Microhabitat distribution of arboreal oribatid mites (Oribatida), associated with the Siberian pine (Pinus sibirica) of Western Siberia.

The species composition of arboreal oribatid mites that live on Siberian pine trees (Pinus sibirica) in the forest-tundra of Western Siberia was examined, specifically of three Siberian pines from two distinct forest stands (six trees in total). Samples of litter were taken near the tree trunk, as well as samples of bark, branches and needles from the tree. In total 144 samples were taken, from which close to 5000 mites were extracted. From the arboreal samples, the mites were extract by heptane flotation. Three species of oribatid mites were recorded for the first time in Russia: Diapterobates brevidentatus, Eueremaeus trionus and Cultroribula berolina. The highest density and the highest dominance index of these species were recorded in arboreal microhabitats. Thirty-one species of oribatid mites were identified in total. No oribatid mites were recovered from the needles of Siberian pine. The density of oribatid mites did not significantly differ among various heights of the crown and trunk. The lowest density of mites was recorded on young branches without needles, whereas other branch hypothetical microhabitats did not significantly differ from each other in terms of oribatid density. The greatest Simpson diversity index was recorded in the plant litter near tree trunks. On trees, the diversity index decreased with the height of the trunk and with the distance of branch sections from the trunk. The dominant species and the degree of their dominance varied among microhabitats and forest stands. Additionally, a high level of dominance of a single oribatid species was observed on tree branches, as well as on the trunk bark located above the bole. In the two forest stands, these species were D. brevidentatus and Ameronothrus dubinini. Based on the analysis of oribatid communities, three microhabitats were identified in the first forest stand: the bole bark, the bark of the trunk above the bole, and the branches. In the second forest stand, bases of tree branches were identified as an additional microhabitat. Oribatids inhabit Siberian pine trees in the severe conditions of the forest-tundra. Arboreal oribatid communities of various microhabitats vary in their qualitative and quantitative characteristics. Also, arboreal and forest litter communities of oribatid mites vary significantly.