Extension of the planting period of Norway spruce container seedlings: risks related to the drought – growth stage dynamics and handling practices

Abstract

Helenius, P. 2005. Extension of the planting period of Norway spruce container seedlings: risks related to the drought − growth stage dynamics and handling practices. Dissertationes Forestales 3. 46 p. The first aim of this study was to investigate the possibility of extending the planting period of Picea abies container seedlings from May to June and July without the risk of excessive mortality and growth restrictions due to drought. The second aim was to investigate risks related to thawing practices of frozen-stored seedlings. To achieve the first aim, 1.5-yr-old actively growing seedlings were exposed to different preplanting drying and postplanting drought periods. Seedlings kept dormant (sensu shoots not elongating) by prolonged frozen storage were also exposed to postplanting drought periods. To achieve the second aim, 1-yr-old frozen-stored seedlings were exposed to different thawing durations and temperatures before planting in mid-June. Height growth and root egress of actively growing seedlings planted in late June-early July decreased when exposed to postplanting drought as affected by the soil water content at planting and atmospheric evaporative demand during drought periods. Survival and growth under drought were also decreased by preplanting drying of root plugs and seedlings. However, mortality of actively growing, well-watered seedlings was negligible when exposed to drought periods not longer than 2 to 3 weeks. Prolonged frozen storage until late June had no observable negative effect on needle carbohydrate concentration and subsequent seedling outplanting performance. Contrary to actively growing seedlings, drought periods had no effect on root egress and chlorophyll fluorescence, and only moderate effect on xylem water potential of dormant seedlings. However, actively growing seedlings showed much greater root egress than dormant seedlings, except when exposed to very long (≥ 3 weeks) drought periods after planting. Frozen-planting may adversely affect seedling performance at soil temperatures prevailing in Fennoscandia in spring or early summer, especially when soil is dry. Thawing over 4 to 8 days at 9−12 °C ensures complete thawing of the root plugs and unaffected field performance of frozen-stored seedlings.

Influence of Root System Characteristics on Black Spruce Seedling Responses to Limiting Conditions

“…Karst.) seedlings, with root plugs wet to saturation before planting, had much reduced mortality rates until three to four weeks of drought compared to dry root plug seedlings [58,59]. In our study, even if submitted to a moderate water stress, BR seedlings were more rapidly impacted by limited irrigation compared to containerized seedlings.…”

Seed quality attributes in seedling production of Norway spruce (<i>Picea abies</i> (L.) Karst.)

“…Seedlings planted the following spring are either packed in cardboard boxes and stored in freezers, or unpacked seedlings are stored in open fields under natural or artificial snow cover. The handling of freezer stored Norway spruce seedlings prior planting is presented in detail in Helenius (2005).…”

Covering Norway spruce container seedlings with reflective shading cloth during field storage affects seedling post-planting growth

“…Dormant, actively growing and short day treated Norway spruce (Picea abies (L.) Karst) seedlings are recommended to be planted in spring (May to mid-June), summer (June to late July) and autumn (August to September), respectively (Luoranen et al 2005(Luoranen et al , 2006(Luoranen et al , 2018Wallertz et al 2016). The need to extend the planting season over the summer months, when the seedlings are actively growing and susceptible to drought during storage, is becoming more relevant due to labour shortages and mechanised planting solutions (Helenius 2005;Helenius et al 2002;Laine et al 2016;Laine 2017;Ersson et al 2018).…”