The pine weevil (Hylobius abietis) is the largest cause of seedling mortality in Swedish conifer plantations. Insecticides have earlier been used to protect seedlings but are not a sustainable option. New types of protections have been developed, and there are several coatings available that can be applied on the seedlings’ stem to prevent weevils from debarking. However, there are concerns that the coatings might have negative effects on seedling physiology and be less effective than insecticides.

The purpose of this project was to compare insecticides with alternative protections. Both practical plantations and field experiments with containerized seedlings of Norway spruce (Picea abies), either treated with insecticides, different coatings or unprotected, were measured.

Results from field experiments showed that coatings were as effective as insecticides in protecting seedlings against pine weevil damage. Two years after planting between 1–7% of the protected seedlings had died due to pine weevil damage, and 28% of the unprotected seedlings. Although the mortality was quite low among protected seedlings, almost 40% had been attacked during the experimental period. For unprotected seedlings, this number was around 60%. Growth of the seedlings did not differ between protections.

In addition to the field experiments, surrounding practical plantations were also measured. Seedlings planted in practical plantations had a higher overall mortality than seedlings planted in field experiments, but mortality and damage caused by pine weevils were similar.

An experiment was also carried out in a greenhouse to investigate how seedlings with different protections reacted to drought stress. Three different levels of drought stress were applied, but no differences in shoot growth, neither between treatments nor protection, could be found.

In summary, the results show that the coatings provide as good protection as insecticides. The results also show that the coatings do not adversely affect seedling growth or stress tolerance.

Natural regeneration from seeds of Norway spruce (Picea abies (L.)Karst.) was studied in relation to climate and soil factors around 27 plantations in western Norway. The age of the mother trees was 40-60 years. The total number of seedlings was recorded at 10 m2 plots from the edge of the canopy and with 10 m distance along parallell taxation lines into the surrounding vegetation. The soil was classified according to scarification type and the coverage of the main mosses and vascular plants was also recorded. The seedlings were classified into height classes.=

The regeneration increased with increasing degree of scarification and with increasing distance from the coast. It reached a maximum about 23 m from the edge of the plantation. Inside the canopy there was very little regeneration due to unfavorable light conditions. The plantations were chosen in order to study the succession after disturbance, e.g. clearcutting or windthrows. Maximum regeneration was found the first years after the disturbance, in accordance with soil conditions. The survival rates of the established seedlings, however, seemed to be low and in the abscense of grazing the spruce seedlings seemed to be easily competed out by birch seedlings. In some areas the plants were partly damaged by grazing from sheep, deer or cattle. High occurrance of pioneer plants like Rubus idaeus, Gymnocarpium dryopteris and Polytrichum commune was related to strong spruce regeneration while bracken (Pteridium aquilinum), grasses like Molinia coerula and Deschampsia flexuosa and peat mosses (Sphagnum spp.) was negatively correlated with seedling density.

Norway spruce (spruce) is one of the dominant conifer species in Sweden. In the young spruce stand, naturally regenerated broadleaves, specially birches, are abundant. Consequently, a mixture of spruce and birches is prevalent in young Swedish forests. Mixed stands of spruce and birch have the potential to simultaneously produce timber and provide large ungulates with a significant amount of forage during the regeneration phase. While the growth and yield of such mixtures are well studied, little is known about potential trade-offs between timber and forage production and which management techniques are suitable for meeting both goals. In this study, a precommercial thinning (PCT) experiment with four different PCT strategies was used to study the trade-off between production and available forage for ungulates in a spruce-birch mixture. The four PCT strategies were: 1) keeping 2000 birch stems ha-1 with 2000 spruce ha-1, 2) removing all birches within 0.75 m radius around spruce, 3) removing all birches, and 4) no PCT (control). After three growing seasons of experiment establishment, we found no difference in volume production between plots where all broadleaves had been removed and plots where 2000 birches ha-1 were kept. As spruce main stems' production was not negatively affected by retaining 2000 birches ha-1 in PCT, this treatment might be a potential PCT strategy to combine high growth of main stems with the increased availability of forage for browsing animals.

Decades of purposeful breeding of Norway spruce (Picea abies (L.) Karst.) in the Northern Europe have resulted in up to 35% increase in wood production. Vegetative propagation of productive and robust elite clones can help to sustain high-quality timber provision of the species, which is facing various risks due to changing climate. For adequate accounting of genetic gains in growth models, the altered tree growth dynamics among different clones must be understood, yet essential information about the long-term growth dynamics up to the age of maturity of improved boreal trees is still lacking. We examined increment cores from sparsely-planted (5 × 5 m) clonal Norway spruce plantation in eastern Latvia at rotation-age (50 years) with delayed inter-tree competition, in order to disentangle the clonal effect on diameter growth-function parameters. Mixed-effect modelling approach for the diameter-age relationship was used, applying the clone as a random effect on the parameters of the Chapman–Richard base equation. The realized genetic gains for the diameter at breast height (DBH) at the final harvest age varied from -6.3 to +24.0% over the trial mean. All three model parameters were significantly affected by the clone, and their genetic coefficients of variation (CVg) ranged between 11.0 and 17.1%, with growth rate being the highest. The CVg of parameters exceeded the CVg of DBH (8.1%), hence suggesting a potential for genetic improvement of the asymptotic DBH and more rapid radial growth trajectory. We suggest further deriving and testing of the dynamic base-age invariant function for use in practical forestry and tree breeding, incorporating clone-specific set of genetic modifiers for the model parameters to improve the prediction accuracy for genetic entries with various selection gains. Furthermore, height growth reconstruction is underway in the trial to examine clone-specific growth differences and sensitivity to climate indices.

Planting density is an important factor affecting reforestation success and outcomes. Tree density impacts the renewal of forests and sustainability of their management. In boreal forests, mechanical site preparation is used before planting to improve soil conditions; creating microsites that ensure seedling survival and growth is essential to maintain ecological functions of forest ecosystems after disturbances. This especially true for sites prone to paludification, where the rapid accumulation of organic matter significantly reduces tree growth, and hence, affects forest productivity. However, the potential effects of mechanical site preparation in interaction with planting density remain unclear. Our objective was to understand these interactive effects on the composition of the understory and the growth of planted black spruce, in managed sites subject to paludification. The study was carried out in the Clay Belt region of northwestern Quebec, Canada, on a site made up of nine experimental sectors of approximately 20 ha each. After careful logging, sectors were treated by harrowing, disc-trenching or left unprepared (harvest-only). Each sector was then divided into two sub-sectors that were planted with black spruce seedlings, at a density of either 1200 seedlings/ha or 2500 seedlings/ha. The composition and diversity of vascular and non-vascular plants in the understory, soil fertility, and growth of the planted trees were evaluated 10 years after planting and interpreted as a function of site preparation and planting density. The results of this study will improve our knowledge on the effects of initial stand density and site preparation on tree and understory development in disturbed paludified sites.

Global warming may dramatically reduce the area of the boreal climate zone. The southern boundary of this zone, which is conventionally delineated by the 6°-isocline of biotemperature, is shifting northward, and the numeric experiments carried on the latest versions of the Earth System Models (ESM) suggest that the extension of this zone in Europe would be limited to Norway by the end of this century under the pessimistic scenario of climate change (SSP5-8.5). How long a Norway spruce forest may survive outside of the boreal climate zone? In the northwest of Moscow region (Russia) such forests can still be found, although this territory does not belong to the boreal climate zone since the second half of the XIX century. The study of spruce forests remained at the territories of this sort, delineated through processing of the historical climate data, may help to evaluate the resilience of spruce forests to the retreat of the boreal climate zone as projected by using ESM outputs.

Black spruce (Picea mariana) is one of the most common tree species in the boreal forest and is the second most harvested pulp species in Minnesota, USA, representing 648,000 ha of forest land. The primary disease agent of black spruce forests in Minnesota is eastern spruce dwarf mistletoe (Arceuthobium pusillum). While research exists on the pathology and life history of the mistletoe, little information is known about how mistletoe influences stand dynamics and subsequently forest management decisions. We used a unique approach to explore these unanswered questions with on-the-ground field sampling and surveys, focus groups and interviews with foresters and logging professionals. Vegetation data were sampled at multiple scales across northern Minnesota. At the state level, modeling of mistletoe presence and absence has proven to be difficult – with models detecting differences among black spruce stands which may be caused by numerous factors (productivity, past management practices, and mistletoe). At the stand scale, vegetation data were collected from 30 black spruce stands at various levels of mistletoe infection. The presence of mistletoe levels significantly increased tree species diversity. However, higher levels (> 50% of black spruce infected with mistletoe) did show high levels of tree mortality in all vegetation layers. High levels of mistletoe infection in black spruce stands was hypothesized to decrease harvest suitability. However, information collected from both foresters and logging professionals challenged this hypothesis. Forester survey results suggest a stand needs 50% or higher mistletoe infection before a tract will have challenges selling at auction. Interviews and focus groups with logging professionals suggest the degree of mortality is more important than the level of mistletoe during sales. While eastern spruce dwarf mistletoe does cause mortality of black spruce, it also can increase tree species diversity and thus potential resilience to changing climate conditions without impacting the ability of these stands to be actively managed.

Drought may become more frequent in northern latitudes and could reduce forest health and increase mortality. Trees can partially adjust in situ to changing environmental conditions, including heat and aridity, through plasticity of growth responses and physiological characteristics. This ability of trees to cope with drought events may also be related to memory effects from having experienced similar events in the past. Trees without prior exposure to drought may be more affected by water shortage. Such plasticity may exist in Norway spruce, an important timber species across northern Europe and eastern North America. This research investigates whether: 1) A two-season, artificial drought treatment in a randomized complete block design improved responses to a subsequent natural drought event in Sweden, and 2) if growth responses were linked to hydraulic traits of the xylem. Tree-ring measurements were used to assess drought resistance and resilience. Differences in drought resilience were compared between untreated control trees and trees that previously experienced an artificial drought from a rainfall exclosure treatment. Further, differences in resilience were tested for association with tree height and diameter as well as wood density and hydraulic wood structure. Results show that the prior exposure to artificial drought reduced diameter and height growth but increased resilience to a subsequent natural drought event. Additionally, this increased resilience is associated with thicker cell walls and smaller cell lumen, signifying acclimation by transitioning to a safer water-conducting system. These results suggest that, at the expense of height and diameter growth, Norway spruce may have some ability to adjust to drier conditions.

The ability of plantations to provide ecosystem services relies on interdependent actions, notably the control of competing vegetation to provide planted seedlings with adequate resource levels. While short-term results from silviculture trials can inform about resource acquisition and use by planted seedlings during the establishment phase, longer-term monitoring is required to develop integrated vegetation management strategies and decision support tools. Using a subset of plots from an experiment established in Ontario (Canada), we aimed at evaluating the 15th-y effects of herbaceous and woody competition on planted Picea glauca size and growth. The experiment comprised twelve plots representing three randomly distributed replicates of the following treatments: i) removal of woody and herbaceous vegetation; ii) removal of woody vegetation only; iii) removal of herbaceous vegetation only; and iv) no vegetation control. We achieved selective control of woody or herbaceous vegetation (or both) with a combination of manual clipping, weeding and directed foliar application of glyphosate. Seedlings were planted in May 2004 and measured periodically for height and diameter afterwards. Preliminary results suggest that 15 years following planting, treatments had a significant effect on height; the tallest trees were found in plots with herbaceous vegetation control only, followed by trees that had grown in plots with woody vegetation control only. Seedlings planted in plots subjected to removal of both woody and herbaceous vegetation were not significantly taller then those planted in control plots, a result of severe frost damages in the past. Annual growth rates in height between year 10–15 were maximized in plots with complete or woody vegetation control, and lowest in plots with no vegetation control. We observed a similar trend for 15th-y diameter. Further analyses including nutritional, soil, as well as microbial and plant community data will provide insights into the mechanisms responsible for treatment effects.

Spruce forests in logged sites mainly regenerate through a phase of deciduous species dominance. The aim of our study was to determine the influence of the forest edge on the number and growth of birch and spruce trees. The research was conducted in North-West Russia (64.38 N 41.78 E). We tallied the number and height of young spruce and birch plants along 28 transects each running for 100 m perpendicular to the forest–cutover edge (50 m into the cutover and 50 m into the forest). We divided each transect into 4 sections: forest, forest-side edge (8 m from the edge into the forest), cutover-side edge (8 m from the edge into the cutover), and cutover. The number of spruce and birch plants was counted in three height categories: small (up to 0.5 m), medium (0.5–1.5 m), and large (higher than 1.5 m). Two years after logging, the total amount of spruce regrowth in the forest section did not differ any significantly from the other zones, amounting to an average of 4000 plants ha-1. In the 3rd year after logging, the number of spruce and birch saplings in the cutover increased several-fold. The number of birch saplings in the cutover exceeded 70000 plants ha-1. Five and ten years after logging, favorable conditions for the emergence and establishment of spruce regrowth were found only in the transition zone between the forest and the cutover. There, the total amount of young spruce trees was 9000 ha-1. In general, the studies have confirmed that the remaining forest has a significant effect on spruce regeneration, and the impact zone covers a distance of 8–10 m – around the half-height of mature spruce trees. The mature spruce stand prevents the appearance and growth of deciduous trees.

Extensive climate-driven bark beetle disturbances destroy coniferous forests across Central Europe and North America. A minor proportion of trees, however, escape herbivore. Despite extensive literature dedicated to bark beetle processes, detailed understanding of host tree survival is still lacking. In this study, we investigate environmental and biotic factors related to tree resistance to bark beetle mass attacks. We used remotely sensed (Landsat 5 and Google Earth) and field data to uncover drivers of Norway spruce (Picea abies) survival during formidable bark beetle (Ips typographus) outbreak using logistic regression model fit in likelihood framework. The dataset comprised 598 trees, including 184 surviving (Last Trees Standing, LTS), and 414 reference trees originating from natural old-growth spruce mono-dominated forest that belongs to Bohemian Forest and is located at the border of Germany, Czechia and Austria. Results of clustering analysis showed non-random spatial pattern of LTS distribution within 12386 ha study area. Results of grouping analysis based on potential solar radiation, Topographic position Index, and Tasseled-Cap wetness index indicate that LTS tend to occur at higher reliefs on 1000 m scale. We hypothesized that competition limits tree carbon reserves required to mobilize induced tree defenses, while soil moisture availability strengthens tree vigor and resistance capacities. We assumed that under epidemic conditions bark beetles tend to attack larger potential host trees that provide substantial amount of feeding substrate to maintain growing population. We also hypothesized that self-shading, on the one hand, influences stem microclimate conditions and decreases amount of volatile compound emissions attractive for beetles, and, on the other hand, modifies temperature-dependent bark beetle behavior. Non-linear logistic regression results (pseudo-R2 = 0.85, bias = 0.99) show that tree survival probability decreases with increasing stand density and stem diameter, while trees with longer crowns growing in more mesic environments have higher chance to survive.

Study of natural variation is an efficient method to elucidate how plants adapt to local climatic conditions, a key process for the evolution of a species. However, it is challenging to determine the genetic basis of adaptive variation especially in forest trees which have large and complex genomes. Norway spruce is a shade tolerant conifer in which the requirement of far-red light for growth increases latitudinally northwards. In the current work, hypocotyl-length followed a latitudinal cline in response to SHADE (low red:far-red ratio). RNA-sequencing revealed differential gene expression in response to SHADE, between a southern and a northern natural population in Sweden. Exome capture included analysis of uniquely large data set (1654 trees) that revealed missense variations in coding regions of nine differentially expressed candidate genes, which followed a latitudinal cline in allele and genotype frequencies. These genes included five transcription factors involved in vital processes like bud-set/bud-flush, lignin pathway and cold acclimation, and other genes that take part in cell-wall remodeling, secondary cell-wall thickening, response to starvation and immunity. Findings from this work primarily suggests that the northern populations of Norway spruce are better adapted towards disease resistance under shade by up-regulation of lignin pathway that is linked to immunity and it forms a concrete basis for local adaptation to light quality in Norway spruce, one of the most economically important conifer tree species in Sweden.

Forests with Norway spruce (Picea abies (L.) Karst.) are secondary communities formed under the influence of centuries-long activity (logging, fires, and planting) in the central part of the Russian plain (the Moscow region). The study addressed the question: what the nature of spruce forests dynamics is and what are the prospects of their development within the transition zone from coniferous–broad-leaved to broad-leaved forests? The investigated area is in the Central part of East European (Russian) Plain – 35°10' - 40°15 'E, 54°12' - 56°55' N, its area is 4.58 million ha (taking into account the territory of "New Moscow" with an area of 0.15 million ha). Remote sensing data and modeling approach were applied to estimate the spatial structure and dynamics of spruce forests. The actual proportion of spruce and spruce – small-leaved forests according to our estimates is 21.7% from total forested area. It is shown that despite significant anthropogenic impact and high proportion of plantations in the composition of modern spruce forests (about 60–80%), their floristic and typological diversities correspond to such properties of zonal broad-leaved – coniferous communities. The direction and rate of succession dynamics in spruce forests are analyzed based on the current composition of populations of the main forest-forming species (spruce, pine, birch, aspen, oak, linden, ash). This allowed to develop the dynamic model (DM) of forest communities with the participation of spruce for several decades. We also developed the retrospective model (RM) of spruce forests dynamics for the 30-year period using historical Landsat 5 mosaics: the forward mosaic for the period 1990, and the hindward mosaic for the 2010. Field relevés (dated 2005-2019) were used as the training sample. Overall accuracy for an independent test sample (20% of the selected points) was 0.63. We compared RM with the results of the modern distribution of coniferous forests from our previous study which was based on Landsat-8 mosaics and on a MaxEnt method. The comparison of two models of succession dynamics (DM and RM) revealed the most noticeable and similar directions of forest dynamics. At the same time, we identified a set of features which indicate the risks of threats to the sustainable development of coniferous forests under the existing forest management regime in the Moscow Region. RM highlights the main trend of the forest cover transformation – the decrease of spruce forests under the insufficient care.