Spruce Forest Research Articles

Abstract Disturbance to spruce forests from wind and bark beetles is projected to worsen. It has been suggested that mixed-species forests could provide a more disturbance-resilient option than spruce monocultures. We used dynamic optimization to study how profitable mixed forests are compared to pure spruce forests by examining two similar neighboring stands facing a windthrow risk. We found that under high current windthrow risk levels in northeastern Finland, Norway spruce ( Picea abies )-only forests are more profitable than mixed forests consisting of spruce and silver birch ( Betula pendula ). However, if the windthrow risk to spruce trees increases by 35% compared to its current level, and the risk level of birch remains at its current level, mixed forests become more profitable. When carbon is priced at €50 per ton of CO 2 , the additional income from carbon storage in mixed forests outweighs the economic advantage of spruce timber, making mixed forests more profitable—even if the risk to spruce increases by only 25%. Hence, mixed-species forests become increasingly profitable as carbon prices rise. Therefore, mixed-species forestry represents a cost-efficient strategy for adapting to increasing environmental risks and mitigating climate change.

Abstract Key message Norway spruce ( Picea abies L.)-dominated production forests in southern Sweden had a significantly lower amount of deadwood and saproxylic beetle diversity compared to similar nature reserves, especially with regard to red-listed species. The species composition of beetles in reserves also differed from all young production forests. Enhanced conservation measures are essential to maintain biodiversity in production forests. Context Forests are the most important biomes globally for biodiversity, and a high diversity in structures is important for species richness. In Sweden, 87% of the forest area is used for wood supply, which may affect forest structures and biodiversity. Aims The aim of this study was to quantify the differences in the amount of deadwood and the saproxylic beetle diversity between typical Picea abies L. production forest stands of different ages and natural or near-natural forests. Methods In the current study, we sampled saproxylic beetles and amount of deadwood in stands of spruce forests in southern Sweden that represent four different parts of the forestry cycle, and compare this with nearby, recently protected spruce dominated nature reserves. In addition, we also sampled five old forest reserves in the region. Results The amount of deadwood was significantly higher in reserves than in production forests. In total, 478 saproxylic beetle species were caught and identified (in total 71,000 individuals). Overall, the highest species numbers were found in new and old reserves and 65–85 - year - old production forests, while the lowest number was found in production forests of 15–25 and 35–45 years. The odds of finding nature value indicator species and red-listed species were significantly lower in all production forest types except 65–85 - year-old ones compared to new nature reserves. This could be because clear-cutting practices did not become the main method for timber extraction until the early 1950s, meaning that some of the 60–85-year-old stands may never have been subjected to clear-cutting practices. However, old nature reserves had a clearly different composition regarding obligate saproxylic species, nature value indicators, and red-listed species compared to all production forest types. Conclusions The results bear relevance to the Swedish Forestry Act established in 1993, stating that the environmental goal and the goal of high wood production is equally important, since our forest types cover the period before and after. However, our results show that the 15–25-year-old forests are as species poor as the 35–45-year-old ones indicating that there was a lack of biologically important structures also after the change in policy.

Abstract. Soil organic carbon (SOC) is often retained more effectively in aspen-dominated forests compared to coniferous forests in North America, yet the reasons why are unclear. A potential driver could be differences in SOC protection mechanisms. Over decades to centuries, chemical (e.g., mineral association) and physical (e.g., aggregation) processes can work to preserve SOC stocks, which can vary across cover types. To investigate this hypothesis, we evaluate controls on SOC concentrations in the Coal Creek watershed (CO, USA), a montane ecosystem dominated by quaking aspen and Engelmann spruce and underlain by granite and sandstone. We examined a combination of biological, chemical, physical, and environmental conditions to evaluate potential abiotic and biotic mechanisms of SOC preservation at multiple depths. As expected, we observed greater SOC concentrations under aspen compared to spruce. Growing-season soil moisture, temperature, and CO2 and O2 varied with slope position and aspect, and thus forest cover type. Dissolved organic carbon (DOC) was lower under aspen compared to spruce. Exo-enzyme data indicate that aspen soil microbes likely access more organically bound resources; consistent with this, soil organic N exhibited higher δ15N values, hinting at a greater degree of organic matter processing. Finally, aspen soils exhibited greater root abundance, and aspen mineral soils revealed smaller mean aggregate diameters compared to conifer sites. Our data suggest enhanced biotic activities in aspen-dominated forest soils that promote both chemical and physical protection of SOC in aspen- relative to spruce-dominated forests, which may have implications for DOC export.

Archaeorhizomycetes is a class of globally widespread soil-dwelling fungi, originally proposed to be associated with plant roots, but their ecology and nutritional mode are not clearly defined. To increase the knowledge about Archaeorhizomycetes' ecology and biogeography, we investigate how they are distributed along major environmental gradients, as well as different soil compartments. To assess their abundance and diversity, we use both short- and long-read metabarcoding with class-specific primers for the long reads. The short-read sequences revealed that Archaeorhizomycetes is proportionally abundant and a dominant fungal class in alpine vegetation types, as well as boreal spruce and pine forests. The long-read sequences revealed high phylogenetic diversity of Archaeorhizomycetes, with 120 OTUs grouping into 13 clades with potentially differing ecologies and biogeographic distributions. Vegetation types and climate primarily structure the Archaeorhizomycetes community, while community composition was similar in litter, soil, and roots. However, Archaeorhizomycetes were significantly more abundant in soil and plant roots than litter, supporting the idea that Archaeorhizomycetes depend on the presence of plant roots. Our study illustrates that targeted group-specific amplification coupled with long-read sequencing is a powerful approach for exploring the diversity and ecology of specific fungal groups.

Norway spruce (Picea abies (L.) H. Karst.) and Scots pine (Pinus sylvestris L.) are among the most valuable tree species in the Lithuanian forests. Pure stands, which comprise approximately one-quarter of Lithuania’s forest area, provide an important framework for studying tree responses to thinning and susceptibility to species-specific diseases and damage. This study investigated stem health and quality in two experimental Scots pine stands (32 and 39 years old) and four experimental Norway spruce stands (36–43 years old) to assess the influence of the initial stand density and thinning intensity. Each stand consisted of five plots with different initial densities and was subjected to varying thinning regimes from stand establishment. Tree locations were mapped using the pseudolite-based positioning system TerraHärp, and local tree density was calculated. Stem health and damage were assessed using ICP-Forests methodology. Our results showed that across initial densities of 1000–4400 trees ha−1, tree dimensions (diameter and height) were similar, regardless of thinning intensity. The highest levels of stem damage and competition-induced mortality occurred in the densest, unthinned stands, with deer browsing and scraping from fallen trees being the most common damage agents. In contrast, thinned stands exhibited a higher incidence of stem rot (Heterobasidion annosum (Fr.) Bref.), particularly for Norway spruce. Finally, stand density alone did not consistently explain the patterns of tree mortality in either the pine or spruce stands. These findings suggest that cultivating Scots pine and Norway spruce at lower initial densities with minimal thinning may reduce the damage and losses caused by fungal infection. Finally, novel techniques, such as the pseudolite-based positioning system for geolocating trees and drone imaging for assessing tree health, have proven valuable in facilitating field surveys.

The aim of this work was to summarize the data on the ecological, biological, and morphological features of Calcipostia guttulata (Polyporales, Basidiomycota) by using the original materials, revised herba-rium specimens, data on molecular barcoding of original collections, the available literature, and iconography and information stored on the GBIF portal. It was shown that C. guttulata is a widespread, but rare polypore in the Holarctic; is confined to the early stages of drying of coniferous stands, primarily spruce forests; and is a poorly studied headwood pathogen and a saprotroph that colonizes coniferous deadwood and, less often, fallen trees. The morphological diagnosis of C. guttulata was clarified. Its substrate spectrum, distribution, and relationships with insects, which are important for forest pathology, have been identified most fully to date. The conservation status of the species and the prospects for its use in biotechnology are discussed.

Dynamic processes in indigenous spruce phytocenoses have been studied in the challenging climatic conditions of the subtundra zone, moderated by the heat brought from the south by the waters of the large Pechora River. Field material has been collected on permanent sample plots during 3 periods (2005–2006, 2013, 2022) in spruce forests of different types. The dynamics of the size structure and vitality status of woody plants in indigenous spruce forests have been analyzed based on the variability of tree stem diameters at a height of 1.3 m and the height of undergrowth. The data obtained show that with an increase in the average diameter of spruce trees in stands of subtundra spruce forests of different types, the coefficient of variation increases. The distribution of trees by absolute diameter classes is characterized by a slight stretch, usually with 1 maximum shifted to the left. In spruce forests developing on swampy-podzolic soils, most of the trees belong to small diameter classes (≤10 cm). In spruce forests of the green-moss type group, the interval of diameter classes is extended due to the presence of large trees in the stands. This dimensional structure is typical for the indigenous spruce forests of the middle taiga. The distribution of the total stand of timber by diameter classes is described as a pulsating curve with a single maximum, which, in some cases, may be interrupted at larger diameter classes. The size of the undergrowth has turned out to be more variable over time. Under the canopy of stands of subtundra spruce forests, a continuous renewal process is being observed. Stationary monitoring of the viability and damage of trees and undergrowth, based on a visual assessment of the plant by the crown, has shown an improvement in both the upper layers of the tree canopy and the lower layers of the undergrowth. The stand and undergrowth, which have been characterized as weakened at the beginning of the observation, moved into the healthy category during the monitoring period. The results of the research are part of the environmental monitoring of self-regulating spruce forests in the Pechora River basin. Long-term scientific work on permanent sample plots allows us to study the variability of plant communities and their response to global change, which contributes to a deeper understanding of the mechanisms underlying these changes, as well as ways of adapting to them. The data obtained will serve as a basis for further environmental monitoring and forecasting of the state of self-regulating Pechora forests.

Forest stand composition and structure are key factors affecting the productivity, resilience, and ecological functioning of forest ecosystems under changing climatic conditions. However, quantitative assessments comparing different stand types and mixture degrees remain limited, particularly for Central European beech–spruce forests. The study aimed to evaluate the production potential of Norway spruce (Picea abies [L.] H. Karst.) and European beech (Fagus sylvatica L.) in three different stand structures; specifically, two monocultures (A1_EB, A2_NS), two even-aged mixed stands (B1_EB, B2_NS), and one structurally rich stand (C_NS) were studied. The Forest Training Enterprise Křtiny in the Masaryk Forest, South Moravia, Czech Republic (397–553 m a.s.l.) managed all these stands. The competitive environment among the variants was not statistically significant; however, the production parameters showed substantial differences. The structurally rich spruce stand (C_NS) exhibited more than 40% higher production compared to the other spruce variants (A2_NS and B2_NS). Analysis of five-year basal area inkrement (BAI) periods from 1991 to 2020 consistently confirmed the highest values for the C_NS variant, with significant differences (p < 0.05) in most observed intervals. The results demonstrate the strong production potential of the structurally rich stand, especially for Norway spruce, under Central European conditions. In contrast, European beech showed a more moderate growth pattern, with no statistically significant differences observed across the five-year intervals. The study supports silvicultural strategies that promote mixed and spatially heterogeneous stand structures as a mean to increase both productivity and ecological stability.

Forest health status impacts biodiversity of invertebrates. An example from spruce forests of a sandstone landscape, Bohemian Switzerland National Park, Central Europe

Norway spruce (Picea abies (L.) H. Karst.) is a primary forest-forming species in the European part of Russia, both in terms of its distribution and economic importance. A number of studies indicate that one of the reasons for the disturbance of spruce forests is linked to rising temperatures, particularly the detrimental effects of extreme droughts. The aim of our research is to identify changes in the structural and functional organization of mature spruce forests at the center of the East European Plain. The study was conducted in intact spruce forests using resurveyed vegetation relevés within the Smolensk–Moscow Upland, with relevés repeated after 40 years (in 1985 and 2025). Changes in structural and functional parameters of spruce communities were analyzed. The results showed that significant disturbances of the tree layer led to changes in the vegetation of subordinate layers, as well as the successional dynamics of spruce forests. It was found that following the collapse of old-growth spruce stands, two types of secondary succession developed: (1) with the renewal of spruce and (2) with active development of shrubs (hazel and rowan) and undergrowth of broadleaved species. It was also demonstrated that the typological diversity of the studied communities changed over 40 years not only due to the loss of the tree layer and the formation of new “non-forest” types but also because several mixed spruce-broadleaved communities transitioned into broadleaved ones, and pine–spruce communities of boreal origin shifted to nemoral types. An analysis of the complete species composition of spruce forests based on Ellenberg’s scales scoring revealed changes in habitat conditions over the 40-year period. A noticeable trend was an increase in the proportion of thermophilic and alkaliphilic species, indicating a shift toward a nemoral vegetation spectrum. It is expected that under the current forest management regime, the next 40 to 60 years will see a decline in the proportion of spruce within mixed stands, potentially culminating in the complete collapse of monospecific spruce forests in the center of the East European Plain.

In recent years, the four-eyed fir bark beetle (Polygraphus proximus Blandford, hereinafter referred to as P. proximus), a stem pest of Far Eastern origin, has been spreading rapidly across the regions of Russia, inhabiting fir stands. The P. proximus can lead to a significant reduction in the stock of fir stands, as well as to the disappearance of the species from the composition of forest plantations. The purpose of the study is to assess the changes in the stock and share of fir stands in the species composition of plantations due to the influence of the P. proximus in the conditions of the South-taiga region of the European part of the Russian Federation, Perm Krai. The objects of the study are fir stands growing on the territory of the forestries of Dobryanka and Perm. The materials of the acts of forest pathology surveys conducted by forest pathologists of SBI PK «Gosleskhoz» and the Center for Forest Protection of the Perm Krai in the period from 2022 to 2024, which recorded the drying out of fir stands from the effects of the P. proximus, were ana-lyzed. As a result, it is established that, on average, in plantations of all types of forests after the impact of P. proximus, the share of dead fir trees exceeds the share of living trees, and the participation of fir in the composition formula of forest stands decreases by 1 unit as a result of drying out. In linden spruce forests, the proportion of dead trees exceeds the proportion of living trees by an average of 2.5 times! The complete death of fir stands is noted in 21.4% of cases, with the largest proportion of completely dead fir stands recorded in linden forest type plantations (14.2%). According to the authors, the high mortality of fir trees in the conditions of the linden forest type is explained by the low share of fir stands in the species composition of the plantations of this type of forest. The weak statistically significant inverse correlation between the proportion of fir in the composition of stands and the proportion of trees affected by P. proxi-mus is found.

Abstract This study investigates the impact of torrefaction on municipal solid waste (MSW) fractions, focusing on energy recovery, calorific value enhancement, mass yield reduction, and energy densification under both nitrogen (N2) and carbon dioxide (CO2) atmospheres. As waste production increases globally, driven by population growth and industrialization, there is growing interest in waste‐to‐energy conversions to address both energy demand and waste management concerns. Torrefaction, a thermochemical pretreatment, enhances the properties of solid waste to make them more suitable for energy recovery processes like pyrolysis and gasification. This study demonstrated that torrefaction effectively addresses the low energy content of MSW, achieving an energy densification ratio up to 1.73. The process showed high energy efficiency, with energy recovery ranging from 69.3% to 99.15%, while different waste fractions exhibited varied behaviours during torrefaction. Lemon peels exhibited the highest energy densification while paper cups achieved the highest energy recovery but minimal energy densification. Wood waste fractions, such as white spruce sawdust and forest residues, demonstrated balanced performance with high energy recovery and moderate energy densification, making them ideal candidates for prioritizing high energy recovery applications. The results show that the use of CO2, representing flue gas, enhances volatile release and improves energy densification in some fractions, particularly forest residues, compared to N2, while also promoting better carbon retention at higher temperatures. Overall, this study highlights the importance of waste stream selection, torrefaction atmosphere, and temperature optimization to improve the efficiency of MSW torrefaction, offering insights for the use of flue gas torrefaction in waste‐to‐energy processes.

Mycobiome and microbiome resilience of alpine Norway spruce forests in response to disturbances: Can soil and endophytic microorganisms help drive an efficient forest management?

Balancing biodiversity, carbon, and profit with pathogen risk: Effects of felling age and thinning in spruce forests.

Abstract. Early detection of bark beetle (BB) infestations in Norway spruce forests is essential for effective forest management. While UAV imagery offers high-resolution data, selecting appropriate crown pixels to detect subtle spectral changes during early BB infestation stages is still a challenge that needs further investigation. This study examines the impact of automatic Individual Tree Crown Delineation (ITCD) methods in detecting early-stage BB infestations, particularly during the green-to-yellow stage. On July 19, 2022, high-resolution multispectral UAV imagery (2 cm) was acquired using the DJI Phantom 4 Multispectral sensor over a 4-hectare forest plot in Krkonoše National Park, Czech Republic. Treetop detection was performed using local maxima filtering, while four ITCD algorithms: Buffer, Marker-Controlled Watershed Segmentation, thiessen polygons, and seeded region growing, were used for crown delineation. Spectral data from five bands and five vegetation indices were extracted for each automatic ITCD method, as well as for manually delineated crowns, across 11 infested and 11 healthy trees. Spectral separability was assessed using the Mann-Whitney test. The findings revealed that the 3-meter fixed window filter effectively detected treetops but encountered challenges with double detections and missing smaller trees. Seeded region growing proved the most accurate for crown delineation. Statistical analysis showed that red-edge and near-infrared spectral bands, along with vegetation indices (NDVI, GNDVI, OSAVI, and RENDVI), successfully separated healthy from infested trees using both automatic ITCD and manual delineation. However, manually delineated crowns exhibited greater sensitivity to spectral variations, especially in the red band, making manual delineation more effective for early-stage BB detection. While automatic ITCD methods excelled in detecting Excess Green Index (ExG) differences. Though, automatic ITCD methods are computationally efficient, manual delineation or refinement of automatic ITCD is needed for accurate monitoring of subtle spectral changes during BB infestations (green-to-yellow transition). Precise crown delineation and early BB detection rely on high-quality pre-processing, expert knowledge (of infestation stages by foresters), and field observations (e.g., tree positioning using GPS or total station and BB symptoms), with multitemporal imagery aiding in tracking infestation progression within the tree crowns.

The elemental composition of Norway spruce needles in spruce forests with varying degrees of heavy metal contamination in the North-West of Russia has been considered. The aim of the research has been to evaluate the content of Cu, Zn, Mn, Fe, Ni, Pb, Cd and Cr and their pair correlations in the needles of Norway spruce trees in stands located at a distance of 5–31 km from metallurgical enterprises and thermal power plants and near roads with different traffic intensity. Sample collection and determination of the amount of elements in the needles have been carried out using standard techniques. Data analysis has been performed using the Python 3.8 programming language. The comparison has been performed using nonparametric methods. The contamination of the sample plots has been characterized using the coefficients of concentration, the same as Contamination Factor (CF), of elements in the needles and the total indicator of contamination. The average level of pollution has been detected at sites 5 and 12 km from the metallurgical enterprise in the city of Gatchina, the Leningrad Region, and 25 km from the Cherepovets State District Electric Power Station (50 km from the city of Cherepovets), the Vologda Region. Low levels of pollution have been noted near highways in the Luybansky Forestry of the Leningrad Region, 5 and 12 km from the Cherepovets State District Electric Power Station. The elemental composition of the needles at all sites has been characterized by a slightly lower content of Cu, Ni, Mn, and Zn and a significantly higher amount of Pb, Cd, and Cr than in the background stands of Northern Europe. In the area closest to the city of Gatchina, a Mn deficiency has been detected in fir trees of the 1st layer and undergrowth. Reliable Spearman correlation coefficients have been found for the median content of Cu and Cr (r = 0.89, the Gatchina Forestry), Pb and Cd (r = 0.83, the Kaduy Forestry), Ni and Cd, as well as Ni and Pb (r = 0.89 and r = –0.88 near highways in the Lyubansky Forestry) in the needles. The results of the research can be used to improve the methodology for environmental monitoring of territories using spruce as a bioindicator.

ABSTRACT Heterobasidion root rot caused by Heterobasidion parviporum is the most destructive disease affecting Norway spruce, while H. annosum s.s. is the primary causal agent of root rot in Scots pine. Early diagnosis of these pathogens is essential for effective disease management. Dogs, with their highly developed sense of smell, may have significant potential to detect forest pathogens before they cause severe damage. In this study, we evaluated whether trained volunteer dog-handler teams could identify Heterobasidion spp. from wood, fruit bodies, or mycelia in vitro and in vivo, aiming to enhance early detection of Heterobasidion root rot in pine and spruce forests. Dogs were successful both in young and mature pine stands to detect trees infected by H. annosum s.s. Seven dogs indicated H. annosum s.s. with a mean sensitivity of 72% and mean precision of 84% in young pines. Three dogs indicated infection with a mean sensitivity of 88% (precision 99%) in mature pines. Five of nine dogs achieved sensitivity over 70% in indoors scent discrimination line-up test. The results indicate that dogs can be used as an aid in searching for Heterobasidion spp. in Scots pine and Norway spruce stands, but further testing is needed in larger areas.

Abstract Sitka spruce (Picea sitchensis (Bong.) Carr.), is the most common tree species in UK’s commercial forests. Tree species diversification of the UK’s commercial forests is currently occurring to make them more resilient to new pests and pathogens and climate change. The potential ecosystem implications of this transition are poorly understood. Our aims are to, (i) list the biodiversity known to be supported by Sitka spruce as this has not been collated previously, and (ii) assess the changes, in both ecosystem functioning and biodiversity supported, if Sitka spruce forests are diversified with any of 34 other tree species. Using records from across the UK, we identified 564 species that use the Sitka spruce trees as a living space or for feeding. Most of these associated species were non-specialist and found on a wide range of other trees. Data from an extensive literature review showed that diversification with broad-leaved trees would potentially result in faster nutrient cycling and litter decomposition with potential implications for carbon storage in the litter layer. Diversification with Oak (Quercus petraea/robur (Matt.) Liebl.), sycamore (Acer pseudoplatanus L.), Scots pine (Pinus sylvestris L.), birch (Betula pendula/pubescens Roth), beech (Fagus sylvatica L.), and Norway spruce (Picea abies (L.) H. Karst.) provide the greatest biodiversity benefits both through supporting the biodiversity found on Sitka spruce and additional biodiversity thought to be absent on Sitka spruce. However, except for sycamore, none of these tree species will grow in long-term intimate mixed stands with Sitka spruce. Therefore, we propose that diversification of Sitka spruce plantations should be carried out as ‘blocky mixes’, i.e. small blocks of single tree species, with tree diversity occurring within a management unit, as a pragmatic approach to support timber production and provide biodiversity benefits. However, the optimal size and spatial arrangement of such blocks requires further assessment.

This paper aims to analyze the patterns and dynamics of long-term atmospheric pollution (deposition of Pb, Cd, and Hg) and its impact on Picea omorika (Pančić) Purk (Serbian spruce) forests in Tara National Park. Due to changing ecological conditions, these relict-endemic forests have experienced significant habitat loss and fragmentation of their last remaining refugia. In this study, we analyze heavy metal deposition patterns and dynamics and the content of these metals in the Serbian spruce forest (soil and biomass). The heavy metal content was analyzed and compared with ICPF (International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests) data across Serbia, revealing the level of environmental risk these ecosystems face from air pollution in comparison to other forest ecosystems in the country. Four Serbian spruce forest clusters stand out compared to others, with the highest long-term heavy metal deposition and elevated levels of lead, cadmium, and mercury detected in both soil and biomass at these sites. These findings may serve as a guide for identifying priority locations for future monitoring, facilitating the implementation of the Critical Loads concept. It also highlights the need for revision of forest management practices in protected areas and the implementation of buffer zones.

Climate change affects carbon sequestration dynamics and phenology in forests, especially in alpine and subalpine regions. Here, long-term trends in climate, net ecosystem CO2 exchange (NEE), net carbon uptake period (CUPnet) and their drivers were investigated, using 26 years of flux measurements in a subalpine spruce forest (CH-Dav, Switzerland; 1997 to 2022). CUPnet length, start (SOS) and end of season (EOS) were extracted from smoothed daily NEE time series. We used machine learning to determine the importance of environmental drivers on daily NEE and CUPnet. Annual mean and maximum air temperatures (Tair) increased, while soil water content (SWC) decreased significantly between 1997 and 2022. Annual C sinks increased from 1997 to 2012, leveled off between 2012 and 2015, followed by a decline. Annual NEE was strongly related to CUPnet length, SOS, and EOS. No significant trends in CUPnet, SOS, or EOS were detected, most likely indicating ecophysiological acclimation, that is, physiological adjustments to changing environmental conditions over the past 26 years. We identified 48 days with significant negative trends in mean daily NEE over the 26 years, that is, stronger net C uptake or weaker net C loss, particularly in spring and autumn, but no significant positive trends. Daylength, incoming shortwave radiation (Rg), SWC, and minimum Tair were the main drivers of daily NEE. SOS was mainly driven by daylength and Tair, EOS by daylength and Rg. Thus, the spruce forest benefited from higher temperature between autumn and spring, with higher net C uptake during favorable conditions and reduced C loss when winter photosynthesis compensated respiration. However, high summer temperatures increasingly limited NEE, suggesting adverse effects for subalpine Picea abies forests in the future. Our study demonstrated that identifying driver contributions to NEE dynamics at daily time scales allows better understanding of the complexity of climate change impacts on forest C dynamics.