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

Abstract

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. West. J. Appl. For. 18(4):267–275.

Comparison of planting success in one-year-old spring, summer and autumn plantings of Norway spruce and Scots pine under boreal conditions

“…Extending the planting season into the summer months can even improve the growth of planted Norway spruce (Helenius et al 2005;Luoranen et al 2006) seedlings because of the favorable temperature conditions for the growth and rooting of the seedlings. However, the risk for stress events, such as drought periods, is higher in the summer months than in spring, when the water content of the soil is naturally higher (Grossnickle et al 2000(Grossnickle et al , 2005Grossnickle and Folk 2003;Helenius et al 2005;Luoranen et al 2006).…”

“…However, to ensure the proper field performance of seedlings after planting, they must be in good condition at the time of planting (Helenius et al 2002;Grossnickle 2005). Actively-growing seedlings are more susceptible to drought and mechanical injury and early autumn frost damage, than seedlings planted while dormant (Deans et al 1990;Grossnickle et al 2000;Grossnickle and Folk 2003). On the other hand, drought risks in summer plantings may be reduced through the careful handling, storage, deep planting and watering of the seedlings (Helenius et al 2002(Helenius et al , 2005Luoranen and Viiri 2016).…”

“…This is because previous trials extending the planting season are in carefully-established experiments, and applicable only in restricted geographical areas. Additionally, the seedling material (Grossnickle and Folk 2003), the handling, shipping and field storage of the seedlings (Helenius et al 2002) as well as the site preparation and planting quality Wallertz et al 2018), affect together with a number of abiotic and biotic risks (Wallertz et al 2016) on the regeneration results in practical forestry. Their effects on the regeneration results may also vary largely depending on planting date, tree species and geographical region.…”

Duration Limits on Field Storage in Closed Cardboard Boxes before Planting of Norway Spruce and Scots Pine Container Seedlings in Different Planting Seasons

“…For Scots pine (Pinus sylvestris L.), it is suggested that container seedlings are only planted in spring or early summer due to their growth rhythm and growing conditions in their typical planting sites in Nordic countries [3][4][5]. Similarly to the Nordic countries, summer plantings in July and August are also performed for different pine and spruce species in North America [6,7]. The extension of the planting season is a major prerequisite for enhancing the cost-competitiveness and facilitating the growth of the Nordic mechanized tree planting business [8].…”

Fall Acclimation and the Lift/Store Pathway: Effect on Reforestation

“…Fall lifted interior spruce seedlings are typically only freezer stored because there needs to be four to six months between lifting and spring planting [9,17,142]. Short term cooler storage is used in summer planting programs for hardened interior spruce seedlings [157]. Fall lifted seedlings are usually placed in frozen storage at -2 to -4 °C and as low as -6 °C [158] while still maintaining seedlings of high quality.…”