| From West by Northwest.org Arts & Letters Reading Off the Charts: Earthworms Gone Bad By Amy Stewart Jul 8, 2005
Amy Stewart’s new book, The Earth Moved, is a wonderful gardener’s-eye-view of those indispensable soil builders, earthworms. She covers a multitude of wormy topics. Why starting your own mail-order worm business is a bad idea. How worms changed New Zealand. The tricks to successfully keeping a worm bin at home (as Amy does). Why clover and earthworms go together. The fascinating sex life of earthworms. Darwin’s paper-triangle experiments on worm intelligence. Why no-till gardening is better for worms. The new use of worms as pollution biomonitors. Stroking a worm in your hand to mesmerize it. How to use worm castings to get whiteflies off rose bushes. And more. The Earth Moved: On the Remarkable Achievements of Earthworms is a fascinating and informative study of those hidden heroes that inhabit a world we can’t even see. Still, as shown in the following excerpt, in at least a few situations, worms are doing more harm than good. Introduction courtesy of Green Prints, The Weeder's Digest. I arrived in Minnesota on a clear, chilly day. It was May, but there was still snow on the ground. I met researchers Lee Frelich and Cindy Hale at the university, and they agreed to show me the forest where earthworms were causing such a problem. It took less than an hour to get there from campus, and on the way Cindy told me that most people react with genuine surprise when they find out what she’s working on. “People always tell me, ‘I thought earthworms were good for the soil,’ and I tell them that they are, in some settings. But these European worms have invaded a forest that evolved without them over the last ten thousand years. Remember, this whole area was covered by glaciers until the end of the Ice Age. When the ice melted, there wouldn’t have been any worms.” Cindy didn’t set out to study worms. She began her work as a forest ecologist, and in the process she and her colleagues noticed something changing in Minnesota’s forests. Ferns were disappearing, wildflowers had all but vanished, and young tree seedlings couldn’t take root. Forestry experts couldn’t figure out what was happening, but they knew the forest couldn’t survive without this critical understory of small plants. The understory was dying. Lee, her doctoral supervisor, recalled how puzzling the situation was at first. “A couple plants really took over in some of the forests and replaced all the ferns and wildflowers that used to grow there. Pennsylvania sedge, which looks like grass, and one other plant, jack-in-the-pulpit, started to carpet the forest floor. People used to call me all the time asking what was going on in our forests. Nobody knew.” Then somebody published an article about the changes that take place in the ecology between urban and rural areas,” Cindy said. “It mentioned, in a kind of offhand way, that increases in earthworm populations might be causing changes in understory plant populations of New York forests. That’s when it finally occurred to us to go out into the forest with a shovel and dig.” What they found were nine species of worms, including Lumbricus terrestris and other exotic species. Darwin noted how clever the nightcrawler was when it came to pulling leaves and pine needles into its burrow. But even he failed to realize how this efficiency, this special skill, could be destructive on such a large scale. Earthworms, the Minnesota research team has learned, can— and do—consume the entire leaf fall of a forest in a single season. Small plants and tree seedlings flourish in the damp, sweetsmelling, slowly decaying layer of forest floor. This layer, the duff, is built up over many years. It contains leaves and other organic matter in all stages of decay. Many of the native plants that once flourished in the forest produce seeds that have intricate germination strategies. A seed might take two or three years to germinate, going through a complicated cycle that depends on this spongy duff layer. Now that the forest floor is bare, most small plants have simply disappeared. “We’ve seen a loss of eighty to ninety percent of all understory plants in some areas,” Cindy said. “That’s where we find the most earthworms. They just expand their population to fit the available food source. They multiply until there are enough of them to eat all the leaf litter on the soil’s surface. And the ten or twenty percent of plants that do survive? The deer get those.” I could hardly believe what she was telling me. I thought about the redwood forests back in California. I couldn’t imagine those forests without ferns, native columbine, moss. “It’s just so counterintuitive to think of earthworms as pests,” I said. “Does it ever sound strange to hear those words coming out of your mouth?” “Not anymore.” She’d been studying this problem for four years. “But, yeah, that’s what I have to remind everybody. Earthworms are great in a compost pile. They’re wonderful for agriculture. They do till the soil. They do add nutrients. They do all the wonderful things everyone has always believed them to do. But when they move into a forest that has evolved without earthworms, they can actually have negative effects on the native plants.” I told her what I knew about the earthworm migration from Europe: that they arrived in potted plants, ship ballast, even in cocoons on the soles of shoes. How did they get into Minnesota’s forests? Have they just slithered in that direction over the years? “Think about it,” Cindy said. “You’ve been at the lake fishing all day. You still have a few bait worms left when you’re finished. What do you do with them?” “Dump them in the soil,” I said slowly, feeling a little uneasy as I thought about the bait-stand worms I’ve dumped in my own garden. “Exactly. That’s how they’re getting in. That, and ATV tires that have mud caked in them, and fill dirt people bring in when they build a cabin, and potted plants for landscaping projects. People are bringing them in. They couldn’t move this fast on their own.” Lee added, “Wilderness managers have known for a long time that you shouldn’t just bring a new species into an environment like this. There’s a threshold effect that can happen in an ecosystem. It can tolerate just so much change, then it snaps like a rubber band. There are wilderness areas in Michigan where they’ve banned live bait since 1965. They might not have known exactly what the worms could do to the forest, but they knew better than to bring exotic species in where they could reproduce unchecked.” Cindy and Lee have encountered their fair share of skeptics. “After all,” Cindy said, “We’re working against generations of— well, of common knowledge! It just makes sense that worms are good for the soil. But when I take people out to the forest and they see what’s happening, I can make believers out of them.” Lee told me that when he first applied for funding to do this research, he met a lot of resistance. “Earthworm researchers are working so hard to prove all the benefits that worms bring to the soil. Nobody wanted to fund research that showed they might be a pest.” “A couple years ago I went to an ecological conference on hardwood forests,” Cindy added. “I sat in the back of every presentation and at the end I raised my hand and asked, ‘Do you have worms in your forest?’ I must have sounded nuts. But you know what? Nobody knew. I got one call from a guy who worked in the Department of Resources in New Hampshire. He’d been telling everybody for years that they should keep worms from being imported into the forest. Nobody believed him. There just aren’t a lot of people looking into this yet.” Then she said something that no earthworm scientist had said to me. “They can be so beneficial, or so destructive,” she said. “They are literally ecosystem engineers. They are the very base of the ecosystem. Their actions drive everything else that happens. And yet a lot of ecologists out there pay no attention to earthworms at all.” On the way back to the car, I asked Cindy about the animal population of the forest. She had described the forest floor as a crucial component that affects everything else. Do other animals depend on the forest floor for their survival, animals that the earthworms have displaced? “Sure,” she said. “As worms come into the forest, we see a shift from voles and shrews to mice. There are all kinds of frogs and other amphibians that live in that duff layer. And there’s even a ground warbler that nests in the forest floor. It’s called an ovenbird because its nest looks like a little oven. We’re only just starting to look at that.” It’s hard to believe that a creature as small as an earthworm could push ground-dwelling birds and animals out of a forest, but this is exactly what they think is happening. That’s not all: insects that live in the duff layer—including microscopic creatures such as springtails—may be disappearing before they have even been identified and described. The change in soil texture could lead to erosion, especially in the summer when water runs across hard, bare ground in sheets. Even the composition of the soil can change; the presence of earthworms can lead to an increase in bacteria and a decrease in fungi populations, which could in turn affect which plant types proliferate and which struggle or fail entirely. I looked up at the bare branches high above me. How could an earthworm push something as enormous as a tree out of the forest? But there was no doubt that they were accomplishing something out there in the woods, in their slow, methodical way. I thought about the logging protests in the redwood forests back home, and the tree sitters living high in the canopy. The fight to save those forests happens aboveground. It is a battle for the part of the forest that we can see: branches, leaves, tree trunks. But the fate of this forest in Minnesota lies entirely with the part of the forest we can’t see: the dark underground. I asked Lee and Cindy what they thought should happen next. You can’t put up a fence to keep out earthworms. What do they want the public to do? “We’ve got to educate wilderness managers and the fishing community,” Lee said. “They’ve either got to ban live bait altogether or at least stop dumping their leftover worms on the ground at the end of the day. We need to manage the deer population, since they’re grazing on the few plants that do survive. There are some forests in southern Minnesota that are completely invaded by earthworms, but they’ve been able to keep the deer count low, and the understory’s managed to survive.” “Look,” said Cindy, “worms by themselves only travel a few meters a year. You do the math—it would take them about a hundred years to travel a quarter-mile. If we can keep people from bringing them into the forests, we’ve got some time. There’s plenty of forest land that is still worm-free. We can keep it that way for quite a while.” From THE EARTH MOVED: On the Remarkable Achievements of Earthworms by Amy Stewart. © 2004 by Amy Stewart. Reprinted by permission of Algonquin Books of Chapel Hill. No portion of this publication may be reproduced or distributed in any form whatsoever or stored in a database or retrieval system without the prior written permission of Algonquin Books of Chapel Hill. Readers may order THE EARTH MOVED: On the Remarkable Achievements of Earthworms by Amy Stewart from Algonquin Books directly online. Amy Stewart lives in northern California with her husband, two cats, and several thousand worms. She is the author of "From the Ground Up: The Story of a First Garden," a Barnes and Noble Discover title, and is the garden columnist and book critic for the North Coast Journal. Here articles appear in a number of magazines, including Organic Gardening, the San Francisco Chronicle, and the San Diego Union Tribune. She is the zone 9 correspondent for OrganicGardening.com and the California gardening contributor for Bird Watchers Digest. © Copyright 2000-2004 by West by Northwest.org |
