Non-native earthworms are prevalent and abundant in eastern deciduous forests, often greatly outnumbering native earthworms. As ecosystem engineers, native and non-native earthworms have differential effects on nutrient cycling and plant communities. We examined patterns of earthworm abundance, richness, and community composition across a suburban to rural gradient (suburban lawns to suburban woodlots to large contiguous forests). Specifically, we tested the hypotheses: 1) native earthworms would be more abundant in large contiguous forest than in suburban landscapes because natives are adapted to undisturbed habitats, 2) Non-native earthworm richness and abundance would be higher in suburban landscapes than large contiguous forests because human activities increase invasion events, and 3) the more recent invasive, Amynthas, would be increasing in abundance and range in recent years. We assessed these hypotheses with a thirteen-year data set. We have been surveying earthworm communities in forests since 2007 and suburban lawns since 2015 in the Roanoke Valley in Virginia.
Results/Conclusions
Native earthworms were very rare in the Roanoke Valley. Of the more than 3,000 earthworms sampled since 2007, we found fewer than 10 native earthworms (Diplocardia). Counter to our hypothesis, all native earthworms were in suburban lawns. We found support for our second hypothesis; non-native earthworms (primarily European Lumbricidae) had higher richness and abundance in suburban woodlots compared to large contiguous forests. We found mixed support for our third hypothesis. Amynthas was moving into more sites, but its abundance was not increasing uniformly across sites. Taken together, our mixed results suggest earthworm community dynamics do not appear follow invasion theory predictions. Understanding invasion patterns of these ecosystem engineers is important in this era of human-induced, global change.