Middens of the earthworm Lumbricus terrestris (Lumbricidae): microhabitatsfor micro- and mesofauna in forest soil

In September 1994 microflora (microbial biomass, basal respiration, specifi c respiration), microfauna (Nematoda) and mesofauna (Gamasina, Uropodina, C ollembola, Oribatida) in middens of the deep-burrowing earthworm Lumbricus terrestris and in the surrounding (non-midden) soil were investigated in a beechwood (Fagus sylvatica) on limestone. In middens C and N content, C/N r atio, microbial biomass, basal respiration and specific respiration were si gnificantly higher than in non-midden soil. The abundance of Gamasina and U ropodina (mainly Dinychus perforatus and Trachytes aegrota) and biomass of Nematoda (especially that of bacterial feeders and omnivores) were higher i n the middens whereas most oribatid mite taxa (Brachychthonidae, Oppiidae, Poronota) preferred the non-midden soil. Total density of Collembola differ ed little between midden and non-midden soil. However, three species of Iso tomidae (Isotoma violacea, Folsomia quadrioculata and F. manolachei), Onych iurus furcifer and Stenaphorurella denisi were more abundant in middens, wh ereas Lepidocyrtus lanuginosus was more abundant in non-midden soil. Genera lly, even closely related species or other taxa responded differently to th e presence of middens as indicated by principal component analysis (PCA). I t is concluded that middens of L. terrestris contribute to the patchiness a nd heterogeneity of the forest floor and serve as important microhabitats f or some soil animals. Middens are - at least temporarily - preferred habita ts or refuges for several groups of soil animal species while others avoid middens as habitats or are detrimentally affected by environmental conditio ns in middens. The structural and temporal dynamics of this microhabitat ma y partly be responsible for the coexistence of large numbers of species, e. g. allowing various prey species (Nematoda, Collembola) to reach high densi ties. It is concluded that the increased biomass of bacterial feeding nemat odes and euryoecious Collembola was caused by an increased microbial biomas s in the middens and that predacious Gamasina and Uropodina benefited from this increased prey density but were unable to effectively control prey pop ulations. The flourishing of most animal taxa in earthworm middens where th e amount of food was higher than in non-midden soil supports the view that bottom-up forces dominate in decomposer communities.