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Accurate knowledge of site conditions and their effects on regeneration establishment is important for selecting the most appropriate tree species and regeneration methods for a given regeneration site. This study examined the response of the first-year field performance of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth.) seedlings in boreal forests to variables available in open forest and natural resources datasets. Survival, height increment and damage of planted tree seedlings and the success of direct seeding of pine were analysed on a total of 284 plots (1000 m2) in 18 regeneration experiments established in 2020–2022 in southern and central Finland. The height increment of silver birch was higher than that of conifers, while the lowest mortality rate was found for spruce. In the generalised linear mixed models, topographic wetness index, soil texture, site type and growing stock at clearcut explained the species-specific survival and height increment of planted seedlings and the success of pine seeding. Low-cost, open geospatial data effectively provide useful details on the site conditions suitable for diversifying tree species composition in boreal forests instead of monocultures. [ABSTRACT FROM AUTHOR]

Hylastes species are known to cause damage to conifers in plantations in northern Sweden, and in recent years an increase in seedling damage has been observed in southern Sweden. However, there are few studies on Hylastes spp and the damage it can cause, so there is a lack of knowledge regarding pest management. In order to investigate an eventual interaction between damage by Hylastes spp and the more well-known Hylobius abietis (L) we registered damage by these species. Unprotected spruce seedlings were compared with seedlings protected from Hylobius abietis by a mechanical coating or with an insecticide. The effect of mechanical site preparation (MSP) was studied, with half of the seedlings being planted in unprepared soil and the other half after MSP. Both seedling protection and MSP significantly reduced the level of damage caused by Hylastes spp. MSP reduced the proportion of affected and killed seedlings and reduced the level of damage at the root collar. Protecting the seedlings reduced the level of damage, and no difference was found between seedlings treated with an insecticide and those provided with a coating. Similar responses were observed with both containerized and plug plus seedlings. In conclusion, measures against Hylobius abietis seem to also prevent damage by Hylastes spp. [ABSTRACT FROM AUTHOR]

This study examined the carbon (C) concentration of the major tree species (Scots pine, Norway spruce, and Birch) in Sweden based on destructively sampled biomass data. The examination was made using single trees and comprised three components: branches with needles, stemwood with bark, and stump with roots. We developed a weighted C concentration estimator accounting for fresh weights of tree components to infer the C concentration at the population level. Significant differences in C concentration (%) were found among species, with the highest in pine (50.671 ± 0.211), followed by spruce (49.518 ± 0.164) and the lowest in birch (49.347 ± 0.241). Additionally, the C concentration varied among tree components, regardless of tree size, growth rate, and site conditions. At the national level, we applied the estimated species- and component-specific C concentration constants to the measured total biomass of the major tree species from the National Forest Inventory. This extrapolation revealed that the average C concentration of major trees across all forestlands in Sweden was approximately 50.012%. These findings have significant implications for accurate C sequestration reporting in the LULUCF sector. [ABSTRACT FROM AUTHOR]

Hamra National Park in the province of Dalarna in central Sweden was established in 1909 to protect a unique unlogged old-growth forest. In 1922, Henrik Hesselman set up two permanent plots in Hamra to be able to follow the development of the forest over time. In 2022, we re-inventoried the Scots pine-dominated plot and found that (1) the number of trees in the plot almost doubled from 593 trees in 1922 to 1013 trees in 2022, (2) Norway spruces are starting to take over the initially Scots pine-dominated plot, (3) the basal area of dead trees has increased by 286% and (4) the variability in annual Scots pine growth has increased over the studied time period. Given this strong deviation from the original state of the forest, we suggest restoring part of the forest to its early-1900s state while allowing the permanent plot to evolve naturally. [ABSTRACT FROM AUTHOR]

There is growing interest in continuous cover forestry in Sweden. The historical domination of even-aged forest management means there is a need to focus on methods for transforming even-aged to uneven-aged stands. Practical conversion management today is highly adaptive, and the possibility of failures, such as persistent lack of tree recruitment, must be allowed for. We used simulations to evaluate various scenarios in which conversion management is introduced at different development stages in even-aged stands and then abandoned in favour of clear-felling. A shift towards an inverse J-shaped diameter distribution at the end of the simulations was most evident in northern Sweden and with an early introduction of conversion forestry. The largest losses were incurred in a scenario where the conversion management started with removing larger trees at pre-commercial thinning: it reduced the volume of production by up to 25% and, if clear-felled, resulted in a lower land expectation value than conventional management. Earlier decision to abandon conversion management reduced the losses, but the effect of timing was minor. In summary, the results indicate that conversion management could be started and abandoned without any major economic loss during the timeframe of a normal rotation. [ABSTRACT FROM AUTHOR]

Bark beetle (Ips typographus) outbreaks have the potential to damage large areas of spruce-dominated forests in Scandinavia. To define forest management strategies that will minimize the risk of bark beetle attacks, we need robust models that link forest structure and composition to the risk and potential damage of bark beetle attacks. Since data on bark beetle infestation rates and corresponding damages does not exist in Norway, we implement a previously published meta-model for estimating I. typographus damage probability and intensity. Using both current and projected climatic conditions we used the model to estimate damage inflicted by I. typographus in Norwegian spruce stands. The model produces feasible results for most of Norway's climate and forest conditions, but a revised model tailored to Norway should be fitted to a dataset that includes older stands and lower temperatures. Based on current climate and forest conditions, the model predicts that approximately nine percent of productive forests within Norway's main spruce-growing region will experience a loss ranging from 1.7 to 11 m3/ha of spruce over a span of five years. However, climate change is predicted to exacerbate the annual damage caused by I. typographus, potentially leading to a doubling of its detrimental effects. [ABSTRACT FROM AUTHOR]

Butt rot is a main defect in Norway spruce (Picea abies (L.) Karst.) trees and causes large economic losses for forest owners. However, little empirical research has been done on the effects of butt rot on harvested roundwood and the magnitude of the resulting economic losses. The main objective of this study was to characterize the direct economic losses caused by butt rot in Norway spruce trees for Norwegian forest owners. We used data obtained from seven cut-tolength harvesters, comprising ~400,000 trees (~140,000 m³) with corresponding stem profiles and wood grade information. We quantified the economic losses due to butt rot using bucking simulations, for which in a first case, defects caused by butt rot were included, and in a second case, all trees were assumed to be free of butt rot. 16% of trees were affected by butt rot, whereby butt rot tended to occur in larger trees. When butt rot was present in a tree, the saw log volume was reduced by 48%. Proportions of roundwood volume affected by butt rot varied considerably across harvested stands. Our results suggest that butt rot causes economic losses upwards of 7% of wood revenues, corresponding to € 18.5 million annually in Norway. [ABSTRACT FROM AUTHOR]

Allometric models based on limited sub-samples are widely used for predicting forest-scale information. Here, we develop allometric models for the branch surface area of the widespread conifer species Picea abies [L.] Karst. Branch surface area is a proxy for the capacity of tree branches to intercept and store water and air pollutants. Based on "probability proportional to size" sampling, we measured the surface area for 285 branches and then calculated the branch surface area of 30 trees (and their 3298 branches). We developed allometric models to estimate the total surface area of branches, as well as their number and diameters, for trees across a range of diameters (DBH), heights, and crown ratios (CR). We show that DBH and CR play significant roles in branch characteristics. The branch surface area was linearly related to the stand basal area. Reducing stand density will proportionally reduce interception capacity. The approach outlined here may help stimulate further studies (more species, regions, and management practices) required to optimize stand density for ecosystem services related to crown characteristics, such as hydrology, forage quality, and quantity or capacity for air pollutants. [ABSTRACT FROM AUTHOR]

This study's objectives were to suggest harmonised criteria for the definition of mixed forests for two Nordic countries, describe their principal mixture types, and provide an overview of their current extent. We used national forest inventory data compiled in Finland and Sweden, considering the forest available for wood supply (FAWS), excluding seedling and sapling plots before canopy closure. The definition of the mixed forest was based on the threshold criteria, which indicate the basal area proportion of the dominant tree species of the total in a stand. The proportion of mixed forests increased with higher threshold criteria: 21% to 42% in Finland and 24% to 49% in Sweden, as the threshold criterion was changed from 65% to 85%. With a threshold criterion of 75%, the area of mixed FAWS was 5.6 million ha (31% of FAWS) in Finland and 6.5 million ha (36%) in Sweden. The dominant mixture type was the pine-spruce-birches mixture (31%) in Finland and the pine-spruce mixture (29%) in Sweden. The proportion of peatland forest of mixed forests was similar in the countries: 9-10%. The mixed forests proportion increased from north boreal to hemiboreal, increasing with more mature development classes. [ABSTRACT FROM AUTHOR]

Taper models, which describe the shape of tree stems, are central to estimating stem volume. Literature provides both taper- and volume models for the three main species in Norway, Norway spruce, Scots pine, and birch. These models, however, were mainly developed using approaches established over 50 years ago, and without consistency between taper and volume. We tested eleven equations for taper and six equations for bark thickness. The models were fitted and evaluated using a large dataset covering all forested regions in Norway. The selected models were converted into volume functions using numerical integration, providing both with- and without-bark volumes and compared to the volume functions in operational use. Taper models resulted in root mean squared error (RMSE) of 7.2, 7.9, and 9.0 mm for spruce, pine, and birch respectively. Bark thickness models resulted in RMSE of 2.5, 6.1, and 4.1 mm, for spruce, pine, and birch respectively. Validation of volume models with bark resulted in RMSE of 12.7%, 13.0%, and 19.7% for spruce, pine, and birch respectively. Additional variables, tree age, site index, elevation, and live crown proportion, were tested without resulting in any strong increase in predictive power. [ABSTRACT FROM AUTHOR]

Cavity nesting birds depend on the availability of tree cavities for breeding, but the structure of the surrounding environment may also impact cavity occupancy. Here we investigated the effects of forest structure on occupancy rates of excavated cavities and similar-size nest boxes by cavity nesters in managed southern boreal forests in Finland. We recorded the occupancy over five breeding seasons (2017–2021) and derived forest structure parameters from high-resolution thematic raster maps. We found a high occupancy rate in nest boxes (81%), but lower rates in natural cavities excavated in forest interior, forest edges and retention trees (42-46%). The analyzes focusing on Paridae only revealed that the occupancy rates in nest boxes were decreasing with increasing amounts of Norway spruce and deciduous tree foliage biomass, and tree height, but increasing with the proportion of Scots pine. In forest interior cavities, we found a negative effect of stand age but a positive effect of the proportion of spruce. We conclude that the benefits of nest boxes can be maximized by considering specific forest parameters when deploying them. In excavated cavities the occupancy rates are likely more dependent on the varying internal quality than on the forest structure. [ABSTRACT FROM AUTHOR]

In the context of global warning, sustainable development, bioeconomy and circular economy, it is of great interest to find better valorizations of by-products of the wood processing industry. The aims of this study were to investigate the effects of the longitudinal position on the stem and of the silviculture on bark chemical composition of three softwood species used in wood industry. Bark was sampled at three different heights (top, middle and bottom) on the trunk of four trees of Picea abies, Abies alba and Pseudotsuga menziesii grown under different silvicultural treatments and subjected to analytical procedures to determine holocellulose, lignin, suberin, hemicelluloses, α-cellulose, ash and extractives contents. Contents of the different polymers tend in general to decrease slightly with tree height, while extractives content increased with height. These results were explained by higher amount of outer bark at the bottom of the trunk containing more polymerized materials and more unpolymerized free sugars in the young tissues at the top of trunk. The effect of the silvicultural treatment has been more difficult to characterize. Chemical composition of the bark differs slightly according to the position of sampling along the trunk. Suberin content is particularly important at the bottom of P. menziesii trees. [ABSTRACT FROM AUTHOR]

In a fertiliser experiment in a Norway spruce forest in SE Norway, four treatments were applied in a block design with three replicates per treatment. Treatments included 3 t wood ash ha−1 (Ash), 150 kg nitrogen ha−1 (N), wood ash and nitrogen combined (Ash + N), and unfertilised control (Ctrl). Treatment effects on understory plant species numbers, single abundances of species and (summarised) cover of main species groups were studied. Two years after treatment there were no significant changes for species numbers or abundances of woody species, dwarf shrubs or pteridophytes, nor for Sphagnum spp. in the bottom layer. The cover of graminoids decreased in Ctrl plots. Herb cover increased significantly in Ash + N and N plots due to the increase of Melampyrum sylvaticum. In Ash + N plots, mosses decreased significantly in species number, while their cover increased. Moss cover also decreased significantly in N plots. The species number and cover of hepatics decreased significantly in Ash and Ash + N plots. Hepatics cover also decreased in Ctrl plots. Both the lichen number and cover decreased in Ash + N plots. Single species abundances decreased for many bryophytes in fertilised plots. To conclude, fertilisation had modest effects on vascular plants, while bryophytes were more strongly affected, especially by Ash + N. [ABSTRACT FROM AUTHOR]

Stand-level growth and yield models are important tools that support forest managers and policymakers. We used recent data from the Norwegian National Forest Inventory to develop stand-level models, with components for dominant height, survival (number of survived trees), ingrowth (number of recruited trees), basal area, and total volume, that can predict long-term stand dynamics (i.e. 150 years) for the main species in Norway, namely Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and birch (Betula pubescens Ehrh. and Betula pendula Roth). The data used represent the structurally heterogeneous forests found throughout Norway with a wide range of ages, tree size mixtures, and management intensities. This represents an important alternative to the use of dedicated and closely monitored long-term experiments established in single species even-aged forests for the purpose of building these stand-level models. Model examination by means of various fit statistics indicated that the models were unbiased, performed well within the data range and extrapolated to biologically plausible patterns. The proposed models have great potential to form the foundation for more sophisticated models, in which the influence of other factors such as natural disturbances, stand structure including species mixtures, and management practices can be included. [ABSTRACT FROM AUTHOR]

We studied tree-level dynamics (stem slenderness and growth) in spruce- and pine-dominated stands after intermediate commercial thinning of different type (low, crown normal, and crown strict) and intensity (standard and extreme), for two 5-years growth periods. Thinning treatments were included in modeling as numerical variables based on how they changed the stand- and tree-level conditions (in terms of mean diameter of remaining trees and basal area of larger trees removed). Stem slenderness significantly decreased with time for both species and all types only in the extreme intensity (excluding low thinning for pine). Regarding basal area growth, for both species it was slightly higher in low than crown thinning, and much higher in extreme intensity for all thinning types. Pine had a lower basal area growth in the second period after thinning compared with the first one. Height growth differences were not found across treatments. Concluding, extreme thinning increased individual tree basal area growth and decreased stem slenderness for both species compared with thinning carried out according to the standard guidelines. Across types, there were only small differences, hence crown thinning seems a viable option to the widely used low thinning in Fennoscandia. [ABSTRACT FROM AUTHOR]

Precision forestry allows decision-making on tree level or pixel level, as compared to stand-level data. However, little is known about the importance of precision in thinning decisions and its long-term effects on within-stand variation, stand economy and growth. In this study, silviculture was optimized for Net Present Value (NPV) in 20 conifer-dominated forest stands in hemi-boreal southern Sweden. The precision-thinning approach, Precision Thinning (PT), is compared with a stand-level approach, Stand Level Thinning (SLT) that is optimized for the same criteria but based on stand-level data. The results suggest no substantial long-term benefit or drawback in implementing thinning decisions based on pixel-level data as compared to stand-level data when optimizing stand economy. The result variables NPV and Mean annual increment of living stem volume (MAInet) were not higher for PT than for SLT. The within-stand variation in basal area (m2/ha−1) was lower at the end of the rotation compared to the start of the simulation for both SLT and PT. At the end of the rotation, SLT had higher variation in basal area compared to PT. However, pixel-level information enables adapting the silviculture to the within-stand variation which may favour other forest management goals than strictly financial goals. [ABSTRACT FROM AUTHOR]

Short-term trials on cultivated soil were planted with families of Norway spruce that had shown epigenetic memory effects in early tests up to age two years. Measurements and assessments were made of phenology traits, tree heights and stem defects until age 16 years in these trials. The memory effects of the temperature conditions during embryo development and seed maturation were confirmed for the timing of bud flush and for start and cessation of shoot elongation at age six years. The mean differences in timing of these events caused by temperature treatments were on average less than two days. They were considerably larger for families with strong effects on terminal bud set at the end of the first growing season. The memory effects did not result in a prolonged shoot growth period, nor did they affect height growth. Interaction effects expressed in adaptive traits between factorial treatments of temperature and daylength during seed production were large in the short-term trial and were still present at age nine years. The results presented demonstrate that strong memory effects observed in early tests may also be expressed in phenology traits for at least the next five growing seasons. [ABSTRACT FROM AUTHOR]

To develop recommendations for tree selection in Continuous Cover Forestry (CCF), access to valid tools for simulating growth at individual tree-level is necessary. To assist efforts to develop such tools, in this study, long-term observation data from two uneven-sized Norway spruce plots in southern Sweden are used to evaluate old and new individual-tree growth models (two established Swedish models, two new preliminary models and included as a reference, a Finnish model). The plots' historical management records and site conditions are the same, but their last thinning treatment differs. Observed diameter increment at tree-level is investigated in relation to treatment. Individual tree growth residuals of tested models are evaluated in relation to tree diameter, treatment, projection length and sensitivity to the predictor mean stand age. Furthermore, the relations between displayed residuals and basal area local competition are analysed. The analyses indicate that active thinning made annual diameter increment independent of tree diameter above a threshold level, while the absence of thinning supported a concave relationship. All tested models displayed a significant linear bias leading to overestimation of small trees' growth and increasing underestimations of larger trees' growth with tree diameter. All distance-independent models displayed residual trends related to local competition. [ABSTRACT FROM AUTHOR]

Various site preparation methods are used in Swedish forestry. However, some methods can lead to unnecessary disturbance, which could be avoided by using variables from digital elevation models in management decisions. The current study aimed to investigate how different site preparation methods, and their intensities, affect Norway spruce (Picea abies (L.) Karst.) regeneration. Additional aims were to clarify how these methods affect soil disturbance and vegetation development, along with how variables from digital elevation models could be used in silvicultural decision-making. Experimental sites were established in southern Sweden to assess five different site preparation treatments with different planting densities: (1) conventional disc trenching 2500 seedlings/ha (DT2500); (2) low intensity disc trenching 1250 seedlings/ha (LDT1250); (3) low intensity disc trenching 2500 seedlings/ha (LDT2500); (4) low-intensity patch-wise 1250 seedlings/ha (PW1250); and (5) patch-wise 2500 seedlings/ha (PW2500). Site preparation intensity had no effect on seedling growth and, survival or vegetation development; the tested treatments differed in terms of soil disturbance. Planting spot properties and weather conditions influenced the seedling performance. DTW and slope could not substantially explain either seedling growth or survival. The results indicate that the choice of site preparation method should consider flexibility when planting while adapting the level of disturbance accordingly. [ABSTRACT FROM AUTHOR]

When modelling forest growth, capturing the effects of climate change is needed for reliable long-term predictions and management choices. This remains a challenge because commonly used mensurational forest growth and yield models, relying on inventory data, cannot account for climate change effects. We developed hybrid physiological/mensurational basal area growth and yield models, which combine physiological response to climatic conditions and empirical relations. We included climate and site effects by replacing time with light sums of photosynthetically active radiation and modifying the latter with monthly soil water, vapour pressure deficit, temperature, and frost days. When parameterised with permanent sample plot data for Scots pine and Norway spruce across Sweden, the hybrid models could reproduce observations well, although with no increase in precision compared with time-based mensurational models. When considering different climate scenarios, a significant impact on productivity from climate change emerged. For example, a 2 °C warming enhanced Scots pine production by up to 14% in regions where temperatures were originally cooler and soil water deficit was low (i.e. northwest Sweden), but depressed it, up to 9%, elsewhere. Hence, climate-sensitive models that take local variations into account are necessary for accurate predictions and sustainable forest management. [ABSTRACT FROM AUTHOR]

How seedling mortality and browsing affects species composition of regenerating forests has been mostly studied on a small scale. Yet, large-scale analyses based on extensive data are essential for robust prediction of species composition in young forests. In this study, we used a dataset from a national inventory of young forests (1–4 metres in height) to investigate the species composition of young forests across Sweden. We found that most of the regenerated forest area (almost 90%) was planted with Norway spruce (southern Sweden) and Scots pine (northern Sweden). Regeneration of Norway spruce was generally relatively successful but as a consequence of seedling mortality and browsing, almost 40% of the area regenerated with Scots pine will probably not develop into pine-dominated stands. Thus, low survival of Scots pine seedlings and trees can profoundly change the trajectory of species composition of the young forest from what was originally intended, and a large proportion of the young stands may develop into mixtures of conifers and broadleaves. While such mixtures may benefit certain biodiversity and ecosystem services, a loss of Scots pine dominated stands may also have adverse impacts on the economic returns as well as pine-dependent biodiversity and recreational values. [ABSTRACT FROM AUTHOR]

Old trees are important for biodiversity, and the process of their identification is a critical process in their conservation. However, determining the tree age by core extraction, ring counts, and eventually, cross-dating by means of dendrochronology is labor-intensive and expensive. Here we examine the alternative method of estimating determining tree age by visual characteristics for old Norway spruce and Scots pine trees. We used forest stands previously identified as "Old tree habitats" by visual criteria in Norwegian boreal forests. The efficiency of this method was tested using pairwise comparison of the age of core samples from trees within these sites, and within neighboring sites. Age regression models were constructed from morphological traits and site variables to investigate how accurately old trees can be detected. Cored trees in the Old-tree habitats were on average 41.9 years older than compared to a similar selection of trees from nearby mature forests. Several characteristics such as bark structure, stem taper and visible growth eccentricities can be used to identify old Norway spruce and Scots pine trees. Old trees were often found on less productive sites. Due to the wide range of environments included in the study, we suggest that these findings can be generalized to other parts of the boreal zone. [ABSTRACT FROM AUTHOR]

The influence of thinning on growth, development, and yield of a spruce understory and a pine overstory was examined based on an experiment including five stands in southern Finland. Two thinning intensities (regular and heavy) were applied to the pine overstory. They were combined with four treatments in the spruce understory: total removal, retention of 800 and 1600 stems ha−1, and untreated. The plots were remeasured at 5-year intervals during the monitoring period of 10–15 years. The results indicated that thinning of the pine overstory significantly promoted the diameter growth of the spruce understory trees throughout the 10–15-year study period without notable delay, and height growth with a substantial lag during the first 5-year period. The influence was swifter and greater with heavier thinning. Thinning of the understory did not influence the height growth of the dominant understory spruces or the growth of the overstory. Complete removal of the understory resulted did not consistently influence growth of the overstory. It was concluded that a spruce understory seemed to thrive and grow relatively well under an overstory of pine, but repeated thinnings in the overstory were required to sustain understory vitality and growth in a prolonged two-storied situation. [ABSTRACT FROM AUTHOR]

In Fennoscandia, mixtures of Norway spruce (Picea abies Karst.) and Scots pine (Pinus sylvestris L.) are of increasing interest, since they may deliver simultaneously a wide variety of benefits. However, there is still lack of information on how young mixed stands in managed production forests would develop under even-aged management with artificial regeneration of spruce. We inventoried ten such stands (age range: 8–26), with soil properties, tree characteristics, and locations recorded in three plots. In each plot, five sample trees of both species were selected, and their past diameter and height growth were reconstructed through stem analysis. We compared species-specific mean stand parameters, and we modeled the individual tree growth. Spruce and pine had reached similar mean size, with only slight differences. The spatial distribution of the two species was even across the plots. Only 8% and 1%, respectively, of the total pine and spruce trees were damaged, with browsing the most common damage cause (62% for pine). The modeling results suggest that pine had only a small competitive advantage on spruce, and less so in higher fertility sites. Our observations showed that it is possible to develop single-storied pine–spruce mixture with the help of careful management. [ABSTRACT FROM AUTHOR]

Treatments added to young conifer stands aiming to compensate for the loss of nutrients and alkalinity associated with whole-tree harvesting for bioenergy purposes have the potential to affect the growth of competitors to the conifers. Three different nutrient compensation treatments were applied to a young Picea abies (L.) Karst. stand in south-west Sweden, 2 or 3 years following final felling. The treatments were; fine fraction of harvest residues (15 Mg dw ha−1); granulated wood ash (4.1 Mg dw ha−1); nitrogen-free vitality fertiliser (twice 1.5 Mg ha−1); untreated control. Root biomass and total biomass of graminoids (mainly Deschampsia flexuosa (L.) Trin) were significantly greater in the wood ash and vitality fertiliser treatments than in the residues and control treatments. The aboveground and coarse root biomass of naturally regenerated birch (Betula spp.) and the aboveground biomass of dwarf shrubs (mainly Calluna vulgaris (L.) Hull.) and bottom layer were not affected by the treatments. Calcium and magnesium concentrations in the aboveground biomass of graminoids and phosphorus concentration in the biomass of bottom layer were significantly the highest in the vitality fertiliser treatment. Thus, nutrient compensation with vitality fertiliser or granulated wood ash may increase competition from graminoids in the establishment phase. [ABSTRACT FROM AUTHOR]

Stump removal is considered as the most effective method to reduce losses caused by root rot fungi, including Heterobasidion root rot. To evaluate the persistence of Heterobasidion spp. in root fragments left on site after stump removal, and to analyse the ecological impact of stump removal, five permanent sample plots were established in Latvia and samples were taken immediately after stump removal and 6 years later. In total, 1008 roots of 200 Picea abies stumps were measured and sampled immediately after stump removal. In total, Heterobasidion was detected in 0.7% of healthy looking roots, 2.0% of discoloured roots and 21.4% of decayed roots. Six years later, a total of 203 root fragments were collected in stump removal areas, and Heterobasidion was isolated from 1.5% of the collected root pieces. Fungal diversity was higher in root fragments collected in sample plots 6 years after stump removal compared with fungal diversity in roots immediately after stump extraction, and the species were significantly different. In conclusion, stump removal could be used in areas heavily infected by root rot fungi, and this method will likely not have a negative effect on the total amount of saproxylic fungi. [ABSTRACT FROM AUTHOR]

Admixtures of birch in Norway spruce plantations are being promoted as a means to increase habitat and species diversity. The implications of this mixture were analysed with regional survey data from southern Sweden. Permanent sample plots from the Swedish National Forest Inventory (NFI), with Norway spruce and admixture of birch, were used to describe the temporal trends in the admixture, regarding species composition and competitive strength. Observations from thinned plots show a higher harvest removal in birch (35%) than for Norway spruce (19%). Observations without thinnings in the period before measurement showed that individual birch tree growth was lower compared to Norway spruce and it decreased even more with increasing stand age and competition. In addition, a complementary field survey, with multiple distributed sample plots in each stand, was used to detect within-stand variation of species composition and density. Although within-stand heterogeneity was larger in mixed stands in terms of species composition, it was not different from Norway spruce monocultures in terms of stand density. These two surveys show that the admixture of birch, for several reasons, decreases over stand age and although birch increases tree species diversity, it does not necessary imply a change in density. [ABSTRACT FROM AUTHOR]

The aim of this study was to analyze and compare the performance of Norway spruce seed sources from Swedish stands of East European origin (SweEast) with material from Swedish (SweSO) and East European (EastSO) seed orchards, and with material from Swedish (SweS) and East European (EastS) unimproved stands. The seed sources were field tested at six locations in southern Sweden and assessed for growth and phenology. The assessment of growth traits indicated that trees from SweSO and EastSO had 9–15% greater growth with respect to tree height and diameter in comparison to trees from Swedish local unimproved stands (SweS). Trees from SweEast and EastS showed around 5–7% greater growth. With respect to phenological traits, the expected later bud burst for EastS and EastSO in comparison to SweS, SweSO and SweEast was verified. However, SweEast exhibited earlier bud burst compared to EastS than what could be explained by pollination by Swedish pollen. This was explained by early land race formation for that trait. A strong positive correlation was observed between bud burst and frost damage, which indicates that earlier bud burst does indeed increase the risk of damage from late spring frost at frost-prone sites. [ABSTRACT FROM AUTHOR]

The effect of site preparation (mixed mounding and removal of the humus layer) under a shelterwood of mixed boreal forest along a forest interior-edge gradient on Norway spruce (Picea abies) seedlings was studied two years after planting. Mounds had a positive effect on root development, ectomycorrhiza formation and the absorption of nitrogen (N) and phosphorus (P) in the seedlings, and augmented their survival, growth and biomass. Humus removal had an adverse effect on the root biomass and ectomycorrhiza formation. A decreased soil fertility after the removal of humus led to a low N and P content in the seedlings. Two years after planting, humus removal had not affected the growth of the seedlings, but reduced their biomass. The influence of the forest edge, compared to the interior plot, was mostly associated with a decrease in the stand density, reduced amount of litter and increased light availability for the seedlings. [ABSTRACT FROM AUTHOR]

The effects of early selection in a nursery on field performance were studied in an experiment comprising 2665 cutting-propagated clones of Picea abies (L.) Karst, deriving from 151 half-sib families. The clones were selected from 13,050 seedlings that were evaluated genetically using a randomized block design and measurements of height and growth rhythm in the nursery. The selected clones were assigned to six groups based on various criteria related to growth and phenology and to a comparison group of randomly selected clones. A group selected for height in the nursery gave an average gain in height after 6 years in the field of 9.1% compared with the randomly selected clones. Purely visual selection of plants with superior height, without considering the results of genetic evaluation, gave a gain of 3.8%. The gain in diameter after 12–14 years in the field was about two percentage units less but followed the same pattern. Other groups showed intermediate or less gain. Non-additive effects, expressed as clone-within-family effects, made substantial contributions to the total genetic gain. A test design that allows for genetic evaluation in the nursery appears to be a realistic option for achieving substantial gains in growth. [ABSTRACT FROM AUTHOR]

Norway spruce (Picea abies) is a widely used Christmas tree species in the Nordic countries. Postharvest needle retention is an important characteristic for Christmas trees and compared to many fir (Abies) species, Norway spruce has poor postharvest needle retention. This trait is one of the most important qualities in choice of natural versus plastic trees. In this study, current year shoots were cut from 30 Norway spruce seedlot sources, including the most widely used Norwegian Christmas tree provenances, and tested to identify genetic variation in postharvest needle retention. Current year shoots were collected from one field in November and December 2018, and from three fields in October, November and December 2019. The current year shoots were displayed indoors under controlled conditions and allowed to dry. Differences in postharvest needle retention were seen between seedlots, harvesting dates and locations. Our study indicates possibilities of selecting for improved postharvest needle retention in Norway spruce seed sources. Furthermore, postharvest needle retention should be considered as one characteristic to add in the ongoing Norway spruce Christmas tree breeding program. [ABSTRACT FROM AUTHOR]

Knowing credible records of harvested timber is in the interest of the forest owner, forest entrepreneur and timber-sector stakeholder. Therefore, the objective of the research was to determine the share of unrecorded Norway spruce timber volume in length allowance on the total timber volume produced by harvester technology in Czechia. We analyzed 176,980 merchantable logs (total volume of 10,333 m3) produced by 15 harvesters. Primary data were obtained from.stm files. Logs were categorized into five grades according to metric and qualitative requirements of the customers, also butt logs were distinguished. Statistical analysis were processed in the Statistica 13 package. Results showed that 1.99% of the volume of produced timber were excluded from the primary forestry records. Mean unrecorded volume of length allowance to assortments that contained both the cross-cut and cutting window allowances, varied from 2.99% up to 3.16%, while 0.27% to 0.46% of volume were unrecorded for those assortments that contained only the cutting window. In higher quality grades, we found shorter logs had a higher mean relative volume of length allowance than longer logs. The mean relative volumes of length allowances also varied between butt and other logs. [ABSTRACT FROM AUTHOR]

Effects of species composition on the growth of Norway spruce – Scots pine mixtures had earlier only been studied in unthinned stands. Individual-tree thinning responses in mixed stands were studied to test for the presence of mixture effects in more open stands. Data were collected from 28 temporary sample plots with varying species proportions in 7 thinned spruce-pine stands on medium fertile sites in Eastern Norway. Effects of neighborhood species composition on the individual-tree basal area growth before and after thinning were tested for to detect mixture effects. Spatially-explicit competition indices were used to describe release during thinning in the growth models. Neighborhood species composition only had a minor effect on the thinning response of spruce. Growth before thinning of both species and the thinning response of pine were not affected by species composition. Release had a strong effect on the thinning response of both species. Low density of the studied stands and the more dominant position of pine compared to spruce in mixture, even after the thinning from below, explained some of the observed effects. [ABSTRACT FROM AUTHOR]

Phenotyping of genetic resources that are used for development of new improved and adapted forest reproductive materials is costly. Therefore, high-throughput-phenotyping from a standard equipped unmanned aerial vehicle (UAV) with a RGB (red, green, blue) camera was used to develop a canopy height model (CHM) of a dense field trial of 15-year-old trees of Norway spruce. The site represents a typical situation of genetic testing on abandoned farm field land, where spacing between trees often are around 1-1.5 m. The CHM was used to estimate total height, intra-annual height growth and phenology of individual trees. The estimates were based on individual tree grid cells assigned according to the original planting grid. Intra-annual growth and phenology could not be estimated accurately, whereas total tree height to the uppermost whorl was accurately estimated provided that the trees were correctly identified. However, the apices of suppressed trees were often misidentified due to overhanging branches from more dominating neighboring trees. The method represents a cost and time efficient alternative to manual height measurements of the intermediate and dominating trees in closed stands. The accuracy is sufficiently high for most breeding purposes when total tree height is the target trait. [ABSTRACT FROM AUTHOR]

A method for simulation of distributions of structural timber properties based on geographical data and stand-level forest inventory data is presented. The method is based on Monte Carlo simulation of randomly selected sites from volume distributions of standing timber, in our case from the Norwegian National Forest Inventory. Simulation models of density, modulus of elasticity and bending strength were estimated from data from 2369 boards of Norway spruce from 27 sites in Norway. The models were estimated as mixed models including covariate models with fixed effects of latitude, altitude, site index and stand age, random site effects and residual variances, representing the within-site variances. Correlations between the simulated properties were obtained by transformation of the random effects in the simulations. The transformations were based on Cholesky decomposition of the correlation matrices of the random site-effects and the residuals of the simulation models. The simulations provide distributions for timber from each selected site and from all selected sites within defined areas, with different limitations on geographical data and stand-level forest inventory data. Simulations of Norway spruce from Eastern Norway are presented for demonstration, comparing timber from maturity classes, altitudes and site indices. [ABSTRACT FROM AUTHOR]

Tree biomass models are increasingly needed for the estimation of carbon storage and for testing and parameterizing process-based growth models, but most biomass models have been estimated using data from even-aged stands. Here we took measurements from individual Norway spruce trees grown in uneven-aged stands in Southern Finland to characterize tree structure and to estimate the biomasses of tree components. Using the data, we tested various structural biomass equations developed for even-aged stands for their suitability to uneven-aged stands. The test trees had longer crowns than usually found in an even-aged Norway spruce stand, ranging from 55 to 85% of total tree height. The average proportion of total biomass in branches and foliage was 13.8 % and 7.0 %, respectively. The average wood density of the test trees was slightly higher than that reported for Norway spruce trees of comparable size. The structural relationships found in trees under even-aged management were applicable to trees growing in uneven-aged stands but required re-parameterization. In particular, the trees had higher branch and stem biomass than trees of same stem and crown dimensions on average in even-aged stands. The relationship of crown ratio and the slenderness index on an uneven-aged stands also differed from those reported in even-aged stands. [ABSTRACT FROM AUTHOR]

Growth data from 15 progeny trials were analyzed to assess realized and expected genetic gains associated with improved Norway spruce (Picea abies Karst.) stock in southern Finland. The study materials included 257 seedlots originating from 9 wild stands and 17 seed orchards. The measurement data were collected between 22 and 30 years of age. First-generation seed orchard progenies showed a clear superiority over unimproved trees with a realized genetic gain of 8.4% in height growth, 9.0% in diameter growth, and 20.6% in stem volume growth. The respective genetic gains expected from 1.5-generation seed orchards were 12.8%, 13.5% and 36.9%. Stem slenderness and survival did not differ between groups of improved and unimproved trees. The interaction between genetic groups and sites was insignificant for all the traits, suggesting overall robustness of the gains across environments. The results do not include the additional genetic gain due to genetic thinnings and thus, they are likely to underestimate the currently realizing gains from genetically thinned first-generation seed orchards. The results are suggested to be primary information for further studies needed to model growth and yield of genetically improved Norway spruce stands over a full rotation. [ABSTRACT FROM AUTHOR]

A new stand-level growth and yield model, consisting of component equations for stand volume, basal area, survival, and dominant stand height, was developed from a dataset of long-term trials for managed thinned and unthinned even-aged Norway spruce (Picea abies (L.) Karst.) forests in Norway. The developed models predict considerably faster growth rates than the existing Norwegian models. Further, it was found that the existing Norwegian stand-level models do not match the data from the thinning trails. The significance of thinning response functions indicated that thinning increases basal area growth while reducing competition related mortality. No significant effects of thinning were found in the dominant stand height growth. Model examination by means of cross-validation indicated that the models were unbiased and performed well within the data range. An application of the developed stand-level model highlights the potential use for these models in comparing different management scenarios. [ABSTRACT FROM AUTHOR]

Uneven-aged forest management has attained increasing popularity. It may benefit biodiversity, buffer against pests and abiotic damages, decrease runoff from clearcuts and improve recreational values. We studied how gap cuttings and single-tree selection cuttings influence browsing damage in spruce-dominated forests in south-central Finland. Overall, browsing damage was especially frequent in aspen and rowan, but also in birch. The larger the basal area left in harvesting, the lower the browsing pressure on birch and rowan; neither the harvesting method nor the seedling density had an independent effect on browsing damage. Although larger tree retention levels may reduce browsing damage, the regeneration and recruitment of shade-intolerant broadleaved trees may be compromised. [ABSTRACT FROM AUTHOR]

In drained forest sites, ditch cleaning (DC) may be needed to restore the drainage function of ditches and maintain favourable growing conditions. The main aims of this study were (i) to estimate the growth responses of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst) stands following DC, and (ii) to test the hypothesis that stand stocking should be less than 150 m3 ha−1 at DC to obtain a growth response. This survey included 14 ditched stands in Sweden on both mineral and peat soils. The methodology was based on evaluating growth rates before and after the DC operation (growth ratio), reconstructing the growth by taking increment cores from the tree trunks. The measured growth was related to growth derived using a growth simulator as if DC had not been conducted. The results showed an average growth increase of 1.6 m3 ha−1 yr−1 for about 25 years after DC in the stands containing 50–200 m3 ha−1. The growth response appeared to be positively related to stand age, trees ha−1 and site index, and negatively related to stand volume, supporting the hypothesis that stand stocking is an important factor to consider when assessing the need for DC. [ABSTRACT FROM AUTHOR]

In Sweden, there is a lack of knowledge about nature conservation management (NCM) practices in voluntary set-aside forests. Estimates indicate that, for unknown reasons, only a small proportion of the NCM needed is carried out. The aims of this study are to (1) describe current practices for NCM of voluntary set-aside areas in Sweden and (2) identify factors affecting whether NCM of these areas is carried out. Twenty-seven semi-structured interviews were held with professional forestry practitioners and the responses analysed applying thematic analysis. NCM in Sweden generally has two main aims: (1) creation of dead wood and (2) promotion of domestic broadleaf tree species. Simplified, these aims are attained through removal of Norway spruce (Picea abies (L.) H. Karst.). The decision to implement NCM is influenced by few incentives and many barriers. Incentives include certification scheme obligations and commitment from dedicated individuals, while barriers include weak internal company incentives, the experienced or anticipated risk of high costs, and experienced or anticipated criticism from internal company experts or public actors. Based on the results, a set of managerial implications was drawn up, aimed at increasing the extent of NCM. [ABSTRACT FROM AUTHOR]

In Nordic climates, the weather allows a narrow time window during spring and summer for forest seedlings to be transplanted from indoor growth to outdoor conditions. If a new method for year-round cultivation under LED lamps is to be successfully introduced in forest nurseries, a cold storage phase for batches produced outside of the vegetation period needs to be included in the concept. Different short-day treatments for induction of cold hardiness in very young seedlings of Picea abies and Pinus sylvestris cultivated solely under LED lamps were investigated. The study compared a combination of two photoperiods (5 h or 8 h) at three different temperatures (5°C, 10°C or 20°C) applied during five weeks. Chlorophyll fluorescence, shoot electrolyte leakage and molecular testing for gene expression of cold acclimation were used to assess the treatments. After a period of three months in cold storage at 2°C, the vitality of the seedlings was evaluated using a root growth capacity test. Lower temperatures during the treatments, especially for Pinus sylvestris, had a significant effect on inducing cold hardiness. The results showed that the photoperiod should not be overly reduced to allow photosynthesis and generation of carbohydrate reserves but it could be optimized to reduce electricity consumption. [ABSTRACT FROM AUTHOR]

Norway spruce (Picea abies (L.) H. Karst) and Scots pine (Pinus sylvestris L.) have different site preferences, but silvicultural recommendations for their regeneration at planting (including site preparation) are often the same. Thus, there is a clear need for greater understanding of species-specific interactions between site preparation and site properties. To meet this need, the species' growth and survival have been monitored at both fertile and poor sites in northern and southern Sweden. At each of these sites, effects of three types of site preparation – removed humus (RH), deep soil cultivation (DSC) and control (C, no site preparation) – were compared. Results show that Scots pine grew more rapidly initially than Norway spruce, and DSC site preparation promoted growth of both species. However, on poor sites there was a delay in growth responses. In addition, removal of organic material in the RH treatment caused a sustained growth check of Norway spruce, but not for Scots pine. This study confirms that it is beneficial to use site preparation as it increases the survival of both species and may increase growth. However, site preparation methods that reduce the amount of organic material in the planting spots should be avoided for Norway spruce. [ABSTRACT FROM AUTHOR]

The emulation of natural disturbances in harvesting has become a widely accepted approach to reach ecologically sustainable forest management. The purpose of this study was to examine the responses of polypore fungi (species richness and composition) on four different cutting methods (selection, gap, patch, and clear-cutting) plus uncut controls, and the creation of high stumps and cut logs in combination with harvesting. Polypores were inventoried one year before, and two and seven years after cutting. A total of 71 polypore species were found, but no red-listed species were recorded seven years after cutting. Irrespective of the treatment, the variation in polypore richness was best explained by the number of deadwood objects in the stands. Species richness per deadwood object was the highest on natural logs. Species richness per volume of spruce deadwood was the highest on small-diameter deadwood and stumps, intermediate on natural logs and lower on cut logs and high stumps. These results indicate that cut logs created in harvesting cannot compensate the loss of deadwood in cutting and energy wood harvesting. Our results demonstrate the difficulty in rapidly creating habitats for red-listed polypores in commercially managed forests. [ABSTRACT FROM AUTHOR]

Foresters need to estimate bark thickness accurately in order to know the merchantable timber volume. Therefore, we developed a precise model for double bark thickness estimation that can be used with harvesters. We fitted a line to data from the Czech standard for bark deductions of Norway spruce (Picea abies (L.) Karst.) based on over-bark midspan diameters. Our model provided smaller deviations from the currently used polynomial model than other methods of bark thickness estimation. Only the diameter class method provided similar results. The mean absolute error (MAE) of the double bark thickness was 0.37 mm for our model or 0.48 mm for the diameter class method. The root means square error (RMSE) in this dataset was 0.43 mm or 0.56 mm respectively. We tested the deviations from the polynomial model on data from 22,442 spruce logs, gathered during forest harvesting in Czechia. Our model provided MAE of 0.34 mm and RMSE of 0.40 mm. Diameter class method provided MAE of 0.38 mm and RMSE of 0.43 mm. We concluded that our model is suitable for practical use in the Czech Republic. Its implementation will allow precise, automated log scaling, reducing at the same time the need for manual scaling. [ABSTRACT FROM AUTHOR]

Autumn sown small seedlings for later transplanting into large containers have been introduced in Swedish forest tree nurseries. Containerized transplants of Norway spruce (Picea abies (L.) Karst.) from three Swedish nurseries were frozen stored during the autumn of 2014 to find out storability and post-storage vitality. Seedling storability was determined by measuring electrolyte leakage after freezing shoots to −25°C (SELdiff−25), by measurements of dry matter content (DMC) of seedling shoots and by the commercial molecular test ColdNSure™. Vitality of seedlings after storage was determined by measuring the leakage of electrolytes from shoots (SEL), and seedlings were also tested in regrowth tests. All three methods for storability assessment gave similar predictions, except in one case where DMC showed "not storable" for successfully stored seedlings. Our results indicated that young transplants can be successfully short term stored before reaching the target levels for safe long-term storage of conventional seedlings. Early storage of young transplants resulted in low post-storage survival and vitality expressed as root growth capacity and shoot electrolyte leakage (SEL). A prolonged duration in storage generally resulted in lower survival as well as lower root growth capacity and higher levels of SEL, especially for seedlings stored at earlier dates. [ABSTRACT FROM AUTHOR]

Genetically improved Norway spruce (Picea abies L. Karst) has been extensively used in operational plantations in Sweden. However, there have been few studies that aimed at verifying the realized genetic gain over a longer time span in plots established with one genetical entry. Two experimental series at six sites in southern Sweden, established purely for this purpose, were assessed. Early height growth of 10 Norway spruce seedlots of different genetic levels was compared. There were significant differences in height at the age of 5 and 8 years between improved and unimproved seed sources and the differences between most advanced material from the breeding front, represented by full-sib crossings of selected plus-trees, and unimproved Swedish spruce were 36% and 30% at the age of 5 and 8 years, respectively. At the same ages, the trees originating from the second round of seed-orchards were 25% and 21% higher than unimproved material. There were also about 20% differences between the best and worst tested full-sib families, indicating large possible gain in the new generation. The study confirmed earlier estimates of genetic gain levels of different seed sources in the breeding program for Norway spruce. [ABSTRACT FROM AUTHOR]

The processes for producing conifer planting stock by somatic embryogenesis (SE) in conifers are described. Implementation of SE presents opportunities and limitations at various stages of the in vitro process. The topic of genetic stability, or somaclonal variation, is a particular concern and reviewed. Following the in vitro processes, several factors affect the successful acclimation, early growth and field performance of SE planting stock. Experiences with other conifer species in the context of commercial production are reviewed. While SE production has historically been a very labor-intensive process, recent advances have been made to automate the various steps. Developments to enable SE for Norway spruce in Sweden are described. [ABSTRACT FROM AUTHOR]

In this paper, we describe the principles and processes for deployment of genetic progress in the breeding program, by way of (1) seed orchards, (2) family forestry, and (3) clonal forestry. Vegetative propagation of cloned material has long been accomplished in Norway spruce by rooted cuttings, and more recently by somatic embryogenesis (SE). Whereas donor plants used for the production of rooted cuttings have a limited productive life due to physiological ageing, SE with cryostorage can at least, in theory, provide a limitless supply of regeneration material. Concepts of genetic variation, gain and diversity are reviewed in some detail, as important background for the papers that follow in this issue. The principal differences between family forestry with vegetative multiplication and clonal forestry are described from the perspective of genetic gain and genetic diversity. [ABSTRACT FROM AUTHOR]

This final paper of the series discusses implications of various aspects of using clones in forestry. Benefits from using clones are considerable. A large benefit arises from the ability to deploy genetic gain much sooner than is possible through conventional seed orchards. This benefit applies even to the use of clones to implement family forestry, even though the clones themselves are not tested. The requirement for genetic diversity at both the stand and landscape levels requires active management to ensure that diversity is conserved. This is achieved partly through the management of breeding populations, as well as by managing the genetic diversity and number of genotypes deployed in clone mixtures. A numerical example is given comparing diversity of clone and seed orchard deployment over time. Many aspects of managing concerns about using clones are about communication to clarify public perceptions and establishing a code of practice. [ABSTRACT FROM AUTHOR]