Invasive lumbricid earthworms in northeastern North American forests and consequences for leaf-litter fauna

Abstract

Colonization of North America by exotic earthworms has been implicated in undesirable changes in soil structure, nutrient cycling, and biodiversity. Invasion by putative European earthworms has a long history in northeastern North America. Partly for this reason, factors that may be continuing to facilitate expansion of earthworm distributions and the consequences of earthworm spread in the Northeast get relatively little attention. We sampled earthworms and environmental attributes at 85 sites in central New York. We additionally sampled leaf-litter fauna at 25 of these sites. We detected no earthworms at 27 of 71 forested sites (38%). Forested sites without detectable earthworm populations were farther from the nearest road and had soils of lower pH than forested sites with earthworms. Proximity of the nearest road was strongly associated with earthworm diversity and abundance, and earthworm biomass was highest in low, moist areas. We found a strong, negative relationship between the biomass of earthworms and abundance of invertebrates in the litter layer. This association was likely mediated by the abundance of organic litter, which was lower at sites with high biomass of earthworms. Sites with only the putative native Bimastos (Dendrodrilus) rubidus had a high mass of leaf litter and large numbers of leaf litter animals despite high densities of this species. We believe that there is potential for further expansion of European earthworm taxa in the Northeast and strong evidence for negative consequences of this expansion. Additional regulations on activities that promote introduction may be necessary.