Contrary to popular belief, the earthworms found in the gardens and forests of New England aren't native. Virtually all of the worms north and west of New Jersey were wiped out during the ice age that ended about 10,000 years ago.Earthworms are an example of an ecosystem engineer, an organism which modifies its environment with the effect of creating, maintaining, or destroying habitat for itself and other organisms. Gardeners and farmers collaborate, intentionally or accidentally, with many different engineering species. Earthworms are only one example. Clover and other "cover" crops, livestock, even trees are other examples.
European earthworms -- or their cocoons -- first hitched rides to the New World on the root balls of colonists' plants or in dirt that was used as ballast in ships to steady them on the long journey across the Atlantic Ocean.
In the 1800s, much of the region's vast forests were cut down for farmland, and worms -- clinging to plants or even plows' wheels -- were introduced to more areas of New England. A patchwork of wormed and worm-free woods was created when forests later reclaimed the farmlands.
Now scientists suspect that humans are again bringing worms into New England's remaining worm-free woods. Fishermen abandon nightcrawlers or other worm bait at fishing holes. Second homeowners are worming their property with landscape dirt and, possibly, compost piles. Hikers and campers unwittingly bring along worm cocoons, wedged in the tire treads of their cars.
- When Worms Turn, The Boston Globe, December 11, 2006, via Invasive Species Weblog
In the gardens around the house, I'm faced with neglected, compacted, weedy and unproductive ground. To rehabilitate the gardens, I need to enlist some ecosystem engineers. I started some small patches of clover, inoculated with nitrogen-fixing bacteria. I want to expand that this year to other areas, including the hell strip between the sidewalk and the street.
Last year I also ordered earthworm cocoons and introduced them into the backyard. That was before I began reading about the damage earthworms can cause to native forests whose assemblage of species evolved without their "help." Knowing what I know now, I would still do this in my yard. This territory has not been "natural" for hundreds of years. But there are natural areas even in New York City which deserve protection. If I lived closer to them, I would be more cautious about what I introduced into my gardens.
We are gardeners of the world. We are ecosystem engineers on a global scale. Like it or not, we are past the point where the natural world can survive, let alone recover from, our predations, intrusions, and blunderings without our help. If we engage in this work consciously, there is some hope that we can reverse some of the damage we've caused.
- Byers, et al (2006), Using ecosystem engineers to restore ecological systems [PDF]