This study aimed to assess the changes in chemical properties and fungal communities in the upper mineral soil layer in managed Scots pine (Pinus sylvestris L.) ecosystems. Study sites were located in the three largest P. sylvestris massifs in Lithuania, and six sampling sites, representing different development stages of the P. sylvestris forest ecosystem, were selected in each of them: mature P. sylvestris forest stands; clear-cuts of former P. sylvestris mature stand; and the P. sylvestris plantations aging from the 1st to 4th year. High-throughput sequencing was performed to evaluate the soil fungus community at clear-cuts, early-stage reforested sites, and mature forests in Lithuania. This study has shown that, among other chemical soil parameters, the mean concentrations of mineral nitrogen (N), total phosphorus (P), and P₂O₅ were slightly higher in the clear-cut sites, and significantly higher in the 1st year plantations compared to the mature forests. The quality filtering after PacBio sequencing showed the presence of 60,898 high-quality fungal sequences, and 1143 fungal operational taxonomic units (OTUs). The most abundant fungal OTU in our study was Archaeorhizomyces sp. 5425_1. In total, 70 mycorrhizal fungal OTUs were found in the soil samples at the studied sites. The most abundant ectomycorrhizal fungus identified was Amanita fulva (Schaeff.) Fr. The highest amount of ectomycorrhizal fungal OTUs was found in the clear-cut sites and in the mature forests. The concentrations of mineral N and P₂O₅ in the upper mineral soil layer did not significantly affect fungal OTUs diversity. Conversely, a relatively strong correlation was obtained between the number of mycorrhizal fungal OTUs and the concentrations of total N and soil organic carbon (SOC), as well as between the numbers of saprotrophic fungal OTUs and the concentration of magnesium ions (Mg²⁺).

Treatment of wood with various physical and chemical factors can change the number of wood parameters, which can also lead to changes in resistance to wood-destroying fungi. This study evaluates the effects of hydrothermal treatments (additives Fe₂O₃ or FeCl₃ with and without commercial tannins, also without additives and fresh wood) on decay and mould fungi resistance of modified wood of Scots pine (Pinus sylvestris), Norway spruce (Picea abies), Douglas fir (Pseudotsuga menziesii), walnut (Juglans regia), and Norway maple (Acer platanoides). For wood samples, the resistance against wood decay fungi Trametes versicolor (white rot) and Coniophora puteana (brown rot) and the resistance against mould fungi Aspergillus niger and Penicillium sp. were assessed. The study findings showed that wood modified with iron compounds could cause a higher resistance to wood-destroying fungi. The weight losses of the modified and control wood, caused by T. versicolor and C. puteana, differed for coniferous and deciduous: the average weight loss of treated pine, spruce, and fir wood caused by C. puteana was higher than that caused by T. versicolor, while these differences on maple and walnut wood were not significant. The wood hydrothermal treatment with Fe₂Cl₃ with and without tannins significantly reduced the weight loss caused by T. versicolor and C. puteana, and the treatment with Fe₂O₃ slightly improved the decay resistance. For the wood, hydrothermally modified with FeCl₃ and FeCl₃ + tannins, the mould area for both tested Aspergillus niger and Penicillium sp. was smallest for the wood of all tested tree species compared to other treatments. A different response was obtained for coniferous and deciduous tree species wood. The spruce wood, followed by fir wood, treated with FeCl₃ with and without tannins, was the most resistant against the mould fungi. Relatively low resistance against the mould fungi was fixed for the maple wood treated by various iron compounds, except the treatment with Fe₂O₃ + tannins, which gave a very positive response against the Penicillium sp.

This study performed a pilot evaluation of the wood quality—defined by a single parameter: dynamic modulus of elasticity (MOEdyn, N mm⁻²)—of small-leaved lime (Tilia cordata Mill.) trees in urban areas. A search of the literature revealed few studies which examined the specifics of tree wood development in urban areas. Little is known about the potential of wood from urban trees wood of their suitability for the timber industry. In this study, an acoustic velocity measuring system was used for wood quality assessment of small-leaved lime trees. The MOEdyn parameter was evaluated for small-leaved lime trees growing in two urban locations (along the streets, and in an urban park), with an additional sample of forest sites taken as the control. MOEdyn was also assessed for small-leaved lime trees visually assigned to different health classes. The obtained mean values of MOEdyn of 90–120-year old small-leaved lime trees in urban areas ranged between 2492.2 and 2715.8 N mm⁻². For younger trees, the values of MOEdyn were lower in the urban areas than in the forest site. Otherwise, the results of the study showed that the small-leaved lime wood samples were of relatively good quality, even if the tree was classified as moderately damaged (which could cause a potential risk to the community). Two alternatives for urban tree management can be envisaged: (1) old trees could be left to grow to maintain the sustainability of an urban area until their natural death, or (2) the wood from selected moderately damaged trees could be used to create wood products, ensuring long-term carbon retention.

We investigated the diversity and occurrence of wood wasps in Lithuania and determined communities of associated fungi. Trapping of wood wasps resulted in three different species, including Sirex juvencus, Urocerus gigas, and Tremex fuscicornis. Fungal culturing from adult females of T. fuscicornis mainly resulted in fungi from the genera Penicillium and Trichoderma. High-throughput sequencing of ITS2 rDNA resulted in 59,797 high-quality fungal sequences, representing 127 fungal OTUs. There were 93 fungal OTUs detected in U. gigas, 66 in S. juvencus, and 10 in T. fuscicornis. The most common fungi were Fusarium sporotrichioides (63.1% of all fungal sequences), Amylostereum chailletii (14.9%), Penicillium crustosum (7.8%), Microascus sp. 2261_4 (5.0%), and Pithoascus ater (2.1%). Among these, only A. chailletii was found in all three insect species with the highest relative abundance in U. gigas (15.2%), followed by S. juvencus (7.7%), and the lowest in T. fuscicornis (0.3%) (p < 0.0003). Correspondence analysis of fungal communities showed a distant placement of different species of wood wasps, indicating that fungal communities in each of these were largely different. In conclusion, the study showed that the economically important tree pathogen A. chailletii was among the most common fungal OTUs associated with siricid wood wasps.