Examining an invasion: Impact of jumping worms on soil properties and soil temperature in a Minnesota hardwood forest

In the Upper Midwest, temperate hardwood forests have been heavily altered following the introduction of invasive earthworms of European, and more recently, Asian origin. Earthworms significantly modify the biological, chemical, and physical composition of soils in these ecosystems by mixing overlying organic horizons with underlying mineral soil layers. The recent invasion of these forests dominated by invasive European earthworms (Lumbricus terrestris, Lumbricus rubellus, Aporrectodea spp.) by ‘jumping worms’ (Amynthas agrestis and Amynthas tokioensis) has created profound and distinct changes to the soil that are not well understood.

We surveyed forests at the University of Minnesota Landscape Arboretum in 2020 and 2021 and established transects with discrete areas of European or jumping worm dominance. We found that these discrete areas had distinct soil features and that jumping worm populations appear to replace Lumbricus spp. populations. Soils in areas dominated by jumping worms had a loose, granular casting layer near the surface, decreased bulk density, increased soil organic matter, increased pH, and higher leaf litter mass than soils in sites dominated by European earthworms. We also measured lower monthly average soil temperature, lower maximum soil temperature, and lower soil temperature variability in our jumping worm dominated sites. Our soil temperature results indicate that Amynthas spp. will not be limited by soil temperatures in advancing much further north than central Minnesota. It remains to be seen how invasive earthworm populations and soil properties will evolve with the continued invasion of jumping worms in the long-term.