ABSTRACT Diversifying tree species is increasingly important for enhancing forest resilience under climate change in Sweden. Douglas-fir (Pseudotsuga menziesii) is a promising alternative to native conifers but seedlings are sensitive to frost damage during establishment on exposed sites. This study evaluated the establishment and early growth of Douglas-fir seedlings planted under low shelters of different compositions. A field experiment in southern Sweden tested five shelter treatments: two densities of naturally regenerated birch (Betula spp.), Norway spruce (Picea abies L. Karst.) shelter, mixed birch-spruce shelter, and a clearcut control. Seedling survival, frost damage, height growth, top shoot elongation, and morphological quality were monitored over five years. Survival was high across all treatments and unaffected by shelter treatment. Frost damage was significantly reduced under all shelter treatments compared with the control, with the strongest protection provided by the densest birch shelter. Shelter also helped preventing multiple leaders, indicating improved seedling quality. No significant negative effects of low shelter on early height or shoot growth were detected. The results demonstrated that a low shelter can effectively mitigate frost risk during Douglas-fir establishment without compromising early seedling height growth, supporting its use as a practical silvicultural tool for climate-adapted forestry in Sweden.

This study explores the genetic diversity and past range dynamics of silver fir (Abies alba) with the objective of delineating the past demography of the species, the main postglacial colonization pathways and the current vulnerability of past glacial refuges. We applied restriction site-associated DNA sequencing (RAD-seq) to 26 A. alba populations to explore their phylogeographic structure and historical demographic changes. Three lineages were identified. One comprised populations from the southern range, whereas northern populations formed two lineages with subtle genetic differentiation between western and eastern populations. Northern Balkan and north-eastern Apennine samples clustered within introgression zones at the intersection of postglacial recolonization routes, consistent with their intermediate geographic positions. Demographic analyses indicated that southern populations remained relatively stable as glacial refugia, whereas northern populations experienced population declines during the middle Pleistocene associated with glaciations. Although the demographic events that shaped the current spatial structure of genetic diversity of silver fir go back to the Pleistocene, human pressure during the Holocene likely led to an abrupt range decline. We present a timely and broadly applicable framework for delineating the phylogeographic lineages of silver fir, leveraging the high resolution provided by SNP markers to identify major genetic discontinuities, contact zones and refugial areas. Inferences of past demographic dynamics indicate that certain rear-edge populations warrant priority in conservation strategies.

Densely packed needles along the shoots of evergreen conifers exhibit shade-acclimated photosynthetic characteristics even under full sunlight.

Field performance of innovative wood protection treatments on early successional macrofouling communities.

Mountain forests provide essential ecosystem services, including protection against natural hazards. However, climate change and the predominance of structurally homogeneous Norway spruce stands increase their predisposition to disturbances such as windthrow, bark beetle infestation, and snow breakage. Given limited resources for proactive and reactive forest management, prioritizing silvicultural interventions is crucial. We present a framework for the spatially explicit assessment of forest predisposition to snow breakage, windthrow, and bark beetle infestation at 10 m resolution across regional scales. The approach integrates high-resolution forest structural and site factor attributes primarily derived from nationally available airborne laser scanning (ALS) data. These attributes are weighted using an expert-based model according to their influence on disturbance predisposition. Weighted values are aggregated and classified into four predisposition classes, from low (< 50th) to extreme (> 95th percentile). Validation of local foresters at 142 reference sites showed significant correlations between forester-rated and modeled predisposition for windthrow and bark beetle, but not for snow breakage. New bark beetle infestations were strongly associated with increasing predisposition classes. Forest structural parameters such as forest mixture and spruce share, development stage, and canopy layering were key predictors and could be determined with high accuracy, enabling detailed and accurate predisposition mapping even in steep terrain. Assessing predisposition to snow breakage remains challenging due to the high stochastic variability in the location, characteristics, and amount of snow fall. As the main predictors are derived from nationwide ALS data, the methodology is transferable to other mountain regions. Developed in close collaboration with practitioners, the framework supports operational forest management by improving prioritization of interventions. • Framework for spatially explicit predisposition mapping in mountain forests. • Use of detailed forest structure parameters based on nationwide airborne laser scanning. • High correlation between predisposition mapping and on-site forester assessment. • Increase of detected bark beetle nests with increasing predisposition class. • Support of spatial prioritization of forest management interventions.

Integrative forest management (IFM) aims at integrating biodiversity conservation and global change adaptation into forest management for the sustainable provision of multiple ecosystem services. In this paper, and in the context of the European project TRANSFORMIT, we have developed a novel definition of IFM and a framework of guiding principles and attributes directing decision-making and objectives. IFM is structured around eight guiding principles and corresponding attributes, encompassing key ecological and silvicultural elements including the promotion of habitat retention, site‑adapted native tree species, natural regeneration, structural diversity, and landscape connectivity, while reducing the ecological impact of forestry operations and enhancing resilience to ecological stress and disturbance. Based on the definition, we explored the alignment of existing forest management concepts in Europe with IFM. Through content analysis, the review evaluates a set of widely used forest management concepts in Europe, including Continuous Cover Forestry, Close‑to‑Nature Forest Management, ProSilva, the Stepping Stone Concept, Retention Forestry, TRIAD, Climate‑Smart Forestry, and Closer‑to‑Nature Forest Management. These concepts were compared to IFM through a literature‑based assessment of their theoretical foundations and implementation strategies. While most concepts overlapped to different extents at the level of principles, the application of the corresponding elements varied across concepts. We subsequently attributed divergences in terminology, emphasis, and implementation in Europe to differing contexts, including disturbance regimes and management traditions. By using IFM as a common framework, our study clarified where existing concepts converge or diverge, thereby helping to close gaps between high‑level management goals and their practical implementation. Using IFM as a benchmark allowed us to compare the respective strengths and weaknesses of established concepts and to suggest improvements through a transparent dialogue between science, practice, and policy. To illustrate the potential actions necessary to implement IFM, we present an exemplary theoretical transition pathway for the transformation of disturbance‑prone Norway spruce monocultures toward more diverse, adaptive and resilient forests. The trajectory underscores that successful implementation of IFM relies on context‑specific, multi‑level planning and should be tailored to local ecological realities and stakeholder networks. In conclusion, IFM provides a unifying but non‑prescriptive concept that is capable of integrating diverse forest management objectives. However, effective implementation requires context‑ and region-specific adaptation, coordination across governance levels and sectors (e.g. forestry, conservation, and rural development), and continuous exchange between science and practice. • IFM provides a unifying framework to compare European forest management concepts • European concepts share goals but differ strongly in how integration is operationalized • IFM supports a coherent implementation across scales and management traditions • Transition pathways link integrative principles to concrete management actions • Operationalizing integration remains the key challenge for biodiversity-oriented forestry

Climate change affects the physiology and growth of trees, as well as the functioning, health, and productivity of forest ecosystems. This also concerns forests dominated by Norway spruce (Picea abies), one of the most important tree species in Europe, both in economic and ecological aspects. In the southern part of its range, the growth of spruce trees will be primarily constrained by limited soil water and high atmospheric vapour pressure deficit in the future. However, there is little information on how the trees will respond to increasing precipitation and the concomitant rise in environmental humidity, predicted for high latitudes. In this article, we evaluated the effects of increasing environmental humidity (soil vs. atmospheric humidity) on needle morphology, water status, and gas exchange in trees in a northern climate, aiming to understand the reasons for the growth decline in response to elevated air humidity revealed in our previous studies. A 15% increase in summer precipitation and the associated change in soil moisture do not considerably affect trees' performance in northern mesic conditions. Growing in increased air humidity (relative humidity elevated by ~5%) did not influence photosynthetic capacity, but it increased the light compensation point of photosynthesis (19.7 → 31.4 μmol m-2 s-1) and dark respiration rate (-0.216 → -0.297 μmol m-2 s-1) of the spruce trees. In light of climate change, both responses reduce photosynthetic output, increasing respiratory losses and reducing the growth potential of trees.

Forest management and species identity shape climate sensitivity and drought resilience in temperate mountain forests.

Tree seedlings at the treeline face various environmental extremes, in particular their needles can heat up close to thermal limits. Unlike mature tree needles, treeline conifer seedlings resist heat-induced water loss better, even though their cuticle lacks an outer layer. To determine whether these differences are due to ontogenetic factors or acclimative responses to higher heat loads, conifer seedlings were exposed to a controlled in situ long-term heat treatment. By comparing the rate of water loss through the cuticle (minimum diffusive conductance, gmin), cuticle thickness, and chemical micro-composition of control versus heated seedlings of deciduous Larix decidua and evergreen Picea abies, we intended to assess the acclimative plasticity in these traits. We also aimed to identify specific heat-induced changes of cuticle structure and function. Controlled in situ long-term heat treatment lasted for 6weeks with air temperature set 10-15K above ambient air (controls) with a set maximum leaf temperature of 42°C. This heat treatment significantly reduced gmin in L. decidua but it was not significant in P. abies. In both species, exposure to heat induced an increase in cuticle thickness, as well as provoking species-specific microchemical responses. Lignification of the middle lamella in L. decidua revealed heat-acclimative potential that likely contributed to reduced cuticular water loss. In P. abies, despite an obvious increase in cuticle thickness, no significant acclimative change was seen in gmin. Flavonoids (kaempferol) were detected throughout cuticle and outer cell wall of both species, but their contribution to reduced gmin is still unresolved. Our results demonstrate that cuticle and cell wall changes in conifer seedlings are species-specific and trait-dependent and highlight the role of epidermal chemistry in shaping resilience to climate warming at the alpine treeline.

ABSTRACT Spruce bark is generated in large quantities during industrial wood processing, yet its higher-value use in particleboards remains limited. Although bark substitution in particleboards has been studied repeatedly, less is known about how a gradual substitution series influences the broader property profile of single-layer particleboards manufactured under one fixed regime while simultaneously evaluating vertical density profile, screw withdrawal resistance and sound absorption. The objective of this study was to determine how replacing wood particles with 10–50% Norway spruce bark affects the physical and mechanical properties of single-layer particleboards. Up to 20% bark, bending properties, screw withdrawal resistance and sound absorption remained comparable with the reference, while IB increased from 0.44 MPa to 0.50 MPa at 10% bark. At 50% bark, the density profile became U-shaped, MOR reached its lowest mean value of 6.8 MPa, IB decreased to 0.39 MPa and MOE to 1,394 MPa. In contrast, equilibrium moisture content decreased from 9.2% to 6.7%, thickness swelling after 168 h from 65% to 49% and water absorption after 168 h from 153% to 129%, whereas board density remained unchanged. Norway spruce bark can replace wood particles up to 20%; higher substitution levels require optimisation of particle composition, resin dosage and pressing conditions.

Photoperiod modulates UV-B-induced acclimation to high light in Norway spruce and Scots pine seedlings.

Climate change and pest outbreaks are increasingly threatening conifer-dominated forests in Northern Europe, highlighting the need for greater species diversity to improve resilience. This study assessed early establishment success of six tree species: European aspen ( Populus tremula ), hybrid aspen ( P. tremula × P. tremuloides ), silver birch ( Betula pendula ), Norway spruce ( Picea abies ), Scots pine ( Pinus sylvestris ), and hybrid poplar ( P. trichocarpa × P. maximowiczii ), across seven sites in southern Sweden. Sites were categorized as either forest land (continuous forest cover >100 years) or forested arable land (former arable land afforested with Norway spruce for 40–70 years). Over three years, we monitored survival, height, and diameter growth. All experimental sites were fenced to exclude browsing. Wood ash was applied to a subset of hybrid poplars to assess its effect on establishment in acidic soils. Our results showed that hybrid aspen, birch, and European aspen had high survival and growth on forest land. On forested arable land, untreated Norway spruce, Scots pine, and hybrid poplar showed low survival, likely due to competition from dense vegetation. However, ash-treated poplar improved survival to approximately 80% and showed strong growth on forested arable sites. Principal Component Analysis indicated overall higher establishment success on forest land for most species, whereas hybrid poplar performed similarly on forest and forested arable land when wood ash was applied. These findings underscore the importance of matching species to site conditions during early establishment and provide empirical evidence to inform species selection for forest regeneration under similar site conditions in southern Sweden. • Site type strongly influenced establishment success of broadleaved trees. • Hybrid aspen and silver birch had the highest survival and early growth on forest land. • Norway spruce and Scots pine performed poorly on forested arable land. • European aspen performed similarly at both site types, demonstrating flexibility. • Results highlight species-site matching for reforestation in southern Sweden.

Success of saprotrophic fungi in wood requires resilience against plant defenses such as condensed tannins, but few studies quantify the variability in fungal tolerance while using well-characterized defence compounds purified from authentic sources. To investigate the antifungal activity of condensed tannins, we quantified the bioactivity of conifer tannins from Scots pine ( Pinus sylvestris ) and Norway spruce ( Picea abies ) against five saprotrophs. Condensed tannins from conifer barks and from Scots pine needles showed moderate antifungal activities despite their low contents, and tannin structure affected their efficacy against the fungi. Fungal sensitivity to condensed tannins was species-specific but did not vary systematically between rot types, indicating that specialization of brown-rot fungi on conifers does not imply better or worse tolerance to conifer tannins compared to non-specialized white-rot fungi. Despite the resilience of some saprotrophs, our analysis suggests generalized antifungal activity of condensed tannins against wood-decaying fungi.

This study investigates the climate sensitivity and resilience of radial growth in eight coniferous and deciduous tree species in the Vienna Woods, Austria. Using dendrochronological methods, we analyzed tree-ring width data from 63 forest plots to assess growth responses to meteorological variability over the period 1933-2023. Historic climate records were used to develop a water balance model, from which we derived seasonal growth factors. Linear mixed effects models were applied to quantify species-specific relationships between tree-ring width and climatic conditions during the current and preceding two years. Tree-ring width responded not only to climatic conditions of the current growing season but also strongly to those of the previous year. Soil moisture and air temperature emerged as the principal drivers of radial growth, with soil moisture positively and temperature negatively affecting ring width. Climatic conditions during June-July of the current year exerted the strongest impact on ring formation. Using regional climate trends and projected air temperature and precipitation trajectories for Central Europe under RCP4.5 and RCP8.5, we forecast future growing conditions for the region. Both scenarios predict an extended growing season, increased transpiration demand, and heightened drought risk - more pronounced under RCP8.5. However, projected increases in precipitation partly offset the drought risk. By combining historical climate sensitivity of radial increment with future climate projections, we modelled expected tree-ring growth for eight tree species. Most species are predicted to experience notable declines in radial growth, with the strongest reductions in conifers, including European larch (Larix decidua), Norway spruce (Picea abies), Austrian pine (Pinus nigra) and Scots pine (Pinus sylvestris). Deciduous species - Sycamore maple (Acer pseudoplatanus), European beech (Fagus sylvatica), and sessile oak (Quercus petraea) - show moderate declines. In contrast, Turkey oak (Quercus cerris) is projected to increase radial growth under future climate scenarios. These findings suggest that forest management in the Vienna Woods and adjacent regions should prioritize the promotion of warm- and drought-tolerant tree species such as Quercus cerris to enhance forest resilience and sustainability in the face of climate change.

Complex landslides contain internally heterogeneous zones that may respond differently to reactivation, complicating tree-ring based chronologies of slope activity. This study combines dendrogeomorphological analysis with electrical resistivity tomography (ERT) to test whether geophysics-based zonation could explain the spatial variability of tree-ring disturbances within a large complex landslide. ERT profiles and geomorphological mapping delineated three mechanically distinct zones: a downslope shallow-landslide sector ( S zone ), a moisture-rich gap infilled by weakly consolidated material ( G zone ), and an adjacent compact block with tension cracks ( B zone ). In total, 200 Norway spruce ( Picea abies (L.) H. Karst) were analysed for reaction wood (RW) and abrupt growth suppression (GS). RW intensity was quantified for each affected ring and GS classified by relative ring-width reduction. RW clearly dominates across the landslide. The S zone shows the highest stem inclinations and RW intensities, indicating enhanced shallow deformation, whereas RW duration is similar among zones. GS occurs everywhere but is proportionally most frequent in the B zone . Correlation analyses show that in the S and G zones , RW intensity and duration relate significantly to stem inclination, while no significant relationships appear in the B zone . These results demonstrate that internal landslide heterogeneity, as delineate by ERT, is reflected in tree-ring responses. Geophysics-based zonation offers an effective framework for interpreting growth disturbances and improves dendrogeomorphic reconstructions of complex slope movements. • Geophysics-based zonation reveals three contrasting landslide zones. • Combining geophysics and tree rings reveals internal landslide variability. • Reaction wood dominates in all three zones. • Growth suppression is dependent on the tree position.

Sheep ( Ovis aries Linnaeus, 1758) grazing has the potential for positive impacts on commercial forestry through weeding competing plants, or to be detrimental if browsing and trampling levels are high. In some regions of Norway, large, forested areas are fenced to minimize depredation risk from recovering carnivore populations on unsupervised sheep, but fences may alter the behavior of sheep leading to differential effects inside and outside of these fences. We estimated Norway spruce ( Picea abies (Karst.) L.) sapling growth and frequency of damage in Inland and Trøndelag counties Norway, and related these to grazing intensity, fenced status, and competing vegetation along 70 transects within 8 fenced and 11 unfenced clearcuts during August 2024. We found that growth of terminal leaders decreased with increasing grazing intensity inside fences, whereas growth increased along with grazing intensity outside fences. Sheep grazing in our study had a positive effect on spruce sapling growth form by decreasing slenderness, measured by height-to-diameter ratio, both inside and outside fences. While less than three percent of saplings were browsed overall, browsing of saplings did increase at higher grazing intensities. Trampling was negligible on all transects. Our results suggest that sheep grazing is compatible with spruce regeneration and carnivore fencing as negative impacts from increasing amounts of sheep resulting in reduced growth of terminal leaders may have been offset by decreasing height-to-diameter ratios. Lower height-to-diameter ratios suggest more resilient saplings that could make them better able to withstand stressors. However, if sheep are allowed to reach high grazing intensities, this balance may not be achieved as browsing increases. With increasing demands on forested landscapes, integrating sheep grazing in carnivore-resistant fences on commercial forests presents an opportunity for multiple-use land management with minimal associated trade-offs. • Sheep grazing, timber production, and carnivore-resistant fences were compatible. • Sheep inside and outside fences affected spruce sapling growth differently. • In all cases, grazing was associated with greater robustness of spruce saplings. • Browsing was infrequent but did increase as grazing intensity intensified.

Quantifying the probability of bark beetle induced damage in central German Norway spruce forests

The genetic parameters at 6, 9 and 12 years were studied in two progeny trials (one half-sib and one full-sib) of silver fir (Abies alba Mill.) in Romania, in order to establish an appropriate breeding strategy for advancing second-generation seed orchards. The half-sib trial (HS) consists of 60 open-pollinated families of plus trees from four first-generation seed orchards, while the full-sib trial (FS) consists of 51 half-diallel crosses of 11 plus trees from one seed orchard. Tree height and diameter were found to be under moderate to strong genetic control at both the family and individual levels. Total height showed a higher percentage of additive genetic variance than diameter in both types of progenies. Additive genetic variances increased with age for the diameter (from 12% to 36%), while for the total height, it decreased (from 76% to 35%). In the HS trial, family heritability was higher than individual heritability for both traits. The highest values of heritability were obtained for total height, both at the individual (0.76–0.35) and family levels (0.88–0.63). In FS progenies, the estimates of the narrow-sense individual heritability were lower than those at the family level and remained almost constant over time. The additive age-age genetic correlations and genetic correlations among growth traits were more stable and stronger in FS progeny than in HS progenies. Expected genetic gains were calculated at individual and family levels for different breeding strategies. The highest genetic gain will be obtained through selection of the best parents. Genetic gain slightly varied over age and for progeny tests. The level of genetic diversity, calculated for selected parents based on the breeding values, was high, while the inbreeding coefficient reduced. Combining the backward selection strategy with SSR analyses allows optimization for seed orchard design in order to mitigate inbreeding depression risks and enhance genetic diversity in the next breeding generation.

Assessing the potential effects of climate change on future forest composition in France.

Volatile organic compounds (VOCs) facilitate aboveground plant communication, but belowground signaling remains less understood. This study explored root-root interactions between Picea abies and Fagus sylvatica saplings in monospecific (Fagus-Fagus) and heterospecific (Picea-Fagus) pairs (n=6), excluding shoot-level VOC communication. Sender plants were treated with jasmonic acid (JA) to simulate herbivory and labeled with 13CO2 and 15NH4NO3 to trace nutrient transfer in a split-root design. VOC emissions and gas exchange were measured over ten days using PTR-TOF-MS and 13CO2-spectroscopy and 13C and 15N were analyzed in roots and shoots via EA-IRMS. Our findings reveal, that (i) JA treatment induced strong de novo terpenoid emissions from P. abies and enhanced emissions of oxygenated VOCs and benzenoids from F. sylvatica, (ii) F. sylvatica receiver plants responded similarly to JA-treated neighbors, indicating belowground signaling, and (iii) responses of receiver plants were more pronounced in the heterospecific treatment. Furthermore, formic acid emissions from soils increased following JA treatment, suggesting altered soil microbial activity. Isotopic analysis revealed C exudation into the rhizosphere and N transfer to receiver plants. These results suggest that belowground signaling enables early upregulation of herbivore-induced defenses in neighboring plants, and that the response intensity is modulated by species identity.