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Published: 24 Jun, 2020

Underground threat to our national parks

FEATURE Earthworms have been viewed as useful creatures in Sweden for a long time, acting as a driving force behind a sustainable cycle. In other parts of the world, their reputation isn’t quite as good. Soil researcher Jonatan Klaminder reckons it’s time to question our attitudes towards these underground diggers — at least when it comes to unused land with high biodiversity.

Text: Camilla Bergvall

The instinct to save earthworms fleeing from rain soaked land is deeply ingrained in many of us. Jonatan Klaminder, Associate Professor at the Department of Ecology and Environmental Science, has also been very positive about these little creatures for a long time — they eat and break down dead plants and oxygenate and drain soil as they move around. It’s only in the last few years he’s had to think again.

“Entire ecosystems are affected when earthworms spread to forests that have been worm-free for thousands of years. Apart from the fact that the structure of the earth changes, the worms drag down that top layer of dead plant parts — the humus layer. This eliminates vital protec-tion from the cold and seed-eating animals that some mountain plants depend on in order to survive,” he says and continues.

“In North America, they’ve introduced restrictions to actively protect their national parks from European worm species. But in our major mountain parks — such as Padjelanta, Sarek and Abisko — there are no restrictions on bringing in earthworms.

The question is, should we restrict this? According to him, it’s extremely difficult to eradicate earthworms once they’ve established themselves in currently worm-free areas,” he says.

We’re concerned that the ability of earthworms to accelerate decomposition may affect soil carbon emissions just as much as future climate change in the areas in which they establish themselves.

Jonatan Klaminder is currently heading a study to identify the extent to which various earthworm species have managed to propagate in the Swedish mountains, and what effects they’re having on the mountain environment.

“We now know that worms spread from agricultural land, lawns and garden composts in the mountains. Among others, we’ve found those plump, pale terrors that alter the soil most, according to American studies. But the question now is how are these species affecting our mountain birch forests. Is this something to be concerned about?”

It's alarming to note that American studies have proven that the presence of earthworms may be behind cascade effects in ecosystems. In other words, when certain plant species disappear, numbers of grazing mammals also decline. 

It’s also worrying to note that worm activity can benefit invasive plant species. But perhaps most terrifying of all, today’s climate models may have to be reworked.

“We’re concerned that the ability of earthworms to accelerate decomposition may affect soil carbon emissions just as much as future climate change in the areas in which they establish themselves. Backed up by the precautionary principle, I’d like to encourage all fishermen — until further notice, at least — to stop releasing their leftover worms into the wild in the mountains. In fact, this is something that I personally have been doing for many years,” says Jonatan Klaminder.

Spread of earthworms

There are currently around 2,000 earthworm species in the world, of which 14 are found in Sweden. Earthworms spread naturally at a rate of 5–15 m/year. Without the help of farmers, and then fishermen as well, they’d have only made it as far as Denmark after the ice age. When earthworms arrived in Sweden and the mountains has not been clarified.

This article was first published in the magazine Think no. 1 2020.