Canadian earthworms. Public enemy number one?
A new study details how the common earthworm is disrupting the ecology of Canadian forests and presently wreaking havoc on maple tree stands in Quebec’s Eastern Townships.
For some time now scientists have been investigating the role played by the lowly earthworm in changing the soil composition of Canadian forests. Almost all earthworm species in Canada are non-native, having come across the Atlantic with European settlers. And although the average gardener loves to see them digging in the dirt and helping to decompose plant matter and aerate the soil, earthworms have become a real threat to some plant species in our forests.
The study’s researchers found that the presence of earthworms in the sugar maple forests of southern Quebec corresponded with a thinning out of the forest floor, with fewer new shoots of red and striped maple, American beech and also two fern species.
“The most likely explanation is that the earthworms consume organic matter in forest litter,” says the study’s lead author Line Lapointe, professor at the Université Laval’s Faculty of Science and Engineering. “This results in soils that can’t hold as much moisture and that in turn interferes with seed germination and the ability of some species’ plantlets to survive.”
Canadian earthworms on a tear…
The dew worm or Canadian night crawler (Lumbricus terrestris) is the species currently causing damage to Canadian forests. (The name is deceiving – it too came from Europe.)
Stephen Westcott-Gratton of Canadian Gardening explains that, unlike in the backyard garden where fast turnover of soil is a plus, forests need to work on slower timelines, hence the trouble with the earthworm. “Once present, the earthworms gorge on the forest floor’s rich leaf litter, leaving the underlying mineral subsoil exposed and effectively wiping out tree seedlings, flowering plants and ferns who suddenly find themselves without a root zone.”
The issue is not one of earthworms charging across the country on their own – they only travel about 5 to 10 metres per year or one kilometer every 100 years – but of human-caused distribution. In Alberta, scientists only began noticing earthworms starting in the mid-1980s. Now, attempts are now underway to limit their spread. The Alberta Worm Invasion Project (yes, such a thing exists) studies the earthworm’s effects on local forests and advocates for more vigilance to prevent their spread.
Researchers with the Project list a number of ways that citizens can help. At the top of the list, anglers need to make sure that they don’t dump unused earthworms after fishing, and off-road enthusiasts should clean the tires of their ATVs to remove earthworms and cocoons. As well, it’s important to avoid transporting leaves, mulch and soil between sites unless you are sure they don’t contain earthworms or cocoons.
But help may be on its way from an international source. Recently, the European Research Council awarded a 1.5 million Euro ($2.27 million dollars Cdn) grant to the German Centre for Integrative Biodiversity Research in Leipzig, to study the effects of European earthworms in North America. According to the Centre, the ECOWORM project grant “will fund the first systematic study on the impact of earthworms on plant communities and soil food webs.”