Bark Beetle Research Articles

Fossil history of bark-beetles (Coleoptera: Scolytidae) with descriptions of two new species

ABSTRACT The presence of fossil bark beetles from the early Cretaceous to the Miocene is discussed. Changes in the diversity of this group over time are presented. Assumptions about trophic relationships are given. Two new species, Hylastes perkovskyi n. sp. from the tribe Hylastini and Chramesus boninoi n. sp. from the tribe Hylesinini, are described, respectively, from Eocene Rovno and Miocene Dominica amber. These are the first records of the genera Hylastes in Rovno amber and Chramesus in Dominican amber.

Reconstruction of the dynamics of the dark coniferous forests of the Teberdinsky Nature Reserve and prospects for their natural recovery after mass drying out

A study was made of the mass drying of the eastern spruce (Picea orientalis (L.) Link) in the Teberdinsky Nature Reserve (North Caucasus). The main cause of the drying was an outbreak of the number of bark beetle (Ips typographus L.) whose mass reproduction occurred in the hot seasons of 2012 and 2015. The existing undergrowth was not affected. By 2019, 7 years after the beginning of the mass drying of spruce, most of the groups of drying had died out, single active bark beetle foci were noted. There are almost no live spruces of the upper tiers left. In small numbers, they have been preserved in the Dombai forestry 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 ability for natural self-healing of the Teberdinsky fir-spruce forests after massive disturbances. In the near future (after the fall of dead wood, which is already happening), the stands of sample plots will be a sparse forest from Abies or Abies with Fagus, and most 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 such a situation, the shortage of seeds will have a particularly negative impact. Therefore, the preservation of preliminary coniferous undergrowth is especially important.

Early detection of Ips typographus infestations by using Sentinel-2 satellite images in windthrow affected Norway spruce forests in Smolyan region, Bulgaria

Strong winds uprooted more than 100 thousand m3 of coniferous trees in natural forest stands nearby the town of Smolyan (the Western Rhodopes) in January 2018. Although damaged trees were quickly removed from the stands, the European spruce bark beetle (Ips typographus) attacked the healthy Norway spruce trees near the windthrow areas in August 2020. Our hypothesis was that the trees were infested by the pest in previous years when no symptoms of attacks were observed. This study was conducted in three spruce stands, located near the windthrow areas and attacked by I. typographus, and in three control (healthy) stands located 5-10 km from the affected areas. We used satellite images captured by Sentinel-2 in September 2017-2020. It was established that in September 2017 (a year before the windthrow), the mean values of the Normalized difference vegetation index (NDVI) in the attacked stands were concentrated between 0.60 and 0.75 (with a maximum at 0.70), indicating that the trees were in good health. During the period 2018-2020 the distribution of mean values of NDVI was stretched between 0.35 and 0.75, which is an indication of evidence of pest attacks on the individual trees. The detail comparison of pixel values of the NDVI in the attacked and control sample plots was made on the base of images captured on 27.06.2020. The mean NDVI values in the three control plots (0.74-0.79) were much higher than the mean values in the sample plots attacked by the pest (0.57-0.65). These results showed that the values of NDVI based on satellite remote sensing data of Sentinel-2 can be used for early detection of I. typographus infestations in spruce stands around the windthrows. These data are important for rapid planning and implementing the sanitary feelings that reduce the pest population.

Testing the Efficiency of the Push-and-Pull Strategy during Severe Ips typographus Outbreak and Extreme Drought in Norway Spruce Stands

Protection of Norway spruce stands using anti-attractants was tested during an outbreak of bark beetles (Ips typographus) in their spring flight. The aims of this study were as follows: (1) to test the proposed experimental design for tree protection; (2) to evaluate height-specific alternatives for dispenser installation on trees; and (3) to evaluate the efficiency of tree protection measures using anti-attractants under bark beetle infestation and drought stress. The experiment was conducted at the forest edges adjacent to recent clearcuts on 10 blocks in the eastern Czech Republic. Each block had three adjacent experimental areas, with 20 trees growing in two rows at the recently cut forest edge (10 trees per row). In front of a block in each of the three areas, four pheromone traps were installed. The treatment area was protected by anti-attractants. The second area served as a so-called switch area, where beetles from the treatment area, as the outflux redirected from the anti-attractant, would start new attacks if not caught in nearby pheromone traps. The third area was a control. We attached anti-attractant tube dispensers on each tree trunk of the treated area at two heights. The results suggest a redirecting effect of anti-attractants, pushing beetles into the switch area and causing subsequent attacks, which was greater than in areas containing treated trees. There was no difference between two dispensers placed at 1 and 8 m height and both at 1 m. A switching effect of beetle attacks occurring outside of the treated areas was observed. Mounting anti-attractant dispensers on tree trunks at one low position above the ground can be substantially less labour-intensive and as efficient as positioning them at two different heights. For areas affected by severe drought and extremely dense bark beetle populations, the use of anti-attractants did not prove effective.

Keystone structures maintain forest function for Canada lynx after large-scale spruce beetle outbreak

Central to species conservation in an era of increased disturbance from climate change is understanding the primary mechanisms that facilitate how forest-dependent species respond to changes in forest structure and composition. Here, we leveraged a natural experiment to investigate how changed forest structure and function pre-spruce-beetle (Dendroctonus rufipennis) and post-beetle disturbance influenced the regional distribution of Canada lynx (Lynx canadensis) at their southern range periphery. We compared the distribution of Canada lynx that were reintroduced into Colorado, USA from 1999–2006 to the current (2015–2017) distribution following a spatial large-scale spruce beetle outbreak from 2007 to 2016. Canada lynx did not substantially alter their distribution following the wide-spread alteration of forest structure and composition following the insect outbreak. We used the Bhattacharyya’s affinity metric to document that core (50% isopleth) and overall population ranges (95% isopleth) overlapped significantly at 50% and 77% respectively. In addition, areas of low and high relative use remained similar after the bark beetle outbreak and mapped onto one another in nearly a 1:1 fashion (Spearman rank correlation = 0.92, p < 0.01). The low impact of forest change on distribution was due to the keystone habitat elements (high horizontal forest cover, snowshoe hares) that remained functional. Thus, our results highlight that conservation scientists should increase their focus to understand the underlying mechanisms that impact wildlife distributions as climate-related disturbances becomes ever more amplified.

A checklist of bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) from Siberia and the Russian Far East

A checklist of bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) from Siberia and the Russian Far East

Diversity of Auger Beetles (Coleoptera: Bostrichidae) in the Mid-Cretaceous Forests with Description of Seven New Species

The diversity and abundance of auger beetles were compared with ecologically similar families of other beetles. It was shown that the ecological niche in dead wood, which in the Paleogene belonged to bark and ambrosia beetles, was occupied by Bostrichidae in the Mesozoic. Seven new species, Poinarinius aristovi sp. nov., P. antonkozlovi sp. nov., P. lesnei sp. nov., P. perkovskyi sp. nov., P. zahradniki sp. nov., P. borowskii sp. nov., and P. cretaceus sp. nov. from the subfamily Alitrepaninae of the family Bostrichidae are described from mid-Cretaceous Burmese amber. The key to the species of the genus Poinarinius Legalov, 2018 is given. The new synonym, Alitrepanum Peng, Jiang, Engel &amp; Wang, 2022, syn. nov. to Poinarinius, was established. A list of the fossil Bostrichidae was compiled.

Current Problems of Forest Protection (25–27 October 2022, Katowice Poland)

Forestry is one of the sectors particularly affected by the threats posed by changing climatic conditions. This is reflected in the deterioration of the health status of stands due to the synergistic effect of numerous abiotic and biotic factors. Current forest health problems are due to dynamic, negative changes in the forest environment. While the amount of precipitation remains at a similar level, its distribution varies throughout the year and, in particular, the lack of soil moisture during the growing season leads to the weakening of trees, including the main forest-forming species in Poland such as Pinus sylvestris. The weakening of trees, in turn, leads to species of insect pests that were previously considered secondary becoming primary pests, such as Ips acuminatus. It is likely that weakening of trees also favours increased occurrence of parasitic plants such as Viscum album ssp. austriacum or Loranthus europaeus. Infestations of the hemiparasitic, xylem-secreting pine mistletoe are of great interest because they are spreading rapidly throughout Europe. Drought in forests is not only a long-term water shortage, but also a situation in which plant-fungal relationships are disrupted. Reduced water availability leads to a number of negative changes in the soil and the mycobiota that live there, affecting entire ecosystems. The effects of climate change and increased international trade are leading to the spread of pathogenic fungi and other harmful organisms whose range was previously restricted to the south of our continent. Unfavourable abiotic and biotic factors leading to weakening of oak stands in the western part of Poland have resulted in activation of new pests like Mediterranean oak borer. Intensification of transport and shortening of its duration, as well as climatic changes, favour the introduction of various organisms, including bark beetles (Scolytinae). In Poland, cyclic insect outbreaks are one of the most important problems in forest protection. Developing methods to monitor, prevent outbreaks and control the density of insect populations below harmful levels can be a challenge to consider. Finding an innovative system for applying insecticides to control spruce bark beetle could also be an interesting solution, where insects attracted to pheromones die after contact with the insecticide. Contact with the insecticide has a dual effect: either directly when the tree is treated, or when the bark beetle attempts to invade the tree. Opportunities for the use of biostimulants in forestry and is an attractive way to regenerate plants after negative stressors such as frost, drought or damage caused by improper use of pesticides, as well as the negative effects of diseases and pests. It acts indirectly by stimulating leaf, stem and root development and improving nutrient uptake. The effects of chemical treatments on fungal biodiversity in forests should be studied using powerful molecular tools such as NGS.

FUNGI OBTAINED FROM OLIVE TWIG DIEBACK AND ADULTS OF THE ALIEN PEST XYLOSANDRUS COMPACTUS (EICHHOFF) (COLEOPTERA CURCULIONIDAE SCOLYTINAE)

Olive (Olea europaea L.) is a traditional crop of great socioeconomic importance in the Mediterranean Basin. In 2021, a survey was performed in an Italian nursery located in Central Italy where unusual symptoms and widespread dieback had been observed on young potted olive trees. Twigs and branches of all plants affected by dryness showed the presence of the alien bark beetle Xylosandrus compactus. Woody tissues colonized by X. compactus were transferred into the laboratory and several fungi such as Cladosporium perangustum and Neofusicoccum parvum were then identified. In addition to these species, Geosmithia pallida was also reported for the first time in Italy on this plant. Studies on this bark beetle and its associated fungi are currently in progress to further evaluate potential risks for olive cultivation. Key Words: Olea europea, fungi, bark beetles.

Significant increase in natural disturbance impacts on European forests since 1950.

Over the last decades, the natural disturbance is increasingly putting pressure on European forests. Shifts in disturbance regimes may compromise forest functioning and the continuous provisioning of ecosystem services to society, including their climate change mitigation potential. Although forests are central to many European policies, we lack the long-term empirical data needed for thoroughly understanding disturbance dynamics, modeling them, and developing adaptive management strategies. Here, we present a unique database of >170,000 records of ground-based natural disturbance observations in European forests from 1950 to 2019. Reported data confirm a significant increase in forest disturbance in 34 European countries, causing on an average of 43.8 million m3 of disturbed timber volume per year over the 70-year study period. This value is likely a conservative estimate due to under-reporting, especially of small-scale disturbances. We used machine learning techniques for assessing the magnitude of unreported disturbances, which are estimated to be between 8.6 and 18.3 million m3 /year. In the last 20 years, disturbances on average accounted for 16% of the mean annual harvest in Europe. Wind was the most important disturbance agent over the study period (46% of total damage), followed by fire (24%) and bark beetles (17%). Bark beetle disturbance doubled its share of the total damage in the last 20 years. Forest disturbances can profoundly impact ecosystem services (e.g., climate change mitigation), affect regional forest resource provisioning and consequently disrupt long-term management planning objectives and timber markets. We conclude that adaptation to changing disturbance regimes must be placed at the core of the European forest management and policy debate. Furthermore, a coherent and homogeneous monitoring system of natural disturbances is urgently needed in Europe, to better observe and respond to the ongoing changes in forest disturbance regimes.

No Evidence of Responding Individuals Constraining the Evolution of the Pheromone Signal in the Pine Engraver Ips avulsus

Chemical signals are important mediators of interactions within forest ecosystems. In insects, pheromone signals mediate intraspecific interactions such as mate location and acceptance. The evolution of pheromones in insects has been mostly studied from a theoretical perspective in the Lepidoptera. With this study, we aimed to broaden our understanding of pheromone communication in bark beetles. We first demonstrated that the enantiomeric ratios of ipsdienol produced by male I. avulsus, showed little variation. Subsequently, with field trapping trials we characterized the influence of the enantiomeric ratio of ipsdienol (pheromone component of I. avulsus) on I. avulsus captures and observed a great amount of variation in the receiver preference function. Most importantly, we demonstrated that responding individuals responded indiscriminately to all the enantiomeric ratios produced by the emitting individuals. These observations are consistent with the asymmetric tracking model which postulates that if the limiting sex is the emitting sex, responding individuals should not discriminate between emitted ratios. Consequently, responding individuals do not constrain the evolution of the signal. Our data suggest that, in I. avulsus, the composition of the aggregation pheromone signal might be more responsive to external selection forces, such as predation and metabolic constraints, as suggested by the asymmetric tracking model.

Estimating Tree Health Decline Caused by Ips typographus L. from UAS RGB Images Using a Deep One-Stage Object Detection Neural Network

Various biotic and abiotic stresses are causing decline in forest health globally. Presently, one of the major biotic stress agents in Europe is the European spruce bark beetle (Ips typographus L.) which is increasingly causing widespread tree mortality in northern latitudes as a consequence of the warming climate. Remote sensing using unoccupied aerial systems (UAS) together with evolving machine learning techniques provide a powerful tool for fast-response monitoring of forest health. The aim of this study was to investigate the performance of a deep one-stage object detection neural network in the detection of damage by I. typographus in Norway spruce trees using UAS RGB images. A Scaled-YOLOv4 (You Only Look Once) network was implemented and trained for tree health analysis. Datasets for model training were collected during 2013–2020 from three different areas, using four different RGB cameras, and under varying weather conditions. Different model training options were evaluated, including two different symptom rules, different partitions of the dataset, fine-tuning, and hyperparameter optimization. Our study showed that the network was able to detect and classify spruce trees that had visually separable crown symptoms, but it failed to separate spruce trees with stem symptoms and a green crown from healthy spruce trees. For the best model, the overall F-score was 89%, and the F-scores for the healthy, infested, and dead trees were 90%, 79%, and 98%, respectively. The method adapted well to the diverse dataset, and the processing results with different options were consistent. The results indicated that the proposed method could enable implementation of low-cost tools for management of I. typographus outbreaks.

Development and implementation of a spruce bark beetle susceptibility index: A framework to compare bark beetle susceptibility on stand level

The spruce bark beetle (spruce bark beetle) (Ips typographus) is one of the major disturbance agents in European forests. Damage by spruce bark beetle is expected to increase in the future, as a result of e.g. increased temperatures. However, not all forest stands are equally vulnerable. Therefore, describing the relative difference in susceptibility of different forest stands to spruce bark beetle infestation and to try to estimate changes in susceptibility under different management or climate scenarios is necessary to support decision making on forest management. We present a spruce bark beetle susceptibility index, which describes the relative susceptibility of forest stands to spruce bark beetle infestation. The index is based on empirical findings and expert opinion, and takes both climatic and stand variables into account. The index can be implemented in forest simulation programs. The susceptibility index was implemented in Heureka, a forest decision support system. To demonstrate the use of the index, simulations were run for three management scenarios: baseline; even-aged management focused on conifers, longer rotation: same as baseline but with longer rotation periods and mixed forest: same as baseline but retaining a higher share of broadleaves. For this purpose, an area of 2451 ha consisting of 751 stands was used. The index value per stand per five-year time period was obtained from the simulations. The index was calculated individually, per management strategy, for all 751 stands and thereafter mean index and harvest volume was obtained for the whole area. Mean susceptibility was higher, and harvest slightly lower, in the longer rotation scenario, compared with the baseline, while there were no differences between baseline and mixed. At individual stand level, the differences are more nuanced and, for example, certain stands have lower susceptibility in the mixed compared with the baseline scenario. The ability to simulate forest development and simultaneously get a measure of spruce bark beetle susceptibility will enable forest owners to identify vulnerable stands and evaluate effects of different management decisions to reduce the risk for future economic losses.

Forest dieback reframed and revisited? Forests (re)negotiated in the German media between forestry and nature conservation

In Germany, the impacts of drought, heat and related bark beetle outbreaks on forests have shed light on the ongoing conflict between forestry and nature conservation approaches to forest management. The current forest damages sparked a nationwide debate about the role of forests and their adaptation to climate change. Echoing back to the debate on the German forest dieback in the 1980s, the current situation is commonly framed as forest dieback 2.0. As mass media possess discursive power in attributing specific meaning to topics, it influences public opinion and decision-making processes. Therefore, we conducted a frame analysis of newspaper articles on the impact of the drought years between 2018 and 2020 on forests. The aim was to identify the dominant actors in the debate and how they frame the current damages to German forests. Our results show that the forestry sector, politicians and journalists dominate the debate. Despite the low standing of nature conservationists in the debate, we observed a balanced, yet polarized presentation of forest and nature conservation frames. Whereas environmental factors are depicted as the main cause of forest damages, nature conservationists also blame the forestry sector. At the same time, forests are presented as the main affected as well as the most important factor to solve the crisis in relation to its climate mitigation potential. Forest management practices are identified as key instruments contributing to those solutions. In this regard, actors in the debate instrumentalize forests through dominant climate change discourses in order to legitimize their perspectives. In contrast, the societal responsibility and consequences of the forest damages are neglected.

Predictive accuracy of post-fire conifer death declines over time in models based on crown and bole injury.

A key uncertainty of empirical models of post-fire tree mortality is understanding the drivers of elevated post-fire mortality several years following fire, known as delayed mortality. Delayed mortality can represent a substantial fraction of mortality, particularly for large trees that are a conservation focus in western US coniferous forests. Current post-fire tree mortality models have undergone limited evaluation of how injury level and time since fire interact to influence model accuracy and predictor variable importance. Less severe injuries potentially serve as an indicator for vulnerability to additional stressors such as bark beetle attack or moisture stress. We used a collection of 164,293 individual tree records to examine post-fire tree mortality in eight western USA conifers: Abies concolor, Abies grandis, Calocedrus decurrens, Larix occidentalis, Pinus contorta, Pinus lambertiana, Pinus ponderosa, and Pseudotsuga menziesii. We evaluated the importance of fire injury predictors on discriminating between surviving trees versus immediate and delayed post-fire mortality. We fit balanced random forest models for each species using cumulative tree mortality from 1 to 5-years post-fire. We compared these results to multi-class random forest models using first-year mortality, 2-5-year mortality, and survival 5-years post-fire as a response variable. Crown volume scorched, diameter at breast height, and relative bark char height, were used as predictor variables. The cumulative mortality models all predicted trees that died within 1-year of fire with high accuracy but failed to predict 2-5-year mortality. The multi-class models were an improvement but had lower accuracy for predicting 2-5-year mortality. Multi-class model accuracies ranged from 85% to 95% across all species for predicting 1-year post-fire mortality, 42%-71% for predicting 2-5-year mortality, and 64%-85% for predicting trees that lived past 5-years. Our study highlights the differences in tree species tolerance to fire injury and suggests that including second-order predictors such as beetle attack or climatic water stress before and after fire will be critical to improve accuracy and better understand the mechanisms and patterns of fire-caused tree death. Random forest models have potential for management applications such as post-fire harvesting and simulating future stand dynamics.

Early аnd Late Wood оf Scots Pine under Conditions of Varying Degrees of Lighting

The condition of pine stands in Polissia is deteriorating due to an increase in the number of outbreaks of sharp-dentated bark beetle (Ips acuminatus) against the background of climate change, therefore, the relevance of this problem is beyond doubt. The purpose of the study is to identify the features of the dynamics of late and early Scots pine wood (Pinus Sylvestris L.) in areas with varying degrees of illumination after continuous cutting in the foci of the sharp-dentated bark beetle (Ips acuminatus) in Polissia. Standard dendrochronological, dendroclimatic, and statistical methods are used. It is established that after continuous logging in 2013 in the adjacent areas, on the one hand, there was an increase in the radial growth of pine trees, because the nutrition areas increased and the lighting conditions of trees improved, and on the other hand, trees growing next to the logging area are weakened and have fragile cores, which indicates a loss of wood quality. After cutting, during 2014-2020, the average values of late pine trees of illuminated time trial areas compared to the corresponding values in the control were 43-45%. For early wood, these values ranged from 38-42%. The growth change indices showed, that after the 2013 logging, violations occurred for trees in illuminated temporary trial areas as opposed to the control. The most sensitive to climatic factors were tree-ring chronologies of late wood in the most illuminated trial area. An increase in the sensitivity of the radial growth of pine trees was found depending on the increase in the degree of illumination. The weakening of plantings in the most illuminated area is indicated by the fact that the greatest number of significant relationships between growth and climate were found for the tree-ring chronology of early and late wood, while there was no critical decrease in trends in late and early wood layers. The findings can be used for planning forest management activities

Thirty-Year Dynamics of the Pine Stand Sanitary Conditions of Boyarka Forestry Research Station

The drying up of coniferous forests is a problem for both Europe and Ukraine, where drying area of pine stands covered the Polissia region and spread to other natural areas, therefore, the analysis of pathological factors of the reasons for the weakening and deterioration of the sanitary condition is relevant. The purpose of the study provides for generalisation of the reasons for the deterioration of the sanitary condition of pine stands and pathological processes in dynamics over 30 years. The results are based on data from 12 permanent and 10 temporary sample plots established in a separate subdivision of the National University of Life and Environmental Sciences of Ukraine “Boyarka Forestry Research Station”. The study used empirical and systematic methods. The predominance of drying of pine stands due to infection with the pathogen Heterobasidion annosum ((F.) Bref.) was revealed, at the same time, with the highest infestation coefficient, the dominant species in the stands under study were ash bark beetles Tomicus piniperda L. (54%), Tomicus minor Hartig (46%) with high and medium infestation rates and Monochamus galloprovincialis Olivier with a tree population ratio of 52% and an average degree of population in trunk areas with transitional and rough bark. In the dynamics of observations since 2011, an increase in the index of sanitary condition of pine stands and deterioration of forests due to changes in weather conditions and climate aridity have been established. After the dry growing seasons of 2015-2017, the drying of pine trees with mass reproduction of stem pests was revealed, the infestation coefficient of which indicates the dominance of the sharp-dentated bark beetle Ips acuminatus Gyll. and a large ash bark beetle Tomicus minor which are aggressive species. Since 2019, there has been a decrease in the number of bark beetles due to exceeding the long-term precipitation rate due to a decrease in the temperature at the beginning of the growing season and unfavourable weather conditions for wintering of these insect species. The results obtained would become an informational component in the development of a strategy for managing damaged forest areas

Long-term changes in soil composition in unmanaged central European mountain spruce forests after decreased acidic deposition and a bark beetle outbreak

We studied the effect of tree mortality on nutrient concentrations and pools in soils of two unmanaged mountain forest catchments (Plešné, PL; and Čertovo, CT; Czech Republic) recovering from acidification due to decreasing acidic atmospheric deposition since the late 1980s. Both catchments were situated at similar elevation, and before a bark beetle outbreak were covered by healthy mature Norway spruce (Picea abies) forests. However, differing bedrock [granite (PL) vs mica-schist and quartzite (CT)] resulted in lower concentrations of base cations (except for magnesium), but higher concentrations of aluminium and iron oxyhydroxides in the CT soils, enabling higher phosphorus (P) accumulation. Despite these differences, soils were similarly acidic, with pHH2O from 3.5 to 4.3 and cation exchange capacity (CEC) dominated by exchangeable protons (H+ex) and aluminium in both catchments in 2000. In the PL catchment, >75 % of mature spruce trees died after a bark beetle infestation between 2004 and 2008, and all dead biomass was left on site. Forest damage in the CT catchment was minor. Soil concentrations and pools of exchangeable calcium (Ca2+ex), magnesium (Mg2+ex), potassium (K+ex), and H+ex were tightly related to concentrations of organic carbon (C). Following the tree dieback in the PL catchment, we observed significant (p < 0.05) increases in (1) concentrations and pools of Ca2+ex, Mg2+ex, and K+ex, (2) base saturation (from 30 to ∼ 40 %), (3) CEC:C ratios (i.e., CEC of soil organic carbon), (4) pHH2O, (5) mineral P forms, and (6) total nitrogen (N) in the upper (O and A) soil horizons. Similar changes were less pronounced or negligible in the less impacted CT soils. The elevated litterfall after tree dieback, resulting in the increased input of base cations to forest floor and increased CEC of soil organic C, played a more important role in the decreasing acidity of the PL soils than the continuing decrease in acidic deposition.

Application and Accuracy of Unmanned Aerial Survey Imagery after Salvage Logging in Different Terrain Conditions

The accuracy of the positioning of the data collected by remote sensing platforms is of great importance in forest and wildlife surveys, salvage logging, soil disturbances after felling operations, fire risk management and many other forestry-based research. The significance of bark beetles in silver fir and Norway spruce stands is an essential factor that can affect the increase in biomass quantity and the reduction of its quality. Due to an Ips typographus (L.) outbreaks in the central part of Croatia from 2016 to 2021, salvage logging was performed in an area of 11,940 ha, with terrain slopes varying from 0 to 172.83%. Two plots of similar sizes (&lt;5 ha) and different terrain conditions (flat vs. sloped terrain) were chosen and were measured in June 2022. Measurements included a total station, a real-time kinematic (RTK) GNSS (Global Navigation Satellite System) terrestrial receiver and an unmanned aerial system (UAS) in order to determine the accuracy of a digital terrain model (DEM) generated by a photogrammetric UAS. In total, 175 checkpoints were marked in the field. Four different GCP (Ground Control Point) classes (5, 10, 15 and 20) were used to compare validation points acquired from the original point clouds, imagery and orthophotos to the reference positions. This study showed that, in terms of a forest area recognition after conducted salvage logging, the use of 10 GCPs for terrain evaluation is necessary even in small areas below 5 ha and regardless of terrain slope.

A Sentinel-2 Based Multi-Temporal Monitoring Framework for Wind and Bark Beetle Detection and Damage Mapping

The occurrence of extreme windstorms and increasing heat and drought events induced by climate change leads to severe damage and stress in coniferous forests, making trees more vulnerable to spruce bark beetle infestations. The combination of abiotic and biotic disturbances in forests can cause drastic environmental and economic losses. The first step to containing such damage is establishing a monitoring framework for the early detection of vulnerable plots and distinguishing the cause of forest damage at scales from the management unit to the region. To develop and evaluate the functionality of such a monitoring framework, we first selected an area of interest affected by windthrow damage and bark beetles at the border between Italy and Austria in the Friulian Dolomites, Carnic and Julian Alps and the Carinthian Gailtal. Secondly, we implemented a framework for time-series analysis with open-access Sentinel-2 data over four years (2017–2020) by quantifying single-band sensitivity to disturbances. Additionally, we enhanced the framework by deploying vegetation indices to monitor spectral changes and perform supervised image classification for change detection. A mean overall accuracy of 89% was achieved; thus, Sentinel-2 imagery proved to be suitable for distinguishing stressed stands, bark-beetle-attacked canopies and wind-felled patches. The advantages of our methodology are its large-scale applicability to monitoring forest health and forest-cover changes and its usability to support the development of forest management strategies for dealing with massive bark beetle outbreaks.