Earthworm diversity in urban habitats of Basel (Northwestern Switzerland)

Abstract

The diversity and ecology of the soil fauna in Central European towns is not yet well known. There are references that earthworms, by their biomass, dominate all other animal groups in cities – surpassed only by man. Basel (11 km²) is, with its 170 000 inhabitants, Switzerland’s third largest community. Open green spaces in the city are scarce; the green belt is narrow. Nevertheless, in more than 60 locations studied between 1999 and 2010, 22 species (12 genera) of Lumbricidae were found. Eleven near-natural habitats could be sampled: private front gardens and backyards, wooded river sides, industrially watered flood plain forest plots, and a Zoological Garden with a large number of green spaces built up from imported soil. Nearly a dozen of these species are quite rare in their natural distribution area and in Basel; many of them are riparian, e.g. Aporrectodea georgii, Fitzingeria platyura depressa, and Helodrilus oculatus – while two are strictly endogeic (Allolobophora satchelli, Murchieona muldali). The sampling method “digging and hand-sorting plus mustard meal suspension” yielded the best possible quantitative results in urban habitats. A maximum of earthworm species (18) was sampled in the Zoological Garden, and the intensely used public lawns had the highest mean density and biomass (450 individuals resp. 280 g fresh mass/m²).

Key words:

• Quantitative sampling
• public parks
• private gardens
• green belt
• woodland
• ground-water recharge plants
• synanthropic species