Earthworm density in soil beneath prairie and turfgrass vegetation in residential lawns of Madison, Wisconsin

Background/Question/Methods

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 improve the quality of urban soil. The objective of this study was to examine earthworm density and community structure beneath two vegetation types (prairie gardens and turfgrass) in residential yards in Madison, Wisconsin. We expected increased numbers of earthworms beneath prairie vegetation relative to traditional turf grass because prairie gardens offer greater diversity and availability of plant forage. We also expected seasonal differences in earthworm community structure due to belowground differences in plant biomass. This study includes six residential yards where prairie vegetation was part of the landscaping. We extracted earthworms from the prairie garden and the adjacent turfgrass lawn in March and October of 2007. We placed a metal frame (0.16 m²) on the soil surface and clipped all aboveground plant biomass from within the frame. A mustard solution (7.65 g L^-1) was used to extract earthworms. We tallied the number of earthworms extracted per frame and recorded the maturity, pigmentation, and length of each individual earthworm.

Results/Conclusions

Overall, we found that earthworm number depended more on season than vegetation type, yet their relative community structure differed by vegetation type. Earthworm density was greater in the spring than in the fall (p < 0.10), with no significant effect of vegetation type. Although the total number of earthworms per frame did not differ by vegetation type in the fall, soil beneath prairie vegetation contained more earthworms than the adjacent turf grass lawns in the spring. We extracted a greater percentage of adult earthworms relative to juveniles from soil beneath turfgrass vegetation relative to prairie vegetation (p < 0.10). These results suggest that earthworms were more active near the soil surface in the spring, with a preference of adult earthworms for turfgrass lawn. This project also provided an opportunity to interact with homeowners during earthworm sampling and provide educational outreach about soil biology and urban ecology. Moreover, this technique of using mustard to extract earthworms may be replicated by the homeowner to further monitor how earthworm dynamics vary across the urban landscape.