The oribatid mite community of a German peatland in 1987 and 2012 – effects of anthropogenic desiccation and afforestation

Abstract

Peatlands harbour a large number of specialized plants and animals. In many European countries more than 90% of the peat bogs have been destroyed through drainage for agriculture and forestry. The knowledge on the consequences for soil animals restricted to peatlands is scarce. The current study presents a comparison of the oribatid mite assemblages recorded in 1987 and 2012 from a Sphagnum bog being part of a large peatland complex that has suffered from drainage between the two periods. Furthermore, the oribatid mite fauna of the Sphagnum bog is compared to the fauna of adjacent peatland habitats of different soil moisture, shadowing and vegetation (Molinia meadow, spruce afforestation, birch wood). The study addresses the following questions:
1) which environmental factors determine the oribatid species composition in the peatland complex?
2) how do anthropogenic desiccation and afforestation influence the oribatid mite Assemblage?
CCAs were calculated using the species abundances recorded in 2012 and the Parameters soil moisture, vegetation temperature index, pH, cover of the tree-, herb- and moss layer, cover of herbleaf- litter and needle litter as well as C/N ratio. In total, 87 oribatid mite species were recorded in the Dubringer Moor in 2012. Species Distribution was most closely related to cover of herb-leaf-litter and needle-litter, soil moisture and vegetation temperature index. However, all sampling sites in the spruce forest contained similar sets of common species despite of differences in moisture and vegetation cover. The species composition of the two birch wood sites differed slightly from that of the spruce forest sites. In contrast, the Sphagnum bog was characterized by five tyrphophilic species (Pergalumna nervosa, Pilogalumna tenuiclava, Malaconothrus monodactylus, Mainothrus badius, Nothrus pratensis) that occurred almost exclusively here. The Molinia Meadow as a degenerated part of the Sphagnum bog contained almost no species that were characteristic for the Sphagnum bog site. However, species richness was higher in the Moliniameadow, because a large number of species characteristic for forest Habitats occurred. In the Sphagnum bog, species richness was heavily reduced from 1987 to 2012 from 37 to 10 species and also density was reduced from 164 individuals/100 cm³ to 9 individuals/100 cm³ due to ongoing desiccation. Several bog specific species such as Hoplophthiracarus illinoisensis, Trhypochthoniellus longisetus and Trhypochthonius nigricans have apparently disappeared from the Sphagnum bog today. Characteristic bog species still occurring in the Sphagnum bog in 2012 might be less sensitive to dryer periods and strong water level fluctuations than the species that disappeared since 1987. The results indicate that desiccation in Sphagnum sp. reduces oribatid species richness. However, after vegetational changes to, e.g., a Molinia meadow, oribatid species richness increases again due to immigrating species that are characteristic for forest habitats and euryoecious species. The oribatid mite community composition and densities of tyrphophilic and hygrophilic species appeared to be closely related to Sphagnum bog desiccation and peatland habitat characteristics. Oribatid mites therefore obviously offer the opportunity to evaluate the ecological conditions and degeneration of a peatland.