Invasive European earthworms have been found at multiple sites across Aroostook County, according to University of Maine researchers. That's concerning, because the worms can significantly alter the ecosystem of the forest around them. Credit: Courtesy of the University of Maine

Researchers are concerned that the discovery of invasive European earthworms at multiple sites in Aroostook County could severely alter northern timberlands.

It’s the fourth time that invasive earthworms have been found in The County since the 1950s. Previously, they were found once in 1954 and twice in 1979, according to the University of Maine.

Joshua Puhlick, a research associate in the School of Forest Resources, and his team — Ivan Fernandez, a professor of soil science and forest resources and a cooperating professor at the university’s Climate Change Institute, and Jay Wason, an assistant professor of forest ecology — uncovered the worms at plots in the St. John River Valley and Nashville Plantation.

The worms were found at all 18 sites in Nashville Plantation and at two of 15 near the Seven Islands camp in the valley. None of the worms were found at another site near Sauls Brook west of Eagle Lake.

The discovery is concerning because the subterranean dwellers can significantly alter forest ecosystems.

“Non-native earthworms cause abrupt changes in forest ecosystems and influence forest health, and many natural resource managers are becoming increasingly alarmed about the presence of earthworms in Maine forests,” Puhlick said.

In northern Minnesota, where invasive earthworms also have taken root, the burrowers have caused an 85 percent decline in forest floor biomass and thickness over 17 years, according to the university.

Here in Maine, Puhlick and his team found a 34 percent decline in the median organic horizon carbon stock where the earthworms were uncovered in the St. John Valley, while a 39 percent decline was found at the plots in Nashville Plantation. That’s significant because the organic horizon facilitates plant growth by keeping the soil cool during extreme high temperatures and retaining moisture otherwise lost during droughts or the freeze-thaw cycle.

Earthworms can also increase soil erosion and alter soil nutrient cycles.

While invasive earthworms can be carried into the northern forests aboard logging equipment or discarded by fishermen, climate change is increasing the likelihood that the worms will settle into soil.

“Warming winter temperatures and increasing annual precipitation will likely increase the success of new earthworm introductions across the forests of northern Maine,” Puhlick said.

The results of the study were first published in the journal Forests earlier this year.

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