In the urban landscape, humans are the most significant factor determining belowground diversity. Assessment of soil invertebrate fauna has been carried out in many places, but multi-city comparisons are still rare. Within the framework of the Global Urban Soil Ecology and Education Network (GLUSEEN) we sampled earthworm assemblages along a soil disturbance gradient in five cities, covering four climatic and biogeographical regions. Baltimore (USA), Budapest (Hungary), Helsinki and Lahti (Finland) and Potchefstroom (South Africa) participated in the pilot study. Three questions were addressed: How does urban land use/soil habitat type affect abundance and diversity of earthworms; 2) How do soil properties affect community structure, and 3) How similar are urban earthworm assemblages across regions? Four land use/soil habitat types (ruderal, turf/lawn, urban remnant and reference) were sampled. Each habitat type was replicated five times, resulting in a total of 100 sites. Earthworms were extracted using mustard suspension, and identified to species. Data on edaphic properties, such as carbon and nutrient content, pH and texture were also collected. Published records and our previous data were used to determine regional species pools.
Results/Conclusions
The survey resulted in 19 species belonging to 9 genera and 4 families. The highest total species richness was recorded in Baltimore (16), while Budapest and the Finnish cities had relatively low (5-6) species numbers. As expected, local communities were dominated by peregrine species that have been reported in other urban environments. This similarity in earthworm faunas is partially due to the geographical bias of urban soil fauna research i.e. most studies have been conducted in European cities. At city scale, remnant forests and lawns supported the highest earthworm biomass. Unlike previous studies on microbial and microarthropod communities, soil properties explained neither earthworm community composition nor abundance. Evaluating all cities together, earthworm communities were significantly structured by habitat type. Despite clear differences in climate, soils and biogeography among the studied regions, the earthworm fauna showed remarkable similarity between the cities. However this similarity is a result of combination of different geographical and human history indicating different mechanisms leading to biotic homogenization. Human facilitated dispersal, both at regional and local scales appears to be key in shaping urban earthworm assemblages.