accidental freezing. In addition, this pressure chamber method predicted reductions in field survival and growth caused from several other types of injury. In contrast, root respiration measurements were not consistently related to growth-room survival or growth and this approach does not appear promising as an effective evaluation procedure.
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