Diversity of Slime Moulds (Eumycetozoa) in Three Forest Nature Reserves of the Knyszyn Forest, Poland

The Knyszyn Forest is one of the major lowland forest complexes of north-eastern Poland, yet its myxobiota remains insufficiently documented. We surveyed Eumycetozoa in three forest nature reserves, Krzemianka, Jałówka, and Las Cieliczański, selected as protected sites representing different local habitat and substrate conditions, including spring-fed forest–wetland, mixed forest–peatland, oak–hornbeam, alder and coniferous forest settings to assess local species richness, substrate occurrence, and new distributional records. Field surveys were combined with moist-chamber cultures, and species were identified from mature sporocarps using macro- and microscopic morphology. The inventory yielded 761 occurrence records representing 80 identified taxa. Moist-chamber cultures produced more records and species than field collection, while field surveys detected taxa fruiting naturally during the study period; together, both methods produced a more complete inventory than either method alone. Three species, Paradiacheopsis solitaria, Macbrideola rutilipedata, and Licea operculata, were recorded for the first time in Poland; these national novelties formed part of a broader set of 14 taxa newly documented from north-eastern Poland, defined in this study as the Warmian-Masurian and Podlaskie voivodeships. The remaining regional novelties represent rare taxa previously known from Poland, but not yet reported from this north-eastern region. Most records came from dead wood and bark, especially lignicolous and corticolous substrates, probably reflecting their moisture retention, microbial prey availability and protected surfaces for sporocarp formation, although other dead organic substrates also contributed to the recorded substrate spectrum. The resulting dataset provides a regional baseline for future biodiversity surveys in the Knyszyn Forest.