Beware Darwin's Beloved Earthworm

"It is a significant change to the carbon dynamic and how we understand it works."
"We don't truly understand the rate of the magnitude of that change."
'I was amazed. At the very first plot [in her study area of the boreal forest floor], there was a lot of evidence of earthworm activity."
Cindy Shaw, carbon-research scientist, Canadian Forest Service

"It's just another of the many reasons why you need to know more about systems."
"Because there could be an effect that would enhance climate change and enhance the rising temperatures."
Ingrid M. Lubbers, soil researcher, Wageningen University, Netherlands

"What we see with our model is that forest-floor carbon is reduced by between 50 percent and 94 percent, mostly in the first forty years."
"I'm not sure what their implications are for carbon, but they're pretty aggressive and they seem potentially to be better competitors than European earthworms."
"That's another issue on the horizon."
Erin Cameron, environmental scientist, Saint Mary's University, Halifax, Nova Scotia

Earthworms recently have spread to the north’s boreal forest. In some areas, the biomass of earthworms is 500 times greater than that of moose, a keystone species.   CreditLance King/Getty Images

How could we expect kitchen and garden waste to decompose into compost without the industrious little worm working away diligently to accomplish that most natural of all feats thanks to nature's intervention? Gardeners around the world would go into mourning at the depletion of earthworms should some misfortune of a pathogen afflict them and rout them from the earthworks of our garden beds and borders.

It has always seemed a mystery that earthworms were absent from forest floors. But now their presence is being discovered right there, in forests, doing their work of decomposition and enriching the leaf mass that constitutes the mulch and rich soil of the forest floor. Native earthworms evidently were once abundant in the forests of northern North America. But we're talking ten thousand years ago, during the ice age, when scraping, retreating ice may have expunged them from existence.

Well, they're back! Back in the most northerly-located forests in the world, the boreal forest, a great carbon sink located in northern Canada. Carbon-research scientist Cindy Shaw with the Canadian Forest Service who studies the boreal forest, discovered it was teeming with earthworms. The focus of her study was to determine recovery on the forest floor in the wake of oil and gas activity.

And it was determined that these earthworms now wriggling on the floor of the boreal forest are invasive species from southern Europe that had made their way to the north; brought by European settlers centuries earlier. They have spread through the northern forests helped along by roads, timber and petroleum activity; tire treads, boats, anglers and gardeners. Guilty as charged.

Worms release the carbon stored in the forest floor as they feed, and this concerns climate scientists. "Earthworms are yet another factor that can affect the carbon balance", remarks Werner Kurz, a researcher with the Canadian Forest Service in Victoria, British Columbia. The growing incursion of earthwoms in North America, northern Europe and Russia, could convert the boreal forest, the globe's carbon sponge, into a carbon spout, he fears.

It is, however, currently speculative theory. The threat that it is perceived to be, is so bright and shiny new to boreal forests scientists have no real knowledge as yet how to evaluate how the carbon effect of the earthworms activity will manifest and what it will turn out to be in terms of environmental injuries. That old adage of our propensity to fear what we don't understand ... ? The great unknown and its potentials.

Earthworms break down organic material in the soil, and the nutrients in the soil become available, helping plants and trees grow and which in the process locks carbon into living tissues. Because, you know, without carbon there would be no life. As well, some types of invasive earthworms tend to burrow into mineral soil and from there seal the carbon located there. The problem lies in the issue of earthworms speeding decomposition while releasing carbon dioxide into the atmosphere.

As earthworms proliferate and expand their territorial habitat carbon dioxide is released into the atmosphere. The big question puzzling scientists is" Will the presence of earthworms add more carbon to the atmosphere; or subtract it, as they occupy greater areas of the world's geography? This has been christened the "earthworm dilemma" by Dutch soil researcher Ingrid Lubbers, in a paper published in Nature Climate Change, in 2013.

In warm climates the typical forest floor represents a mixture of mineral soil and organic soil, whereas in a boreal forest, those components tend to remain distinct; one layer of rotting leaves, mosses and fallen woody detritus on top of the mineral soil. It was once thought by soil scientists that cooler temperatures reduced the mixing effect, but now they think the absence of earthworms accounts for the difference.

Spongy leaf litter contains the carbon stored in the boreal soil and most of the invading earthworms in the North American boreal forest appear as the type that devours leaf litter, remaining above ground, and releases carbon. In Erin Cameron's study area of the boreal, she discovered 99.8 percent of the earthworms in the area she studies in Alberta were Dendrobaena octaedra, an invasive species known to eat leaf litter but not to burrow into the soil.

She published the results of a computer model designed to compute the effect on leaf-litter over time. The 2015 study pointed out that carbon, no longer sequestered, goes into the atmosphere. And as a vital part of Earth's carbon cycle, the global boreal forest stores at least one-fifth of the carbon that cycles through air, soil and oceans, according to Sylvia Quideau, soil biogeochemist at University of Alberta.

The boreal absorbs more carbon from the atmosphere than it adds, but it is environmental scientists' fear that this will change. Warmer temperatures could extend the growing season, so trees will grow larger and store more carbon, but rising temperatures also release carbon to the atmosphere. Thawing permafrost results, as does an increase in the number of forest fires. As for earthworms, they add the final, exacerbating touch toward the boreal forest becoming a global source of carbon.

Maybe.