Spruce Stands Research Articles

Výchovný zásah v mladých smrkových porostech jako nástroj mitigace globální klimatické změny?

Although the ongoing global climate change elicits a shift in tree species composition along the vertical gradient, very extensive areas of pure Norway spruce [Picea abies (L.) Karst.] stands still occur out of their ecological optimum in the Czech Republic and Central Europe. Adaptive measures should be applied in these stands to promote productivity and stability. All measurements were performed in the 2018–2021 period on three permanent research plots located in the North-East part of Bohemia (Czech Republic). Based on the results, the most favourable way to increase solar radiation use efficiency expressed by canopy production index (CPI) and leaf area efficiency (LAE) is in-time heavy precommercial thinning application. The highest CPI and LAE values were observed in the Norway spruce stand after heavy pre-commercial thinning application (CPI = 2.00 and LAE = 1.59). In contrast, CPI = 1.26 and LAE = 0.99 were observed after the mild one, and CPI = 0.73 and LAE = 0.60 were reported in the control treatment with no silvicultural intervention. Overall, the presented results indicate a positive effect of heavy pre-commercial thinning on CPI and LAE in pure young Norway spruce stands. However, more effort should be devoted to studying the impact of different pre-commercial thinning intensities on solar radiation use efficacy across a broader gradient of site conditions, and future work should also be extended to other tree species.

Metabarcoding reveals that mixed forests mitigate negative effects of non-native trees on canopy arthropod diversity.

Averting climate change-induced forest diebacks increasingly relies on tree species planted outside of their natural range and on the addition of non-native tree species to mixed-species forests. However, the consequences of such changes for associated biodiversity remain poorly understood, especially for the forest canopy as a largely understudied forest stratum. Here, we used flight interception traps and a metabarcoding approach to study the taxonomic and functional (trophic guilds) composition and taxon richness of canopy arthropods. We sampled 15 monospecific and mixed stands of native European beech, native Norway spruce-planted outside its natural range-and non-native Douglas fir in northwest Germany. We found that the diversity of arthropods was lower in non-native Douglas fir compared with native beech stands. Taxon richness of herbivores was reduced by both conifer species. Other functional guilds, however, were not affected by stand type. Arthropod composition differed strongly between native broadleaved beech and monospecific coniferous (native spruce or non-native Douglas fir) stands, with less pronounced differences between the native and non-native conifers. Beech-conifer mixtures consistently hosted intermediate arthropod diversity and community composition compared with the respective monospecific stands. Moreover, arthropod diversity had a positive relationship with the number of canopy microhabitats. Our study shows that considering arthropod taxa of multiple functional groups reveals the multifaceted impact of non-native tree species on forest canopy arthropod communities. Contrasting with previous studies that primarily focused on the forest floor, we found that native beech hosts a rich diversity of arthropods, compared with lower diversity and distinct communities in economically attractive, and especially in non-native, conifers with few canopy microhabitats. Broadleaf-conifer mixtures did not perform better than native beech stands, but mitigated the negative effects of conifers, making such mixtures a compromise to foster both forest-associated diversity and economic yield.

Different Adaptive Potential of Norway Spruce Ecotypes in Response to Climate Change in Czech Long-Term Lowland Experiment

As a result of climate change, Norway spruce (Picea abies [L.] Karst.) is dying across Europe. One of the primary reasons for this is the cultivation of unsuitable spruce provenances and ecotypes. This study deals with the growth and genetics of the ecotypes of Norway spruce, the most important tree species of the Czech Republic. At the study site, namely Cukrák, an experimental site was established in 1964 to plant three basic spruce ecotypes: low-elevation (LE), medium-elevation (ME) and high-elevation (HE) ecotype. A dendrometric inventory, dendrochronological sampling and genetic analyses were carried out on individual trees in 45 to 46 years old spruce stands. The ME ecotype was the most productive in terms of its carbon sequestration potential, while the HE ecotype had the lowest radial growth. All ecotypes exhibited a noteworthy negative correlation between tree-ring growth and seasonal temperature, annual temperature, previous year September to current year August temperature, June to July temperature, as well as individual monthly temperatures from previous May to current August. The relationship of annual and seasonal precipitation to growth was significant only for the LE and ME ecotypes, but precipitation from previous year September to current year August and precipitation from current June to July were the most significant for all ecotypes, where the ME had the highest r value. The HE ecotype does not adapt well to a dry climate and appears to be unsuitable compared to the other ecotypes under the studied conditions. This study also documented intra-population genetic variation within years of low growth, as evidenced by significant clonal heritability. The selection of the appropriate spruce ecotypes is essential for the stability and production of future stands and should become an important pillar of forest adaptation to climate change.

Norway spruce susceptibility to bark beetles is associated with increased canopy surface temperature in a year prior disturbance

Forest pest infestation is a major driver of tree mortality, altering ecosystem functioning, changing microclimates, and causing significant woodland loss globally. We examined environmental effects on Picea abies susceptibility to bark beetle Ips typographus before and during a multi-year severe outbreak in a protected, natural, Norway spruce-dominated mountain forest in Central Europe. In contrast to recent publications that focus on identifying spectral signatures related to the early (“green”) beetle attack stage, we investigated large-scale signals indicating the predisposition of stands to herbivore infestation in the year preceding the outbreak, using remotely sensed (RS) climate and ecological data. Through partial least square regression, we analyzed interactions between microclimate variables related to susceptible, infested, and healthy spruce stands. Using RS classification maps, we reconstructed the annual forest area changes from 1985 to2020 and linked it to previous climate events.Our findings indicate that the surface temperature in stands subsequently attacked was higher compared to intact stands in the year prior colonization. Over the research period, the forest’s original cover decreased by 50%, with an average annual change of 1.5%. The recorded episodes of above-average tree mortality were linked to extended summer warming and short-term winter temperature declines, accompanied by windstorms. We argue that the use of remotely sensed temperature data can aid in predicting landscape scale spruce susceptibility to bark beetle outbreak one year before the actual attack occurs. This prediction could substantially improve management of forest disturbance, by providing more time to implement preventive or protective measures.

Investigating the abundance and diversity of sawflies (Hymenoptera, Symphyta) within commercial Sitka spruce plantation forests in mid‐Wales

Abstract Sitka spruce is a widely planted and economically important tree species in the United Kingdom; hence, identifying any future biotic or abiotic threats to its productivity is important. Defoliating insects are widely considered to be major forest disturbance agents, and these can include the sawflies (Symphyta), which are well known to reach high population densities that can cause significant outbreak events, leading to tree mortality or impacts on growth. The aim of the current study was to investigate the abundance and diversity of sawflies within stands of Sitka spruce over an elevation range and to evaluate whether there were any potentially important species present. Experimental plots were established in two commercial forest plantations in mid‐Wales, and the adult sawfly community was assessed over a 3‐year period using yellow pan traps. Sixty species of sawfly were caught over the 3‐year period, which accounted for >11% of all known British sawfly species. Results indicated that there were generally greater abundance and diversity of sawflies at lower elevational plots, where temperatures were higher. The most abundant sawfly species captured in the study was the notable defoliator species, the mountain spruce sawfly (Epicenematus montanus), which was found in particularly high numbers in the low‐elevation plot in Hafren forest. A further seven spruce‐associated sawfly species were also caught across the experimental plots. The study highlighted the presence of a number of notable spruce‐associated sawfly species (E. montanus and Pristiphora spp.), some of which have caused significant defoliation of spruce (Picea) species in Europe. The generally higher abundance of these sawflies at lower elevations indicated that Sitka spruce may potentially become more vulnerable to defoliation events caused by sawfly outbreaks in the future, especially when considering current projected climate change predictions.

Effects of Douglas fir cultivation in German forests on soil seepage water quantity and quality

Norway spruce (Picea abies L.) has been a key tree species and timber source in European forests the last centuries and is increasingly suffering from drought and bark beetle infestations due to climate warming. Current management options include replacing of Norway spruce monocultures with pure and mixed stands of European beech (Fagus sylvatica) that is the naturally dominating tree species in Central Europe. Additionally, Douglas fir (Psudotsuga menziesii), a tree species with high water use efficiency and drought tolerance, is being increasingly cultivated to increase the resilience of European forests and meet the future demand of conifer timber in a warming climate. We studied the seepage water quantity and quality with a particular focus on the nitrate (NO3–) concentration and N leaching under pure and mixed stands of Douglas fir, Norway spruce, and European beech at seven sites in Germany. Additionally, we investigated seepage water concentrations of SO4-S, Ca, Mg, K, Al and hydrological variables (interception, canopy throughfall, transpiration). Looking at the seepage water quantity and quality, the best management option is the cultivation of pure beech stands. However, this is associated with the well-known risk of monocultures concerning ecosystem disturbance. Beech stands showed the highest seepage water quantities and the lowest seepage water concentrations of major cations and anions, including NO3–. Seepage water quantity was the smallest under pure Douglas fir compared to spruce and beech stands. The composition effects of stand tree species on seepage water quality and nutrient leaching were site-dependent. At N-rich sites, pure Douglas fir stands showed higher seepage water NO3– concentrations than spruce and beech stands, whereas the tree species effects were small at N-poor sites. With respect to seepage water quantity and quality, cultivation of mixed Douglas fir–beech stands is a promising option for producing conifer timber and at the same time avoiding increased disturbance risks of mono-species forests under a warmer climate. Our results support the recommendation of mixed Douglas fir–beech stands based on soil quality, ecosystem resilience, and forest economic studies.

THE INFLUENCE OF THE TYPE OF FOREST AND THE TYPE OF FOREST GROWING CONDITIONS ON THE STABILITY OF SPRUCE STANDS IN THE ZONE OF CONIFEROUS-DECIDUOUS FORESTS OF THE PERM KRAI

There has been a massive drying out of spruce plantations in recent years. Many versions about the cause of this phenomenon have been put forward by scientists. Despite the active study of the problem of drying out of spruce plantations around the world, a forest management system aimed at reducing the damage from drying out has not been developed yet. Important silvicultural indicators of plantations that can affect their stability are the type of forest growing conditions and the type of forest. The purpose of the study was to establish the influence of the type of forest and the type of forest growing conditions on the resistance to drying out of spruce forests growing in the zone of coniferous-deciduous forests of the Perm Krai. The spruce forests of this territory were the objects of study. The sanitary condition of spruce forests growing in common types of forest growing conditions (B2, C2, C3) and forest types (green moss spruce and pine forest, wood sorrel spruce and pine forest, linden spruce and pine forest, grass spruce and pine forest) of the Perm Krai was determined. The weighted average scores values of the sanitary condition of the spruce forest of the surveyed forest plantations were distributed by forest types and types of forest growing conditions. Statistical indicators of the average weighted scores of the sanitary condition of spruce in different types of forests were obtained. A one-factor analysis of variance was carried out to compare the mean values. It was established that the type of forest and the type of forest growing conditions have an impact on the sanitary condition of spruce stands. The better the forest growing conditions, the more resistant the spruce trees are to drying out, on average. At the same time, soil moisture is more important than soil nutrient status.

Comparison of nutrient and carbon stocks in the aboveground biomass of mature silver fir (Abies alba Mill.) and Norway spruce (Picea abies L. Karst) stands

Comparison of nutrient and carbon stocks in the aboveground biomass of mature silver fir (Abies alba Mill.) and Norway spruce (Picea abies L. Karst) stands

Effect of warming on ground vegetation in Carpathian Norway spruce stands, exemplified by European blueberry (Vaccinium myrtillus L.) nutrient stoichiometry

Despite its small share of total forest biomass, ground vegetation plays an important role in biogeochemical cycles, being able to modify carbon (C) and nutrients fluxes. Global climate warming may affect plant nutrient uptake and the carbon:nitrogen:phosphorus (C:N:P) stoichiometry, the release of nutrients from the soil and soil organic matter, as well as significantly influence the tree stand nutrient supply. In this context, the response of Norway spruce (Picea abies (L.) H.Karst) stands' ground vegetation to warming is uncertain. An open-top chamber soil-warming simulation, lasting two growing seasons, was conducted in a spruce forest. At the end of each of the two growing seasons, before leaf senescence, European blueberry (Vaccinium myrtillus L.) aboveground biomass (leaves and stems) and mineral topsoil samples were collected from the plots. The C, N, P, micronutrient, and macronutrient concentrations were estimated in the samples. Warming caused significant decreases in C, N, and P in the soil. Warming also decreased the C:P and N:P stoichiometric ratios in the soil and increased the C:P ratio in plant stems. Significant increase in foliar C and decrease in foliar P in warmed plots were observed. The most evident effect was reduction of N and P in the soil, which directly affected the plant C:P and soil N:P stoichiometry. Our results show that warming has caused a significant decrease in the content of some nutrients in the aboveground plant tissues of blueberries. Given that N is a limiting factor of ecosystems productivity, its reduction in the soil caused by warming may be a serious threat to proper nutrient uptake and cause disruption of biogeochemical cycles. The decrease in nutrient content in aboveground tissues due to warming can result in disruptions to physiological processes.

Variation in Polycyclic Aromatic Compound (PAC) Concentrations in a Norway Spruce Stand Close to a Major Traffic Route—Influence of Distance and Season

Air concentrations of polycyclic aromatic compounds (PACs) were measured in a Norway spruce (Picea abies) stand at four different distances from a major traffic route near Gothenburg, Sweden, during summer and winter 2019, using passive samplers. In total, the concentrations of 32 polycyclic aromatic hydrocarbons (PAHs) and six dibenzothiophenes (DBTs) and NO2 were analysed. PAC air concentrations were on average 2.5 times higher during the winter compared to the summer. All investigated PAH categories and compounds as well as dibenzothiophene declined linearly with the logarithmic distance from the traffic route. This indicates that the length of pollutant pathways through vegetation is a valid proxy to assess health risks of traffic-related PAC pollutants. Concentrations of heavier PAHs declined faster (concentration at site furthest away from the road was 6% and 33% of concentration at site closest to road, for summer and winter respectively) with increasing distance from traffic compared to lighter PAHs (63% and 68% for summer and winter respectively). As a result, the mix of PAHs changed with the depth into the forest stand (i.e. distance from the road) with potential effects on the toxicity as well as on diagnostic ratios used for source attribution. This is likely caused by different deposition rates among the PAH compounds to the vegetation surfaces, although the exact mechanism needs to be further investigated. This study provides new information that can improve air quality risk assessment and limit the exposure of the population to toxic air pollutants such as PACs.

Time series DNA barcoding provides insight into factors influencing wood-boring and bark-feeding insect communities in Scots pine, Sitka spruce, and Noble fir stands.

Bark-feeding and wood-boring insect pests can have significant negative impacts on conifers and wood production. The damage they cause is expected to increase in the future due to climate change and the growth of international trade. This study employed DNA barcoding of beetle juveniles (Coleoptera) sampled from standing trap trees and cut log piles at regular intervals over a 2-yr period to monitor the beetle community dynamics and associated environmental factors. Tree species was found to have a major influence on beetle communities, most strikingly at the start of early decay stages. Lower species diversity was reported from standing trap tree samples compared to log pile samples, likely due to higher residual defences in dying and recently dead trees. While the species identified from standing trap trees are more likely to be a threat to the forestry sector, the species found in the log piles are more likely to be beneficial due to their high abundance and their ability to compete with pests for breeding substrate. The analysis of beetles collected inside trees revealed additional information on ontogenetic niches and host preferences beyond that acquired solely from flight interception trap data. Our results offer insights on community composition and dynamics of bark-feeding and wood-boring insect species in Welsh conifer forests and provide resources for monitoring and management of potential pest species.

Tree pruning improves tree form but not understory plant production in mixed stands of Sitka spruce and western hemlock, USA

Abstract Precommercial thinning and tree pruning are frequently used together to improve timber quality and wildlife habitat in even-aged Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla) stands. Thinning enhances crop tree growth and understory plant production; however, the benefits and drawbacks of tree pruning have received less attention. Tree pruning was investigated in two long-term experiments on the Tongass National Forest, Alaska, USA. Experiment 1 tracked four uniformly thinned sites for ~30 years that received 2.4, 3.6, and 5.2 m lift, and no pruning treatments. Experiment 2 tracked 11 sites for 16 years that received thinning/no pruning, thinning plus pruning (25% of trees), thinning plus pruning (50% of trees), and no thinning/no pruning treatments. We investigated (i) how pruning lift height affects tree form and understory production and (ii) how pruning density affects canopy closure and understory production. In Experiment 1, pruning reduced butt log taper and did not adversely affect diameter or height in either species. Pruning lift was visible in height-to-live crown measurements. Crown recession occurred first in low lift treatments and later in all treatments until crown form was similar after 28–31 years. Epicormic branching rates in Sitka spruce peaked 6–9 years after treatment before falling sharply. Deer forage declined through time and did not differ between lift treatments. In Experiment 2, canopy closure was lower shortly after thinning and pruning, but did not differ from the control after 16 years. Epicormic branching rates were greater shortly after thinning and pruning but did not differ from the control after 16 years. Deer forage declined with canopy closure and thinned and pruned treatments exhibited greater forage than the control. We conclude that pruning can improve log quality for timber applications but does not enhance understory plant biomass and deer forage over thinning treatment alone.

Variability of Functional Groups of Rhizosphere Fungi of Norway Spruce (Picea abies (L.) H.Karst.) in the Boreal Range: The Wigry National Park, Poland.

Rhizosphere microbial communities can influence plant growth and development. Natural regeneration processes take place in the tree stands of protected areas, which makes it possible to observe the natural changes taking place in the rhizosphere along with the development of the plants. This study aimed to determine the diversity (taxonomic and functional) of the rhizosphere fungal communities of Norway spruce growing in one of four developmental stages. Our research was based on the ITS region using Illumina system sequencing. Saprotrophs dominated in the studied rhizospheres, but their percentage share decreased with the age of the development group (for 51.91 from 43.13%). However, in the case of mycorrhizal fungi, an opposite trend was observed (16.96-26.75%). The most numerous genera were: saprotrophic Aspergillus (2.54-3.83%), Penicillium (6.47-12.86%), Pyrenochaeta (1.39-11.78%), pathogenic Curvularia (0.53-4.39%), and mycorrhizal Cortinarius (1.80-5.46%), Pseudotomentella (2.94-5.64%) and Tomentella (4.54-15.94%). The species composition of rhizosphere fungal communities was favorable for the regeneration of natural spruce and the development of multi-generational Norway spruce stands. The ratio of the abundance of saprotrophic and mycorrhizal fungi to the abundance of pathogens was high and promising for the durability of the large proportion of spruce in the Wigry National Park and for forest ecosystems in general.

The Mechanical Stability of Pure Norway Spruce Stands along an Altitudinal Gradient in the Czech Republic

Norway spruce stands are established and managed along various site conditions in central Europe. Currently, spruce often grows at locations outside of its ecological optimum, resulting in extensive damage elicited by harmful abiotic and biotic factors, which relatively shortens the time to change this adverse status in the adaptation frame by foresters. Except for the rapid change in species composition through clear-cuts, another way is possible, i.e., stabilising current (especially young) spruce stands to extend the time required to implement adaptation measures. The assumption that different site conditions will have to be respected as part of this adaptation was confirmed by our study based on NFI data of the Czech Republic. A semiparametric generalized linear model (GAM) was used to model the relationship between the height-to-diameter ratio and forest stand age, differentially considering particular forest vegetation zones. Spruce stands with lower elevations attain a lower stability (expressed by their height-to-diameter ratio; HDR) than those in the mountains. The HDR culminated in lower and middle altitudes in the first half of the rotation period, representing the most critical timing and effectivity of silvicultural measures. Contrary to previous findings, we found higher HDR values at nutrient-rich sites than those at acid ones, especially up to 50–60 years old. Therefore, more research should be devoted to the issue concerning the same thinning regime under different site conditions.

Carbon footprint and sustainability assessment of wood utilisation in Hungary

Forest management allows the sustained removal of significant amounts of carbon from the atmosphere. Within different activities in the forest, wood utilisation has the most significant man-made environmental impact which affects the carbon balance, which is important to know, to be able to accurately identify its role in climate change. This study aims to determine the carbon footprint of logging during utilisation based on scenario analysis in national default and theoretical assortment structures (11 additional scenarios for each forest stand) within the entire life cycle of raw wood products. Based on a common functional unit (100 m3 of cut wood), a comparative environmental life cycle analysis (LCA) for intermediate and final cutting was performed in shortwood forestry work systems in beech (Fagus spp.), oak (Quercus spp.), spruce (Picea spp.), black locust (Robinia pseudoacacia), and hybrid poplar (Populus x euramericana) stands in Hungary. After obtaining the results, the present study calculated the carbon footprint order for the utilisation life cycle phases and the entire tree utilisation life cycle. The distribution of absolute carbon footprint (ACF: considered emitted CO2 from fossil and biotic origins together) by final cutting exhibited the following order: hybrid poplar (6%)—spruce (8%)—beech (26%)—oak (27%)—black locust (33%). The ACF ranking for the whole technological life cycle (intermediate and final cutting, 400 m3 of cut wood) was hybrid poplar– spruce—oak—beech–black locust. The carbon footprint rankings of the studied stands were expanded to the national level.

Species diversity of forest floor biota in non‐native Douglas‐fir stands is similar to that of native stands

AbstractCultivation of non‐native tree species is a promising option to adapt managed forests to climate change. However, consequences of non‐native tree species on flora, fauna, and microorganisms that occur in forest ecosystems (forest associates) need to be considered when managing forests. We lack a solid understanding of how cultivating non‐native tree species in pure stands and in mixture with native tree species impacts abundance and species diversity of forest associates. We compared abundance, alpha‐, beta‐ and gamma‐diversity of eight forest‐floor‐associated taxa that are relevant for ecosystem functioning (including fungi, plants, arthropods, and small mammals) between different forest ecosystems. We addressed pure stands of non‐native coniferous Douglas‐fir (Pseudotsuga menziesii) and two native species, broad‐leaved European beech (Fagus sylvatica) and coniferous Norway spruce (Picea abies), as well as mixed stands of European beech with each conifer in two regions with differing site conditions in temperate Northwest Germany. Diversity indices revealed differences among species groups. Gamma‐diversity and alpha‐diversity of forest associates in Douglas‐fir and spruce stands were usually higher than in beech stands. Estimates of species diversity of mixed stands are intermediate between estimates for the respective pure stands. Differences in the diversity between the two study regions were highly taxon specific with no clear support for a general trend toward a higher or lower species diversity of forest associates depending on site quality. Abundance values show a pattern similar to our diversity estimates, but with a higher statistical uncertainty. Non‐native Douglas‐fir stands provided habitats to support associated species communities of equally high or higher diversity than stands of native beech or spruce. Mixed stands of non‐native and native tree species may be a management option to achieve different goals, that is, to provide habitats for species that are strictly associated with beech and to increase resilience to climate change. However, the overall diversity of forest‐floor‐associated biota is not improved by cultivating Douglas‐fir or spruce in mixture with beech.

Rapid shift of soil fungal community compositions after clear-cutting in hemiboreal coniferous forests

Clear-cutting is the main forest management method in boreal and hemiboreal forests, but recently its implementation has raised concerns due to its effects on biodiversity, including the soil fungal biota. Forest soil fungi have an important role as mycorrhizal symbionts, decomposers of organic material and root pathogens. There is conflicting information about the effect of clear-cutting and related management practices on fungal assemblages. We aimed to assess the factors that affect the assemblages of major fungal functional guilds (ectomycorrhizal, saprotrophic, pathogenic and yeast fungi) and the changes in soil fungal diversity and community composition after clear-cutting in Norway spruce and Scots pine (retention trees > 5 m3 per ha) stands, and compared the outcomes with alongside control sites (uncut stands). In addition, we tested the effect of the size of the clear-cut area, soil scarification and the forest regeneration method (planting and sowing) on soil fungi. The samples were collected from 50 different clear-cut sites and 50 control sites on two repeated sampling occasions: recently (0–6 months) cut and one year after clear-cutting. Based on high-throughput Illumina sequencing soil fungal communities were affected immediately after clear-cutting, resulting in significantly different fungal structure composition. Soil fungal diversity in both spruce and pine stands increased after one year post-cut compared to control sites, except the richness of ectomycorrhizal fungi in spruce sites. However, the fungal communities showed the highest similarity between control and one year post-cut sites based on principal coordinates (PCO) and Permanova analyses. Nonetheless, relative abundance of ectomycorrhizal (EcM) fungi declined, whereas that of saprotrophs and pathogens increased. In spruce sites, saprotrophic fungi were negatively affected by soil scarification, but this was not evident in pine sites. Forest regeneration by planting after clear-cutting in pine sites resulted in higher ectomycorrhizal fungal richness compared to sowing. Size of the clear-cut area (ranging from 0.4 to 3.1 (5.0) ha) did not affect soil fungal diversity in spruce- and pine-dominated sites. We demonstrated that fungal community composition may recover within one year after clear-cutting in pine- and spruce-dominated hemiboreal forest stands. However, understanding the long-term effects of management on patterns and shifts in fungal biota needs a long-term study.

Prediction of knot size in uneven-sized Norway spruce stands in Sweden

The size of knots is negatively correlated with bending strength in sawn timber and it is therefore used as a quality grading criterion in national roundwood grading standards. Some standards even use the size of the largest knot as the sole estimate for individual log knottiness. The size of knots is determined by crown horizontal extension, which in turn is dependent on the impact of competing trees. Thus, with knot size models that are competition-dependent, roundwood quality due to knottiness can be simulated for different management alternatives. However, these types of models, calibrated on uneven-sized Norway spruce in Fennoscandia, are currently not available. Therefore, the objective of this study is to develop a competition-dependent model framework for prediction of the largest knot size per stem height section, for application within uneven-sized Norway spruce stands. Data from terrestrial laser scanning of an uneven-sized stand in southern Sweden are used to calibrate a modular prediction framework, consisting of interlinked allometric statistical models. Alternative framework sub-models are presented and the preferred model combination can be selected according to context and available input data. The flexible modular format enables further development of separate sub-components for adaptation to growing conditions not covered by the current calibration range.

Optimizing Bacillus thuringiensis (Btk) Aerial Spray Prescriptions in Mixed Balsam Fir-White Spruce Stands against the Eastern Spruce Budworm

Forest protection against eastern spruce budworm, Choristoneura fumiferana (Clemens), relies on aerial applications of Bacillus thuringiensis (Btk). However, Btk prescriptions have been developed for balsam fir (Abies balsamea (L.) Mill.) stands, generating uncertainty as to the relevance of this protection approach on white spruce (Picea glauca (Moench) Voss). The main goal of this study was to evaluate the efficacy of three Btk application treatments (early application, late application, and double application) for protecting white spruce and balsam fir in mixed stands. Our results show that all Btk treatments tested kept defoliation under the 50% threshold on balsam fir (27.7 to 38.1% less defoliation than in controls). In contrast, differences in defoliation among treatments were not significant for white spruce. Larval mortality was significantly lower on white spruce than on balsam fir. The low efficacy of Btk treatments on white spruce may be explained by its shoot phenology (most bud caps were still present during the early application), and its foliar chemistry, which could decrease Btk efficacy. Consequently, many larvae may survive simply because Btk spores do not reach them, or because they may consume sublethal doses. We recommend maintaining the current strategy in mixed stands, as it provides a good protection for balsam fir. Further research is needed to determine the causes of the low efficacy of Btk treatments on white spruce.

Impact of 30 years precipitation regime differences on forest soil physiology and microbial assemblages

Anthropogenic disturbances and climate change affect abiotic and biotic environmental drivers in forest ecosystems. Global warming impacts the soil moisture content, thus influencing the diversity, abundance and functioning of soil microfauna. However, limited studies have been conducted to evaluate the impact of long-term variation in precipitation on soil microfauna. A better understanding of soil microfauna functioning under various precipitation regimes can aid in formulating better prediction models for assessing future climate change impacts. The present study uses a multi-omics approach to capture the variability in the total organic carbon (TOC), total nitrogen (TN), pH, metabolites, microbial biomass and function due to the difference in soil water content mediated by long-term precipitation (30 years) and soil texture differences in two Norway spruce seed orchards. Results showed a positive correlation between TOC, TN, extracellular enzyme activities (EEAs) and phospholipid fatty acids (PLFA) content with higher precipitation, whereas microbial diversity showed an opposite trend. A distinct metabolic profile was observed between the two forest soils. Furthermore, variance partitioning canonical correspondence analysis (VPA) revealed a higher contribution of TOC and TN in shaping the microbial communities than soil pH and conductivity in Norway spruce seed orchards. Our study generates field data for modeling the impact of long-term precipitation variance supplemented by soil texture on soil microbial assemblage and function in Norway spruce stands.