Worms in Urban Pacific NW Forests: A Preliminary Study

In the past few years, we have been analyzing soils in Forest Park (Portland, Oregon) and at control sites in the Mount Hood National Forest to elucidate causes for the dearth of seedlings and saplings in the urban forest. We found significantly deeper O horizons, higher levels of C, and a higher C/N ratio at control sites than at sites in Forest Park. One suggestion as to a cause of our soil findings was the presence of invasive earthworms at more urban sites. Last summer, we censused earthworm populations using a mustard extraction technique at sites in Forest Park and in the national forest. We also measured the depth of the O horizon and rates of soil respiration. We found the depth of the O horizon and the amount of CO2 produced by the soil were significantly greater at control sites than in the urban forest. Neither the number of worms nor the biomass of worms were significantly different; however, there was a tendency of lower worm biomass at the control sites. Because we did not have a large sample size, we intend to continue our investigation of worms and soil characteristics this coming summer