Spruce Research Articles

Research of chipper knives with a modified cutting edge for the production of dimensionally uniform wood chips

The paper is focused on the research of chipper knives with a straight and modified cutting edge in order to determine the energy consumption of the chipping process and the uniformity of the size of the fractions of the designed chipper knife for the production of dimensionally uniform chips. The research took place on two different tree species where the representative of the coniferous tree was the common spruce (Picea abies) and the deciduous tree was the winter oak (Quercus petraea). The research took place on a PTO-powered (power take off) disc chipping machine where it was not modified for research purposes. The results showed that a knife with a modified cutting edge is higher in terms of energy consumption than chipper knives with a straight cutting edge. From the evaluation of the sieve analysis for a chipper knife with a modified cutting edge, the energy chip of uniform granulometric composition is a homogeneous bulk material.

Variation in water uptake pattern of the constructive species Pinus koraiensis: Evidence from water stable isotopes

Plant water uptake plays a crucial role in regulating the water balance for the stability of ecosystems. Previous studies on plant water uptake, focused on arid and semi-arid regions due to water scarcity in these areas, leaving gaps in understanding the strategies and factors affecting plant water uptake in temperate semi-humid regions, where there is a high sensitivity to climate change To assess water uptake patterns through stable isotopes (δD and δ18O), we chose Pinus koraiensis, a dominant species in the broadleaf Korean pine forest, poplar–birch forest and spruce–fir forest of the Changbai Mountain. Our findings indicated that soil water served as the direct water source for Pinus koraiensis, while precipitation, river water, and groundwater indirectly contributed via replenishing soil moisture and subsequently supporting plant water uptake. Within the broadleaf Korean pine forest and poplar–birch forest, Pinus koraiensis primarily extracted soil water from depths of 0–10 cm, accounting for approximately 49.6 % and 54.5 % of its total water uptake, respectively. In contrast, within the spruce–fir forest, Pinus koraiensis primarily extracted soil water from depths 40–50 cm, representing approximately 31.9 % of its total water uptake. In addition, through the partial correlations and variation partitioning analyses, the results revealed that sand content was the driver of the plant water uptake pattern, which affected the fine root distribution by determining the field capacity and bulk density to drive the plant water uptake. Future forest conservation management endeavours will primarily concentrate on protecting soil integrity, reducing soil erosion, maintaining regional water balance, and preserving plant diversity in the Changbai Mountain region.

Isotopic evidence for seasonal water sources in tree xylem and forest soils

AbstractForest trees greatly influence both the routing of water downward into the subsurface and the re‐routing of water upward through water uptake and transpiration. To reveal how the subsurface soil water pools used by trees change across seasons, we analysed 2 years of stable isotope ratios of precipitation, soil water from different depths (using both bulk sampling and suction‐cup lysimeters), and xylem in a mixed beech and spruce forest. Precipitation as well as mobile and bulk soil waters all showed a distinct seasonal signature; the seasonal amplitude decreased with depth, and mobile soil waters fluctuated less than bulk soil waters. Xylem water signatures in both tree species were similar to the bulk soil water signatures and rather different from the mobile soil water signatures. The beech and spruce trees had different isotope ratios, suggesting the use of different water sources, and these differences were larger under dry antecedent conditions than wet antecedent conditions. Despite these differences, both species predominantly transpired waters with a winter‐precipitation isotopic signature throughout the summer, including during wet conditions when more recent precipitation was available. Over most of the sampling dates, the fraction of recent precipitation (i.e. from the preceding 30 days) in xylem water was low, despite both species typically demonstrating the use of both shallow and deeper soil waters. These results provide evidence that the soil water storages used by these trees are largely filled in winter and bypassed by recent precipitation, implying long residence times.

Влияние климата на возрастную структуру древостоев в экотоне северной границы леса на полуострове Ямал

The spatial and temporal dynamics of forest-tundra communities was studied on the Yamal Peninsula within the northern treeline ecotone. The paper presents the results of surveying 12 sample plots and more than 1000 trees of Siberian larch and Siberian spruce. Based on cross-dated tree-ring chronologies, the age structure and dynamics of stands for the last 150 years were obtained. Dynamic processes in stands of the northern treeline ecotone are most pronounced in the sparse forests, where there has been a sharp increase in stand density since the middle of the 20th century. Correlation analysis of tree establishment time with instrumental observations of climatic variables showed that the establishment of new larch and spruce individuals in different stand types is significantly influenced by the amount of precipitation in June-August.

Dry and wet periods determine stem and soil greenhouse gas fluxes in a northern drained peatland forest

Greenhouse gas (GHG) fluxes from peatland soils are relatively well studied, whereas tree stem fluxes have received far less attention. Simultaneous year-long measurements of soil and tree stem GHG fluxes in northern peatland forests are scarce, as previous studies have primarily focused on the growing season. We determined the seasonal dynamics of tree stem and soil CH4, N2O and CO2 fluxes in a hemiboreal drained peatland forest. Gas samples for flux calculations were manually collected from chambers at different heights on Downy Birch (Betula pubescens) and Norway Spruce (Picea abies) trees (November 2020–December 2021) and analysed using gas chromatography. Environmental parameters were measured simultaneously with fluxes and xylem sap flow was recorded during the growing season. Birch stems played a greater role in the annual GHG dynamics than spruce stems. Birch stems were net annual CH4, N2O and CO2 sources, while spruce stems constituted a CH4 and CO2 source but a N2O sink. Soil was a net CO2 and N2O source, but a sink of CH4. Temporal dynamics of stem CH4 and N2O fluxes were driven by isolated emissions' peaks that contributed significantly to net annual fluxes. Stem CO2 efflux followed a seasonal trend coinciding with tree growth phenology. Stem CH4 dynamics were significantly affected by the changes between wetter and drier periods, while N2O was more influenced by short-term changes in soil hydrologic conditions. We showed that CH4 emitted from tree stems during the wetter period can offset nearly half of the soil sink capacity. We presented for the first time the relationship between tree stem GHG fluxes and sap flow in a peatland forest. The net CH4 flux was likely an aggregate of soil-derived and stem-produced CH4. A dominating soil source was more evident for stem N2O fluxes.

Low-severity fires in the boreal region: reproductive implications for black spruce stands in between stand-replacing fire events.

Stand-replacing crown fires are the most prevalent type of fire regime in boreal forests in North America. However, a substantial proportion of low-severity fires are found within fire perimeters. Here we aimed to investigate the effects of low-severity fires on the reproductive potential and seedling recruitment in boreal forests stands in between stand-replacing fire events. We recorded site and tree characteristics from 149 trees within twelve sites dominated by mature black spruce [Picea mariana (Mill.) B.S.P.] trees in the Northwest Territories, Canada. The presence of fire-scarred trees supported classification of sites as unburned or affected by low-severity fires in recent history. We used non-parametric tests to evaluate differences in site conditions between unburned and low-severity sites, and mixed effect models to evaluate differences in tree age, size, and reproductive traits among unburned trees and trees from low-severity sites. Results showed significantly higher density of dead black spruce trees in low-severity sites, and marginally significant higher presence of permafrost. Trees from low-severity fire sites were significantly older, exhibited significantly lower tree growth, and showed a tendency towards a higher probability of cone presence and percentage of open cones compared to trees from unburned sites. Surviving fire-scarred trees affected by more recent low-severity fires showed a tendency towards higher probability of cone presence and cone production. Density of black spruce seedlings significantly increased with recent low-severity fires. Trees in low-severity sites appeared to have escaped mortality from up to three fires, as indicated by fire scar records and their older ages. Shallow permafrost at low-severity sites may cause lower flammability, allowing areas to act as fire refugia. Low-severity surface fires temporarily enhanced the reproductive capacity of surviving trees and the density of seedlings, likely as a stress response to the fire event.

Successional dynamics of carbon sequestration in forests of the eastern United States

AbstractCarbon sequestration in the forests of the eastern United States is an important offset to the country's CO2 emissions. Much of the eastern forestland is the product of reforestation of abandoned agricultural land or recovery following clear‐cutting over a century ago. This has led to concerns that eastern forests are even‐aged and that rates of carbon sequestration will decline as forests increase in carbon. Our objective was to examine the successional dynamics of forest carbon sequestration—using live tree carbon stocks as a proxy for successional status—for the six broadly defined forest types present in the region. We used datasets from the National Forest Inventory (NFI) for the 31 US states from Minnesota south to Louisiana and eastward and analyzed live tree net carbon increment for 2007–2021, the period for which NFI plot remeasurement data were available for all 31 states. Spruce–fir and southern pines were the only forest types for which carbon increment declined even modestly over a significant fraction of the range of live tree carbon observed in the region, and southern pine–hardwood forests were the only forests in which predicted sequestration in live tree carbon declined to zero within the range of carbon stocks observed in the region. Northern hardwood–conifer forests, oak–hickory forests, and lowland forests experienced either no decline or a slight increase in sequestration in live tree carbon across the range of successional status observed in the region. Thus, the average stocks of live tree carbon per unit area increased steadily over the study period. At some point in succession, rates of mortality are expected to increase and balance gross growth, leading to zero net sequestration in live tree carbon. Mature and old‐growth stands, however, are rare in all six forest types, and mortality as a fraction of live tree carbon for all six forest types declined across the range of successional status present in the region. Our results thus provide no support for the hypothesis that the successional dynamics of forests in this region can be expected to lead to near‐term declines in net carbon sequestration.

The impact of natural constraints in linear regression of log transformed response variables

Abstract In linear regression, log transforming the response variable is the usual workaround regarding departures from the assumption of normality. However, the response variable is often subject to natural constraints, which can result in a truncated distribution of the residual errors on the log scale. In forestry, allometric relationships and tree growth are two typical examples a natural constraint; the response variable cannot be negative. Traditional least squares estimators do not account for constrained response variables. For this study, a modified maximum likelihood (MML) estimator that takes natural constraints into account was developed. This estimator was tested through a simulation study and showcased with black spruce tree diameter increment data. Results show that the ordinary least squares estimator underestimated large conditional expectations of the response variable on the original scale. In contrast, the MML estimator showed no evidence of bias for large sample sizes. Departures from distributional assumptions cannot be overlooked when the model is used for predictive purposes. Both Monte Carlo error propagation and prediction intervals rely on these assumptions. In this context, the MML estimator developed for this study can be used to properly propagate the errors and produce reliable prediction intervals.

Volume prediction of young improved Sitka spruce trees in Great Britain through Bayesian model averaging

Abstract More and earlier thinning operations are expected in Sitka spruce planted forests in Great Britain as a result of an increased demand for biomass and faster growth driven by breeding. It is however unknown whether the current models, which were designed to predict volume in adult trees, can provide unbiased volume predictions for the young individuals that are likely to be harvested in future thinning operations. The primary objective of this study was to answer this question. To do this, we used retrospective data from a destructive experiment originally aimed at assessing timber properties to reconstruct the taper and volume of 12 improved Sitka spruce trees at different ages. These volumes were then compared against the predictions from the current methods, which were found to be from moderately to strongly biased. The second objective was to provide proof of concept that a combination of existing volume models and other theoretical volume models could yield less biased predictions. We successfully addressed this objective through the Bayesian model averaging approach. The method, albeit tested with limited data, proved to be a promising alternative until new volume models are released. Further data from other available destructive experiments can be used to refine our calibration.

Xylem safety in relation to the stringency of plant water potential regulation of European beech, Norway spruce, and Douglas-fir trees during severe drought

Key messageNorway spruce operates with larger hydraulic safety margins (HSM) than beech and Douglas-fir despite the known drought sensitivity of spruce, questioning a pivotal role of HSM in drought tolerance.The exceptional 2018/2019 drought exposed Central Europe’s forests to severe stress, highlighting the need to better understand stomatal regulation strategies and their relationship to xylem safety under extreme drought. We studied diurnal, seasonal, and inter-annual variation in stomatal conductance (gs) and leaf water potential (ΨLeaf) in co-occurring European beech (F. sylvatica), Norway spruce (P. abies), and Douglas-fir (P. menziesii) trees in the two summers and related them to hydraulic traits characterizing drought resistance. In 2018, F. sylvatica exhibited a continuous ΨLeaf decline from June to September, as is characteristic for an anisohydric strategy, while P. abies closed stomata early and reached the least negative ΨLeaf-values at the end of summer. P. menziesii showed low ΨLeaf-values close to P12 (the xylem pressure at onset of embolism) already in July. Both conifers closed stomata when approaching P12 and maintained low gs-levels throughout summer, indicative for isohydric regulation. In 2019, all three species showed a linear decline in ΨLeaf, but F. sylvatica crossed P12 in contrast to the conifers. The three species exhibited similar water potentials at turgor loss point (− 2.44 to − 2.51 MPa) and branch P50 (xylem pressure at 50% loss of hydraulic conductance; − 3.3 to − 3.8 MPa). Yet, F. sylvatica and P. menziesii operated with smaller hydraulic safety margins (HSM means: 0.79 and 0.77 MPa) than P. abies (1.28 MPa). F. sylvatica reduced leaf size and specific leaf area in 2019 and increased Huber value. Our species comparison during extreme drought contradicts the general assumption that conifers operate with larger HSMs than angiosperm trees. Contrary to expectation, P. abies appeared as hydraulically less vulnerable than Douglas-fir.

Coniferous Trees as Bioinspiration for Designing Long Reinforced Prestressed Concrete Columns.

This article contains the results of identifying the potential of coniferous trees to act as bioinspiration for the structural design of columns in single-story warehouses subjected to high wind velocity and severe seismic action. This study starts by analyzing the biomechanics of coniferous trees, continues with an abstraction of the relevant features, and ends with the transfer of a design methodology for long reinforced and prestressed concrete columns. To verify the applicability and validity of the mathematical relationships extracted from the bibliographic study to characterize the biomechanics of coniferous trees, a study site is conducted for Norway spruce trees felled by the wind in the Bilbor area. The design methodology for long reinforced and prestressed concrete columns bioinspired by the Norway spruce trees is experimentally validated using two case studies. The first case study deals with the effect of centric prestressing on long concrete columns, and the second on the influence of the walnut shell powder on the adhesion of the reinforcement in concrete. The case studies presented aim to transfer some characteristics from trees to reinforced concrete to improve the performance of long columns under horizontal forces. The results obtained indicate a good approximation of the trees' structural behavior for this site and for ones investigated by other researchers in different forests.

EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF THE EFFECT OF LAYER NUMBER AND THICKNESS ON THE BENDING PROPERTIES OF GLULAM BEAMS

Wooden material is used in structural elements due to its many positive properties. Recent years have witnessed a surge in research directed toward enhancing the mechanical properties of wooden beams through the utilization of materials like steel plates and fiber reinforced polymers (FRP). Layered laminated timber, a composite material crafted from wood, serves as a testament to this endeavor. These laminated timbers constitute intricate engineering elements, fashioned from layers of wood characterized by distinct levels of strength and hardness, systematically arranged as per established guidelines. The present study is geared toward a comprehensive examination of the bending characteristics exhibited by glued beams, fashioned from spruce trees, encompassing six distinct sizes and varying layer counts. The manufacturing process yields beams with diverse cross-sectional profiles, including 3-layer and 7-layer variants. By performing 4-point bending tests of the beams, maximum load carrying capacity, bending strength, and elasticity modulus values were obtained experimentally. In addition to the experimental analyses, numerical models of the produced beams were created using the finite element analysis program, and static analyses were performed. In the experimental results, it was observed that the bending properties of the beams increased as the number and size of layers increased. It was determined that the maximum load carrying capacity, bending strength, and elasticity modulus values obtained as a result of experimental and numerical analysis were very close to each other. Numerical analysis results showed that beams produced with various number of layers and thicknesses can be simulated. It has been determined that the results obtained by creating numerical models instead of experimental analyses for this type of wooden beam may be sufficient.

Estimation of tangential speed of ground moving targets in SAR

In parallel with the development of systems of highly detailed mapping of the underlying surface, methods of ground moving targets indication (GMTI) were also improved. A dramatic improvement in the resolution characteristics of onboard radars occurred after the introduction of mapping modes with synthetic artificial antenna aperture. The advent of synthetic aperture radars (SAR) made it possible to detect ground moving targets (GMT) against the background of reflections from the underlying surface, which made it possible to further implement GMTI algorithms for detecting low-speed moving ground objects. The simple way to carry out GMTI is if the observed target has a radial component of the velocity vector, which generates a Doppler frequency shift in the reflected signal. A more complex situation arises when it is necessary to detect targets moving at a tangential speed relative to the onboard radar. The difficulty of detecting targets moving at tangential speed is due to the fact that target movement in the direction perpendicular to the line of sight leads to deformation of the phase structure of the signal. This particular deformation manifests itself in the appearance of quadratic phase modulation of the reflected trajectory signal. With consistent signal processing in mapping mode, due to the appearance of quadratic phase modulation, the response of the observed moving target will be defocused. To detect the presence of a moving target with tangential speed, it is proposed to use an algorithm similar to the well-known phase difference algorithm for autofocusing radar images. It consists in dividing the implementation of the trajectory signal into two parts, after which the bottom of them is subjected to a complex conjugation procedure. Next, the two implementations are multiplied with each other and the amplitude spectrum of the result of the multiplication is calculated. The shift of the maximum spectral density relative to the origin is proportional to the tangential velocity of the observed target. The sign of the shift (to the right or to the left) depends on the direction of movement of the GMT relative to the velocity vector of the carrier. This algorithm was justified by an analytical method, then its mathematical modeling was carried out. In the case of observation of spruce trees by on-board radar with a high tangential velocity, the error in its estimation increases, which is due to the spreading of the spectrum of the signal reflected from the GMT to reduce the influence of this effect.

Drought increases Norway spruce susceptibility to the Eurasian spruce bark beetle and its associated fungi.

Drought affects the complex interactions between Norway spruce, the bark beetle Ips typographus and associated microorganisms. We investigated the interplay of tree water status, defense and carbohydrate reserves with the incidence of bark beetle attack and infection of associated fungi in mature spruce trees. We installed roofs to induce a 2-yr moderate drought in a managed spruce stand to examine a maximum of 10 roof and 10 control trees for resin flow (RF), predawn twig water potentials, terpene, phenolic and carbohydrate bark concentrations, and bark beetle borings in field bioassays before and after inoculation with Endoconidiophora polonica and Grosmannia penicillata. Drought-stressed trees showed more attacks and significantly longer fungal lesions than controls, but maintained terpene resin defenses at predrought levels. Reduced RF and lower mono- and diterpene, but not phenolic concentrations were linked with increased host selection. Bark beetle attack and fungi stimulated chemical defenses, yet G. penicillata reduced phenolic and carbohydrate contents. Chemical defenses did not decrease under mild, prolonged drought in our simulated small-scale biotic infestations. However, during natural mass attacks, reductions in carbon fixation under drought, in combination with fungal consumption of carbohydrates, may deplete tree defenses and facilitate colonization by I. typographus.

Лесоводственная эффективность проведения несплошной лесозаготовки древесины в сосняках после гидротехнической мелиорации в Сокольском районе Вологодской области

In the Sokolsky district of the Vologda region of Russian Federation, the influence of continuous harvesting of
 wood in drained pine forests on the taxation and macrostructural parameters of common pine trees (Pinus sylvestris L.)
 was determined. The objects of the study are represented by pine forests: the main species is Scots pine (P. sylvestris L.)
 with an admixture of common spruce (Picea abies (L.) H. KARST.) and birch (Betula pendula Roth). The drained forest
 objects were selected after the continuous harvesting of wood and a control stand (without logging), temporary test areas
 (runway) were delimited. Drainage measures in experimental forests were carried out in 1972. Continuous logging was
 carried out in 2005 when skidding technological drags were attached to the main corridor at an angle of 45 degrees. The
 distribution of the number of P. sylvestris L. trees by thickness steps within the boundaries of the runway in 83% (p <
 0.05) of cases tends to normal. Average periodical growth of late wood P. sylvestris L. on the runway after drainage
 increased in the channel position by 30 % (tfact ≥ tst; 4.51 > 2.70; p < 0.01), and after intermittent logging increased by
 19 % (tfact ≥ tst; 1.99 > 1.71; p < 0.1). Carrying out continuous complex harvesting of wood in drained pine forests has a
 positive effect on increasing the stock (by 38%), while in stands without logging – by 28 %.

Выращивание культур кедра сибирского в условиях повреждаемости дикими животными

The research of 26-year-old mixed plantations of Siberian spruce and Siberian stone pine cultivated by biogroups of about 300 pcs/ha (2–5 stone pine seedlings alternating 4–9 spruce seedlings in a row) has shown that the damage rate by moose to them is much lower than to pure stone pine plantations or the mixed ones of Siberian stone pines and Scots pines we have studied before. The share of biogroups containing damaged stone pine trees is 18 %. A third of this number is plantations with damage to all the trees. This is most pronounced in biogroups of 4 to 5 stone pines as well as in case of frequent alternation of biogroups in a row. 76 % living stone pines have been preserved (89.3 % of them without damage to the stem). About two thirds of them (about 500 pcs/ha) grow in the crown of spruce trees adjacent to stone pine biogroups. Prolonged exposure to growing in a spruce tree crown negatively affects the growth of a stone pine’s central shoot and crown. We are the first in the Middle Urals to propose a scheme for cultivating sustained productive mixed plantations of Siberian stone pines and Siberian spruce trees (or Norway spruce trees). Stone pines are planted in biogroups of 2–3 seedlings, beginning the planting strictly on one side of the site. The first biogroup in odd-numbered rows (1, 2, 3, 5, etc.) is planted after 3 spruce seedlings from the beginning of the row, the second and subsequent biogroups in these rows – after 9 spruce seedlings. The first biogroup in even-numbered rows (2, 4, 6, 8, etc.) is planted after 9 spruce seedlings from the beginning of the row, maintaining this sequence until the end of the row. Every row in mixed plantations is concluded with planting no less than 3 spruce seedlings. During silvicultural treatment procedures natural regeneration is completely removed: softwoods – by mechanical means, and hard woods – by ringing or injection of environmentally friendly water-based chemicals. These measures reduce or eliminate the appearance of coppice and, accordingly, food reserve for wild animals. Spruce trees adjacent to stone pine biogroups are cut down while lightening and thinning, which creates the possibility for the growth of stone pines. The proposed method for cultivating plantations of Siberian stone pines and Siberian spruce trees has been patented. It can be introduced into silvicultural practice in the taiga zone where stone pines are grown.

Лесная селекция и генетическое разнообразие древесных пород

In scientific literature there are different views on the connection between forest tree breeding and genetic variability of wood species. This article has aimed to review the current Russian and foreign literary sources on the impact of breeding measures on the level of genetic diversity of forest wood species. Maintaining adequate genetic variability is necessary for adaptation to the environmental changes, as well as for long-term breeding. As soon as seed plantations are the source of improved seeds for forest regeneration, the influence of such factors as the number of clones and background pollination on the level of genetic variability of the progeny has been considered in detail. The data on the minimal clone number in seed plantations in different countries has been presented and the variability of the clones based on their fertility has been discussed. The importance of background pollination in seed plantations has been highlighted as soon as, on the one hand, it reduces the effect of breeding, but on the other hand, it increases the level of genetic variability of the progeny. A decline in genetic diversity of wood species can be caused by clone selection (which is the basis for clonal forestry). However the analysis of literary sources has shown that the reduction in genetic diversity is minimal if scientific recommendations are fulfilled. The use of the seeds from controlled cross-breeding of plus trees selected as a result of genetic evaluation (the so-called family forestry with vegetative propagation) in the somatic embryogenesis of the common spruce increases the level of genetic variability of the progeny. It has been shown that the multiple population breeding system allows to combine intensive long-term breeding and genetic conservation of wood species. The conclusion has been drawn that the implementation of optimally planned wood species breeding programs does not lead to significant narrowing of genetic diversity. On the contrary, forest tree breeding contributes to the preservation of a better gene pool, transmitting it in the process of forest regeneration through improved seeds and clones into homogeneous stands. Moreover, the objects of forest seed growing such as the archives of plus tree clones and forest seed plantations, as well as test cultures contain valuable genetic material ex situ.

Spatial and remote sensing monitoring shows the end of the bark beetle outbreak on Belgian and north-eastern France Norway spruce (Picea abies) stands.

In 2022, Europe emerged from eight of the hottest years on record, leading to significant spruce mortality across Europe. The particularly dry weather conditions of 2018 triggered an outbreak of bark beetles (Ips typographus), causing the loss of thousands of hectares of Norway spruce stands, including in Wallonia and North-eastern France. A methodology for detecting the health status of spruce was developed based on a dense time series of satellite imagery (Sentinel-2). The time series of satellite images allowed the modelling of the spectral response of healthy spruce forests over the seasons: a decrease in photosynthetic activity of the forest canopy causes deviations from this normal seasonal vegetation index trajectory. These anomalies are caused by a bark beetle attack and are detected automatically. The method leads in the production of an annual spruce health map of Wallonia and Grand-Est. The goal of this paper is to assess the damage caused by bark beetle using the resulting spruce health maps. A second objective was to compare the influence of basic variables on the mortality of spruce trees in these two regions. Lasted 6years (2017-2022), bark beetle has destroyed 12.2% (23,674ha) of the spruce area in Wallonia and Grand-Est of France. This study area is composed of three bioclimatic areas: Plains, Ardennes and Vosges, which have not been equally affected by bark beetle attacks. The plains were the most affected, with 50% of spruce forests destroyed, followed by the Ardennes, which lost 11.3% of its spruce stands. The Vosges was the least affected bioclimatic area, with 5.6% of spruce stands lost. For the most problematic sites, Norway spruce forestry should no longer be considered.

More water, less light: how to improve silver fir seeding to convert Norway spruce monocultures into mixed stands in a drier region of Germany

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

Tree‐ and stand‐scale variability of xylem water stable isotope signatures in mature beech, oak and spruce

AbstractIn ecohydrology, water isotopologues are used to assess potential sources of root water uptake by comparing xylem water signatures with source water signatures. Such comparisons are affected by the variability and uncertainty of the isotope signatures of plant water and water sources. The tree‐scale and stand‐scale variabilities of the isotope signatures in stem xylem water are often unknown but are important for sampling design and uncertainty estimation in assessing the sources of tree water uptake. Here, we quantified tree‐scale and stand‐scale variabilities of xylem water isotope signatures in beech, oak and spruce trees in a mature forest on the Swiss plateau. For stem xylem water, sub‐daily replicates and replicates in different cardinal directions showed no systematic differences, but we found systematic differences with sampling height. The observed variability of isotope signatures at different heights along the stem suggests that water residence times within trees need to be considered, along with their effects on the isotope signatures in different compartments (stem, branches, leaves). Further, concerning the hydrogen signatures, we found height‐ and species‐specific offsets (SW‐excess δ2H). Stem xylem water's tree‐scale variability was similar in magnitude to its stand‐scale variability and smaller than the variabilities in branch xylem and bulk soil water around each tree. Xylem water from stem cores close to the ground, therefore, can give a more precise estimate of the isotopic signal of the most recent root water uptake and facilitate more accurate source water attribution.