Diese waschbär ist ein ärgernis! (This raccoon is a nuisance!) Photo by Robert Barber, AKM Images, Inc.
Russian olive, Norway maple, Japanese honeysuckle – in terms of flora alone, the Northeast is inundated by exotic invasive guests that just won’t go home.
But what about people in Russia, Norway, and Japan? Do they have unwelcome biological tourists, too? What happens when the shoe is on the other foot, when our good, harmless species go overseas and, like American college students on spring break, wreak havoc?
Take the American black cherry. Here, it’s a valuable timber species. In Europe, it’s an invasive pest. European soils lack the microbial pathogens that keep the trees sparsely distributed in America; as a result, the tree is rapidly colonizing agricultural land. It’s bad enough in parts of the Netherlands that schoolchildren are instructed to hand-pull cherry saplings on invasive-plant field trips.
Black locust is another tree species that enjoys little fanfare on the other side of the pond. Prized here for its rot-resistant wood and showy spring blossoms, in Europe, black locust is considered one of the 100 worst invasive species on the “Delivering Alien Invasive Species Inventories for Europe” database.
Some common Northeast plants are also creating big problems abroad. Whereas European invader purple loosestrife is colonizing our native wet meadows, Canada goldenrod is accused of the same thing by our friends overseas. Japan has given us Japanese honeysuckle and knotweed; we’ve returned the favor with green-headed coneflower and lanceleaf tickseed.
Plants have the benefit of sturdy seeds for travel, but animals make excellent stowaways. Consider the gray squirrel. Here, it’s a benign staple of parks, forests, and backyards. In Europe, it’s considerably more menacing. Gray squirrels have been displacing native red squirrels in Britain, Ireland, and Italy since they were introduced sometime in the late 19th or early 20th century.
Other animals have been deliberate, if ecologically misguided, imports. North American furbearers were histori- cally popular additions to the European fur trade. That fur is now flying as the American mink devours native water vole populations. Muskrats are damaging river banks and levees in southern Europe, increasing the risk of severe floods. The largest population of raccoons outside of North America is currently found in Germany, where they were introduced by the Third Reich to “enrich the local fauna.” In the 70-some-odd years since, they’ve spread to every surrounding country, prompting a British tabloid to proclaim them “a furry blitzkrieg.”
American game species are similarly problematic. In 1935, white-tailed deer were introduced to Finland for sport, and now they’re spreading through Northern Scandinavia and southern Karelia. The current population of 30,000 deer originates from only four animals provided by Finnish-Americans from Minnesota.
It’s not only economically significant mammals that make the trip abroad. In our ponds, the American bullfrog is a force to be reckoned with. They can and will eat anything they can fit into those gaping mouths. In their native range (eastern and central North America), predators keep populations in check. Unfortunately, South America, the Caribbean, Europe, and Asia lack ecosystems evolved to control (or support) this largest of North American frogs. Their globetrotting is likely due to a wide range of mechanisms, including the pet trade, cultivation for frog’s legs, aquaculture, and even introduction as an aesthetically pleasing pond species.
Scandinavians are doing battle with another of our beloved aquatic animals: the wild brook trout. Here, the brook trout enjoys celebrity status as an angler’s favorite; there, it’s given the rotenone treatment and maligned for its ability to out-compete native fish. For an American parallel, see the common carp, which originally hailed from Asia but was introduced to improve American edible fish stocks.
In the United States, invasive Chinese species – oriental bittersweet and Asian long-horned beetle, for instance – seem especially troublesome. China, however, is plagued by fewer exotic invasive species, the result of the United States being a nation of global immigrants’ while immigration to China has traditionally been more localized.
All of this is changing. With China developing and importing at a breakneck pace, it’s likely that their own invasive plant problems are just beginning. It sometimes takes exotic plants hundreds of years to become established. Already, Spartina alterniflora, a grass common in our coastal marshes, is rapidly turning Yangtze River mudflats into meadows. Other invaders from our neck of the woods include common (and annoying) ragweed, Canadian horseweed, and daisy fleabane (a small white flowering weed). Since the Chinese landscape is under heavy pressure from industrialization and high-impact farming, scientists worry that their landscape is especially ripe for a future alien invasion.
This is, by necessity, a tiny sampling of the problem. Globalization is scattering species to the four winds. To date, the U.S. has spent hundreds of billions of dollars dealing with invasive species. Our own ecological inbox may seem full at the moment, but don’t forget to keep an eye on the outbox. Dutch schoolchildren will thank you.