ughhhhhhhhh noooo stop it! aha! don’t release non-native earthworms in random plots of soil for enhancing gardens or free bait, don’t do it anywhere in North America lmaoooo! stop, it’s so dangerous and extremely harmful, with devastating and surprisingly dramatic and visible biome-wide effects! haha popular tumblr blogs should stop repeatedly and widely sharing advice recommending the release of non-native earthworms and calling it “anti-imperialist praxis” and “bioregional autonomy” and “vegan self-suffiency” lol! dooooon’t! it straight up destroys soil and outright kills forests :/ it directly causes death of understory plants; death of iconic species like goblin fern and serviceberry; elimination of vital fungal networks providing both soil structure and tree-to-tree nutrient-sharing; loss of native invertebrates and amphibians; savannification of the boundary between woodland and tallgrass prairie; death of red maple, sugar maple, and red oak stands; and especially harms hardwoods forests of the Great Lakes and Midwest lmao seriously stooooop it >:(
Anyway for real, I sure hope no one is deliberately releasing non-native and invasive earthworms, or bait worms, anywhere on Turtle Island/North American land, especially west of the Mississippi River or north of the Wisconsin glaciation. Earthworms and bait worms sold in stores are, by and large, not species native to the continent. They severely harm forests and soil ecology, leading directly to disruption of fungal networks; death of saplings and seedlings; death of forest understory plants; replacement of typical understory species with grasses; mortality in adult trees, as well; changes in pH; and other harm, especially devastating in northern hardwoods forests of the Great Lakes region.
Not gonna name names, but several times this year, popular blogs from the [forest-lover, anarchist/leftist/solarpunk, Moomin-fan, environmentalist-ish] realms of Tumblr have widely shared advice recommending the release of non-native earthworms or bait worms into the wild, as a form of “praxis”. I’ve got these posts screenshotted, but since I generally respect people in these circles - and in the interest of avoiding discourse and drama - I’m not going to share them. (A popular post was widely shared in February 2019; another “release store-bought earthworms” post was shared in December 2019.) I appreciate where their hearts are at. But:
From a Phys dot org summary of Great Lakes Worm Watch:
“The western Great Lakes region, which is the area we’re focused on, has no native earthworms,” says ecologist Cindy Hale, a research associate with the Natural Resources Research Institute at the University of Minnesota in Duluth. Native earthworms in the region were all wiped out after the last Ice Age. The current population was brought by Europeans hundreds of years ago, (soil was often used as ballast in ships) and they’re now changing the face of local forests. Anglers are adding to the problem by dumping worms that don’t end up on the end of a hook.
With support from the National Science Foundation (NSF), Hale’s team created the Great Lakes Worm Watch website and outreach programs to stop the spread of non-native earthworms and to clear up the common misconception that they’re harmless. […] Earthworms may be small but when they take over a forest, the impact is dramatic. They cause the rapid incorporation of organic material into the soil, changing its structure, chemistry and nutrient dynamics. What’s known as the duff layer is suddenly removed, and this duff, or decaying organic material on the forest floor, is habitat for several species of insects, spiders, small vertebrates, bacteria and fungi. It is also the primary rooting zone for most plants.“What’s really the biggest negative effect on the plants directly is the removal of their rooting zone. It can cause mortality of adult plants but, furthermore, it can cause a loss of reproductive potential. A lot of these native plants have seeds that have very complex seed dormancy and germination strategies,” says Hale.
Caption by Shireen Gonzaga for EarthSky: “A forest understory with a high diversity of native plants, the result when there are no earthworms in the soil. Image courtesy of Paul Ojanen.”
Caption by Shireen Gonzaga for EarthSky: “Forest soil with an abundance of non-native earthworms can result in a bare understory. Image courtesy of Scott L Loss.”
Non-native worms disrupt fungi networks, alter soil pH, damage seedlings, and allow grasses to gain stronger footholds to replace native/natural forest understory plants (from an EarthSky review of 2016 research by German Centre for Integrative Biodiversity Research):
Bottom line: European earthworms, introduced by early settlers, are changing the physical and chemical characteristics of soil in northern North American forests, creating a decreased diversity in native plants. […] At the top soil layer, earthworms convert fallen leaves to humus. That’s a good thing if you’re growing a garden, but, in a natural forest, it causes a fast-tracking of the release of nutrients instead of allowing the leaf litter to break down more slowly, as it would without the earthworms.
Also, as they burrow through the ground, earthworms disrupt the mutually beneficial symbiotic relationship between fungi and plants. Some deep-burrowing worm species change the pH of upper soil layers by mixing in alkaline soil from deeper in the ground. […]
All of these changes adversely affect native plants that did not evolve in such conditions. For instance, the goblin fern is rarely found in areas with high earthworm density. Other native plants facing threats include largeflower bellwort, trillium and Solomon’s seal. Earthworms also consume the seeds and seedlings of some plant species, influencing what grows in the forest understory.
In some locations, grasses, with their fine root systems that quickly absorb nutrients, dominate the forest floor. Non-native invasive plants that evolved in soils containing earthworms gain an even stronger foothold in these forests.
Cindy Hale, the prominent University of Minnesota-based researcher of non-native earthworms in the Great Lakes region, has published this book through Kollath-Stensaas Publishing:
Non-native worms harm birch trees specifically and hardwood forests generally (excerpt from University of Toronto research, 2016):
The worms can cause dramatic changes to ecosystems by altering soils, reducing leaf litter and disrupting microbial interactions, which reduces biodiversity. Now it seems they are also eating plant seeds in the wild, potentially altering the make-up of forest communities. (…)
“They eat a lot more seeds than we think,” says Cassin [ecologist at University of Toronto in Mississauga], now at the Ontario Invasive Plant Council in Canada.
The study shows another way that earthworms can alter forest ecosystems, particularly for small-seeded species such as birch, says Lee Frelich, an ecologist at the University of Minnesota in St Paul. (…)
Once earthworms have invaded a habitat, they are almost impossible to eradicate, says Erin Bayne, of the University of Alberta in Canada. Conservationists must instead work to keep worms out of pristine habitats, he says, for example by restricting the use of worms as fishing bait and by controlling accidental transport of contaminated soil.
Non-native worms lead to wildflower, fern, and sapling death. In hardwood forests, this loss is probably due partially to how worms degrade the duff layer; the loss of this layer also provokes soil erosion and directly eliminates the forest floor shelter of larger invertebrates and amphibians. When saplings cannot establish themselves, there is tree loss. (From Minnesota Department of Natural Resources)
Studies conducted by the University of Minnesota and forest managers show that at least seven species are invading our hardwood forests and causing the loss of tree seedlings, wildflowers, and ferns.
Sugar maples, important both for forests and human food production, are devastated by the worms (from several years of research by Michigan Technological University across multiple national and state forests in the Upper Great Lakes):
A new study suggests that non-native worms are eating up the forest floor, causing sugar maples to die back and perhaps harming other forest dwellers.
Sugar maples are prized as much for their valuable lumber as for their sugary sap and dazzling fall colors. In Michigan alone, they are the basis of a multi-million-dollar industry. But several years ago, foresters began noticing that the crowns of the big trees appeared unhealthy, with bare limbs and little new growth. “They were losing trees before they could harvest them.” (…)
Great Lakes Worm Watch has some fun links and resources:
You can download a comprehensive key that helps identify earthworm species. Available for free, via Great Lakes Worm Watch:
Text from Great Lakes Worm Watch: “Different plant species respond to earthworm invasions differently. Some native plants appear to be very sensitive, so much so, that they can rapidly disappear when earthworms invade a forest. Some examples of these plants include…”
Worm Watch: “If earthworm invasion leads to changes in the mycorrhizal community of fungi, the diversity of plants that make up the understory would be dramatically changed. Fungi are a preferred food of many earthworm species and they graze it heavily, which could dramatically impact the abundance and composition of fungi in the soil. By grazing fungi on or near plant roots, the earthworms not only can damage the roots, but they prevent the plant and fungi from forming the symbiotic relationship where mycorrhizal fungi exchange nutrients and water for carbohydrates with green plants. If the fungi can’t get enough food, they will die back even further. For some of the native plants that need mycorrhizal fungi, especially when the plant is young and small, survival will be difficult if earthworms prevent this relationship from being formed.”
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