Dataset from an inventory of slime moulds (Eumycetozoa) in two forest nature reserves of the Masurian Lakeland, north‑eastern Poland

Supplementary Material 1
Full myxomycete occurrence records. This record-level dataset contains all 492 collection records, including taxon, acquisition method, dates, moist chamber information, substrate type and substrate species, pH, elevation, geographic coordinates, coordinate precision, collector(s), determiner(s), reserve name, forest address, forest district, forest site type, degradation degree, moisture variant and Natura 2000 habitat code. Records distinguish field-survey collections from moist chamber culture records and should be interpreted as collection incidences rather than direct measures of field abundance.

Supplementary Material 1.1
Monthly field sampling effort in Gązwa and Dębowo Nature Reserves and meteorological context during the study period. The table summarises the number of field outings per reserve for each sampled month, together with mean monthly air temperature, monthly precipitation totals and mean monthly relative humidity.

Supplementary Material 1.2
Substrate-level alpha-diversity metrics and taxon incidence totals. For each substrate code, the file reports taxon richness, Shannon diversity, the Gini–Simpson index and Pielou’s evenness, together with host tree, substrate material, ecological substrate class and, where available, mean soaking-water pH. It also includes total incidence values for each recorded taxon.

Supplementary Material 1.3
Summaries of richness and diversity by ecological substrate class, together with the exploratory Wilcoxon comparison between lignicolous and non-lignicolous substrates. The file reports class-level means and standard deviations for diversity metrics and the test output for the richness comparison.

Supplementary Material 1.4
Univariate Gaussian linear model relating taxon richness to mean soaking-water pH for tree-linked substrates with pH data. The file includes model estimates and summary statistics used to describe the richness–pH relationship.

Supplementary Material 1.5
Non-metric multidimensional scaling ordination scores for substrate codes. The ordination is based on Bray–Curtis dissimilarities calculated from presence–absence data and includes NMDS coordinates together with substrate metadata.

Supplementary Material 1.6
Combined records of slime moulds by host tree and substrate type. The file summarises observed taxon–substrate associations across both reserves and both acquisition methods.

Supplementary Material 1.7
Mean soaking-water pH values from moist chamber cultures. The file summarises pH measurements for tree-linked substrate combinations used in the culture-based part of the study.

Supplementary Material 1.8
Moist chamber cultures established from tree-linked substrates in Gązwa and Dębowo Nature Reserves. The file documents culture identifiers, substrate combinations and cultivation metadata.