•The Czech Republic has become an epicentre of bark beetle outbreaks in Europe.•We identified the transition from wind- to drought-driven outbreak dynamics.•The outbreak triggered a cascade of social ...impacts restricting management operations.•Effective responses require fundamental changes in the regional forest-based sector.
Outbreaks of tree-killing insects are intensifying globally, affecting economies, human well-being, and driving ecosystem transitions. The Czech Republic has recently become Europe’s epicenter of the outbreak of spruce bark beetle Ips typographus, the most aggressive species in Eurasia. We investigated a countrywide outbreak dynamic during the period 2003–2019, with a special focus on the period 2017–2019 when the outbreak reached an unprecedented intensity. In order to identify main outbreak drivers, we investigated annual time series of the volume of trees killed by bark beetles in the Czech districts (n = 77), and a suite of climatic and forest structure-related predictors using Generalized Additive Models. Finally, we reviewed a large body of public materials to understand broader social, ecological, and economic implications of the outbreak.
We found that bark beetles were damaging 0.2–1.4% of Norway spruce growing stock annually across the Czech Republic in the period 2003–2016. This level increased to 3.1–5.4% in 2017–2019, causing the total depletion of spruce in some regions. The long-term bark beetle dynamics (2003–2019) was driven by the combination of wind disturbance and climatic drivers, represented in our study by annual temperature anomaly and Standardized Precipitation-Evapotranspiration Index. However, the effect of wind was diminished during the period 2017–2019, whereas the effect of drought dominated. Our findings thus suggest a transition from wind- to drought-driven bark beetle dynamics.
The outbreak and subsequent large-scale salvaging and wood transportation affected quality of life of people in a broad vicinity of outbreak areas. Extensive management actions aggravated some of the notorious conflicts between forest management and nature conservation, and highlighted the poor harmonization of respective policies. A decrease in timber price, an excessive workload, and other cascading effects caused severe revenue loss, requiring state interventions amounting to ca 260 million EUR in 2018–2019.
We suggest that increasing frequency of climate extremes in combination with the unfavorable forest structure pushed Central European spruce forests to the margin of their ecological space and unfolded large-scale forest transformations. Effective responses will require fundamental structural changes in the regional forest-based sector, particularly aiming at increased social and ecological resilience.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Temperature negatively affects Scots pine and Norway spruce at lower latitudes but positively at higher latitudes.•Summer precipitation has a positive impact on the species at lower latitudes but a ...negative impact at higher latitudes.•The resistance of pine and spruce to drought increased linearly with latitude.•Compared to spruce, pine attained pre-drought growth levels faster and was independent of latitude.
Pinus sylvestris L. (Scots pine) and Picea abies L. H. Karst. (Norway spruce) are the most important economic tree species in Sweden. However, like every other tree species, they are affected by climate change, especially drought conditions. In this study, we analysed the effect of climate variability on the radial growth of Scots pine and Norway spruce in Sweden. Sixteen sites of pairwise monospecific stands of Scots pine and Norway spruce distributed across latitudinal gradients in Sweden (55 – 67 ° N) were used. In each site, we sampled at least 15 dominant/codominant Scots pine and Norway spruce trees without any defect in the sampled plots’ buffer zone (3 – 5 m wide). We performed a correlation analysis between climate variables and the radial growth of the species using different timescales; and regressed the coefficients with latitudes. Thereafter, important climate variables for both species were identified. Our results showed that temperature is the main climate factor affecting the radial growth of Scots pine while Norway spruce is more sensitive to early summer precipitation. The impact of summer precipitation on the radial growth of both species transitioned from a positive to a negative trend across a latitudinal gradient. Conversely, a contrasting pattern was noted in the relationship with summer temperature. The radial growth of both species responded positively to spring temperature, particularly at lower latitudes. The resistance of pine and spruce to drought showed a clear linear increase with latitude (p < 0.001). Compared to spruce, pine showed a better capacity to attain pre-drought growth levels (i.e., resilience) and was independent of latitude. Our findings contribute to the understanding of the spatial patterns of the growth-climate relationship of Scots pine and Norway spruce in Sweden; and could offer useful guidance on adaptive forest management in the face of climate change.
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The European spruce bark beetle, Ips typographus is the economically most important biotic damaging agent of Norway spruce. Efforts to delimit beetle populations by trapping, application of chemical ...insecticides, or mechanically excluding the beetles from their breeding substrates are often expensive and mostly inadequate. The use of natural enemies and viruses is receiving increased research interest as a potential environmentally healthy approach to control pest insect populations, but practical biocontrol methods against I. typographus are still lacking. To learn more about putative enemies of this pest species, we used high-throughput sequencing to determine its viral community using beetles collected at a Finnish forest site. The analysis revealed a diverse community of RNA viruses associated with I. typographus, including novel viruses that could be affiliated with the classified families Benyviridae, Metaviridae, Narnaviridae, Partitiviridae, Phenuiviridae, Solemoviridae, Virgaviridae, Tombusviridae, and proposed family Spiciviridae, as well as unclassified “quenyaviruses”. Based on phylogenetic analysis, the viruses were distinct from, but resembled, unclassified viruses originating from other arthropods, and many of them were distantly related to previously described viruses. The possibility that the viruses could be hosted by other organisms than the beetle itself (associated fungi, nematodes and protozoa) was addressed by bioinformatic and phylogenetic analyses and is discussed.
•Virome of the European spruce bark beetle was surveyed by high-throughput sequencing of total RNA.•A diverse community of previously unknown RNA viruses was discovered.•Most viruses resembled unclassified viruses originating from other arthropods.•The results enhance understanding of the putative enemies and associates of this pest species.
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•Field survey, phenology model, airborne hyperspectral remote sensing were combined.•Remote sensing method using VNIR identified infested trees later than field survey.•Red-edge based indices (REIP, ...ANCB) were more sensitive during early infestation.
Detection in the early phase of bark beetle infestation is a vital task for proactive management strategies, as practiced in most Central European forests, to minimize economic losses due to bark beetle infestation and to mitigate their further spreading. For this work, remote sensing methods are coming to be in great demand as an objective approach to enable monitoring bark beetle infestation even at individual tree level.
This case study monitored bark beetle (Ips typographus) activity at local level in Norway spruce forest in the Czech Republic. The main aim of this study was to compare the remote sensing methods against classical field survey conducted by forest workers in detecting newly infested trees.
To compare these two methods, an extensive field and aerial campaign was conducted in the southern part of the Czech Republic during 2020. Bark beetle infestation was monitored by traditional methods (i.e. field survey) on a weekly basis from mid-March to mid-September. During the same period, aerial scans were performed once per month (seven in total) using a CASI-1500 hyperspectral sensor (visible and near-infrared, 400–1000 nm) with spatial resolution of 0.5 m. This work mapped transition from healthy up to red attack of 75 Norway spruce trees that were infested during the same week. The same number of healthy trees were added to the data set for hyperspectral data analysis. Both groups were analysed by vegetation indices, with emphasis on effect caused in the canopy by bark beetles.
The success rate for bark beetle detection is always associated with acquisition time. In order to define the optimal time for data acquisition, we employed a phenology model for I. typographus (RITY 2.0) to take into consideration bark beetle development.
The results of the experiment showed that classic field survey detected infested trees earlier than did analysis using remote sensing data from the visible and near-infrared region. The difference was 23 days for the most successful indices (i.e. REIP, PRI, and ANCB650–720) in our test. Nevertheless, both methods detected the infested trees within 6 weeks after infestation, which is the recommended period for taking measures to prevent bark beetles from spreading further, and thus hyperspectral imagery can be used as a valid information source for bark beetle detection.
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The interface between decaying plant residues and soil minerals represents an essential soil microenvironment at which soil organic matter forms. The high amount of microbial products and residues ...within this hot spot of microbial activity fosters the formation of mineral-associated organic matter. Besides classical quantitative analyses, our understanding of processes controlling soil organic matter formation greatly benefits from microscopic observations and measurements, which provide spatially resolved information at a meaningful scale for microbial processes and for the association between organic and mineral particles. We studied carbon and nitrogen transfer from fresh-plant residues to the mineral soil, through a litter decomposition experiment in an artificial soil mixture. Needles of Norway spruce (Picea abies L.) were placed in microbatch containers filled with an artificial soil mixture free of soil organic matter. Containers were buried in fresh organic layer material from a Norway spruce stand and incubated for 14 and 42 days. We applied nanoscale secondary ion mass spectroscopy (NanoSIMS) to investigate the spatial distribution of mineral and organic compounds at the needle vicinity and into the mineral soil (0–550 μm from the needle). After 14 days, we depicted the formation of mineral-associated organic matter in the surrounding of the decaying needles. After 42 days, we observed substantial colonization of the needles and the detritusphere by saprotrophic fungi. The fungal hyphae extended into the mineral matrix of the artificial soil acting as vectors for the transfer of litter-derived carbon and nitrogen into the bulk soil. This resulted in an increase of the area covered by organic matter in the detritusphere, with up to 10% of the total investigated area classified as organic matter closely associated with mineral surfaces. Our results provide evidence that the carbon and nitrogen derived from litter decomposition transformed by microorganisms is transferred as mineral-associated organic matter, heterogeneously distributed from the litter source, and still detected 550 μm away from the latter. The close association of newly formed soil organic matter and fine sized minerals suggests that the formation of mineral-associated OM and likely also microaggregates is directly driven by microbial activity in the vicinity of hot spots for plant carbon input (e.g. the detritusphere).
•Fine spatial resolution few hundreds of micrometers from the plant residue.•Formation of mineral-associated organic matter in the vicinity of decaying needles.•Fungal hyphae extend into the mineral matrix of the artificial soil.•Fungi are vectors for the transfer of litter-derived organic matter into soil.•Important microbial pathway for organic matter formation in substrate hot spots.
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•Seasonal trajectories of nine bands and six indices from Sentinel-2 were analysed.•Seasonal change values were better for early detection than absolute reflectance.•Tasselled Cap Wetness and ...SWIR-based NDVI were most successful.•Separation of green-attack trees was best in autumn before next beetle generation.
In the past decade, massive outbreaks of bark beetles (Ips spp.) have caused large-scale decline of coniferous-dominated, prevailingly managed forests of Central Europe. Timely detection of newly infested trees is important for minimizing economic losses and effectively planning forest management activities to stop or at least slow outbreaks. With the advancement of Copernicus services, a pair of Sentinel-2 satellites provides a unique remote sensing data source of multi-temporal observations in high spatial resolution on the scale of individual forest stands (although not allowing for individual tree detection). This study investigates the potential for using seasonal trajectories of Sentinel-2 bands and selected vegetation indices in early detection of bark beetle infestation (so–called green-attack stage detection) in Norway spruce monoculture forests in the Czech Republic. Spectral trajectories of nine bands and six vegetation indices were constructed for the 2018 vegetation season using 14 satellite observations from April to November to distinguish four infestation classes. We used a random forest algorithm to classify healthy (i.e., stands not infested) and infested trees with various trajectories of decay. The seasonal trajectories of vegetation indices separated the infestation classes better than did the individual bands. Among the most promising vegetation indices we identified the tasselled cap wetness (TCW) component and normalized difference index constructed from near and shortwave infrared bands. Analysing the inter-annual change of the indices was more promising for early detection than is single-date classification. It achieved 96% classification accuracy on day of year 291 for the tested data set.The algorithm for early detection of tree infestation based on the assessment of seasonal changes in TCW was applied on the time series of Sentinel-2 observations from 2019 and its outputs were verified using field observations of forest conditions conducted on 80 spruce forest plots (located in spruce monoculture stands). The overall accuracy of 78% was achieved for the separation of healthy and green-attack classes. Our study highlights the great potential of multi-temporal remote sensing and the use of shortwave infrared wavelengths for early detection of spruce forest decline caused by bark beetle infestation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The state of within-stand variation (WSV) in boreal, coniferous production forests and how it is dealt with in thinning operations is a scarcely researched topic. In the autumn of 2018, we surveyed a ...series of Norway spruce (Picea abies (L.) Karst) or Scots pine (Pinus sylvestris L.) dominated production stands scheduled for first commercial thinning from below. Here, we evaluate the potential causes of WSV in basal area, how WSV was addressed in the thinning operations, and finally how the stands and subsequent thinning practice conformed with the basal area target specified in the thinning guidelines. WSV in the yield attributes was defined as the dispersion in a stand attribute within a stand and quantified using the Qn scale estimator (a robust measure of dispersion). First, WSV in basal area at the time of first thinning was evaluated as a function of WSV in stem number and WSV in site index. Next, yield attributes before and after thinning were compared using paired t-tests, and the future development of WSV in basal area was evaluated using linear mixed-effects models. Finally, the thinning practice was evaluated before and after thinning by modelling the compliance with the basal area target as a function of stem number and dominant height, also using linear mixed-effects models. WSV in basal area appeared to be influenced by WSV in site index and WSV in stem number for Norway spruce, but not for Scots pine. Thinning reduced the WSV in basal area, standing volume, and stem number, while dominant height, quadratic mean diameter and basal area weighted mean height remained unaffected. At first thinning, compliance with the thinning guideline increased with increasing stem density and dominant height. However, moderate to high compliance with the basal area target in the thinning guidelines was only reached for plots with elevated dominant height (>15 m) in combination with high stem number (>2250 N ha-1). Thus, the recommended range in dominant height (12–14 m) for first thinning was generally exceeded, which may be attributed to the generally low stem number at the time of thinning. This study suggests that sub-optimal regeneration efforts and management of young forests can lead to WSV across a wide range of stand attributes, and likely also reductions in yield. Thinning decreased WSV in basal area, standing volume and stem number, however, the plots were heavily thinned to such a degree that it could potentially cause production losses.
•Within-stand variation (WSV) and thinning guide compliance were studied at first thinning in Scots pine and Norway spruce stands.•Higher WSV in basal area (BA) in Norway spruce stands (not Scots pine) with elevated WSV in site index and WSV in stem number (N).•Generally low to moderate compliance with the BA target within the recommended interval in dominant height (12 - 14 m).•Full compliance with thinning guides at dominant heights of 15 m for Scots pine and 17 m for Norway spruce for N > 2250 ha−1.•Thinning reduced WSV in standing volume, BA and N, but maintained WSV in dominant height, mean height and quadratic mean diameter.
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•Terrestrial laser scanning (TLS) was applied on a unique drought stress experiment.•The approach revealed three-dimensional change of tree shape due to drought stress.•Drought stress led to smaller ...crown size and lower height growth.•Competition and drought resulted in crowns that were less rough and more compact.•TLS may enable efficient tree vitality monitoring.
Due to climate change, the occurrence of drought events with essential effects on trees will arise. The impact of severe drought stress on trees’ vitality with regard to growth has often been analysed using traditional, easy-to-measure variables, such as diameter at breast height (d1.3). Another commonly used tree-vitality indicator is crown transparency, which is not directly measurable and has to be determined qualitatively by well-trained field experts. In this study, we focused on tree dimensions, as potential vitality indicators, that are difficult to measure. The new approach for the efficient monitoring of tree vitality introduced here revealed three-dimensional change of tree shape due to drought stress.
The unique drought stress experiment “Kranzberg Forest Roof Experiment” (KROOF) was used as a basis for scanning and analysing the growth of Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica L.) under progressively limiting water reserves. Before the start of the experiment in the winter of 2012/2013, terrestrial laser scanning (TLS) was performed and repeated in the winter of 2018/2019. One sample of 21 trees was trenched and roofed (treatment), while additional 26 trees served as untreated reference (control). Using the TLS-point clouds of the two subsequent surveys, structural tree modifications within the 6-year period can be directly visualised, computed and linked to drought stress.
Drought stress led to significantly smaller crown size and lower height growth for both tree species. The crowns of Norway spruce trees increased significantly in transparency and roughness. In addition, high competition combined with drought stress significantly reduced the roughness and increased the compactness of the crown. The periodic annual change in crown projection area (paccpa) as well as the periodic annual height increment (paiheight) differed significantly between control and treatment for both tree species. Under drought conditions, paccpa changed by –0.74 m2 yr−1 and –0.42 m2 yr−1 for spruce and beech trees respectively, whereas the control trees showed a growth of 0.17 m2 yr−1 and 0.62 m2 yr−1 respectively. This means that crowns became considerably smaller under dry conditions. Under drought, the paiheight was 0.09 m yr−1 less for spruce and 0.17 m yr−1 less for beech compared with normal growing conditions. The periodic annual change in crown roughness (pacroughness) was −9.5% yr−1 if local competition increased by one.
Our results show that TLS can offer new opportunities for identifying structural features in trees. Iterative TLS-surveys may extend existing measuring campaigns on common long-term experimental plots, in order to analyse general changes or monitor tree vitality.
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Preparing sustainable and highly efficient biomass-based carbon materials (BBPM) as adsorbents remains a challenge for organic pollutant management. In this work, novel biobased carbon material has ...been synthesized via facile, sustainable, and different single-step pyrolysis chemical methods (KOH, ZnCl2, ZnSO4, and MgCl2) using a Norway spruce bark as suitable and efficient carbon precursor. The effects of each chemical activator on the physicochemical structure of synthesized were thoroughly investigated as well as its performance on the acetaminophen adsorption. The results showed that the use of different chemical activation provoked remarkable differences in the BBPM physicochemical characteristics. The KOH activation generated material with the highest specific surface area (2209 m2 g−1), followed by ZnCl2 (1019 m2 g−1), ZnSO4 (446 m2 g−1), and MgCl2 (98 m2 g−1). The chemical characterization of the carbon materials indicated that the activation of MgCl2 yielded a material around three times more hydrophobic when compared with the other activation methods. The acetaminophen removal showed to be ultrafast, not only due to the BBPM’s microstructure but also to the abundant active sites provided by the different chemical activation methods. The adsorption equilibrium times were reached at 1 min for BBPM-KOH and BBPM-MgCl2 and 15 min for BBPM-ZnSO4 and BBPM-ZnCl2. The adsorption process suggests that the pore-filling mechanism mainly dominates the acetaminophen removal but also some physical-chemical interactions such as hydrogen bonding between the amide group of acetaminophen and oxygenated or nitrogenated groups of biochar, π-π interactions between the aromatic ring of the pharmaceutical and the aromatics of biochar, n-π interaction, van der Waals interactions. The BBPM regeneration studies showed very good cyclability; in the 3rd cycle, the removal was approximately 70% for all four samples. The samples were also used to treat two synthetic effluents, which attained a removal percentage up to 91.9%.
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•Porous carbons were prepared by simple methods using MgCl2, ZnSO4, ZnCl2, and KOH.•KOH activation yielded a porous carbon with a specific surface area of 2209 m2 g−1.•Compared to other chemicals, MgCl2 yielded an extremely hydrophobic material.•Ultrafast acetaminophen adsorption times were reached for all activation methods.•Regeneration studies showed good cyclability at around 70% in the 3rd cycle.
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•We assess the association between forest disturbance history and current structure.•Carpathian spruce forests illustrate multiple pathways of structural development.•Complex structure is associated ...as much with disturbance as it is with stand age.•Unmanaged forests can inform adaptive management intended to foster resilience.
Mixed-severity disturbance regimes are prevalent in temperate forests worldwide, but key uncertainties remain regarding the variability of disturbance-mediated structural development pathways. This study investigates the influence of disturbance history on current structure in primary, unmanaged Norway spruce (Picea abies) forests throughout the Carpathian Mountains of central and eastern Europe, where windstorms and native bark beetle outbreaks are the dominant natural disturbances. We inventoried forest structure on 453 plots (0.1ha) spanning a large geographical gradient (>1,000km), coring 15–25 canopy trees per plot for disturbance history reconstruction (tree core total n=11,309). Our specific objectives were to: (1) classify sub-hectare-scale disturbance history based on disturbance timing and severity; (2) classify current forest structure based on tree size distributions (live, dead, standing, downed); (3) characterize structural development pathways as revealed by the association between disturbance history and current forest structural complexity. We used hierarchical cluster analysis for the first two objectives and indicator analysis for the third. The disturbance-based cluster analysis yielded six groups associated with three levels of disturbance severity (low, moderate, and high canopy loss) and two levels of timing (old, recent) over the past 200years. The structure-based cluster analysis yielded three groups along a gradient of increasing structural complexity. A large majority of plots exhibited relatively high (53%) or very high (26%) structural complexity, indicated by abundant large live trees, standing and downed dead trees, and spruce regeneration. Consistent with conventional models of structural development, some disturbance history groups were associated with specific structural complexity groups, particularly low-severity/recent (very high complexity) and high-severity/recent (moderate complexity) disturbances. In other cases, however, the distribution of plots among disturbance history and structural complexity groups indicated either divergent or convergent pathways. For example, multiple disturbance history groups were significantly associated with the high complexity group, demonstrating structural convergence. These results illustrate that complex forest structure – including features nominally associated with old-growth – can be associated as much with disturbance severity as it is with conventional notions of forest age. Because wind and bark beetles are natural disturbance processes that can induce relatively high levels of tree mortality while simultaneously contributing to structural complexity and heterogeneity, we suggest that forest management plans allow for the stochastic occurrence of disturbance and variable post-disturbance development trajectories. Such applications are especially appropriate in conservation areas where biodiversity and forest resilience are management objectives, particularly given projections of increasing disturbance activity under global change.
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