Influence of physiological status at the time of lifting on cold storage tolerance and field performance of Douglas fir and Sitka spruce.

Abstract

The physiological status of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and Washington origin Sitka spruce (Picea sitchensis (Bong.) Carr.) seedlings was assessed at the time of lifting. Seedlings of both species were sampled periodically from October to May and after cold storage in 1995/96 and 1996/97. Douglas fir only was sampled also in 1997/98. The field performance of seedlings that were planted in a field trial concurrently with the physiology work was evaluated. Shoot cold hardiness showed a clear seasonal pattern and was a good indicator of readiness of seedlings for lifting for planting or cold storage. Seedlings can be safely lifted for field planting when their shoots have hardened to -10 °C in Douglas fir (November to March) and -20 °C in Sitka spruce (late November/early December to March). Equivalent values for judging long-term (more than three months) cold storage tolerance are -20 and -30 °C, respectively. Root electrolyte leakage (REL) values should be considered to augment this information and to assess post-storage vitality. REL values should be <25% for cold storing Douglas fir, but the test is not reliable for judging its readiness-to-lift for field planting. In Sitka spruce, REL values of <20% and <15% indicate readiness for lifting for field planting and cold storage, respectively. Although more resistant to handling stresses later in the season, Douglas fir performs best in the field when freshly planted early in the lifting season (November to December), but Sitka spruce performs best when planted during the period of highest stress resistance (late November/early December to early March).