Invasive earthworms are attacking the boreal forest, with new research predicting how quickly one species is spreading in northeastern Alberta.
Dendrobaena octaedra, one of six species found in forests in northern Alberta, is projected to expand its territory from three per cent of suitable habitat in the boreal forest to 39 per cent by 2056. There, the squirmy invaders chew through the leafy layer that covers the woodland floor, which can harm native plants and animals.
“It’s a large area for a small earthworm species to be spreading,” said Erin Cameron, who co-authored a paper on the sprawl with researchers from the University of Alberta, Simon Fraser University and Ohio State University.
Earthworms are not native to most of Canada, having been wiped out in the last ice age. The worms here now were likely brought by European settlers in soil, with plants and on ships, Cameron said.
The intruders are a gardener’s ally, but the same actions worms are admired for — shredding organic matter and tilling the soil — are harmful to the boreal forest.
“We have this very positive view of (worms in gardens), and rightly so, in those circumstances,” said Erin Bayne, an associate professor at the University of Alberta working with Cameron. “But when they get into native systems that have never had them, they are an ecosystem engineer. They change the system to suit themselves, and there is a consequence.”
By decomposing the thick layer of leaf litter, earthworms alter which plants, invertebrates, birds and small mammals exist. American robins, for example, occur more often in locations where earthworms live.
“Robins, in some cases, are more competitive than other songbirds. It might be leading to some of the songbirds being excluded from areas they would have once been,” Bayne said.
The worm forecast covers a nearly six-million-hectare swath in northeastern Alberta called the Alberta-Pacific (Al-Pac) forest management area. Using worm counts made at 78 sites in 2006, researchers estimated rates of introduction and population spread. The computer model also considered road construction expected in the area, as vehicles, including ATVs, can transport earthworms or cocoons in tire treads.
“Humans are having a really big impact on their spread,” Cameron said.
While some earthworms require a mate, the species studied in the projection can reproduce asexually, so one worm can start a population. The wrigglers, about two to six centimetres in length and a dark purplish hue, are estimated to be spreading about 16 metres a year.
Limiting road development is one way to slow the looming invasion. Another is educating anglers, who aid the earthworms’ trek north by dumping bait on land or in water.
The Alberta Worm Invasion Project, which launched last year, will continue such education work this spring. The website provides teachers with resources tailored to junior high students, and the Worm Tracker app lets citizen scientists add to existing data by counting, measuring and photographing earthworms.
Meanwhile, researchers are working on modelling the effects of earthworms on carbon storage in soil. If earthworms alter the boreal forest from a carbon sink to a carbon source, the consequences would be substantive, Bayne said.
Cameron is now working as a post-doctoral researcher in Finland. This summer, she will travel across that country to determine the distribution of earthworms. The worms that exist in Alberta are native species in Finland.
“It might give us some clues as to what we’d see in the long term in Canada,” she said.