No abstract

Characteristics of planting stock which reflect quality (defined here as performance potential) are categorized as either "performance'" attributes or "materia\"' attributes. Performance attributes. such as root-growth potential. cold hardiness. and stress resistance. are assessed by subjecting whole seedlings to certain environmental regimes and evaluating their response. Because performance attributes are integrators of all or many seedling subsystems. they often correlate well with seedling performance potential; however. they tend to require laborious and time-consumlng procedures. Material attributes. such as dormancy status. water relations. nutrition. and morphology. are assessed by measuring the attribute in question by any number of direct or Indirect methods. Although material attributes are often more easily and rapidly measured than performance attributes. the former generally yield little definitive Information on seedling quality unless values fall well outside of some established range. Of the Northwest nurseries responding to the OSU Nursery Survey. many reported using various methods to assess seedling conditions. However. most methods were used to indicate the desirability of carrying out certain cultural operations. such as irrigation or lifting. rather than to measure seedling quality Itself.

In a greenhouse experiment, potted coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown in miniature "Nelder" (Nelder 1962) plots where growing space varied from 265 to 2555 cm(2) per plant. After thirty weeks, mean plant height, crown biomass and branch number increased significantly (P = 0.0141) with decreasing growing space (increasing plant density). Differences in height growth became apparent about six weeks after sowing. Furthermore, horizontally reflected radiation measured within the Nelder plots showed a decrease in red:far-red ratio (R:FR) from 1.2 at the lowest density to 0.71 at the highest. Plant height was strongly inversely correlated with estimated phytochrome photoequilibrium values (r(2) = 0.893). Field measurements made in a three-year-old variable density plantation also showed a decrease in R:FR with increasing planting density from 300 to 3,000 trees ha(-1). These results support the hypothesis that young Douglas-fir seedlings are able to detect, through the phytochrome system, the presence of nearby seedlings owing to the depletion of R relative to FR in the spectra reflected by the foliage of the adjacent plants. They then adjust their growth allometry in a way that reduces the possibility of being over topped by these future competitors.

Owing to frozen ground, nurseries in interior Oregon, Washington, and British Columbia are often unable to lift bare-root seedlings during midwinter when they are in peak physiological condition. Therefore, seedlings are normally lifted in the fall and planted either immediately or after overwinter storage, or lifted in the spring and planted either immediately or after brief storage. The objective of this study was to ascertain which of the above strategies produced planting stock with the highest physiological quality. The species evaluated were lodgepole pine (Pinuscontorta Dougl.) and interior spruce (Piceaglaucaengelmannii complex). Seedlings were grown in a Weyerhaeuser Canada nursery near Armstrong, B.C., and lifted on nine dates spanning early October 1982 to late March 1983. Seedling quality was evaluated at each lift date and following 2 and 6 months in freezer (−1 °C) storage. Evaluations consisted of measurements of dormancy release index, root growth potential (RGP), stress resistance (SR), and frost hardiness (FH). The main effects of lift date and storage duration were generally highly significant on all seedling-quality attributes. Lift date × storage duration interactions were also highly significant in most cases. Dormancy weakened throughout winter in the nursery, with accumulated chilling. Storage slowed the release of dormancy for most lift dates. RGP was very high in fall-lifted seedlings, but declined rapidly after storage. RGP again increased in late winter, but was not appreciably affected by storage except for March-lifted seedlings. SR was relatively high in fall-lifted seedlings and very low in spring-lifted seedlings. SR was also reduced by storage, especially after 6 months. However, SR did not fall as rapidly in stored seedlings as it did in seedlings left in the nursery bed. FH was −30 °C in early October; during midwinter FH was beyond the limit of measurement (−40 °C). Seedlings of both species appeared to deharden in storage, but at a relatively slow rate. The best operational strategy seems to be fall lifting, beginning November 1, with overwinter freezer storage. Spring-lifted seedlings tended to exhibit low RGP, low SR, low FH, and poor storability.

Two-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings from four western Washington and Oregon provenances were lifted from the nursery on December 11, 1979, January 21, February 13, and March 11, 1980, following the accumulation of about 600, 1170, 1550, and 1800 chilling hours (temperature ≤5 °C), respectively. They were tested for bud dormancy (rest) intensity and vigor immediately after lifting and following 2 and 6 months in freezer (−1 °C) storage. Dormancy weakened exponentially with accumulated nursery chilling, with seedlings from all four provenances responding in a like manner. The rate of dormancy release was substantially retarded by freezer storage, so that by late March stored seedlings were more dormant than those remaining in the nursery beds. Dormancy weakened in storage more rapidly in high-elevation provenances than in provenances from lower elevations. Early-lifted seedlings lost dormancy more rapidly in storage than did late-lifted seedlings. Vigor following a 6-week greenhouse trial was good or excellent in all but the December-lifted unstored seedlings and the March-lifted unstored and 6-month stored seedlings.