Terrestrial invertebrates in flooded grassland: A literature review

Abstract

I reviewed information from 73 sources on soil animals in flooded grassland, focusing on soil macrofauna: snails and slugs (Gastropoda), earthworms (Lumbricidae), potworms (Enchytraeidae), woodlice (Isopoda), millipedes (Chilopoda, Diplopoda), Diptera, and other insect larvae. While the database on earthworms was rather comprehensive, studies on all other soil fauna groups, especially regarding their role in wetlands were few and showed major research needs. The survival strategies of the groups were compared systematically. Annelids and insect larvae had the best physiological adaptations, other groups only reacted with evasion by active or passive movement and by recolonization and reproduction from resistant stages. There were no typical “wetland species” in soil macrofauna, only tolerant hygrophilous species. Flooding of grassland immediately reduced diversity, abundance, and biomass of all groups of soil macrofauna. Their community structure was altered, and well-adapted species, often wide-spread opportunists, became more abundant while others disappeared. The effects increased with the duration of flooding and rising temperature but were usually compensated for during the next soil-dry period. A meta-analysis classified sites according to duration, frequency, and seasonality of inundation. In general, species numbers and abundances of earthworms, woodlice, and millipedes tended to be lower in frequently and/or extensively flooded sites. Only gastropods are favored by moderate winter flooding. In bogs, even when they are waterlogged the entire year, species numbers are distinctly higher than the most frequently flooded sites. The impact of episodic summer flooding events is transitional and less pronounced than that of regular winter flooding. Earthworms re-establish soil structure after flooding, and they are, next to dipteran larvae, an important prey for wetland birds. Slow, moderate flooding in winter, waterlogging in spring, and a landscape mosaic with non-flooded refuge sites is recommended for water management policies favorable for both soil fauna and wetland birds.