Bioindication in peatlands by means of multi-taxa indicators (Oribatida, Araneae, Carabidae, Vegetation)

Peatlands host a large number of highly specialised species and are important carbon storage and freshwater reservoirs, but are heavily threatened by, e.g., peat extraction and drainage. For improved protection of peatlands, the development of an ecological assessment system is necessary. Existing systems based, for instance, on peat formation and water level are rather coarse and differ between countries. The aim of the present study was therefore to evaluate the predictive power of biodiversity indicators - particularly invertebrates (Oribatida, Araneae, Carabidae) and vegetation - for more finely reflecting environmental conditions in Sphagnum-dominated peatlands in order to determine which taxonomic groups should be included in an ecological assessment system for peatlands. Therefore, we selected three plots in each of four peatland study sites in a German low mountain range and sampled the taxonomic groups using standard methods appropriate to represent assemblage structure and site diversity (Oribatida: Sphagnum samples; Araneae, Carabidae: pitfalls traps; vegetation: vegetation surveys). Our results indicate the necessity of implementing different taxonomic groups into an overall ecological assessment system, as all of them reacted differently to different ecological gradients. Oribatid mites were the best predictors of moisture, one of the most important factors in peatlands. Ground-dwelling spiders responded to several different factors; most remarkably, they strongly correlated with landscape area covered by peatland-related Natura 2000 habitat types, as a proxy for habitat quality. Carabidae most strongly correlated with the size of the Sphagnum plots, moss cover and moisture, but their species richness was very low. Vegetation, as the best established indicator group in peatlands, showed the weakest correlations to the tested environmental parameters, probably due to short-term changes in environmental conditions and a delayed response of the plant community. Hence, the set of most relevant environmental parameters can only be represented when multiple taxa are included in an assessment system. Also, overall biodiversity is not represented by a single taxon, because the correlation in assemblage similarity between the taxonomic groups was low. Considering ecological sensitivity, sampling effort (=number of samples and necessary site visits), taxonomic stability and state of knowledge on species' habitat requirements, we therefore suggest the inclusion of ground-dwelling spiders, oribatid mites and vegetation in an ecological assessment system for peatlands, complemented by a few sensitive, easy to recognize indicator species of other taxonomic groups.