IMPACTS OF THE EPIGEIC EARTHWORM DENDROBAENA-OCTAEDRA ON ORIBATID MITE COMMUNITY DIVERSITY AND MICROARTHROPOD ABUNDANCES IN PINE FOREST FLOOR - A MESOCOSM STUDY

The effects of the invasion of the epigeic earthworm Dendrobaena octae dra on the pine forest floor oribatid mite community and the abundance s of microarthropods were studied in mesocosm. The study was conducted in intact soil cores (30 cm diameter x 25 cm) from the pine forest at constant moisture content and 15 degrees C for 6 months. D. octaedra was added to half the cores at abundances equivalent to its 1993 field density of 250 immatures and 70 matures m(-2). At 3 and 6 months, ear thworm densities and microarthropod abundances were assessed. High ear thworm densities increased the similarity between the oribatid communi ties in adjacent soil layers/horizons. Oribatid dominance by Oppiella nova decreased and overall oribatid diversity increased in the earthwo rm treatment at 3 months. At 6 months oribatid species richness increa sed in the earthworm treatment. Earthworm activities had varying effec ts on abundances of oribatid species and groups of microarthropods, bu t maximum abundances tended to occur at intermediate levels of earthwo rm activity. (C) 1998 Elsevier Science B.V.