CER researchers have examined the effects of urbanization on soil fauna as a function of climate

Using the statistical method of meta-analysis, researchers from the ELKH Centre for Ecological Research (CER), the Hungarian University of Agriculture and Life Sciences and Denmark's Aarhus University analyzed 103 urbanization studies from around the world in order to understand the impact of urbanization on soil fauna. The researchers examined the changes in the species richness of soil fauna and their levels of abundance as a function of climatic conditions. They found that the species richness of groups of soil fauna that are sensitive to stronger soil compaction and have limited mobility in general, such as earthworms, snails and springtails, is negatively affected by urbanization. Urbanization has a favorable effect on the mobile, well-adapted groups of woodlice, millipedes and centipedes in drier climates due to the large amount of watering that takes place. In humid climates, however, the drier urban environment resulting from more intense evaporation and more rapid runoff of precipitation reduces their abundance. The paper presenting the results was published in the international scientific journal Science of the Total Environment.

A single gram of soil can contain up to ten billion microbes, and a handful of it can be home to thousands of free-living, (i.e. non-parasitic) nematodes. Several thousand, and potentially up to 100,000 springtails and soil-dwelling mites might be present in one square meter of earth. Soil fauna provide many ecosystem services to humans. Earthworms are the so-called “ecosystem engineers”, capable of greatly transforming their environment by intensively mixing the soil. They can create thousands of kilometers of channels per hectare, thus helping water to enter the soil, loosening it and contributing to the formation of humus. Soil-dwelling mites can play many roles in the food chain, functioning as herbivores, predators and decomposers, and they feed on dead organic matter and help convert them into nutrients. Soil-dwelling nematodes can be bacterivores, herbivores or predators. Decomposing springtails regulate soil-dwelling bacteria and fungi, and also pollinate mosses. Snails, woodlice and millipedes are all decomposers, while centipedes are exclusively carnivores. Among ground beetles, however, there are herbivores that control the spread of weeds, mixed feeders, and predators that help with biological defense.

Urbanization (i.e. the increase in the area and population of cities) radically transforms habitats. The soil is degraded or replaced, planted with non-native plants, and often covered with asphalt, concrete and buildings over wide swathes, with vibrantly green lawn also being maintained in many areas throughout the year. However, these transformations endanger and can even eliminate the habitats of various fauna groups.

The researchers found that the species richness of earthworms, snails and springtails decreased in cities ‒ where there is more covered area and less natural green space ‒ compared to suburban and rural areas. The probable reason for this is the fact that these groups are generally limited in their mobility, so it is more difficult for them to move between isolated areas in an urban area, and they are sensitive to soil compaction, which is more pronounced in cities than in the suburbs or countryside due to the greater amount of trampling and traffic. In terms of abundance, they found that urbanization favored woodlice, millipedes and centipedes. These are mobile groups that are flexible in terms of their nutritional intake, allowing them to easily thrive in an urban environment. If climatic conditions are also taken into account, though, it turns out that the above statement regarding abundance is only true in cities with a lower level of annual rainfall, while the effect of urbanization reduces abundance in humid climates. The reason for this is probably the fact that in urban areas with drier climates, vegetation is maintained by watering, which favors the reproduction of soil fauna, while in wet climates, due to the more intense evaporation caused by asphalt and concrete and faster precipitation runoff, the environment is drier, which is unfavorable for soil fauna. For this reason, the researchers recommend that urban green areas be managed in such a way that makes them as similar as possible to the natural environment surrounding the city, rather than creating an alien environment for soil fauna by over-watering or covering too many areas.