The morphology and seasonal changes in cold hardiness, dormancy intensity and root growth potential of rooted cuttings of Sitka spruce

The morphological and seasonal changes in physiological attributes of Sitka spruce cuttings derived from juvenile selections were compared with that of conventional transplants growing in Ireland in 1997/98. Differences between stock types for most morphological characteristics were small from an operational viewpoint. Cuttings had significantly fewer branches per unit height and a poorer shoot:root ratio. The cuttings were less cold hardy in October and November and flushed more rapidly in the greenhouse when lifted in November compared with the transplants. Therefore, there may be a higher risk of frost damage to cuttings if planted on frost-prone sites. Furthermore, since dormancy intensity and stress resistance levels las indicated by cold-hardiness levels) were lower in the cuttings than in the transplants in the October-November period, the window of opportunity for commencing lifting of cuttings may be delayed when compared with conventional transplants. The root growth potential (RGP) in both stock types was generally good, but in February cuttings had a lower RGP than the transplants. These differences in RGP were probably related to the effects of the dormancy cycle on root growth phenology. The reason for the different physiological response of cuttings compared with transplants is unclear. Possible reasons include selection in the nursery bed and the effects of ageing or phase change.