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Over the last decades, climate change has triggered an increase in the frequency of sprucebark beetle (Ips typographusL.) in Central Europe. More than 50% of forests in the Czech Republic areseriously threatened by this pest, leading to high ecological and economic losses. The exponentialincrease of bark beetle infestation hinders the implementation of costly field campaigns to prevent andmitigate its effects. Remote sensing may help to overcome such limitations as it provides frequent andspatially continuous data on vegetation condition. Using Sentinel-2 images as main input, two modelshave been developed to test the ability of this data source to map bark beetle damage and severity.All models were based on a change detection approach, and required the generation of previous forestmask and dominant species maps. The first damage mapping model was developed for 2019 and2020, and it was based on bi-temporal regressions in spruce areas to estimate forest vitality and barkbeetle damage. A second model was developed for 2020 considering all forest area, but excludingclear-cuts and completely dead areas, in order to map only changes in stands dominated by alivetrees. The three products were validated with in situ data. All the maps showed high accuracies (acc>0.80). Accuracy was higher than 0.95 and F1-score was higher than 0.88 for areas with high severity,with omission errors under 0.09 in all cases. This confirmed the ability of all the models to detectbark beetle attack at the last phases. Areas with no damage or low severity showed more complexresults. The no damage category yielded greater commission errors and relative bias (CEs=0.30-0.42,relB=0.42-0.51). The similar results obtained for 2020 leaving out clear-cuts and dead trees provedthat the proposed methods could be used to help forest managers fight bark beetle pests. These bioticdamage products based on Sentinel-2 can be set up for any location to derive regular forest vitalitymaps and inform of early damage.

Austria has been facing two outbreaks of the European spruce bark beetle, L., in the last ten years. In this study, we compile data of damage caused by L. as well as storm and snow breakage from 2002 to 2022 in two regions affected by these bark beetle outbreaks based on the Documentation of Forest Damaging Factors in Austria and analyze them in context of climatic factors. The first outbreak started in 2015 and affected Norway spruce forests at low elevation (< 600 m) in the north of Austria. Annual damage peaked in 2018 at 3.3 million m (representing 2.6% of total growing stock in the area). The second outbreak started in 2021 and affected mountainous spruce forests in the south of Austria. In this case extensive damage by storm in 2018 and snow breakage in the two following winters preceded the bark beetle outbreak. Annual damage by L. reached 1.7 million m (2.4% of growing stock) in 2022. Most forests are located on steep mountain slopes and have important protective function against natural hazards. High temperatures allowed completion of two generations up to 1,400 m elevation. Linear regression models showed that damage by L. was significantly affected by climatic water balance. This effect was stronger in the north than in the south. We discuss the different patterns of the outbreaks and challenges for bark beetle management in the context of climate change.

The bark beetle, Ips typographus (L.), is a major pest of Norway spruce, Picea abies (L.), causing enormous economic losses globally. The adult stage of the I. typographus has a complex life cycle (callow and sclerotized); the callow beetles feed ferociously, whereas sclerotized male beetles are more aggressive and pioneers in establishing new colonies. We conducted a comparative proteomics study to understand male and female digestion and detoxification processes in callow and sclerotized beetles. Proteome profiling was performed using high-throughput liquid chromatography-mass spectrometry. A total of >3000 proteins were identified from the bark beetle gut, and among them, 539 were differentially abundant (fold change ±2, FDR <0.05) between callow and sclerotized beetles. The differentially abundant proteins (DAPs) mainly engage with binding, catalytic activity, anatomical activity, hydrolase activity, metabolic process, and carbohydrate metabolism, and hence may be crucial for growth, digestion, detoxification, and signalling. We validated selected DAPs with RT-qPCR. Gut enzymes such as NADPH-cytochrome P450 reductase (CYC), glutathione S-transferase (GST), and esterase (EST) play a crucial role in the I. typographus for detoxification and digesting of host allelochemicals. We conducted enzyme activity assays with them and observed a positive correlation of CYC and GST activities with the proteomic results, whereas EST activity was not fully correlated. Furthermore, our investigation revealed that callow beetles had an upregulation of proteins associated with juvenile hormone (JH) biosynthesis and chitin metabolism, whereas sclerotized beetles exhibited an upregulation of proteins linked to fatty acid metabolism and the TCA cycle. These distinctive patterns of protein regulation in metabolic and functional processes are specific to each developmental stage, underscoring the adaptive responses of I. typographicus in overcoming conifer defences and facilitating their survival. Taken together, it is the first gut proteomic study comparing males and females of callow and sclerotized I. typographus , shedding light on the adaptive ecology at the molecular level. Furthermore, the information about bark beetle handling of nutritionally limiting and defence-rich spruce phloem diet can be utilized to formulate RNAi-mediated beetle management.

Automatic identification of forest patches disturbed by the spruce bark beetle Ips typographus L. is crucial to reveal the rules of following bark beetle outbreaks on the landscape scale. Landsat imagery provides free resources to outline past and present gradations of bark beetle outbreaks (BBOs). The objective of this study is to identify the most sensitive vegetation index through different method of vegetation index differencing to identify past and actual bark beetle outbreaks. Six Landsat Thematic Mapper (TM) images, from 2005–2009 and 2011, were converted into selected vegetation indices (VIs) sensitive to conifer tree health in a Norway spruce–dominated forest in the High Tatra Mountains. The Vegetation Condition Index (VCI), Moisture Stress Index (MSI), Normalised Difference Moisture Index (NDMI), Normalised Difference Vegetation Index (NDVI),   Disturbance Index (DI) and Changed Disturbance Index (DI´) were calculated separately for every year, and the methodology of vegetation index differencing was applied to multiple two-year time periods (2005–2006, 2006–2007, 2007–2008, 2008–2009 and 2010–2011), thus producing the Changed Vegetation Index (ΔVI). A set of thresholds was established on ΔVI to classify disturbed and undisturbed forest due to BBOs; the sensitivity of different VIs to identify BBO was equally evaluated. The highest accuracies of classifications were reached in 2007 and 2011 (kappa index of agreement >70% and >40%, respectively), which were characterised by an epidemic phase of a BBO. All selected VIs were highly sensitive to BBOs, except for NDVI. The stable threshold value for change detection is not widely applicable to detect past forest disturbances caused by bark beetles, however. Finally, for further research of the epidemic phases of BBOs, we recommend the utilisation of the vegetation indices VCI, MSI and NDMI to detect BBOs because of their simplicity and easy interpretability.

—The mass drying of the eastern spruce ( Picea orientalis (L.) Link) in Teberdinskyii Nature Reserve (North Caucasus) was studied. The main cause of the drying was an outbreak of the number of bark beetles ( Ips typographus L.), mass reproduction of which occurred in the hot seasons of 2012 and 2015. The existing undergrowth was not affected. By 2019, seven years after the beginning of the mass drying of spruce, the majority of the drying groups had died out, and single active bark beetle foci had been noted. There are almost no live spruce trees in the upper layer left. In small numbers, they have been preserved in the Dombai forest in mixed stands of Picea orientalis (L.) Link, Abies nordmanniana (Stev.) Spach, and Fagus orientalis Lipsky. As our study showed, the stands of two of the four forest areas of the reserve originated in a treeless space (250 and 350 years ago). Subsequently, three of the four underwent one strong, but local disturbance during their existence. Reconstruction of the history of dark coniferous stands of the surveyed forest areas shows a high capability for natural self-healing of the Teberda fir–spruce forests after massive disturbances. In the near future (after the fall of dead wood, which is already happening), the stands of the sample plots (SPs) will be a sparse forest of Abies or Abies with Fagus , and the majority of the sample plots will become open stands with single Abies trees. The modern mass drying of the eastern spruce as a result of bark-borne epiphytotics has a much larger scale of disturbances both in the area and in the degree of destruction of the stand. This is fundamentally different from the disturbances of the past. In this situation, the shortage of seeds will have a particularly negative impact. Therefore, the preservation of the preliminary coniferous undergrowth is especially important.

To study potential consequences of climate-induced changes in the biotic disturbance regime at regional to national scale we integrated a model of Ips typographus (L. Scol. Col.) damages into the large-scale forest scenario model EFISCEN. A two-stage multivariate statistical meta-model was used to upscale stand level damages by bark beetles as simulated in the hybrid forest patch model PICUS v1.41. Comparing EFISCEN simulations including the new bark beetle disturbance module against a 15-year damage time series for Austria showed good agreement at province level ( R ² between 0.496 and 0.802). A scenario analysis of climate change impacts on bark beetle-induced damages in Austria’s Norway spruce [ Picea abies (L.) Karst.] forests resulted in a strong increase in damages (from 1.33 Mm³ a −1 , period 1990–2004, to 4.46 Mm³ a −1 , period 2095–2099). Studying two adaptive management strategies (species change) revealed a considerable time-lag between the start of adaptation measures and a decrease in simulated damages by bark beetles.

Biological infestations in forests, e.g. the insect outbreaks, have been shown as favoured by future climate change trends. In Europe, the European spruce bark beetle ( Ips typographus L.) is one of the main agents causing substantial economic disturbances in forests. Therefore, studies on spatio-temporal characterization of the area affected by bark beetle are of major importance for rapid post-attack management. We aimed at spatially detecting damage classes by combining multidate remote sensing data and a non-parametric classification. As study site served a part of the Bavarian Forest National Park (Germany). For the analysis, we used 10 geometrically rectified scenes of Landsat and SPOT sensors in the period between 2001 and 2011. The main objective was to explore the potential of medium-resolution data for classifying the attacked areas. A further aim was to explore if the temporally adjacent infested areas are able to be separated. The random forest (RF) model was applied using the reference data drawn from high-resolution aerial imagery. The results indicate that the sufficiently large patches of visually identifiable damage classes can be accurately separated from non-attacked areas. In contrast to those, the other mortality classes (current year, current year 1 and current year 2 infested classes) were mostly classified with higher commission or omission errors as well as higher classification biases. The available medium-resolution satellite images, combined with properly acquired reference data, are concluded to be adequate tools to map area-based infestations at advanced stages. However, the quality of reference data, the size of infested patches and the spectral resolution of remotely sensed data are the decisive factors in case of smaller areas. Further attempts using auxiliary height information and spatially enhanced data may refine such an approach.

European forest disturbance—due to wind, bark beetles and wildfires—has increased in association with climate changes, but future disturbance-response remains highly uncertain. Now, research based on an ensemble of climate change scenarios indicates that an increase in forest disturbance is probable in the coming decades, with implications for forest carbon storage. Disturbances from wind, bark beetles and wildfires have increased in Europe’s forests throughout the twentieth century 1 . Climatic changes were identified as a key driver behind this increase 2 , yet how the expected continuation of climate change will affect Europe’s forest disturbance regime remains unresolved. Increasing disturbances could strongly impact the forest carbon budget 3 , 4 , and are suggested to contribute to the recently observed carbon sink saturation in Europe’s forests 5 . Here we show that forest disturbance damage in Europe has continued to increase in the first decade of the twenty-first century. On the basis of an ensemble of climate change scenarios we find that damage from wind, bark beetles and forest fires is likely to increase further in coming decades, and estimate the rate of increase to be +0.91 × 10 6 m 3 of timber per year until 2030. We show that this intensification can offset the effect of management strategies aiming to increase the forest carbon sink, and calculate the disturbance-related reduction of the carbon storage potential in Europe’s forests to be 503.4 Tg C in 2021–2030. Our results highlight the considerable carbon cycle feedbacks of changing disturbance regimes, and underline that future forest policy and management will require a stronger focus on disturbance risk and resilience.

Bark beetles are among the most devastating biotic agents affecting forests globally and several species are expected to be favored by climate change. Given the potential interactions of insect outbreaks with other biotic and abiotic disturbances, and the potentially strong impact of changing disturbance regimes on forest resources, investigating climatic drivers of destructive bark beetle outbreaks is of paramount importance. We analyzed 17 time-series of the amount of wood damaged by Ips typographus, the most destructive pest of Norway spruce forests, collected across 8 European countries in the last three decades. We aimed to quantify the relative importance of key climate drivers in explaining timber loss dynamics, also testing for possible synergistic effects. Local outbreaks shared the same drivers, including increasing summer rainfall deficit and warm temperatures. Large availability of storm-felled trees in the previous year was also strongly related to an increase in timber loss, likely by providing an alternative source of breeding material. We did not find any positive synergy among outbreak drivers. On the contrary, the occurrence of large storms reduced the positive effect of warming temperatures and rainfall deficit. The large surplus of breeding material likely boosted I. typographus population size above the density threshold required to colonize and kill healthy trees irrespective of other climate triggers. Importantly, we found strong negative density dependence in I. typographus that may provide a mechanism for population decline after population eruptions. Generality in the effects of complex climatic events across different geographical areas suggests that the large-scale drivers can be used as early warning indicators of increasing local outbreak probability.

Low-cost, miniaturized hyperspectral imaging technology is becoming available for small unmanned aerial vehicle (UAV) platforms. This technology can be efficient in carrying out small-area inspections of anomalous reflectance characteristics of trees at a very high level of detail. Increased frequency and intensity of insect induced forest disturbance has established a new demand for effective methods suitable in mapping and monitoring tasks. In this investigation, a novel miniaturized hyperspectral frame imaging sensor operating in the wavelength range of 500–900 nm was used to identify mature Norway spruce (Picea abies L. Karst.) trees suffering from infestation, representing a different outbreak phase, by the European spruce bark beetle (Ips typographus L.). We developed a new processing method for analyzing spectral characteristic for high spatial resolution photogrammetric and hyperspectral images in forested environments, as well as for identifying individual anomalous trees. The dense point clouds, measured using image matching, enabled detection of single trees with an accuracy of 74.7%. We classified the trees into classes of healthy, infested and dead, and the results were promising. The best results for the overall accuracy were 76% (Cohen’s kappa 0.60), when using three color classes (healthy, infested, dead). For two color classes (healthy, dead), the best overall accuracy was 90% (kappa 0.80). The survey methodology based on high-resolution hyperspectral imaging will be of a high practical value for forest health management, indicating a status of bark beetle outbreak in time.