Influence of Earthworms on Plant and Soil Invertebrate Communities of the Cleveland Metroparks

No native earthworms exist in the Great Lakes region of Ohio. All earthworms found in previously glaciated areas of the United States either migrated from unglaciated areas or were introduced as a result of human activities such as agriculture and sport fishing. Non-native earthworms may facilitate dramatic changes in structure and function of plant and invertebrate communities of forest ecosystems. This study examined how the presence of non-native earthworms within the Cleveland Metroparks may correspond with plant and soil invertebrate communities. Special attention was given to the Asian earthworm, Amynthas spp., a recent arrival to northeastern Ohio and a particularly aggressive colonizer. Earthworms and leaf litter were sampled at a set of well-characterized study plots. Length-based allometric equations available in the literature were applied to measure earthworm biomass of most species, and here a new equation for Amynthas was derived. A computer-based method was used to measure length and required less time and effort and produced values of significantly lower variability than the traditional ruler method. Higher abundances and biomasses of earthworms were associated with degraded plant communities. Although decreased litter mass correlated with greater earthworm activity, invertebrate communities were not degraded in fact there appeared to be a modest beneficial effect. Earthworm activity changed soil chemistry as demonstrated by selective decreases in soil carbon, nitrogen, and phosphorus. Soil composition also affected earthworm communities as low pH favored an acid-tolerant species and was associated with moderate earthworm densities. A strong negative interaction between abundances of Amynthas and those of other exotic earthworms was found, yet Amynthas did not exert a distinctive influence upon plant or invertebrate communitie