Introduction of the epigeic earthworm Dendrobaena octaedra changes the oribatid community and microarthropod abundances in a pine forest

The effects of the activities of the epigeic earthworm Dendrobaena octaedra on the oribatid community and microarthropod abundances were studied in a 90-year old pine forest over 2 years. Oribatids were extracted from the L and FH layers and the Ah and Bm horizons at 1 and 2 years and data were analyzed using principal component analysis (PCA). High worm biomass correlated positively with oribatid species richness and diversity in the L layer. In the FH layer, worm biomass accounted for 83% of the variation in the oribatid community data and correlated negatively with oribatid species richness. High worm biomass correlated with decreases in the abundances of 18 oribatid species, and the total abundances of adult and juvenile oribatids, astigmatids, mesostigmatids, Actinedida and Arthropleona in the FH layer. These effects were attributed to the changes in the physical structure of the organic layers of the soil. In the Ah and Bm horizons the C–N ratio accounted for 72–97% of the variation in the oribatid species and microarthropod group data. The abundances of O. nova, other Oppioidea, several Brachychthoniidae, C. cuspidatus and adult (in the Ah horizon only) and juvenile oribatids, and Arthropleona were positively correlated with the C–N ratio. This reflected the mixing of less decomposed organic matter into the lower horizons by D. octaedra.