In Finland, there is a desire to extend the planting season from spring and early summer to autumn, and to use the closed cardboard box storage method for both dormant and non-dormant seedlings. This thesis examined the effects of planting practices and the growing environment on the early performance of boreal container seedlings, and specifically: i) What are safe durations for the field storage of non-dormant Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) seedlings in closed cardboard boxes and open tray storage for different planting seasons (I); ii) How planting success differs in one-year-old spring, summer, and autumn plantings of Norway spruce and Scots pine in practical forestry (II); iii) How the planting depth and/or planting season affect the early field performance of small-sized silver birch (Betula pendula Roth) and Scots pine container seedlings (III) and iv) How warmer growing conditions affect the growth and emissions of biogenic volatile organic compounds in boreal seedlings in a controlled field experiment (IV). Non-dormant conifer seedlings can be stored in closed boxes for three days in August and a week in May, September, and October, whereas for open-stored seedlings the duration is a couple of days longer (I). Norway spruce plantings can be successful from spring to autumn if seedling storage, duration, and planting instructions are followed carefully. In Scots pine, it is still recommended to plant seedlings only in spring and early summer due to the higher failure risk (II). Deeper planting (60-80 % of shoot underground) may also enhance the early field performance of small-sized seedlings (III). Silver birch might benefit more from climate warming compared to conifer seedlings (IV). To ensure forest regeneration success with boreal tree species, recommendations for seedling materials, storage, and planting practices in different planting seasons should be carefully followed.
The main aim of this work was to study the magnitude of phenotypic variation in different growth, wood density (WD) and wood anatomy properties, and correlations between these, in 41-year-old clones and provenance hybrid clones of Norway spruce (Picea abies (L.) Karst.). Additionally, the development of height and autumn frost hardiness in their seed offspring, under different temperature and/or atmospheric CO2 concentration treatments, were studied under greenhouse conditions over one growing season.
Local Finnish clone V43, and two Finnish–German V449 and V381 provenance hybrid clones had higher stem volume than the average of the 25 genotypes included in the study (Paper I). They had also relatively high overall WD compared to the average of all the genotypes. The geographical transfer of father parent trees affected the overall WD. The averages for tracheid length, double cell-wall thickness (2CWT) in both earlywood (EW) and latewood (LW), and lumen diameter in LW, differed in five genotypes selected for detailed analyses of wood anatomy (Paper II). These parameters and the number of rays correlated with the widths and wood densities of EW and LW. The 2CWT of the tracheids closest to resin canals differed from that in the normal tracheids (Paper II). These differences may be partly affected by the origins of the genotypes.
Under greenhouse conditions, elevated temperatures increased the height growth in seedlings. It delayed the onset of autumn frost hardiness development and shortened its duration. Elevated CO2 did not affect the development of height and frost hardiness. None of the genotypes showed both superior growth and frost hardiness (Paper III).
A need for further studies on wood anatomy – for example, to consider genotype-specific variations in structural compounds – emerged based on this work. The obtained understanding of phenotypic variation in different genotypes may provide support for tree breeding in the future.
The aim of this work was to improve the protocol of somatic embryogenesis (SE) and propagation efficiency in Norway spruce (Picea abies (L.) Karst.), which would enable the integration of SE into Finnish breeding programme and the nursery practices applied to seedlings. The studies specifically investigated the following three areas: i) how maturation, cold storage, germination and growing conditions (laboratory–nursery interface) affect the survival and height growth of emblings (Papers I and II); ii) how to improve the efficiency of embling production from genotypes from wide genetic backgrounds (Papers I and II); and iii) how to increase propagation efficiency by rooting cuttings from emblings, and produce field testing material by combining SE and the rooting of cuttings (Papers II and III). To evaluate the possibility of improving the efficiency of SE in the laboratory–nursery interface, a series of experiments were conducted. The cost structure of SE, and the effects of improvements on costs, was estimated.
As a result, the protocol improvements doubled the yield of cotyledonary embryos, nearly doubled embling survival, and increased the height growth of emblings in the nursery by so much that sufficient planting height was reached one year less than before. Emblings were also obtained from 356 genotypes (50% thawed), and embling cuttings rooted well in conditions similar to those used for seedling cuttings. The protocol improvements also reduced embling production costs by 75%. Based on this work, emblings may be grown in nurseries after one week of in vitro germination, without any measures that differ from seedlings after transplanting. Propagation efficiency may be further increased by rooting embling cuttings. Furthermore, large-scale clone testing can be initiated with 5–12 emblings acting as cutting donors.
The demand for mechanized tree planting is expected to increase in the future. This dissertation assessed mechanized tree planting in Finland and suggests ways to improve its current productivity. The work on which this thesis is based was described in five peer-reviewed articles (I–V) addressing four specific research questions (SQs) that focus on productivity and cost-competitiveness, automation, capacity utilization, and the quality of planting work.
While productivity of mechanized planting is higher than manual methods, it is not yet cost-competitive. However, increasing efficiency by skilled operators and worksite selection make it possible for mechanized planting costs to remain lower than those of excavator spot mounding followed by manual planting. Increasing productivity and reducing operating costs are possible with an effective automatic seedling feeding system, although the Risutec APC is not yet sufficiently developed to reach that goal. Planting machine capacity is underutilized and could be utilized more effective to enhance productivity and cost-efficiency. Technical availability of planting machines in Finland is good, and the quality of mechanized planting work is high. Optimization and integration of the entire mechanized planting chain from the nursery to outplanting is important to minimize total cost.
In summary, for mechanized planting to be effective the following criteria must be satisfied: machine reliability; highly-skilled machine operator; suitable worksite; seedling quality, availability, and supply to worksite. In the future, it is important to continue developing new and existing machines to enhance productivity, e.g., by continuously working planting machines.