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Irruptions by boreal seed‐eating and frugivorous birds are assumed to be driven by the production of seeds and fruits, crops of which are highly variable between years. Using data from Sweden, we tested whether irruptions of Common Crossbills Loxia curvirostra were correlated with low Norway Spruce Picea abies seed production in the same year as the irruption and/or high seed production in the year prior to an irruption. Similar tests were made for Parrot Crossbill Loxia pytyopsittacus irruptions in relation to Scots Pine Pinus sylvestris seed production. In northern Europe, these conifers represent the key food species of the two crossbill species, respectively. Despite differing times that seeds take to mature and asynchronous seed production between the two conifer species, including a 3‐year cycle for Norway Spruce, the two crossbill species often irrupted in the same year as one another. Analyses showed that irruptions into Britain and other parts of western Europe by both crossbill species were correlated with low seed production by Norway Spruce in Sweden. Low seed production by Scots Pine had a marginally non‐significant additive effect on both crossbill species. In a second set of analyses, the best‐fitting model was one in which low seed production by both conifers in a given year and high seed production in the previous year were each correlated with large numbers of irrupting Common and Parrot Crossbills. The models indicate that the incidental co‐occurrence of low seed production of Norway Spruce and Scots Pine in a given year, after a year of high seed production, may result in an irruption. The seed production of Norway Spruce and Scots Pine in Sweden was correlated with production by the same species in Finland, indicating widespread synchrony of cropping across northern Europe. [ABSTRACT FROM AUTHOR]

Adaptive forest management gains importance as climate and disturbance regimes continue to change. Norway spruce monocultures are particularly vulnerable to those changes. Thus, there is a strong demand to convert pure spruce stands toward better adapted forest ecosystems. Silver fir has similar wood properties as Norway spruce, but is less vulnerable to droughts. Yet, little is known how to efficiently admix silver fir into Norway spruce monocultures. We analyzed seedling abundance in mature Norway spruce monocultures 1 year after soil scarification and silver fir seeding in a relatively dry region of southern Germany. Our objectives were to study the effect of soil scarification and seeding on regeneration density and to identify drivers of seedling abundance. We collected data on regeneration, forest structure, as well as soil and light conditions at 103 scarified and 25 untreated control plots. We used non-parametric independence tests to compare scarified and untreated plots. Subsequently, we used boosted regression trees to investigate the drivers of seedling abundance. Norway spruce strongly benefited from soil scarification (P  < .001), with seedling numbers even exceeding those of silver fir. Both species thrived in soils with high plant available water capacity. In contrast, seedling numbers were overall negatively affected by light. Moreover, we found a higher density of silver fir regeneration at greater distance from neighboring trees and in soils devoid of carbonate. Our study indicates that water, not light, is the limiting factor for both Norway spruce and silver fir seedlings in the study region. Seeding silver fir will likely be most effective underneath an intact canopy on deep, fine-textured soils without carbonate, while maximizing the distance to Norway spruce trees. In conclusion, silver fir seeding can be optimized to become an effective adaptive measure to diversify Norway spruce monocultures, and thus to create more resistant and resilient forest ecosystems. [ABSTRACT FROM AUTHOR]

The pressure to plant seedlings in unprepared instead of prepared soil in forest regeneration is increasing, although seedlings' growth in unprepared soil is poorer. One way to improve seedlings' growth could be to add arginine phosphate to the planting hole at the time of planting. In field studies, abiotic and biotic damage normally disturbs studies which seek to determine growth effects, especially in unprepared soil. The study's aims were (i) to clarify whether it was possible to investigate the differences between varying soil layer structures mimicking site preparation methods and seedling treatments in simulated planting places in partly controlled conditions; and (ii) to investigate the effects of arginine phosphate (arGrow® Granulat) on the growth, especially root growth, of Norway spruce (Picea abies (L.) H. Karst.) and Scots pine (Pinus sylvestris L.) container seedlings in those simulated planting places. Seedlings of both tree species were planted in 40 l pots sunk partly into the soil in a sandy field. Before planting, pots were filled with soil layers mimicking layers in soil without any site preparation treatment and in spot mounds. After one growing season, the differences in growth parameters between treatments were small in Norway spruce seedlings, and no significant benefits of arginine phosphate were observed. The soil in the spruce pots was fine-textured and contained a thick organic layer. More studies in more common forest soil types suitable for Norway spruce seedlings are needed to be sure about the growth responses. In Scots pine seedlings, adding arginine phosphate granules to the planting holes improved the growth of seedlings at least in the first summer after planting in soil layers mimicking no mechanical site preparation situation, and the growth improvement may even have compensated the mounding effects. In conclusion, mimicking site preparation methods in large pots was a promising method by which the differences between site preparations methods as well as effects of seedling treatments, in our case arginine phosphate, on the growth of conifer seedlings, can be tested. [ABSTRACT FROM AUTHOR]

Ips typographus is the most important tree‐killing bark beetle in Europe. In the north, it overwinters either in the bark of its host tree or in the ground, while in central Europe, overwintering in trees is most common. Few studies have estimated winter mortality of I. typographus in northern Europe. Mortality of I. typographus adults overwintering in killed trees was estimated by comparing densities per m2 bark of live (one winter) and dead adults (five winters), and proportion of dead adults (one winter), in bark samples collected before and after winter in Sweden. Densities of live and dead larvae of predatory Medetera spp. (Dolichopodidae) were recorded in the bark samples (one winter), as was the amount of bark removed by woodpeckers from I. typographus‐killed trees during winter foraging (five winters). Mortality of I. typographus adults overwintering in the ground was estimated by spring sampling of soil (three winters). The density of I. typographus live adults in trees was 3% lower after winter, while densities of dead adults was 6% higher and 5% lower respectively during two different outbreaks (differences after vs. before winters were non‐significant). The proportion of dead adults was 4% higher after winter (significant). Winter mortality of adults overwintering in the ground was on average 58%. The density of Medetera was 6% and 8% lower after winter for live and dead larvae, respectively (non‐significant). The amount of remaining bark on standing killed trees was on average 8% lower after than before winter (significant). [ABSTRACT FROM AUTHOR]

Wood is increasingly being used in construction as an alternative to steel and concrete. As wood is an inhomogeneous material, this has a strong effect on its static and dynamic properties. When timber is used as a load-bearing component, there is a possibility that it will be exposed to unfavourable weather conditions (wind) or dynamic environments (vibrations), leading to fatigue of the material. In this article, the effects of load frequency and load magnitude on the durability of Norway spruce wood (Picea abies) were investigated. The frequencies of 5 and 10 Hz were compared at three load levels of 70%, 80% and 90% of the static breaking force. The research results show that the load magnitude has a major influence on the dynamic strength at the same fatigue frequency. Each increase in load means a lower dynamic strength of the spruce, which is reflected in the load cycles achieved. In addition, the dynamic properties of spruce wood deteriorate with an increasing loading frequency, which is more pronounced at higher loading forces. These test results are the basis for determining the Wöhler curve, which is required as input data for the material properties in numerical calculations to determine the durability of the material. [ABSTRACT FROM AUTHOR]

Plant defence mechanisms, including physical barriers like toughened bark and chemical defences like allelochemicals, are essential for protecting them against pests. Trees allocate non-structural carbohydrates (NSCs) to produce secondary metabolites like monoterpenes, which increase during biotic stress to fend off pests like the Eurasian spruce bark beetle, ESBB (Ips typographus). Despite these defences, the ESBB infests Norway spruce, causing significant ecological damage by exploiting weakened trees and using pheromones for aggregation. However, the mechanism of sensing and resistance towards host allelochemicals in ESBB is poorly understood. We hypothesised that the exposure of ESBB to spruce allelochemicals, especially monoterpenes, leads to an upsurge in the important detoxification genes like P450s, GSTs, UGTs, and transporters, and at the same time, genes responsible for development must be compromised. The current study demonstrates that exposure to monoterpenes like R-limonene and sabiene effectively elevated detoxification enzyme activities. The differential gene expression (DGE) analysis revealed 294 differentially expressed (DE) detoxification genes in response to R-limonene and 426 DE detoxification genes in response to sabiene treatments, with 209 common genes between the treatments. Amongst these, genes from the cytochrome P450 family 4 and 6 genes (CP4 and CP6), esterases, glutathione S-transferases family 1 (GSTT1), UDP-glucuronosyltransferase 2B genes (UDB), and glucose synthesis-related dehydrogenases were highly upregulated. We further validated 19 genes using RT-qPCR. Additionally, we observed similar high expression levels of detoxification genes across different monoterpene treatments, including myrcene and α-pinene, suggesting a conserved detoxification mechanism in ESBB, which demands further investigation. These findings highlight the potential for molecular target-based beetle management strategies targeting these key detoxification genes. [ABSTRACT FROM AUTHOR]

Key message: A novel periodic site index is introduced for the quantification of dynamic forest site productivity. The measure is age-independent, sensitive to environmental changes and efficient for the estimation and prediction of stand height and stand volume increment. Context: Accurate and up-to-date prediction of site productivity is crucial for the sustainable management of forest ecosystems, especially under environmental changes. Aims: The aim of this study was to introduce a novel concept: a periodic site index based on growth-effective age for the quantification of dynamic forest site productivity. Methods: The growth-effective age based periodic site index is estimated from repeated or multi-temporal measurements of stand dominant height. Furthermore, a recursive procedure to update the underlying site index model is presented by using repeated measurements of stand dominant height. The database used in this study comprised repeated measurements of 945 Norway spruce (Picea abies L.) experimental plots at 508 different locations in Southwest Germany. Results: The evaluation shows that periodic site index is statistically superior to the conventional site index, based on chronological stand age, for estimating stand height and stand volume increment. The analysis of temporal differences between growth-effective stand age and chronological stand age and between periodic site index and conventional site index in the period 1900 to 2020 reveals trends referring to stand age and site productivity, which corroborate earlier regional studies on forest growth trends due to environmental changes. Conclusions: The periodic site index is a better indicator for site productivity than conventional site index. Under conditions of environmental changes, conventional site index is biased, whereas the growth-effective age based site index provides an unbiased estimate of stand height development. With the more widespread application of remote sensing techniques, such as airborne laser scanning, the availability of multi-temporal stand height data will increase in the near future. The novel concept provides an adaptive modeling approach perfectly suited to these data for an improved estimation and prediction of forest site productivity under environmental changes and can straightforwardly be applied also to uneven-aged and multi-species stands. [ABSTRACT FROM AUTHOR]

Key message: Data acquisition of remote sensing products is an essential component of modern forest inventories. The quality and properties of optical remote sensing data are further emphasised in tree species-specific inventories, where the discrimination of different tree species is based on differences in their spectral properties. Furthermore, phenology affects the spectral properties of both evergreen and deciduous trees through seasons. These confounding factors in both sensor configuration and timing of data acquisition can result in unexpectedly complicated situations if not taken into consideration. This paper examines how the timing of data acquisition and sensor properties influence the prediction of tree species proportions and volumes in a boreal forest area dominated by Norway spruce and Scots pine, with a smaller presence of deciduous trees. Context: The effectiveness of remote sensing for vegetation mapping depends on the properties of the survey area, mapping objectives and sensor configuration. Aims: The objective of this study was to investigate the plot-level relationship between seasonality and different optical band configurations and prediction performance of common boreal tree species. The study was conducted on a 40-ha study area with a systematically sampled circular field plots. Methods: Tree species proportions (0–1) and volumes (m3 ha−1) were predicted with repeated remote sensing data collections in three stages of the growing season: prior (spring), during (summer) and end (autumn). Sensor band configurations included conventional RGB and multispectral (MS). The importance of different wavelengths (red, green, blue, near-infrared and red-edge) and predictive performance of the different band configurations were analysed using zero–one-inflated beta regression and Gaussian process regression. Results: Prediction errors of broadleaves were most affected by band configuration, MS data resulting in lower prediction errors in all seasons. The MS data exhibited slightly lower prediction errors with summer data acquisition compared to other seasons, whereas this period was found to be less suitable for RGB data. Conclusion: The MS data was found to be much less affected by seasonality than the RGB data. Spring was found to be the least optimal season to collect MS and RGB data for tree species-specific predictions. [ABSTRACT FROM AUTHOR]

A breeding population of the tree-killing European spruce bark beetle Ips typographus was detected in England for the first time in 2018 and was initially assumed to have arrived with infested timber. To test the hypothesis that the beetles are dispersing naturally across the English channel, extensive trap networks were deployed in 2021 and 2022 to track the flight activity of the beetles from an outbreak hotspot in France and Belgium to southern England, including parallel 'coastal' traps on either side of the channel. Beetles were caught all along the transect, decreasing in abundance with distance from the outbreak area. Linear modelling indicates that beetles dispersed into England during 2021 and 2022, and that during a large-scale dispersal event in June 2021, beetles could have penetrated more than 160 km inland. The 2021 dispersal event initiated new incursions of the beetle in southeast England and demonstrates the extraordinary distance I. typographus may move under outbreak conditions. Our findings support the hypothesis of a damaging forest pest aerially dispersing across the barrier of the English channel and suggest that future incursions of this and other plant-associated pests may move via the same pathway. [ABSTRACT FROM AUTHOR]

The European spruce bark beetle Ips typographus is a widespread pest in Norway spruce-dominated forests in Eurasia. Predicting its phenology and voltinism is crucial to plan forest management measures and to mitigate mass outbreaks. Current phenology models are based on constant temperatures inferred from laboratory experiments; however, insect life cycles under natural conditions are rather driven by diurnal and seasonal temperature fluctuations. Therefore, phenology models based on fluctuating temperatures would reflect field conditions more realistically and might thus improve model predictions. In a laboratory experiment, we investigated the development of I. typographus, applying mean temperatures between 3 and 35 °C and diurnal temperature oscillations of up to ± 15 °C. Subsequently, we calibrated developmental rate models and applied them to climate data, in order to assess the effect of temperature fluctuations on voltinism under field conditions. Our results showed that diurnal temperature oscillations significantly affected developmental rates. Compared to constant temperatures, development was faster at temperature oscillations falling below the lower developmental threshold, and slower at temperature oscillations exceeding the developmental optimum. Furthermore, short exposures to suboptimal temperatures affected I. typographus less than expected from constant conditions. Natural temperature fluctuations thus accelerate development under cool, shaded conditions, whilst slowing it under hot, sun-exposed conditions, thereby ultimately affecting voltinism. Our findings highlight the importance to account for diurnal temperature fluctuations for more accurate predictions of developmental rates of I. typographus in natural thermal environments, and provide the fundament for improving current phenology models to support effective bark beetle management in a warming climate. [ABSTRACT FROM AUTHOR]

The rhizosphere is the hotspot for microbial enzyme activities and contributes to carbon cycling. Precipitation is an important component of global climate change that can profoundly alter belowground microbial communities. However, the impact of precipitation on conifer rhizospheric microbial populations has not been investigated in detail. In the present study, using high-throughput amplicon sequencing, we investigated the impact of precipitation on the rhizospheric soil microbial communities in two Norway Spruce clonal seed orchards, Lipová Lhota (L-site) and Prenet (P-site). P-site has received nearly double the precipitation than L-site for the last three decades. P-site documented higher soil water content with a significantly higher abundance of Aluminium (Al), Iron (Fe), Phosphorous (P), and Sulphur (S) than L-site. Rhizospheric soil metabolite profiling revealed an increased abundance of acids, carbohydrates, fatty acids, and alcohols in P-site. There was variance in the relative abundance of distinct microbiomes between the sites. A higher abundance of Proteobacteria, Acidobacteriota, Ascomycota, and Mortiellomycota was observed in P-site receiving high precipitation, while Bacteroidota, Actinobacteria, Chloroflexi, Firmicutes, Gemmatimonadota, and Basidiomycota were prevalent in L-site. The higher clustering coefficient of the microbial network in P-site suggested that the microbial community structure is highly interconnected and tends to cluster closely. The current study unveils the impact of precipitation variations on the spruce rhizospheric microbial association and opens new avenues for understanding the impact of global change on conifer rizospheric microbial associations. [ABSTRACT FROM AUTHOR]

Considerable efforts have been made to replace formaldehyde-containing adhesives in the manufacturing of wood products, particularly particleboard, with natural alternatives. One promising solution is the liquefaction of lignocellulosic materials such as wood using glycerol (C3H8O3) under sulfuric acid catalysis (H2SO4). The aim of this study was to investigate the chemical composition and properties of spruce and oak biomass after liquefaction and to evaluate its potential as a formaldehyde-free adhesive substitute. All samples were liquefied at 150 °C for 120 min in five different wood–glycerol ratios (1:1 to 1:5). The liquefaction percentage, the insoluble residue, the dry matter and the hydroxyl (OH) number were determined as characteristic values for the polymer properties of the liquefied samples. The results showed the liquefaction percentage was up to 90% for spruce and oak. The insoluble residue ranged from 10 to 29% for spruce and from 10 to 22% for oak, the dry matter ranged from 54 to 70% for spruce and from 51 to 62% for oak, while the highest xydroxyl number was 570 mg KOH/g for spruce and 839 mg KOH/g for oak. Based on these results, liquefied wood was shown to be an effective natural alternative to synthetic resins in particleboard adhesives and a way to reduce formaldehyde emissions. This research not only supports environmentally sustainable practices but also paves the way for various bioproducts derived from liquefied biomass and points to future avenues for innovation and development in this area. [ABSTRACT FROM AUTHOR]

Animals representing a wide range of taxonomic groups are known to select specific food combinations to achieve a nutritionally balanced diet. The nutrient balancing hypothesis suggests that, when given the opportunity, animals select foods to achieve a particular target nutrient balance, and that balancing occurs between meals and between days. For wild ruminants who inhabit landscapes dominated by human land use, nutritionally imbalanced diets can result from ingesting agricultural crops rich in starch and sugar (nonstructural carbohydrates [NCs]), which can be provided to them by people as supplementary feeds. Here, we test the nutrient balancing hypothesis by assessing potential effects that the ingestion of such crops by Alces alces (moose) may have on forage intake. We predicted that moose compensate for an imbalanced intake of excess NC by selecting tree forage with macro‐nutritional content better suited for their rumen microbiome during wintertime. We applied DNA metabarcoding to identify plants in fecal and rumen content from the same moose during winter in Sweden. We found that the concentration of NC‐rich crops in feces predicted the presence of Picea abies (Norway spruce) in rumen samples. The finding is consistent with the prediction that moose use tree forage as a nutritionally complementary resource to balance their intake of NC‐rich foods, and that they ingested P. abies in particular (normally a forage rarely eaten by moose) because it was the most readily available tree. Our finding sheds new light on the foraging behavior of a model species in herbivore ecology, and on how habitat alterations by humans may change the behavior of wildlife. [ABSTRACT FROM AUTHOR]

Most tree species underwent cycles of contraction and expansion during the Quaternary. These cycles led to an ancient and complex genetic structure that has since been affected by extensive gene flow and by strong local adaptation. The extent to which hybridization played a role in this multi‐layered genetic structure is important to be investigated. To study the effect of hybridization on the joint population genetic structure of two dominant species of the Eurasian boreal forest, Picea abies and P. obovata, we used targeted resequencing and obtained around 480 K nuclear SNPs and 87 chloroplast SNPs in 542 individuals sampled across most of their distribution ranges. Despite extensive gene flow and a clear pattern of Isolation‐by‐Distance, distinct genetic clusters emerged, indicating the presence of barriers and corridors to migration. Two cryptic refugia located in the large hybrid zone between the two species played a critical role in shaping their current distributions. The two species repeatedly hybridized during the Pleistocene and the direction of introgression depended on latitude. Our study suggests that hybridization helped both species to overcome main shifts in their distribution ranges during glacial cycles and highlights the importance of considering whole species complex instead of separate entities to retrieve complex demographic histories. [ABSTRACT FROM AUTHOR]

We studied how management intensity and climate severity affect volume growth, timber yield, carbon stocks, and the amount of deadwood in Scots pine (Pinus sylvestris (L.)), Norway spruce (Picea abies (L.) Karst.), and silver birch (Betula pendula Roth.) dominated stands in the Republic of Karelia and Arkhangelsk region of northwest Russia. Using the forest ecosystem model (SIMA) under different climates (current and representative concentration pathway scenarios, RCP4.5 and RCP8.5), no-thinning, low, medium, and high intensity thinning rotational forestry regimes were simulated. Under RCPs, the volume growth and timber yield (5%–53%), carbon stocks (1%–22%), and deadwood amounts (11%–75%) increased for all Scots pine and silver birch stands. The use of low intensity management increased volume growth and carbon stocks (3%–16%) and deadwood amount (up to 60%) under RCPs, but not timber yield (±3%) in these stands. For Norway spruce stands, the volume growth (5%–26%), timber yield (23%–75%), and carbon stocks (5%–15%) decreased under RCP8.5, but deadwood amount increased (up to 142%). Intensive management increased volume growth (4%–19%), timber yield (4%–63%), carbon stocks (up to 14%), and deadwood amounts (up to 49%). Our results highlight that effects of climate severity and management intensity are site and species-specific for Eurasian's boreal forests. [ABSTRACT FROM AUTHOR]

The article discusses the relevance of increasing the sowing qualities of forest seeds. The results of studies on the influence of humic preparations on the sowing qualities of the European spruce (Picea abies) are presented. The positive effect of the studied humic preparations on the germinative energy and germinating ability of seeds was noted. The best effect is obtained when processing seeds which have reduced sowing qualities. The dependence of germinating ability of seeds on duration of soaking in the working solution of humic preparations and the content of the active substance in them has been established. The best indicators of germinating ability and germinative energy were noted when the seeds were soaked for 20 hours in a humic preparation with a humic acid content of 9.9 g/l. [ABSTRACT FROM AUTHOR]

This paper deals with the bonding characteristics of cross-laminated timber (CLT) panels made of Silver birch (Betula pendula Roth.), European aspen (Populus tremula L.), and Norway spruce (Picea abies (L.) H. Karst.) wood. Three-layered single-species CLT panels were manufactured using birch, aspen, and spruce lamellae bonded with a one-component polyurethane (PUR) adhesive. Spruce CLT panels were used as reference. The bonding characteristics of CLT were assessed based on bond shear strength, total and maximum delamination, and wood failure percentage. The reference spruce CLT met both criteria (Delamtot ≤ 10%, Delammax ≤ 40%) for passing the delamination test, where up to 80% of the test samples passed. The aspen and birch CLTs met the criterion for maximum delamination (26.5% and 33.2%, respectively), but exceeded the maximum allowed value for total delamination (12.7% and 13.2%, respectively). However, the minimum requirement of 70% wood failure percentage (WFP) was met for all CLT types, with aspen CLTs achieving 83.7% and birch CLTs 76.9%. The spruce CLTs achieved an average bond shear strength of 1.9 N/mm2, while both hardwood CLTs had significantly higher values, with the aspen CLT at 3.3 N/mm2 and the birch CLT at up to 3.9 N/mm2. Based on the results obtained, it can be concluded that cross-laminated timber (CLT) made from hardwoods like aspen and birch is suitable for environments with low humidity fluctuations. [ABSTRACT FROM AUTHOR]

A study was conducted to improve the effectiveness of silvicultural production of structural sawn timber from softwoods. It intends to explore prediction methods for mechanical timber quality. The study material was obtained from six stands divided into age groups of approximately 40- and 80-year-old trees (examining the influence of age). The stands were differentiated by their applied thinning system of thinning from below or above (examining the influence of the thinning system). Resulting from these different levels of data, i.e., stand parameters, tree anatomy, and visual board properties are examined and analyzed in ordinal logistic models and linear mixed models. Visual board properties were discerned by means of the German standard for visual grading of sawn timber. The mechanical board properties were measured in on-edge bending strength tests and allocated into strength classes, which were modeled in dependence of visual characteristics and forestry conditions. The evaluation of mechanical properties attributed a significant loss of timber quality to short rotation periods, non-ideal water supply, and a single-tree management system. The prediction capabilities of models based on site and tree characteristics were on par with the accuracy of visual grading. Management adaptations by intense thinning from above can lead to a significant decline in Norway spruce (Picea abies L.) timber quality when site factors coincide. Particular care should be taken in the management of locations with high yield potential. Non-destructive evaluation based on site characteristics combined with terrestrial laser scan data of tree characteristics has potential as a pregrading method. [ABSTRACT FROM AUTHOR]

The Ore Mountains were historically one of the most polluted areas in Europe, where high sulphur dioxide concentrations and a high level of atmospheric deposition led to a vast decline in Norway spruce stands in the mountain ridge plateau. In this article, we evaluate the trends in the atmospheric deposition load, soil chemistry, tree nutrition, crown defoliation and height increment in a network of twenty research plots monitored for last thirty years in this region. The decrease in sulphur and nitrogen deposition was most pronounced at the end of 1990s. Extreme values of sulphur deposition (100–200 kg.ha−1.year−1) were recorded in throughfall under mature Norway spruce stands in the late 1970s, and after felling of the damaged stand, the deposition levels were comparable to open plot bulk deposition. Nitrogen deposition decreased more slowly compared with sulphur, and a decrease in base cation deposition was observed concurrently. The current deposition load is low and fully comparable to other mountain areas in central Europe. Accordingly, the health of young spruce stands, as assessed by defoliation and height increment, has improved and now corresponds to the Czech national average. On the other hand, no significant changes were observed in the soil chemistry, even though some of the plots were limed. Acidic or strongly acidic soil prevails, often with a deficiency of exchangeable calcium and magnesium in the mineral topsoil, as well as decreases in available phosphorus. This is reflected in the foliage chemistry, where we see an imbalance between a relatively high content of nitrogen and decreasing contents of phosphorus, potassium and calcium. Despite the observed positive trends in air quality and forest health, the nutritional imbalance on acidified soils poses a risk for the future of forest stands in the region. [ABSTRACT FROM AUTHOR]

Carbon emissions and environmental concerns have led to the aspiration to reduce peat extraction and its use as a growing medium (GM). In Nordic Forest tree seedling production, Sphagnum peat has been almost exclusively used as a GM in seedling containers due to its good properties and availability. This study examined the feasibility of several peat-reduced and peat-free GM in container tree seedling production of the key tree species in Nordic forestry (Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L. Karst.) and silver birch (Betula pendula Roth) as well as Russian larch (Larix archangelica P. Lawson & C. Lawson ex Trautv.) and common alder (Alnus glutinosa (L.) Gaertn.). Pure or mixed GM, consisting of low-humified Sphagnum peat (pure as a control), harvested Sphagnum moss, wood fiber, cow manure digestate from a biogas plant, and a common reed compost were tested. Seedlings were grown in controlled conditions in greenhouse experiments and also in larger-scale commercial tree nurseries. Peat-reduced media containing peat of at least 50 vol% provided growth that is similar to pure Sphagnum peat for the tested species and container types. All the studied alternative media can yield marketable seedlings, although commonly of reduced size and requiring special adjustments in growing management. The studied media have a potential to reduce or replace peat in seedling production, but adjustments of their physical and chemical properties, as well as of seedling fertigation and management procedures, are required. The economic feasibility and environmental sustainability of these GM, as well as the outplanting success of seedlings grown in these media, remain to be studied. [ABSTRACT FROM AUTHOR]

Scots pine (Pinus sylvestris L.) has higher early growth rates than Norway spruce (Picea abies (L.) H. Karst.). To help efforts to understand possible reasons for this difference and identify appropriate regeneration methods, we labeled seedlings with 15N in the nursery to probe nitrogen (N) uptake and retranslocation in Scots pine and Norway spruce seedlings at both harsh and fertile sites in southern and northern Sweden. For this, 15N dilution was measured during the first two years after planting. We also examined the potential N2-fixation capacity in fine roots after 5–7 growing seasons. Use of 15N-labeled seedlings enabled clear discernment of contributions of uptake of new N and retranslocation of old N to new foliage. Scots pine seedlings had higher proportions of N derived from uptake (Ndfu) than Norway spruce seedlings, and higher growth. Scots pine seedlings were less responsive to site preparation treatments compared to Norway spruce that has a greater need for appropriate silvicultural measures to grow well. After the second growing season, the contribution of N derived from retranslocation (Ndfr) to N in new foliage had diminished to 10–20% at all except the harshest site, where both species were more dependent on Ndfr. The potential N2-fixation capacity in fine roots of the two species differed, but in both cases the contribution of N2-fixation to N-acquisition was negligible. [ABSTRACT FROM AUTHOR]

Introduction: Soil drought during summer in Central Europe has become more frequent and severe over the last decades. European forests are suffering increasing damage, particularly Norway spruce. Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco), a non-native tree species, is considered as a promising alternative to build drought-resilient forests. The main goal of this study was to investigate the intraannual radial stem growth and sap flow performance of Douglas-fir along a precipitation gradient across Germany under severe drought. Material and methods: Sap flow and stem radial changes of up to ten trees each at four sites with different precipitation regimes were measured in combination with volumetric soil water content during the growing season of 2022. Measurements of stem radial changes were used to calculate the trees' stem water deficit, a proxy for tree water status and drought stress. Results: The severe summer drought of 2022 led to an early growth cessation and a significant reduction in daily sap flow at all four sites monitored. We could identify a site-specific threshold in soil water availability ranging between 21.7 and 29.6% of relative extractable water (REW) under which stem water reserves cannot be replenished and thereby inhibiting radial growth. We could also demonstrate that at this threshold, sap flow is heavily reduced to between 43.5 and 53.3%, and for a REW below 50%, sap flow linearly decreases by 1.1-2.0% per 1% reduction in REW. This reduction tends to follow the humidity gradient, being more pronounced at the most oceanic characterized site and suggesting an adaptation to site conditions. Even though Douglas-fir is considered to be more drought stress resistant than Norway spruce, growth and sap flow are greatly reduced by severe summer drought, which became more frequent in recent years and their frequency and intensity is likely to increase. Conclusions: Our results suggest that timber production of Douglas-fir in Central Europe will decline considerably under projected climate change, and thus pointing to site specific growth constraints for a so far promising non-native tree species in Europe. [ABSTRACT FROM AUTHOR]

Introduction: In recent years, Norway spruce (Picea abies L.) forests in Central Europe have faced escalating threats from bark beetles, primarily Ips typographus (L.), and other species, such as I. duplicatus (Sahlberg). Outbreaks are partially attributed to weakened tree defense resulting from drought periods induced by climate change. This study examines Norway spruce's physiological and metabolic reactions to acute drought stress during the growing season and evaluates its susceptibility to I. typographus and I. duplicatus. Methodology: In order to induce drought stress, mature Norway spruces had their roots covered with a roof in April 2021, depriving them of water. Control trees were left with free access to natural rainwater. Over 5 months of the growing season, soil water potential, bark temperature, tree trunk circumference, and sap flow were monitored. Roofed trees and controls were sampled in July, August, and September and analyzed for non-structural carbohydrates and the two classes of defensive compounds, phenolics and terpenes. Furthermore, two different bioassays in tubes and boxes were performed using adult I. typographus and I. duplicatus beetles to assess host choice and acceptance. Results: Roofed trees exhibited signs of stress as early as July, resulting in decreased tree trunk and a consequent increase in non-structural carbohydrate content. Defensive metabolites remained largely unaffected except for an increase in diterpenes in September. In bioassays, I. typographus preferred boring into the bark of roofed trees in August in tubes and in September in boxes. This increased tree acceptance correlated with increased levels of soluble carbohydrates in the phloem. I. typographus and I. duplicatus beetles showed higher mobility in boxes in August and September on roofed trees but not in July, even though bark surface temperatures were elevated in roof-covered trees during all three bioassay periods. Conclusion: The study revealed rapid physiological responses of trees to acute drought stress, although not many changes were observed in defense traits. Despite the absence of natural bark beetle attacks, drought trees were more accepted by I. typographus than naturally watered trees. This response may indicate the beetles' preference for trees with phloem of higher nutritional quality induced by the acute drought stress conditions. [ABSTRACT FROM AUTHOR]

Provenance trials provide a valuable opportunity to evaluate the impact of extreme events on growth and wood properties. In this study, we have evaluated 81 Norway spruce provenances, tested in three provenance trials established in the Romanian Carpathians in 1972. The response to drought of the Norway spruce provenances has been examined using the following tree resilience indices: resistance, recovery, resilience, and relative resilience. The relationship between climate and growth, the correlations between wood traits, and the coordinates of the origin and tree resilience indices were also analysed. In each provenance trial, there were significant differences between provenances and years regarding wood widths and latewood percentage (LWP). Regarding drought extreme events, the years when they occurred in all three provenance trials were 2000 and 2003. Significant differences between provenances for at least one tree resilience index have been found in all provenance trials, for the year 2000. By using subperiods of 25 years, changes in the relationship between climate and growth have been observed. Several provenances with high radial growth and good resistance and/or recovery have been identified. Provenances that performed better in common garden experiments could be used in assisted migration, even in the proximity of the current natural range. [ABSTRACT FROM AUTHOR]

We present a database of Norway spruce phenotypic traits measured over a period of 51 years in provenance trials planted across western Germany. These trials are part of the 'Inventory Provenance Test 1964/68 with Norway spruce' (IPTNS) that tested a total of 1,100 provenances collected across Europe, both from the species natural and artificial range. Phenotypic traits (first height, later diameter at breast height, survival) were recorded at 33 trial sites of 100 provenances, each a subsample from the entire collection area that represents an approximately comparable climate space. The dataset contains 424,781 records of the same 65,518 trees ranging from age 7 to 51. Overall, it captures the considerable genetic and phenotypic intraspecific variation present in Norway spruce and should be of interest to various fields including quantitative genetics, ecology, biogeography and the adaptive management of forests. [ABSTRACT FROM AUTHOR]

In Europe, Pinus sylvestris and Picea abies are the most common coniferous tree species used in commercial forestry, which rely on high‐quality reproductive material for successful reforestation. Clear‐cut harvested forest sites are often replanted using tree seedlings, which are produced in forest nurseries using seeds from seed orchards. However, incidences of fungal diseases in seedling production show that a better knowledge of seedborne fungi, including fungal pathogens, is needed to manage diseases in forest nurseries. This study aimed to assess seedborne fungal communities associated with commercial seeds of P. abies, P. sylvestris and Larix sp. seeds originated from geographically separated regions in Sweden, Belarus, Finland and Poland. Fungal communities were obtained first from the seed surface and then from the seed tissue. These were analysed using high‐throughput sequencing of the ITS2 rDNA region. The results showed that fungal diversity and community composition differed between the seed surface and the seed tissue. Picea abies accommodated a higher fungal diversity than P. sylvestris. In addition, a strong host affinity of the fungal community composition on the seed surface and a weaker association in the seed tissue was found. Fungal communities on P. abies and P. sylvestris seed surface differed significantly between geographical regions, whereas no regional differences were found in the seed tissue. The seedborne fungal communities included a high proportion of plant pathogens, among which the most abundant were Sydowia polyspora (13.3%), Phoma herbarum (11.2%) and Sirococcus conigenus (3.8%). In conclusion, the results showed (a) characteristic fungal diversity and community composition between the seed surface and the seed tissue; (b) a host‐specific fungal community composition on the seed surface and in the seed tissue; (c) regional difference in fungal communities on P. abies and P. sylvestris seed surface, thus the movement of seeds between different regions can contribute to the spread of fungal diseases; and (d) the presence of a high incidence of seedborne fungal pathogens which suggest a potential need of preventative or control measures to reduce the occurrence of these fungi on the seed surface. [ABSTRACT FROM AUTHOR]

Spatial information on forest composition is invaluable for achieving scientific, ecological, and management objectives and for monitoring multiple changes in forest ecosystems. The increased flow of optical satellite data provides new opportunities to improve tree species mapping. However, the accuracy of such maps is affected by training data, and in particular on the homogeneity of individual classes. Thus, we evaluated the effect of data homogeneity in tree species classification. We performed tree species classification by considering different ways to partition data into tree species classes. The class sets considered were (i) only mixed coniferous and mixed deciduous forest classes, (ii) single-species classes, (iii) single-species, mixed coniferous and mixed deciduous classes, and (iv) single-species, mixed coniferous and mixed deciduous classes and a true mixed class. Using data from the Swedish National Forest Inventory, we varied the threshold that defined dominating species. Tree species were classified for a study area in central Sweden using Sentinel-2 data and two classification approaches: Bayesian inference and random forest (RF). Images were selected by class separability and the most informative images based on variable selection with RF. The most informative images tended to be selected by both methods. However, in forests with tree species of similar spectral behaviour, image selection on the basis of class separability was found to be more reliable. More accurate classification results were achieved as the number of classes decreased and the threshold of plot purity increased. The Bayesian classification approach of only mixed coniferous and mixed deciduous classes gave the highest OA, always greater than 90%. When discriminating between pure plots of Birch (Betula spp.), Spruce (Picea abies), Scots pine (Pinus sylvestris) and Lodgepole pine (Pinus contorta), the best OA values were 84% for Bayesian and 80% for RF. In more complicated scenarios, RF resulted in higher overall accuracies (OA). [ABSTRACT FROM AUTHOR]

Wood branches subjected to bending develop reaction wood to accommodate both tensile and compressive stresses. For softwood, such as Norway spruce and Scots pine, compression wood (CW) develops in the lower parts, while opposite wood (OW) develops on the upper parts of the branch. It is likely that the ratio of CW to OW is optimised for mechanical load bearing by nature. This hypothesis was tested with an analytical beam model using experimental data of stiffness and strength of CW and OW at CW fractions from 0 to 100%. It was found that there is indeed a maximum bending moment capacity around 35% CW, like literature values of CW content in softwood branches. For all compositions, compressive or tensile strength of OW was governing the behaviour. [ABSTRACT FROM AUTHOR]

Over the past few decades, increasing populations of cervid species in the Baltic region have reduced the quality and vitality of cultivated Norway spruce (Picea abies (L.) Karst.) stands. This study evaluated the effect of bark stripping on the volume growth of spruce trees in Latvia. Data collection took place in two forest stands. In each stand, 20 Norway spruce trees were sampled, 10 with visible bark damage scars and 10 control trees. Stem discs were collected from control trees at specified heights (0 m, 0.5 m, 1 m, 1.3 m, and 2 m, and then at one-metre intervals up to the top) and from damaged trees at additional specific points relative to the damage. Each disc was sanded and scanned; tree ring widths were measured in 16 radial directions using WinDendro 2012a software. Annual volume growth reconstruction was performed for each tree. Changes in relative volume growth were analysed in interaction with scar parameters, tree type (damaged/control), and pre-damage volume using linear regression models. The significance of parameter interactions was assessed using analysis of variance (ANOVA). Pairwise comparisons of estimated marginal means (EMMs) were conducted using Tukey's HSD post hoc test. No significant effect of bark stripping on the total stem volume increment was detected. However, the length of bark stripping scars had a significant impact on relative volume growth in the lower parts of the stems. These findings underscore the importance of further research examining a broader spectrum of cervid damage intensity and the effects of repeated damage on tree survival and growth. [ABSTRACT FROM AUTHOR]

In the context of climate change, methods to improve the resistance of coniferous trees to biotic and abiotic stress are in great demand. The common plant response to exposure to vastly different stressors is the generation of reactive oxygen species (ROS) followed by activation of the defensive antioxidant system. We aimed to evaluate whether seed treatment with physical stressors can activate the activity of antioxidant enzymes and radical scavenging activity in young Picea abies (L.) H. Karst seedlings. For this, we applied seed treatment with cold plasma (CP) and electromagnetic field (EMF) and compared the response in ten different half-sib families of Norway spruce. The impact of the treatments with CP (1 min—CP1; 2 min—CP2) and EMF (2 min) on one-year-old and two-year-old P. abies seedlings was determined by the emergence rate, parameters of growth, and spectrophotometric assessment of antioxidant capacity (enzyme activity; DPPH and ABTS scavenging) in needles. The results indicated that the impact of seed treatment is strongly dependent on the genetic family. In the 577 half-sib family, the activity of antioxidant enzymes catalase (CAT), ascorbate peroxidase (APX), peroxidase (POX), and glutathione reductase (GR) increased after EMF-treatment in one-year-old seedlings, while similar effects in 477 half-sib family were induced by CP2 treatment. In two-year-old seedlings, CP1-treatment increased CAT, APX, POX, GR, SOD, DPPH, and ABTS activity in the 457 half-sib family. However, no significant impact of the treatment with CP1 was determined in one-year-old seedlings in this family. The application of novel technologies and the consideration of the combinatory impact of genetic and physical factors could have the potential to improve the accumulation of compounds that play an essential role in the defense mechanisms of P. abies. Nevertheless, for different resistance and responses to stressors of plants, their genetic properties play an essential role. A comprehensive analysis of interactions among the stress factors (CP and EMF), genetic properties, and changes induced in the antioxidant system can be of importance both for the practical application of seed treatment in forestry and for understanding fundamental adaptation mechanisms in conifers. [ABSTRACT FROM AUTHOR]

Wood extractives have proven strong anti-oxidative properties which may be used to mitigate surface deterioration caused by photolytic effects and free radical formations. An interesting challenge regarding wood extractives is understanding how they behave in terms of treating natural wood surfaces to reduce anti-oxidative processes that arise from exposure to the main environmental factors. In this study, the possible efficacy of chestnut (Castanea sativa Mill.) extractives derived from native (CH) and thermally modified wood (TMT CH), as a means of protecting against UV exposure in poplar (Populus spp.) and spruce (Picea abies Karst.) wood, was evaluated. Chestnut wood was first thermally modified at 180 °C for 3 h, and the extractives were obtained by the accelerated solvent extraction technique (ASE) and subsequently used to treat wood surfaces. Samples were immersed in extractive solutions and exposed to artificial UV-weathering exposure, then contact angle and colour stability were monitored during the process. An FTIR analysis of the photo-degradation process of poplar and spruce surfaces was also executed. Extractives of TMT chestnut changed the total colour variation in both poplar and spruce wood. A much darker colour compared to the extractives of native wood was observed and an increase in ∆E* from 9.75 to 30.76 and 6.24 to 22.97 in poplar and spruce was calculated. The stability of the colour depended both on the surface wood and the type of extractive. The initial contact angle remained almost unchanged in the poplar wood surface and only slightly increased in spruce regardless of whether they were treated with extractives from native or TMT chestnut wood. A strong reduction in contact angle after the accelerated UV exposure test was observed, especially in spruce treated with CH extractives. FTIR analysis confirmed the lower levels of chemical degradation of surfaces observed by colorimetry, where TMT CH extractives formed more stable chemical bonds than native extractives. The comparative analysis in this study clarified the complex relationships between the effects of high-temperature modification of wood and the potential protective role of TMT extractives on some wood surfaces. [ABSTRACT FROM AUTHOR]

We studied the dynamics of stable carbon (δ13C) and nitrogen (δ15N) isotopes in litter from Norway spruce (NSL) (Picea abies) and Scots pine (SPL) (Pinus silvestris) during in situ decomposition over a period of more than 4 years. Relative to initial values, δ13CNSL showed a weak enrichment (0.33‰), whereas δ13CSPL was depleted (−0.74‰) at the end of decomposition. Both litter types experienced a depletion in δ15N during decomposition; δ15NNSL decreased by −1.74‰ and δ15NSPL decreased by −1.99‰. The effect of the selective preservation of acid-unhydrolyzable residue (AUR) in lowering δ13C of the residual litter was evident only in SPL. In the NSL, only in the initial stage did C/N have a large effect on the δ13C values. In the later stages, there was a non-linear decrease in δ13CNSL with a simultaneous increase in AUR concentrations, but the effect size was large, suggesting the role of lignin in driving δ13C of residues in later stages. Depletion in 15N in the residual litters concomitant with the increase in N concentration suggests bacterial transformation of the litter over fungal components. A consistent decline in δ15N values further implies that bacterial dominance prompted this by immobilizing nitrate depleted in 15N in the residual litter. [ABSTRACT FROM AUTHOR]

Our study explores the impact of sudden gap formation on the bark volatile and internal chemical profiles of Norway spruce trees during the initial dry year of research plot 2018 following gap formation. We investigated the annual variation in two main physiological traits of Norway spruce trees at the forest edge (FE) and in the forest interior (FI): bark monoterpene (MT) emission spectra and internal phloem MT composition. Given that gap formation increases the solar radiation dose and temperature for trees at the forest edge, we hypothesized that the concentrations of airborne terpenes released from the tree bark and internal phloem terpenes will increase as a consequence of induced tree defenses. Our findings demonstrate significant increases in both airborne terpene concentrations and internal terpene composition in trees at the forest edge compared to the control trees in the forest interior. This study provides novel insights into the annual dynamics of bark monoterpenes following forest edge establishment and underscores the physiological changes experienced by trees in response to the gap formation.

Abstract Background Forest geneticists typically use provenances to account for population differences in their improvement schemes; however, the historical records of the imported materials might not be very precise or well-aligned with the genetic clusters derived from advanced molecular techniques. The main objective of this study was to assess the impact of marker-based population structure on genetic parameter estimates related to growth and wood properties and their trade-offs in Norway spruce, by either incorporating it as a fixed effect (model-B) or excluding it entirely from the analysis (model-A). Results Our results indicate that models incorporating population structure significantly reduce estimates of additive genetic variance, resulting in substantial reduction of narrow-sense heritability. However, these models considerably improve prediction accuracies. This was particularly significant for growth and solid-wood properties, which showed to have the highest population genetic differentiation (QST) among the studied traits. Additionally, although the pattern of correlations remained similar across the models, their magnitude was slightly lower for models that included population structure as a fixed effect. This suggests that selection, consistently performed within populations, might be less affected by unfavourable genetic correlations compared to mass selection conducted without pedigree restrictions. Conclusion We conclude that the results of models properly accounting for population structure are more accurate and less biased compared to those neglecting this effect. This might have practical implications for breeders and forest managers where, decisions based on imprecise selections can pose a high risk to economic efficiency.

Trees that are categorised by their light requirements have similarities in their growth strategies and adaptation mechanisms. We aimed to understand the complex responses of elevated air humidity on whole tree fine root carbon (C) exudation (ExC) and respiration rate, morphology, and functional distribution in species with different light requirements. Three light-demanding (LD) species, Populus Ã--wettsteinii, Betula pendula, and Pinus sylvestris, and two shade-tolerant species, Picea abies and Tilia cordata saplings were grown in growth chambers under moderate and elevated air relative humidity (eRH) at two different inorganic nitrogen sources with constant air temperature and light availability. The proportion of assimilated carbon released by ExC, and respiration decreased at eRH; up to about 3 and 27%, respectively. There was an indication of a trade-off between fine root released C and biomass allocation. The elevated air humidity changed the tree biomass allocation and fine root morphology, and the responses were species-specific. The specific fine root area and absorptive root proportion were positively related to canopy net photosynthesis and leaf nitrogen concentration across tree species. The variation in ExC was explained by the trees' light-use strategy (p < 0.05), showing higher exudation rates in LD species. The LD species had a higher proportion of pioneer root tips, which related to the enhanced ExC. Our findings highlight the significant role of fine root functional distribution and morphological adaptation in determining rhizosphere C fluxes in changing environmental conditions such as the predicted increase of air humidity in higher latitudes. [ABSTRACT FROM AUTHOR]

The European spruce bark beetle, Ips typographus (L.), is the most important forest pest in Europe due to the profound impacts of periodic outbreaks on ecosystem goods and services. Herein, we evaluated the responses of I. typographus to different doses of verbenone (SPLAT® Verb, 10% (−)‐verbenone by weight; ISCA Inc., Riverside, CA, USA) in traps baited with its aggregation pheromones. Results are based on 1,492,289 I. typographus collected in five experiments over 3 years. SPLAT® Verb inhibited the response of I. typographus to baited traps out to 14 m from the point of release (dollop) and for >80 days at a dose of 75 g per dollop. Reductions in trap catch ranged from 34% to 93% depending on the dose of verbenone, age of SPLAT® Verb dollops, distance from dollops and the environment. In forest stands, significant reductions in trap catch were observed at distances up to 14 m from the point of release, with the largest reductions observed at 0 m (93%) and 2 m (64%). In an open area, significant reductions in trap catch were observed at distances up to only 2 m from the point of release, with the largest reduction observed at 0 m (66%). The much lower active inhibitory range of verbenone in the open area appears to be explained by less stable accumulations of verbenone in the surrounding air. There was a significant negative correlation between trap catch and the amount of verbenone measured in air in the vicinity of traps. We also observed inhibition of the sixtoothed spruce bark beetle, Pityogenes chalcographus (L.), another important forest pest in Europe, at all doses (20, 40, 75 and 100 g) of SPLAT® Verb that were evaluated. The implications of these and other results to the management of I. typographus are discussed. [ABSTRACT FROM AUTHOR]

Effective management of bark beetle infestations requires prompt detection of attacked trees. Early attack is also called green attack, since tree foliage does not yet show any visible signs of tree decline. In several bark beetle systems, including mountain pine beetle and European spruce bark beetle, unpiloted aerial vehicle (UAV)-based remote sensing has successfully detected early attack. We explore the utility of remote sensing for early attack detection of southern pine beetle (SPB; Dendroctonus frontalis Zimm.), paired with detailed ground surveys to link tree decline symptoms with SPB life stages within the tree. In three of the northernmost SPB outbreaks in 2022 (Long Island, New York), we conducted ground surveys every two weeks throughout the growing season and collected UAV-based multispectral imagery in July 2022. Ground data revealed that SPB-attacked pitch pines (Pinus rigida Mill.) generally maintained green foliage until SPB pupation occurred within the bole. This tree decline behavior illustrates the need for early attack detection tools, like multispectral imagery, in the beetle's northern range. Balanced random forest classification achieved, on average, 78.8% overall accuracy and identified our class of interest, SPB early attack, with 68.3% producer's accuracy and 72.1% user's accuracy. After removing the deciduous trees and just mapping the pine, the overall accuracy, on average, was 76.9% while the producer's accuracy and the user's accuracy both increased for the SPB early attack class. Our results demonstrate the utility of multispectral remote sensing in assessing SPB outbreaks, and we discuss possible improvements to our protocol. This is the first remote sensing study of SPB early attack in almost 60 years, and the first using a UAV in the SPB literature. [ABSTRACT FROM AUTHOR]

The photosynthetic acclimation of boreal evergreen conifers is controlled by regulatory and photoprotective mechanisms that allow conifers to cope with extreme environmental changes. However, the underlying dynamics of photosystem II (PSII) and photosystem I (PSI) remain unresolved. Here, we investigated the dynamics of PSII and PSI during the spring recovery of photosynthesis in Pinus sylvestris and Picea abies using a combination of chlorophyll a fluorescence, P700 difference absorbance measurements, and quantification of key thylakoid protein abundances. In particular, we derived a new set of PSI quantum yield equations, correcting for the effects of PSI photoinhibition. Using the corrected equations, we found that the seasonal dynamics of PSII and PSI photochemical yields remained largely in balance, despite substantial seasonal changes in the stoichiometry of PSII and PSI core complexes driven by PSI photoinhibition. Similarly, the previously reported seasonal up-regulation of cyclic electron flow was no longer evident, after accounting for PSI photoinhibition. Overall, our results emphasize the importance of considering the dynamics of PSII and PSI to elucidate the seasonal acclimation of photosynthesis in overwintering evergreens. Beyond the scope of conifers, our corrected PSI quantum yields expand the toolkit for future studies aimed at elucidating the dynamic regulation of PSI. [ABSTRACT FROM AUTHOR]

Introduction: Drought-induced embolism formation in conifers is associated with several tracheid and pit traits, which vary in parallel from stem apex to base. We tested whether this axial anatomical variability is associated with a progressive variation in embolism vulnerability along the stem from apex to base. Methods: We assessed the tracheid hydraulic diameter (Dh), mean pit membrane area (PMA) and the xylem pressure at 50% loss of conductivity (P50) on longitudinal stem segments extracted at different distances from the stem apex (DFA) in a Picea abies and an Abies alba tree. Results: In both trees, Dh and PMA scaled with DFA0.2. P50 varied for more than 3 MPa fromthe treetop to the stembase, according to a scaling of -P50 with DFA-0.2. The largest Dh, PMA and P50 variation occurred for DFA<1.5 m. PMA and Dh scaled more than isometrically (exponent b=1.2). Pit traits vary proportionally with tracheid lumen diameter. Discussion and conclusions: Apex-to-base trends in tracheid and pit traits, along with variations in P50, suggest a strong structure-function relationship that is influenced by DFA. Although the effect of DFA on P50 has not been extensively explored previously, we propose that analyzing the relationship between P50 and DFA could be crucial for a comprehensive assessment of embolism vulnerability at the individual level. [ABSTRACT FROM AUTHOR]

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]

Lignocellulosic biomass represents an excellent alternative to fossil fuels in terms of both energy production and raw material usage for a plethora of daily-use products. Organosolv pretreatment is a fractionation technique able to separate lignocellulosic biomass into individual streams of cellulose, hemicellulose, and lignin under controlled conditions. Sawdust, the by-product of sawmill processing of Picea abies wood, was the subject of our investigation in this work. The aim was to evaluate the effects of different parameters of the organosolv process of spruce sawdust on the yield of components and how this affects the enzymatic saccharification of cellulose. Sixteen distinct pretreatments were performed with ethanol concentrations of 50 and 60% v/v at 180 and 200 °C for 15 and 30 min. Half of the pretreatments contained 1% sulfuric acid as a catalyst, while the other half were acid-free. Thereafter, the effects of different variables on the yield of products were assessed and compared to determine the ideal pretreatment condition. The results showed that cellulose-rich pulps, with cellulose content as high as 55% were generated from an initial mass of 37.7% spruce sawdust with the reactor operating at 180 °C for 30 min using 60% ethanol and 1% sulfuric acid. With the pretreatments performed with the catalyst at 200 °C, hemicellulose was almost entirely removed from the pulps obtained. The recovered hemicellulose fraction was composed mainly of monomers achieving up to 10 g/100 g of biomass. Delignification values of up to 65.7% were achieved with this pretreatment technique. Fractionated lignin presented low levels of sugar and ashes contamination, with values as low as 1.29% w/w. Enzymatic saccharification of the pretreated pulps yielded 78% cellulose hydrolysis, with glucose release higher than 0.54 g/g of biomass, indicating the potential of the pulps to be applied in a fermentation process. [ABSTRACT FROM AUTHOR]

Forest ecosystems are facing increasing challenges like natural disturbances. Despite positive disturbance impacts on the diversity of several taxonomic groups, there are still concerns, whether the drastic canopy opening can lead to a turnover from forest to open habitat species.We sampled arthropods along a disturbance gradient in Norway spruce (Picea abies)‐dominated protected areas across Central Europe using Malaise traps and metabarcoding.To analyse changes in arthropod communities in terms of forest affinities along the disturbance gradient, we explored the potential of a list of forest affinities (LFA) that provides information about species affinities from closed forest to open habitats.Our results show that the mean forest affinity decreased with increasing disturbance severity. This trend was accompanied by a decrease in forest‐associated species as well as community shifts for open and mixed habitat species. Responses varied between taxa and were most apparent in Coleoptera.Overall, the changes did not come with a complete replacement of forest specialists by species with higher affinities for mixed and open landscapes nor a drastic loss of forest species. Furthermore, we observed severely disturbed plots with a high mean forest affinity and vice versa, which calls for further studies using these kinds of species classifications.The LFA can provide additional information how species associated with forests habitats can react to environmental changes beyond increasing amounts of deadwood resources. Using additional trapping methods and determination techniques might increase the explanatory power of such analyses along ecological gradients. [ABSTRACT FROM AUTHOR]

Despite a clear preference of the Eurasian Three-toed Woodpecker Picoides tridactylus for spruce trees as foraging sites by both males and females, some studies showed intersexual resource partitioning that allows competition for food to be minimized. The objective of the study was to characterize foraging sites of the Three-toed Woodpecker in the primeval stands of the Białowieża National Park (BNP, Poland) in relation to sex. Although the woodpeckers foraged on seven tree species, both males and females foraged predominantly on spruce (83% and 90% of the observations, respectively). Selection indices showed a significant preference for dead spruce trees for both sexes and additionally for live spruce trees in the case of females. Spruce trees where woodpeckers foraged were twice as thick as those available, regardless of whether they were dead or alive. The only feature differentiating the feeding sites of males and females was the diameter of the part of the tree at foraging locations. This suggests that there is some niche partitioning between the sexes of the Three-toed Woodpecker in primeval stands of the BNP. Our research clearly showed that even in the very rich environment of the BNP, abounding in various forms of dead wood, large dead spruce trees are crucial for the Eurasian Three-toed Woodpecker. [ABSTRACT FROM AUTHOR]

In response to the decline of Central European spruce monocultures driven by various factors, the Demonstration Object of Reconstruction of Spruce Forests (DORS) was established in Husárik locality, Javorníky Mts., northwestern Slovakia. The area includes the Husárik trial site, where the applicability and efficiency of different artificial regeneration methods are studied. The trial was established on a 24-ha area cleared following the outbreak of spruce bark beetles in 2011. Its altitude is 800 m a.s.l., aspect NW, slope 30%, the soil is Ranker on the soft flysch sandstone bedrock. Our study covered 4 conifers - Norway spruce (spruce), European larch (larch), silver fir (fir), and Douglas fir (doug fir). Each species was regenerated using 4 different approaches: planting of commercial bareroot transplants (BR), planting of container transplants (CON), direct seeding (DS) and vegetative cell seeding using seed shelters (VCS). Results concerning the nine-year development of transplants and seedlings, along with the calculation of cost-efficiency, are presented. As to the species, BR and CON transplants of spruce and larch reached the best survival and height. The DS larch was the most cost-efficient method of establishment of a successfully established plantation (survival > 50%; stem height > 2/3 of the weed height; ratio of damaged individuals < 50%) with a total cost of 2 372 EUR·ha-1. On the contrary, the slow initial growth of fir and Douglas fir and their extensive damage resulted in the incomparably higher cost of establishment of their successfully established plantation, such as 4 980 EUR·ha-1 for five-years-old BR fir transplants. Our findings documented that current efforts related to the restoration of salvage-felled clearings remained difficult, especially in the case of introduction or reestablishment of coniferous tree species more vulnerable to open site conditions. [ABSTRACT FROM AUTHOR]

Species in the genus Picea are well-suited for afforestation on high altitudes and latitudes, but are fairly intolerant to high temperatures. In this study, Picea pungens, Picea abies, and Picea omorika were subjected to 45 °C, 40 °C, 35 °C, and ambient temperature (CK) for 6 h, and then allowed to recover for 28 d. Changes in phenotype, relative water content (RWC), and maximal photochemical efficiency (Fv/Fm) of photosystem II (PS II) were observed to ascertain their thermal tolerance. Overall, all three species were negatively affected by exposure to 45 °C, but P. pungens exhibited full recovery, with the highest RWC, while P. omorika exhibited partial recovery, and P. abies showed minimal recovery. The PS II of all three species were damaged after 45 °C treatment, but that of P. pungens exhibited the most dramatic recovery, with Fv/Fm recovering from 0 to 0.26. In conclusion, P. pungens was found to exhibit the greatest thermal tolerance, followed by P. omorika and P. abies. Thus, thermal tolerance should be considered as a tool for species selection for future reforestation endeavor in the face of climate change that is expected to bring high summer temperature events. [ABSTRACT FROM AUTHOR]

The karst region in southwest China is one of world's largest continuous karst landforms in the world, renowned for its unique landscapes and abundant biodiversity. This study collected 49 leaf samples (21 herbaceous plants and 28 woody plants) from the typical karst zone in Puding County, China, and determined the content of elements in plant leaves using ICP-OES. The concentration characteristics and discrepancy of trace elements (Cr, Cu, Fe, Mn, Pb, Sr, and Zn) in herbaceous and woody plants were analyzed employing statistical analysis models. The results revealed that there were significant differences in the concentrations of trace elements between herbaceous and woody plants. The median concentrations of trace elements in herbaceous plants and woody plants, ranked from high to low, were: Fe > Sr > Mn > Zn > Cr > Cu > Pb and Fe > Sr > Mn > Cr > Zn > Pb > Cu. The outcomes of the correlation analysis revealed discernible differences in the interactions of trace elements within the leaves of herbaceous and woody plants. Principal component analysis (PCA) indicated that Cu, Mn and Zn were influenced by different mechanisms from Cr, Fe, Pb and Sr in plant system. Orthogonal partial least squares discriminant analysis (OPLS-DA) showed that Pb and Cr had stronger distinguishing capabilities between herbaceous and woody plants compared to other elements. The OPLS-DA model was likely considered an optimized model for tracing element sources from different plant species, which has a greatly applied potential in source identification of plant-derived trace elements in a complex environment. [ABSTRACT FROM AUTHOR]

The high stability of stands with structures similar to natural ecosystems justifies adopting their composition as a management goal. Increasing the proportion of spruce in mixed forests and in deciduous forests in the Romanian Carpathian region, against the backdrop of climate change, may affect their stability. The natural distribution of tree species was investigated to establish natural forest types for defining future stand compositions. A forest in the Făgăraș Mountains of the Southeastern Carpathians was selected, and the mapping results were applied to a management unit of 4303.2 ha. Site conditions (e.g., altitude, exposure, etc.) are ecologically determined factors influencing the natural distribution of tree species and significantly influence species proportions. These factors, incorporated into models, estimate species proportions in future stand compositions with a root mean square error (RMSE) of 20%–24%. By adopting forest-type compositions as a management goal, the composition at the management unit level approaches that of natural ecosystems existing in 1950: Norway spruce (Picea abies (L.) Karst.) will decrease from 80.5% to 32.4%, while European beech (Fagus sylvatica L.) will increase from 12.5% to 41.7%, Silver fir (Abies alba Mill.) from 0.6% to 15.8%, and other species from 6.4% to 10.1%. Restoring ecosystems affected by their transformation into spruce monocultures leads to increased biodiversity and mitigates the effects of climate change, ensuring the long-term functionality of forest ecosystems, which are essential conditions for sustainable forest management. [ABSTRACT FROM AUTHOR]

This study aimed to assess the adaptive capacity of the dominant tree species in Lithuania, namely Scots pine, Norway spruce, and silver birch, to current climate conditions based on their changes in transpiration expressed through the tree sap flow intensity. The species-specific responses were investigated at two typical edaphically different forest sites with water-limited and water-saturated soils. Contrasting events like overflow in 2017 and drought in 2019 provided an opportunity to detect the adaptative capacity of the monitored tree species to these meteorological extremes. Norway spruce trees, due to having both the most intense sap flow at the beginning of the growing season and the longest period of active transpiration, demonstrated the highest annual transpiration rate, regardless of the hydrological regime of the site. Their decreased resilience to subsequent biogenic damage caused by pests due to a significant decrease in sap flow density during intense and prolonged droughts may reduce their importance in Lithuanian forestry. Silver birch trees, which demonstrated a reduction in sap flow after a drought following the untimely drop of their leaves and the end of active vegetation, even at the end of a prolonged warm period, can be seen to not have appropriate adaptations to current climate conditions. Scots pine trees are the best adapted to mitigating the recent threats of climate change. [ABSTRACT FROM AUTHOR]

This study examines the impact of ungulate browsing on the understory dynamics of the Cansiglio Forest, the only European beech high forest in the Southern Limestone Alps. Utilizing seven pairs of fenced versus unfenced forest stands established over two decades, we assessed how fencing affects understory structure and tree regeneration. Significant differences were found in cover, height and vascular species composition in both tree regeneration and shrub layers. Fenced areas showed a significantly higher number and greater average height of young trees, supporting the hypothesis that ungulate browsing negatively impacts tree regeneration. Despite previous studies attributing the lack of silver fir (Abies alba Mill.) regeneration primarily to red deer (Cervus elaphus Linnaeus, 1758) browsing, our findings did not show a significant association of this species with fenced conditions. While Rubus abundance was higher inside fenced areas, overall vascular species richness did not differ. Our results highlight the evident effects of ungulate browsing and suggest the need to consider other factors influencing forest regeneration and understory development. Future research should establish additional study replicates, balanced across diverse site and stand structure conditions, to further explore these dynamics. [ABSTRACT FROM AUTHOR]