Clonal variation and damage dynamics in Norway spruce: Towards the selection of climate-resilient genotypes

Effect of bark beetle (Ips typographus L.) attack on bark VOC emissions of Norway spruce (Picea abies Karst.) trees

Timing of red-edge and shortwave infrared reflectance critical for early stress detection induced by bark beetle (Ips typographus, L.) attack

The European spruce bark beetle is a major disturbance agent in Norway spruce forests in Europe, and with a changing climate it is predicted that damage will increase. To prevent the bark beetle population buildup, and to limit further spread during outbreaks, it is crucial to detect attacked trees early. In this study, we utilize Sentinel-2 data in combination with a risk map, created from geodata and forestry data, to detect trees predisposed to and attacked by the European spruce bark beetle. Random forest models were trained over two tiles (90 × 90 km) in southern Sweden for all dates with a sufficient number of cloud-free Sentinel-2 pixels during the period May–September in 2017 and 2018. The pixels were classified into attacked and healthy to study how detection accuracy changed with time after bark beetle swarming and to find which Sentinel-2 bands are more important for detecting bark beetle attacked trees. Random forest models were trained with (1) single-date data, (2) temporal features (1-year difference), (3) single-date and temporal features combined, and (4) Sentinel-2 data and a risk map combined. We also included a spatial variability metric. The results show that detection accuracy was high already before the trees were attacked in May 2018, indicating that the Sentinel-2 data detect predisposed trees and that the early signs of attack are low for trees at high risk of being attacked. For single-date models, the accuracy ranged from 63 to 79% and 84 to 94% for the two tiles. For temporal features, accuracy ranged from 65 to 81% and 81 to 92%. When the single-date and temporal features were combined, the accuracy ranged from 70 to 84% and 90 to 96% for the two tiles, and with the risk map included, the accuracy ranged from 83 to 91% and 92 to 97%, showing that remote sensing data and geodata can be combined to increase detection accuracy. The differences in accuracy between the two tiles indicate that local differences can influence accuracy, suggesting that geographically weighted methods should be applied. For the single-date models, the SWIR, red-edge, and blue bands were generally more important, and the SWIR bands were more important after the attack, suggesting that they are most suitable for detecting the early signs of a bark beetle attack. For the temporal features, the SWIR and blue bands were more important, and for the variability metric, the green band was generally more important.

Over the last decades, climate change has triggered an increase in the frequency of spruce bark beetle (Ips typographus L.) in Central Europe. More than 50% of forests in the Czech Republic are seriously threatened by this pest, leading to high ecological and economic losses. The exponential increase of bark beetle infestation hinders the implementation of costly field campaigns to prevent and mitigate its effects. Remote sensing may help to overcome such limitations as it provides frequent and spatially continuous data on vegetation condition. Using Sentinel-2 images as main input, two models have 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 forest mask and dominant species maps. The first damage mapping model was developed for 2019 and 2020, and it was based on bi-temporal regressions in spruce areas to estimate forest vitality and bark beetle damage. A second model was developed for 2020 considering all forest area, but excluding clear-cuts and completely dead areas, in order to map only changes in stands dominated by alive trees. 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 detect bark beetle attack at the last phases. Areas with no damage or low severity showed more complex results. 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 proved that the proposed methods could be used to help forest managers fight bark beetle pests. These biotic damage products based on Sentinel-2 can be set up for any location to derive regular forest vitality maps and inform of early damage.

Climate change is estimated to increase the risk of the bark beetle (Ips typographus L.) mass outbreaks in Norway Spruce (Picea abies (L.) Karst) forests. Habitats that are thermally suitable for bark beetles may expand, and an increase in the frequency and intensity of droughts can promote drought stress on host trees. Drought affects tree vigor and in unison with environmental features it influences the local predisposition risk of forest stands to bark beetle attacks. We aimed to study how various environmental features influence the risk of bark beetle attacks during a drought year and the following years with more normal weather conditions but with higher bark beetle populations. We included features representing local forest stand attributes, topography, soil type and wetness, the proximity of clear-cuts and previous bark beetle attacks, and a machine learning algorithm (random forest) was applied to study the variation of predisposition risk across a 48,600 km2 study area in SE Sweden.Forest stands with increased risk of bark beetle attack were distinguished with high accuracy both during drought and in normal weather conditions. The results show that during both study periods, spruce and mixed coniferous forests had elevated risk of attack, while forests with a mix of deciduous and coniferous trees had a lower risk. Forests with high average canopy height were strongly predisposed to bark beetle attacks. However, during the drought year risk was more similar between stands with lower and higher canopy height, suggesting that during drought periods younger trees can be predisposed to bark beetle attacks. The importance of soil moisture and position within the local landscape were highlighted as important features during the drought year.Identifying areas with increased risk, supported by information on how environmental features control the predisposition risk during drought, could aid adaptation strategies and forest management intervention efforts. We conclude that geospatial data and machine learning have the potential to further support the digitalization of the forest industry, facilitating development of methods capable to quantify importance and dynamics of environmental features controlling the risk in local context. Corresponding methods could help to direct management actions more effectively and offer information for decision-making in changing climate.

Impact of bark beetle ( Ips typographus L.) disturbance on timber production and carbon sequestration in different management strategies under climate change

Examining the potential for early detection of spruce bark beetle attacks using multi-temporal Sentinel-2 and harvester data

Effects of salvage logging and sanitation felling on bark beetle (Ips typographus L.) infestations

На території Ботанічного саду Харківського національного університету (ХНУ) ім. В. М. Каразіна на хвойних породах визначено 4 види короїдів: короїда-типографа (Ips typographus L.), гравера звичайного (Pityogenes chalcographus L.), соснового короїда-крихітку (Crypturgus cinereus Herb.) та тайгового короїда-крихітку (C. subcribrosus Eg.). Відзначено, що з роду Abies лише п’ять видів не мали ознак заселення, а саме: A. balsamia, A. cephalonica, А. concolor, A. grandis, А. violacea. Picea koraiensis та P. alba не були заселені короїдами, але на стовбурі помічено спроби заселення. Встановлено, що форму P. obovata «Glauca» заселяли всі визначені види короїдів. Найбільш поширеним на ялині серед інших видів короїдів виявився Ips typographus. Серед 198 обстежених дерев визначено: живих із відсутністю ознак заселення короїдами – 27,3 %, зі спробами заселення – 9,1 %, заселених короїдами – 63,6 %.

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.

This study considered the mechanical properties of primary blue-stained sapwood of Norway spruce infested by the bark beetle Ips typographus. Nineteen stems from Stammerberg (ZH, Switzerland) were harvested in three different seasons and after different periods of bark beetle outbreaks. Density, Brinell hardness including elastic recovery after load, and key strength properties were tested on blue-stained wood and non-infected controls. Differences in mechanical properties were analysed according to the stand and storage time of the stems after the bark beetle attack. Spruce harvested at a late stage after the bark beetle attack (2–3 months) showed a clear reduction in impact bending strength, a significant loss in surface elastic recovery after indentation during Brinell hardness test, and a striking number of specimens with brittle fracture behaviour during Three-Point-Bending. Light microscopy and the results of the mechanical tests give clear evidence to suggest that wood-degrading fungi are already active in addition to the sap-staining fungi. Especially after larger outbreaks of bark beetles, it must be assumed that sapwood of Norway spruce does not only show the typical blue stain, but also incipient stages of wood degradation by wood-degrading fungi.

Bark beetle (Ips typographus) outbreaks have the potential to damage large areas of spruce-dominated forests in Scandinavia. To define forest management strategies that will minimize the risk of bark beetle attacks, we need robust models that link forest structure and composition to the risk and potential damage of bark beetle attacks. Since data on bark beetle infestation rates and corresponding damages does not exist in Norway, we implement a previously published meta-model for estimating I. typographus damage probability and intensity. Using both current and projected climatic conditions we used the model to estimate damage inflicted by I. typographus in Norwegian spruce stands. The model produces feasible results for most of Norway’s climate and forest conditions, but a revised model tailored to Norway should be fitted to a dataset that includes older stands and lower temperatures. Based on current climate and forest conditions, the model predicts that approximately nine percent of productive forests within Norway’s main spruce-growing region will experience a loss ranging from 1.7 to 11 m3/ha of spruce over a span of five years. However, climate change is predicted to exacerbate the annual damage caused by I. typographus, potentially leading to a doubling of its detrimental effects.

The temporal gradations of the investigated phenolics in Norway spruce bark after bark beetle (Ips typographus) attack followed the general eco-physiological concept. Treatment with salicylic acid inhibits bark beetle colonisation, alleviates the phenolic responses and activates the synthesis of condensed tannins on later sampling dates. Conifer bark is the target of numerous organisms due to its assimilated transport and nutrient storage functions. In the presented study, 100 mM salicylic acid (SA) was applied onto Norway spruce stems prior to being infested with bark beetles (Ips typographus L.), to study the temporal gradation of changes in condensed tannins (CT) and total phenolics (tPH) and their significance for mediating stress-tolerance. A significant accumulation of CT was monitored in untreated trees in response to progressive bark beetle infestation occurring from May onwards. In SA-treated infested trees, the CT values remained at control levels until May, but after the re-treatment of infested trees in June, the concentrations of CT rose significantly in comparison to the controls. The tPH values dropped 16 days after SA-treatment, independent of infestation, and later on remained at control level until July. In contrast, tPH contents accumulated in untreated infested trees in May, eased in June and increased again in July, when the trees were affected by the second generation of bark beetles. To sum up, in May and July when the highest beetle-flight activity was monitored the metabolic shift of phenolics within untreated infested trees differed significantly from the response of SA-treated trees. In addition, on SA-treated trees less entrance holes were monitored over the whole period of sampling when compared to untreated infested trees. These results provide evidence that SA-treatment alleviates the phenolic responses, activates the synthesis of condensed tannins and inhibits bark beetle colonisation.

During the past decade bark beetle (Ips typographus) attacks killed nearly all of the Norway spruce [Picea abies (L.) Karst.] stands in the unmanaged zone in the highlands of the Bavarian Forest National Park. This study was conducted to predict if and how long the catastrophic event might cause elevated nitrate NO3(-) concentration in seepage water, and if the presence of ground vegetation may reduce NO3(-) leaching. A chronosequence approach was used to investigate NO3(-) leaching before and after the death of trees. Additionally, the impact of ground vegetation coverage on NO3(-) leaching was determined. Flux weighted yearly NO3(-) concentrations were significantly elevated in the first 5 yr after the dieback compared with intact stands (27 micromol(c) L(-1)), with highest concentrations in the fifth year after the dieback (579 micromol(c) L(-1)). Lowest NO3(-) concentrations were observed 17 yr after the dieback (10 micromol(c) L(-1)). Suction cups in places without ground vegetation showed significantly higher NO3(-) concentrations of 163 to 727 micromol(c) L(-1) (Year 2-5 after the dieback) than suction cups without vegetation. However, net uptake of N by ground vegetation observed during the first 7 yr after the dieback was low on a plot scale. Compared with other severe disturbances in forests, NO3(-) concentrations were elevated for a longer period. Due to high rates of precipitation, NO3(-) dilution occurred and concentrations remained mostly below the European critical level for drinking water. Part of the observed heterogeneity in NO3(-) concentrations could be attributed to different patterns of ground vegetation coverage.

Coniferous forests cover 41% of Bosnia and Herzegovina, with Norway spruce ( Picea abies ) being an ecologically and economically important species. Bark beetles, especially the European spruce bark beetle ( Ips typographus ), pose a major threat, often causing large-scale dieback. Factors such as wind, drought, terrain exposure, and slope can increase susceptibility to outbreaks. This study aimed to assess the influence of these factors on forest health in bark beetle outbreak areas, based on stump measurements after sanitary logging.Fieldwork was conducted in spring 2024 on five known bark beetle hotspots managed by “Šumsko privredno društvo Zeničko-dobojskog kantona” d.o.o. Zavidovići. Data collected included stump diameter, wood decay, bark thickness, tree coordinates (via AlpineQuest), exposure, and slope. Analyses were performed in STATGRAPHICS Plus using one-way ANOVA and Bonferroni correction.A total of 507 stumps were analyzed. About 81% were in diameter classes 31–50 cm and 51–80 cm and nearly 48% showed central wood decay. Terrain exposure and slope significantly influenced stump diameters, with the largest averages on SW exposure and 2–5% slopes. Stump diameter also significantly affected decay size, while bark thickness showed no significant variation across exposure or slopes.This research confirmed that Norway spruce in diameter size categories 31–50 cm and 51–80 cm is most vulnerable to bark beetle attacks. This susceptibility is further intensified if trees are located on south-facing, moderate slopes. Central wood decay was present in nearly half of the observed tree stumps, leading to the conclusion that its presence is another predisposing factor for bark beetle attacks. Bark thickness on the observed tree stumps did not vary significantly on different terrains, which is a result that differed from the results obtained in other similar studies.