The aim of this study was to compare colonization of pine chips without supplements and pine chips supplemented with forest litter, peat and lignite by mites (Acari), and particularly oribatid mites (Oribatida) in a two-year cycle. The study was conducted in the years 2013-2014, on microplots established in a belt of trees in a nursery in Białe Błota within Bydgoszcz Forest District. The experiment was established on four microplots (1 x 1 m). It included the following variants: C - pine chips alone, Lf - pine chips inoculated with fresh forest litter, Lf+Pe - pine chips enriched with deacidified high peat (20%) (pH 5.5-6.5) and inoculated with the litter, Lf+Li - pine chips enriched with granulated lignite (20%) inoculated with the litter.
In the first year of the study, mite abundance in the chips inoculated with forest litter was significantly higher than that on microplot C. In the second year of the experiment, the abundance of these microarthropods decreased probably due to unfavorable weather conditions. The most common group of mites were usually oribatid mites that accounted for 19.7 to 80.4% of all mites. An analysis of seasonal dynamics of Oribatida abundance over the entire study cycle revealed a clear increase in their numbers in non-supplemented pine chips only on the last sampling date. Oribatida abundance in Lf variant was similar at the beginning and end of the study. Contrary to that, their number decreased in the chips supplemented with peat, and particularly those enriched with lignite. In total, 36 species of oribatid mites were identified on all microplots. The greatest boost in species diversity after the introduction of forest litter was observed in Lf chips and the smallest in Lf + Li variant. Oribatula tibialis was the most common oribatid mite in the investigated substrates. Low numbers of Oppiella nova and Tectocepheus velatus, the species having trophic associations with fungi, may indicate poor colonization of the chips, particularly those enriched with lignite, by saprotrophic organisms.