In 2017, a 560-ha area of hybrid poplar plantation in northern Poland showed symptoms of tree decline. The leaves appeared smaller, yellow-brown, and were shed prematurely. Twigs and smaller branches died without distinct cankers. Trunks decayed from the base. The phloem and xylem showed brown necrosis. Ten percent of the trees died 1–2 months after the first appearance of the symptoms. None of these symptoms were typical for known poplar diseases. The trees’ mycobiota were analysed using Illumina sequencing. A total of 69 467 and 70 218 operational taxonomic units (OTUs) were obtained from the soil and wood. Blastocladiomycota and Chytridiomycota occurred only in the soil, with very low frequencies (0.005% and 0.008%). Two taxa of Glomeromycota, with frequencies of 0.001%, occurred in the wood. In the soil and wood, the frequencies of Zygomycota were 3.631% and 0.006%, the frequencies of Ascomycota were 45.299% and 68.697%, and the frequencies of Basidiomycota were 4.119% and 2.076%. At least 400 taxa of fungi were present. The identifiable Zygomycota, Ascomycota, and Basidiomycota were represented by at least 18, 263 and 81 taxa, respectively. Many fungi were common to the soil and wood, but 160 taxa occurred only in soil and 73 occurred only in wood. The root pathogens included species of Oomycota. The vascular and parenchymal pathogens included species of Ascomycota and of Basidiomycota. The initial endophytic character of the fungi is emphasized. Soil, and possibly planting material, may be the sources of the pathogen inoculum, and climate warming is likely to be a predisposing factor. A water deficit may increase the trees’ susceptibility. The epidemiology of poplar vascular wilt reminds grapevine trunk diseases (GTD), including esca, black foot disease and Petri disease.

Effects of different pre-planting soil preparations and post-harvest wood debris applications in a clear-cut Scots pine plantation, on the abundance, diversity, and activity of culturable microorganisms were investigated. The investigation was done 9 years after the re-plantings had been done. This formed part of an investigation of silvicultural practices for conservation and the biological control of Armillaria and Heterobasidion in northern temperate forests (Poland). The treatments being compared, were expected to have altered the soil’s physical and chemical properties, and consequently, its biological properties. Only soft-rot microfungi from the Ascomycota and Zygomycota were detected in the soil. Fungi, including those antagonistic to Armillaria and Heterobasidion, were more abundant after shallow ploughing than after deep ploughing or ridging, and where chipped rather than coarse wood debris was left on the soil surface or incorporated. Scots pine trees had the most biomass and the least mortality after ridging and leaving coarse wood debris on the surface (associated with only a relatively moderate abundance of fungi)

This study provides an operational-scale assessment of internal decay caused by Porodaedalea pini in managed Scots pine stands based on data collected during harvesting operations. Unlike previous studies relying on indirect indicators such as fruiting bodies, this work quantifies the actual proportion of logs affected by decay under real-world production conditions. Although the mean decay share was relatively low (3.29%), substantial variability among stands was observed. A moderate relationship between stand age and decay occurrence was detected; however, statistical models showed limited explanatory power, highlighting the influence of additional stand-level factors. A potential threshold around 110 years may indicate an increased risk of decay in overmature stands. These findings underline the importance of incorporating decay risk into forest management decisions while acknowledging the uncertainty associated with predicting internal decay under operational conditions. These results may support forest management decisions regarding rotation age and timber quality risk assessment.