Earthworms in the Urban Environment: Can Population Augmentation Improve Urban Soil Properties?

Urban forests perform essential ecological functions, and their performance is dependent on soil quality, which is often degraded by human activity. Because earthworms play a key role in soil health, augmenting earthworm populations in urban soils may improve tree performance. However, we know very little about earthworm ecology in highly urbanized soils. The objectives of our study were: (1) to assess earthworm demographics across a range of urban land uses and (2) to evaluate earthworm augmentation techniques for rehabilitating disturbed soils and improving tree growth.

1. We conducted an observational study across three landuse types to assess earthworm abundance and diversity as well as associated soil properties. Earthworm abundance and biomass in were affected by land use type, disturbance time frame, and seasonality. Earthworm abundance and biomass were affected by a suite of complex soil and temporal variables, and soil temperature and moisture seemed to be the most influential properties.

2. We conducted an earthworm inoculation experiment on a compacted cut-fill field soil with a very low existing earthworm population. In 2008, three soil treatments (control, compost, and compost + earthworm) were applied to 2 m2 plots into which two common urban tree species with contrasting soil tolerances were planted (Acer rubrum and Cornus florida). We measured soil physical and chemical properties along with earthworm survival and soil respiration. Earthworm inoculation did not succeed in improving bulk density or increasing soil organic matter, yet it was successful in increasing soil CEC, Fe, and Mn relative to compost only effects.