Dothistroma septosporum, the primary causal agent of Dothistroma needle blight, is one of the most significant foliar pathogens of pine worldwide. Its wide host and environmental ranges have led to its global success as a pathogen and severe economic damage to pine forests in many regions. This comprehensive global population study elucidated the historical migration pathways of the pathogen to reveal the Eurasian origin of the fungus. When over 3800 isolates were examined, three major population clusters were revealed: North America, Western Europe, and Eastern Europe, with distinct subclusters in the highly diverse Eastern European cluster. Modeling of historical scenarios using approximate Bayesian computation revealed the North American cluster was derived from an ancestral population in Eurasia. The Northeastern European subcluster was shown to be ancestral to all other European clusters and subclusters. The Turkish subcluster diverged first, followed by the Central European subcluster, then the Western European cluster, which has subsequently spread to much of the Southern Hemisphere. All clusters and subclusters contained both mating-types of the fungus, indicating the potential for sexual reproduction, although asexual reproduction remained the primary mode of reproduction. The study strongly suggests the native range of D. septosporum to be in Eastern Europe (i.e., the Baltic and Western Russia) and Western Asia.

When natural regeneration of Quercus robur stands is hampered by an insufficient acorn yield, human assisted sowing of acorns collected in non-affected stands and stored for some period of time is performed. To inhibit the development of fungi and acorn deterioration during storage, thermotherapy is usually applied by submerging acorns for 2.5 h in water heated to 41 °C. This research aimed to test the effect of four thermotherapy treatments of different durations and/or applied temperatures as well as short-term storage at −1 °C or 3 °C on acorn internal mycobiota and germination. Fungal presence in cotyledons was analyzed in 450 acorns by isolation of mycelia on artificial media, followed by a DNA-based identification. Germination of 2000 acorns was monitored in an open field trial. Thermotherapy significantly decreased fungal diversity, while storage at 3 °C increased the isolation frequency of several fungi, mainly Penicillium spp. The most frequently isolated fungi did not show a negative impact on acorn germination after short-term storage. The study confirmed the efficiency of thermotherapy in the eradication of a part of acorn internal mycobiota, but also its effect on the proliferation of fast-colonizing fungi during storage. However, the latter showed to be more stimulated by storage conditions, specifically by storage at 3 °C.

Chestnut blight is a disease of Castanea species caused by the ascomycete Cryphonectria parasitica. The fungus originates from eastern Asia (Liu et al., 2007) and has little effect on the native host trees Castanea crenata (Japanese chestnut) and Castanea mollisima (Chinese chestnut) (Roane et al., 1986) but it has caused severe epidemics resulting in widespread death and dieback of Castanea dentata (American chestnut) in North America, where the fungus was introduced in the late 19th century (Anagnostakis, 1987), and Castanea

Small rodents (Rodentia, subfam. Murinae: real mice, Arvicoline voles) greatly affect natural regeneration, stability and dynamics of forest communities worldwide. Every 3–4 years rodent damage in Croatian state forests is the most severe in forest regeneration stands, especially in pedunculate oak (Quercus robur L.) and narrow-leaved ash (Fraxinus angustifolia Vahl.) forests, where rodents can seriously impede natural regeneration by damaging seeds, stems and roots of saplings. These negative interactions are an even bigger challenge nowdays as pedunculate oak and narrow-leaved ash have become more vunerable in the last decades and are known as the most sensitive species of lowland forests in Croatia due to microclimatic and macroclimatic changes and the unfavourable interaction of a whole series of anthropogenic, abiotic and biotic factors. In the last 40 years, in Croatian state forests, rodent management consisted of monitoring and mainly rodenticide use. Trying to implement IPM (Integrated Pest Management) postulates into practice over the years, different prevention methods against small rodents were tested, but not many came to use. The aim of this research was to look into different logging residue management approaches and their effect on the rodent damage in two pedunculate oak forest regeneration stands in central Posavina in Croatia. Rodent damage on stem and root of tree saplings was recorded by visual inspection on three plots (5x5 m) with scattered logging residue, and one plot (5x5 m) with no residue at one micro-depression site (95 m a.s.l.), and on one micro-elevation (99 m a.s.l.) site. Plots with scattered logging residue represented a type of forest residue management in which logging debris (branches) is cut to smaller lengths and distributed evenly at the forest regeneration stand. Plot with no logging debris represented a residue management method in which wood mass is completely removed from the regeneration stand after felling. We counted, determined and inspected tree saplings found at chosen plots for rodent damage (on stem and roots) and also determined the average weight and moisture content of logging residue (branches around 5–7 cm in diameter) found at the site. In spring 2017, 3380 tree saplings (2978; 81% pedunculate oak, 7; 0.2% narrow-leaved ash and 395; 11.7% other deciduous species) were inspected for rodent damage. At micro-depression site, on a plot with no logging residue, only 13.4% of the saplings were damaged, while the average share of damaged saplings on three plots with scattered residue was more than six times higher; 87.8%. The average mass of the logging residue weighed at site with scattered residue was 10.14 kg kg/m2 and moisture content was 19.2%. At micro-elevation site, 25.4% of the saplings were damaged on a plot with no logging residue, while the average share of damaged saplings on three plots with scattered residue was two times higher; 51.4%. The average mass of the logging residue weighed at SRP 1–3 was 5.1 kg/m2. We also determined moderately strong positive correlation (R=0.69133) between the mass of logging residue and rodent damage and strong negative correlation (R=–0.89598) between wood moisture content of the logging residue and rodent damage. In years ahead, with unpredictable climate effects and potentially very variable small rodent dynamics, removing the logging residue after the felling could represent a residue management that contributes to a more effective and ecologically based rodent management. It could also become a usable preventive method within IPM and help prevent sever rodent damage, even during the outbreaks in pedunculate oak regeneration stands.

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Large-scale ash (Fraxinus spp.) dieback caused by the fungus Hymenoscyphus fraxineus has been a major concern throughout Europe for more than two decades. Most of the related research has been focused on Fraxinus excelsior L., and there is still little information on fungal involvement in the dieback of Fraxinus angustifolia Vahl, especially in roots and stem bases, which play an important role in decline progress and tree stability. The objectives of this study were to identify fungi present in visually healthy and symptomatic wood tissues in basal parts of narrow-leaved ash trees in different decline phases, in order to determine the possible role of these fungi and their importance in the dieback process. The stem bases and roots of 90 trees in three different health categories, determined based on crown defoliation, were sampled in natural stands affected by ash dieback. Isolated fungal cultures were identified based on the rDNA ITS (Internal transcribed spacer) region and their association with tree health status was analyzed. In total, 68 different fungal taxa were confirmed, including Hymenoscyphus fraxineus and Armillaria spp., which were mainly present in roots, although overall in lower frequencies than on common ash in other studies. Most frequently isolated fungal taxa, which encompassed 51% of all obtained isolates, were Trichoderma spp., Ilyonectria robusta, Fusarium solani, Cladosporium cladosporioides, and Diaporthe cotoneastri. Their associations with tree health categories and presence in both symptomatic and visually healthy wood indicate that they act as opportunistic pathogens and early colonizers of weakened ash tissues. Research also revealed that, although the extent of crown defoliation and presence of root and stem necroses were associated, basal symptoms occurred on a number of trees with healthy looking crowns, meaning they can develop independently.

Common beech is one of the most widespread and important European tree species, widely used in timber industry and for energy production. Under specific set of complex factors, it facutatetivly develops false heartwood, which considerably decreases market demand and value of processed logs. Due to its properties, false heartwood is more susceptible to attack of wood decay fungi, which leads to further loss of wood quality and value. One of the most common fungi able to cause heart rot in beech is Meripilus giganteus, known for its spread in the basal parts of the tree, where it can affect most valuable sections of round wood. The aims of this study were to monitor the distribution of fungus and appearance of its fruiting bodies in research area, and to analyze the extent of fungus impact on shape and size of false heartwood and occurrence and length of rot in infected trees, while taking into account the observed stem damage as a possible influential factor. Fruiting bodies occurrence, life span and position on a tree were monitored during a six-year period. For trees with confirmed infection, stem damage was evaluated and appointed to one of four size classes. False heartwood shape and share in associated stem cross-section were observed and measured on 1–4 cross-sections per tree at different heights, and compared between infected and uninfected trees. If present, length of wood decay extent on butt-log was measured. The obtained results confirmed increased susceptibility of mature trees to infection, which seemed to occur mostly via roots from where mycelium spread into stem base. It was found that Meripilus giganteus has a significant impact on enlargement and change of FH shape from cloud- to star-like, up to approximately 5 m of the stem height, thus causing devaluation of the first assortments. The presence of rot was confirmed on the majority of infected trees, extending averagely 0.5 m into the first processed log, causing the loss of utilizable volume and thus the value of round wood. Stem damage category showed no significant effect on false heartwood or rot, supporting the prevailing impact of the fungus.

Native narrow-leaved ash (Fraxinus angustifolia Vahl) and introduced green ash (F. pennsylvanica Marshall) are two most common ash (Fraxinus spp.) species in Croatian lowland forests, taking a significant place in these ecosystems. In the recent past it has been observed that narrow-leaved ash seed yields have reduced, emphasising the importance of good health status of those collected, as they are used for seedling production and consecutive regeneration of forest stands or afforestation. Given that insects could be an important factor affecting ash seed health status, the aim of this research was to gain insight into the species being present and their frequency in the ash seeds. In total 2.500 narrow-leaved ash and 1.000 green ash seeds from seven different locations were screened for insect presence. Analysed seeds were categorized as undamaged, insect damaged or empty, and observed insect specimens were identified by morphological and molecular genetic analysis. Green ash seeds revealed higher insect infestation in comparison with native ash species, with weevil Lygniodes bischoffii being the most numerous pest found. Narrow-leaved ash seeds were mostly occupied by the native weevil species, L. enucleator. Besides these pests, larval, pupal, and adult stages of parasitoid wasps (Hymenoptera) and larval stage of the seed eating moth Pseudargyrotoza conwagana (Lepidoptera) were found in both ash species. However, given that pests detected in this study prefer urban areas or were present in a very small number of seeds, where they were often followed by parasitoids, it can be concluded that insects currently do not have a significant negative impact on the reproduction of narrow-leaved ash and green ash in forest stands.