Impacts of invasive Asian (Amynthas hilgendorfi) and European (Lumbricus rubellus) earthworms in a North American temperate deciduous forest

Current understanding of earthworm invasions in North America is founded on studies of European species belonging to a single family (Lumbricidae); the ecological effects of taxa from other regions are largely unknown, despite many reports of established populations. Amynthas (Megascolecidae), a genus of invasive Asian earthworm, has increasingly been documented in North American regions lacking native earthworms. We present results from complimentary field and laboratory experiments designed to (1) evaluate potential impacts of Amynthas hilgendorfi on forest–floor nutrient cycling, leaf-litter decomposition, and soil structure, (2) compare these impacts to those of a better-understood invasive European species, Lumbricus rubellus, and (3) test for interactive effects between these species. While each species increased litter-decomposition rates in laboratory mesocosms, the effect of L. rubellus was greater than that of A. hilgendorfi . Each species also increased concentrations of mineral forms of soil nitrogen and phosphorus in the laboratory, and the increases caused by A. hilgendorfi were greater than those of L. rubellus . A. hilgendorfi increased mean soil aggregate size in the field while L. rubellus did not. Additionally, we determined the growth rate of A. hilgendorfi in the field and found that at 1.35 mg AFDM/day, the rate was greater than most published values for invasive European species. Treatment effects were stronger in laboratory mesocosms than field enclosures. No interactive effects between the two species were observed. These results suggest that the effects of A. hilgendorfi can be significant and, like those of European species, are undesirable from the perspective of meeting conservation goals.