Earthworms may decrease organic carbon storage in soil by increasing the release of carbon dioxide from soil. In North America, introduced earthworm species are spreading. Global warming is likely to increase winter temperatures, thereby expanding the suitability of many soils in North America for introduced earthworms.
The study by Filley and colleagues was performed in Maryland USA. It study showed that earthworms in tulip poplar forest preferred certain types of leaf litter, with a resulting change in soil chemistry. Earthworms preferred to eat the biopolymer cutin present in leaves instead of lignin present in stems in litter. Cutin is a waxy material.
In North America, introduced earthworm species are spreading. The authors of this study speculate that this process may impact on the amount of carbon in soil, in particular through increased release of carbon dioxide.
A later study by Addison (2009) provides detail about the spread of European species of earthworm in Canada. At the end of the last ice age, there were only 8 native species of earthworm present in Canada, all with limited geographical range. Now there are an additional 19 species are present in Canada, and several of these additional species occur widely.
Previously, studies in forest soils in Minnesota and New York State, USA, indicated that invasive earthworms substantially reduce soil carbon storage. The hypothesis underlying this effect is that global warming is likely to increase winter temperatures, thereby expanding the suitability of many soils in North America for introduced earthworms.
1. Filley TR, Boutton TW, Liao JD, Jastrow JD & Gamblin DE (2008) Chemical changes to non-aggregated particulate soil organic matter following grassland-to-woodland transition in a subtropical savanna. Journal of Geophysical Research, Biogeosciences. 113, Co3009, doi:10:1029.2007/JG000564.
2. Addison JA (2009) Distribution and impacts of invasive earthworms in Canadian forest ecosystems. Biological Invasions 11: 59-79.