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The effect of nursery cultural and handling techniques on Douglas-Fir seedling quality Turner, Jennifer R.

Abstract

This study investigated the effects of nursery cultural regime on the quality of coastal Douglas-Fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) container seedlings. Douglas-Fir seedlings from Oregon and Vancouver Island provenances (i.e. populations) were lifted in the 1999/2000 winter on four dates, subjected to four cold storage lengths at a temperature of -2°C or +1°C, and thawed (-2°C storage only) for one or three weeks. The three-week thawing period decreased root growth capacity and chlorophyll fluorescence measures of initial survival potential below their quality thresholds. Degree-days to terminal bud break decreased with the later lift dates, longer storage lengths, and the longer thaw duration. Field survival and growth were high for all treatments tested. Only chlorophyll fluorescence was correlated with a field performance measure (relative height increment). Up to four blackout treatments that started on one of three dates in the summer of 2000 with 10 or 20 days between multiple blackouts were tested on Douglas-Fir seedlings from a Washington provenance. A Vancouver Island provenance, given a blackout dormancy induction regime commonly used at Pelton Reforestation, was also included for comparison. Increasing the number of blackout treatments resulted in lower caliper increment, lower days to terminal bud break in winter, and higher cold hardiness on October 12. Early blackout start dates decreased the overall height increment and root growth capacity. The Vancouver Island provenance developed cold hardiness later in the fall and lost cold hardiness sooner in early spring than did the Washington provenance. The normal lift/cold storage regime used by the nurseries does not adversely affect seedling quality. However, an extended thawing period upon cold storage removal or extended on-site storage is detrimental to seedling quality. Although measures of initial survival potential and dormancy were correlated with each other, only a weak correlation was found between initial survival potential and field performance under the field conditions in this study. Blackout regimes commonly used by British Columbia nurseries can decrease the RGC in late fall, cause quicker dormancy release and decrease the caliper.

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