Earthworm Population Density Beneath Prairie Vegetation and Turfgrass in Madison WI.

Although earthworms represent only one type of soil macrofauna, they play a critical role in soil nutrient cycling and soil structural development and thus may help mitigate the effects of urbanization on soil. This study includes five residential yards where a garden of prairie vegetation was included as part of the landscaping. We expected increased numbers of earthworms beneath prairie vegetation relative to adjacent turfgrass lawn because prairie gardens offer greater diversity and availability of plant biomass. We also asked whether earthworms exhibited seasonal preferences in vegetation type. We used a mustard solution to extract earthworms from within 0.16 m² frames placed on the soil surface, taking measurements in March and October of 2007. We tallied the number of earthworms per frame and we recorded the maturity, pigmentation, and length of each individual earthworm. Overall, we found earthworm density differed across the five sites, ranging from 128 to 310 m^-2 (p < 0.0001) but depended on the vegetation type and the season (p < 0.01). In the fall, earthworm density was similar between vegetation types, but in the spring, soil beneath prairie vegetation contained more earthworms than the adjacent lawns (217 and 275 m^-2, respectively). We extracted a greater percentage of adult earthworms relative to juveniles from soil beneath turfgrass relative to prairie vegetation (p < 0.10). These results suggest earthworms living in the urban environment may be most active near the soil surface in the spring beneath prairie vegetation, yet earthworms that had reached maturity tended to reside below turfgrass vegetation.