Reactions of soil Collembolan communities to inundation in floodplain ecosystems of the Upper Rhine Valley

Flooding causes periodic disturbances in the biocoenoses of floodplain ecosystems. Such coenoses can thus be considered, in a succession-theoretical sense, to be pulse-stabilised subclimax successional stages. The reactions of Collembolan coenoses in floodplain forests, which had been formally cut off from the active inundation regime, to renewed flooding were studied in the Upper Rhine Valley over four years. Directly after the reintroduced inundation, many of the study sites were characterised by disturbed communities. In the following years, the Collembolan community structure, especially in the softwood alluvial sites, became clearly balanced and showed changes in species composition and dominance structure. Especially in the later years of the study, the Collembolan communities of the lowest, most often flooded, softwood sites were characterised by few species in high individual numbers. The communities of these sites and the upper-softwood sites became clearly dominated by hydrophilous or hydrotolerant species, respectively: an increasing adaptation to wetland conditions. In the hardwood alluvial sites, which were rarely or not flooded at all, the most species-rich communities were found. These showed species compositions different from those of the other, lower sites. Based on the different inundation intensities during the different study years as well as the different elevations above normal water levels of the various study sites, different reactions of individual species to inundation could be identified. These were further supported by correlation and factor analyses between the abundances of the individual species and hydrological data as well as by information known about life-cycle strategies and behaviour of these species. Together, these help provide a better understanding of the structure and reactions of the Collembolan communities in floodplain habitats, where a stabile mixture of hydrophilous, hydrotolerant and euryoecious woodland species appears necessary for functionally stabile, resilient soil-animal communities.