Abstract Water is a critical factor in forest production and its sustainable development. In addition, it contributes to the stability of forest ecosystems, essential for the growth and development of individual trees and stands. Electrical resistivity tomography (ERT) is the ideal method for detecting soil moisture among currently available methods. The advantages over other methods are mainly in the non-destructiveness of the measurement, i.e. it does not disturb the soil body. In this work, we deal with the influence of forest management on the dynamics of soil moisture and soil water storage. The measurements were carried out in the core zone of the Dobroč primaeval forest (plots Dobroč 1, Dobroč 2, Dobroč 3), in the buffer zone of the Dobroč primaeval forest with a predominance of European beech (Beech forest) and in the spruce monoculture near the buffer zone (Spruce forest). Measurements were made using ERT using the time-lapse method, while the detected soil resistance was calibrated to soil moisture. To calibrate the spatial variability of moisture, we used the time domain reflectometry (TDR) method to determine the volumetric soil water content. By calibrating between TDR and ERT using calibration equations, we determined the quantity of retained soil water within the measured profile. The results showed that the lowest soil water storage was on the spruce stand plot (53.31 ±9.55 dm3 m–3). On the contrary, the highest soil water storage was found on the Dobroč 2 plot (133.14 ±5.37 dm3 m–3). The decrease in soil water storage was the highest in the managed spruce forest. According to the amount of retained soil water, it appears to be the most resistant forest ecosystem of the Dobroč primaeval forest. The trend of soil water storage was more balanced in these ecosystems during the growing season than in areas outside the primaeval forest. Average soil water storage also reached higher values in these plots. The knowledge gained from the study can inform decisions about forest management in Slovakia and contribute to both the mitigation of climate change effects and the adaptation of forests, ensuring that the hydrological functions of forest ecosystems are maintained.

Abstract Assessing frost tolerance of hybrid poplar clones in the temperate zone is a key factor to select genotypes used for plantation forestry to intensify wood production and to strengthen forests’ adaptability to extreme weather conditions. This study aimed to evaluate frost resistance of ten poplar clones, aged 7 years, in eastern part of Ukraine. We analyzed frost resistance by comparing the average tissue damage indices of control plants with those exposed to frost temperatures of –25 °C and –30 °C. Cluster analysis further classified the clones into four distinct groups based on their frost resistance potential. Clones, which have been cultivated or intercrossed in Ukraine since the 1960s, are more resistant to frost due to the acclimatization of their parental individuals. Clones ‘Gulliver’ (P. deltoides), ‘Lvivska’ (P. × euramericana cv. ‘Regenerata’ × P. trichocarpa), and ‘Nocturne’ (P. trichocarpa × P. lasiocarpa) are characterized by the highest frost resistance in eastern Ukraine. Clones ‘Strilopodibna’ (P. × euramericana × P. nigra cv. ‘Italica’), ‘Perspektyvna’ (P. × euroamericana cv. ‘Regenerata’ × P. lasiocarpa), ‘Dorskamp’ (P. × euroamericana cv. ‘Dorskamp’), and ‘Ghoy’ (P. × euroamericana cv. ‘Ghoy’) were the most damaged by frost. The OLS regression model explained 64% of the variability in tissue damage, with clone and freezing temperature being the most influential factors (R2 = 0.640, Fstat = 17.49, p < 0.0001). In conclusion, our study demonstrated the importance of testing cultivars under local climatic conditions before using them on a commercial scale.

Abstract Cork oak (Quercus suber L.) mortality events have spurred scientific research into new afforestation techniques, particularly the use of fertigation to accelerate tree growth and hasten the onset of the productive phase when cork stripping becomes feasible. This study examines the effects of fertigation on the development of root and aerial systems, with the objective of determining if fertigation can eventually be discontinued without compromising tree vitality. Six seven-year-old trees growing under natural conditions were selected for analysis, grouped into three pairs, each with similar crown sizes but subjected to different watering regimes – fertigation and rainfed. These trees were analyzed using the Fastrak Polhemus method, focusing on seven parameters: volume, area, length, root diameter, root-to-shoot ratio, shape area, and circularity. Analyses were conducted both graphically and using partial correlation statistics. The findings indicate that tree size accounted for the most significant differences in these parameters. Conversely, fertigation was associated with an increase in trunk volume, while rainfed conditions led to larger root diameters, likely as an adaptation to drought. The most pronounced differences were observed in smaller trees, where both groups exhibited unbalanced but opposing root-to-shoot ratios: rainfed trees invested more in root development, while fertigation trees prioritized aerial growth. The impact of irrigation on the development of below-ground and above-ground biomass in arid regions is crucial in the context of ongoing climate change, which will further intensify drought during the growing seasons.

Abstract This paper presents a comparative study on the pathogenicity of Metarhizium pemphigi against different insect pests (Ips acuminatus, Ips sexdentatus, Taphrorychus bicolor, Oulema melanopus, Oxycarenus lavaterae, and Corythucha arcuata) under laboratory conditions. The mortality rates were determined for different conidia concentrations. Overall, the average mortality rate for all insect species tested was 21.05 ±7.41% after treatment with 2 × 105 conidia/ml and 98.79 ±1.21% after treatment with 2 × 109 conidia/ml. Mortality rates varied significantly among insect species, especially at lower conidia concentrations. Depending on the tested insect species, the mean values of LC50 and LC90 varied from 0.29 to 77.80 × 106 conidia/ml and from 10.14 to 417.10 × 106 conidia/ml, respectively, with probit regression slopes ranging from 0.74 to 0.90. The tested strain of M. pemphigi was the most virulent to T. bicolor and also showed high efficacy against I. acuminatus, C. arcuata, and O. melanopus. Conversely, I. sexdentatus displayed the lowest susceptibility to this fungus. Estimated mean survival times of the insects, after treatment with 2 × 106 conidia/ml, ranged from 5.32 to 9.05 days, depending on the insect species. The shortest survival time was estimated for T. bicolor, and the longest for O. lavaterae. The study highlights the potential of M. pemphigi for biocontrol of the tested insect species and calls for further research to explore its full capabilities and potential applications.

Abstract The continuous threat of ongoing climate change and related weather anomalies challenge forest ecosystems. The phytosociological structure of forests plays a crucial role in determining their resilience to various abiotic and biotic stressors. Furthermore, stand density, which partly regulates the allocation of resources within individual trees, is a vital aspect of understanding forest functioning. This study was conducted in Norway spruce (Picea abies [L.] Karst.) forests in the Czech Republic, where we investigated the influence of tree density on sap flow rates within three predefined directions corresponding to sun position during the morning (5:00–11:10 hours; East), noon (11:10–15:10 hours; South), and evening (15:10–21:10 hours; West) intervals. Tree density was calculated within a 10 m radius buffer around each sap flow measured tree using high spatial resolution aerial imagery acquired by Unmanned Aerial Vehicle. Sap flow was measured at 10-minute intervals for 25 selected trees during the nine hottest summer days in 2019. Our data reveals an inverse correlation between sap flow and tree density, underscoring the substantial impact of neighboring tree density on transpiration. This relationship was most pronounced during midday, followed by the evening and morning hours, suggesting higher heat loads on the trees and forest grounds during the midday. Our findings emphasize the critical role of stand density in modulating forest functioning and underscore the importance of maintaining specific canopy densities as part of effective silvicultural practices in the face of ongoing climate change.

Abstract Understanding the dynamics of ungulates is crucial for proper wildlife management and conservation efforts. Where high densities of ungulates are present and exceed the carrying capacity, damage occurs in both the forestry and agriculture sectors, moreover human safety is endangered through road accidents. This study explores the evolution of deer populations in the Baltics, Central, and Eastern Europe through the analysis of hunting bag data, which represents the total number of specimens harvested annually. By utilizing hunting bag statistics reported by wildlife managers and hunters, this research aims to provide a more reliable indicator for population trends compared to traditional wildlife monitoring techniques, which may suffer from issues such as double counting, underreporting, or different estimation methods. The study focuses on the evolution of hunting bag numbers for red deer (Cervus elaphus L.), roe deer (Capreolus capreolus L.), and fallow deer (Dama dama L.) between 2012 to 2022. The primary metrics used in the description of growth and statistical analyses were the hunting bags and population parameters such as the sex ratio. The findings of this study indicate that hunting bag data have shown an increasing trend during the study period. The sex ratio of the harvested specimens seems to play a role in annual growth only in the case of roe deer. Based on different harvesting rates, the population estimates for the year 2022 were projected. This research confirms similar trends in population growth for the studied species and also indicates an increase in damage caused by high densities of ungulates. The study underscores the significance of integrated approaches in assessing ungulates populations and their ecological roles, contributing to future wildlife management practices.

Abstract Droughts, amplified by climate change, pose a significant threat to the success of both artificially and naturally regenerated forests. Understanding how these changes affect the initial stages of saplings development is crucial for forest establishment, particularly for ecologically and economically important species like Norway spruce and sessile oak in Central Europe. This study investigated the impact of crown reduction (CR) by 50% of crown length on saplings of each species. Automatic dendrometers were installed on 24 saplings per species to precisely monitor growth and water-related stem changes. The main objective was to investigate the potential ameliorative effect of CR on water-stressed saplings during their initial development. Our study hypothesized that CR, by decreasing leaf area and consequently water use, would improve water availability and facilitate sapling growth. The results indicate that CR may enhance soil water availability thereby supporting the growth of water-stressed Norway spruce saplings but not those of sessile oak. The tree water deficit – an indicator of tree water status – significantly improves in Norway spruce saplings subjected to CR (p < 0.05). Conversely, this treatment resulted in the depletion of stem water status in sessile oak saplings. The species-specific growth phenology revealed that CR led to an increase in the number of growing days for Norway spruce compared to sessile oak saplings. In summary, CR may be considered a beneficial method for alleviating stress in Norway spruce saplings, especially during drought. In addition, further testing in field conditions is necessary to confirm these results.

Abstract Fomitopsis pinicola [Sw.] P. Karst. is one of the most common wood-decaying macrofungi which is adapted to growth under different environmental conditions, but little is known about its intraspecific variation in spatial distribution, function and substrate specificity in different habitats. To understand how the geographical distribution, trophic mode and host specificity of this fungus vary across different habitat categories, we analysed its habitat and trophic preferences using Slovakia (Central Europe) as an example. For this purpose we studied and compared the archived material (fungarium items and field notes) from 1954 to present, obtained from own collections and external sources. The occurrence of F. pinicola in forests and quasi-natural habitats is related to the distribution of Norway spruce. Contrariwise, sites with its presence in public urban spaces are scattered throughout the whole territory of Slovakia. The occurrence of F. pinicola as a saprotroph is highest in forests and lowest in public urban spaces, where it accounts for 90.1% and 27.7% of the total number of records, respectively. F. pinicola was also shown as an important pathotroph of broadleaves in public urban spaces, where pathotrophy concerns as high as 72.3% of relevant records. Prunus species are the most frequently infested woody plants, accounting for 81.3% of these records. In silico analysis of available F. pinicola ITS sequences indicates its genetic homogeneity in Central Europe and the adjacent regions. Thus, the observed differences in trophic modes and host preferences of F. pinicola from different habitats cannot be explained by its intraspecific genetic variability.

Abstract Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) is considered one of the most promising introduced tree species for use in forestry in Central Europe. The formation of vital and stable forest stands with a certain share of Douglas fir (DF) requires the application of appropriate silvicultural measures, such as thinning. The article evaluates the growth response of DF to the initial experimental thinning. Eight stands were analysed on nutrient-rich sites in the three forest vegetation zones (Querceto-Fagetum, Fagetum, Abieto-Fagetum). The analysis includes both stands dominated by DF and stands where DF is only interspersed. The thinning was applied when the dominant tree height ranged from 5 to 20 m. A dominant tree height of 10 m was used as the threshold to define well-timed thinning. The data were analysed using Bayesian hierarchical modelling, and generalized hierarchical models were employed. DF promising trees responded to early thinning with significant acceleration of radial growth, leading to improvements in height-to-diameter ratio (HDR) and crown ratio (CR) parameters. The response of DF promising trees to delayed thinning was negligible. Neither early nor delayed thinning had a detectable effect on height growth of the DF promising trees. The result confirms the necessity of initiating thinning for DF stands at the stage of thickets. The thinning should ideally begin when the dominant tree height is between 4 to 5 meters. At this stage, it is possible to positively influence diameter growth and mitigate the deterioration of individual tree stability as well as the stability of the whole stand.

Abstract Forest health assessments (FHA) have been carried out at European level since the 1980s in order to identify forest damage. The annual surveys are usually conducted without the use of remote sensing tools. However, the increasing availability of remote sensing observations potentially allows conduct FHA more wide-spread, more often, or in more comprehensive and comparable way. This literature review systematically evaluated 110 studies from 2015 to 2022 that use remote sensing for FHA in Europe. The purpose was to determine (1) which tree species were studied; (2) what types of damage were evaluated; (3) whether damage levels are distinguished according to the standard of the International Co-operative Program on Assessment and Monitoring of Air Pollution Effects on Forests (ICP-Forest); (4) the level of automation; and (5) whether the findings are applicable for a systematic FHA. The results show that spruce is the most studied tree species. Damage caused by bark beetles and drought were predominantly studied. In most studies only 2 damage levels are classified. Only four studies were able to perform a comprehensive FHA by identifying individual trees, classifying their species and damage levels. None of the studies investigated the suitability of their remote sensing approach for systematic forest health assessments. This result is surprising since programs such as SEMEFOR analyzed the potential of remote sensing for FHA already in the 1990s. We conclude that the availability of new satellite systems and advances in artificial intelligence and machine learning should be translated into FHA practice according to ICP standards.