Spring Versus Summer Spruce Stocktypes of Western Canada: Nursery Development and Field Performance

This article summarizes information on the performance of spring versus summer spruce (Picea glauca, Picea engelmannii) stocktypes grown in western Canada. The spring planted stocktype is grown over one growing season in the nursery, hardened in late summer, goes through acclimation in the fall, lifted within a fairly broad window in late fall and early winter when it is considered winter-hardened, and then frozen-stored until planting in the spring This stocktype is planted across a fairly broad spring planting window. In contrast, the summer planted stocktype is grown over one or two growing seasons in the nursery, lifted during late spring to early summer for planting in a narrow planting window in mid summer. These stocktypes are quite different in their phenology during final stages of nursery development, through stock quality assessment and initial performance in the field. For this reason, the discussion centers on comparing important morphological and physiological attributes between these two stocktypes. The stocktype used for spring planting programs has a high level of stress resistance just after planting (i.e., freezing tolerance: index of injury at -6°C of 11%; drought tolerance: osmotic potential at turgor loss point of -2.2 MPa). This stocktype starts to lose this high level of stress resistance as seedlings break bud and undergo shoot development within weeks of being planted on reforestation sites. The stocktype used for summer planting programs has a low level of stress resistance just after budset (i.e., freezing tolerance: index of injury at -6°C of 43%; drought tolerance: osmotic potential at turgor loss point of -1.6 MPa). This stocktype has a rapidly changing phenology resulting in an increasing level of stress resistance and decreasing growth potential (primarily in the root system), whether budset is induced naturally or by a short-day cultural treatment. Thus, timing of lifting plays a critical role in the success of summer stocktypes. The spring-plant stocktype has both shoot and root growth, while the summer-plant stocktype only root growth during the first season on a reforestation site. During the second growing season, both stocktypes have a similar pattern of shoot and root growth across the growing season.