Alien Invaders

Alien species, non-native species, exotic species. These are plants, animals or other organisms that have been abruptly (compared to natural migrations) introduced to an ecosystem, usually by human doings-often accidentally, but sometimes intentionally. This phenomenon has caused dramatic changes worldwide, and continues to do so.

I recently learned that many of our most familiar "wild" flowers are non-native and have been around for centuries. Seeds hitched across the Big Pond with early European immigrants. Each summer I'm happy to see the 6 foot tall flowering spikes of fuzzy leaved Common Mullein that stand at attention like soldiers reviewing a parade. What country girl hasn't picked a bouquet of Queen Anne's Lace and marvelled at its umbrella of tiny white florets?

These roadside weeds are rather benign, but for an example of negative effects, one word: kudzu. A noxious vine, kudzu strangles and smothers everything in its path. It was aggressively planted by the U.S. government in the 1930's for erosion control before it was discovered that in our humid southern states it grows just too well.

European starlings (Sternus vulgaris) were brought to North America by a man who wanted to seed our continent with all the birds that are mentioned in Shakepeare! The descendants of the original 75-100 birds released in New York's Central Park in the 1890's now number more than 200 million. Starlings have voracious appetites, migrate in flocks of up to 100,000 birds, and have contributed to the decline of the bluebird, purple martin and tree swallow.

Not all non-native species are home wreckers, but those that are earn another moniker: invasive, although this term is passing out of favor in ecological circles. (Truth be told, a native species may be invasive as well, meaning it rapidly colonizes an area, such as the Maryland state flower, the Black-eyed Susan. )

By any name, an exotic invasive species does not "smell" sweet-- but through no fault of its own really. In its homeland, it probably evolved to be in relative harmony with its surroundings. But transplanted to a new environment, it may have few or no natural predators, no competing species, and other species may have no natural resistance to it. The result is imbalance and perhaps irrevocable degradation of indigenous flora or fauna.

Since species are interdependent, when one species goes it can take others with it in a chain reaction. This dynamic has severely impacted the vulnerable islands of Hawaii. Seventy three percent of U.S. extinctions have occurred in Hawaii. Feral goats, pigs and sheep are some of the worst offenders there.

We learned how wolves benefitted the ecosystem when they were eradicated (by homo sapiens) from places like Yellowstone. Without wolves, elk proliferated and began overgrazing vegetation, which in turn affected other species, increased erosion, and impaired water quality. The ecosystem there is now mending due to the much publicized, and controversial, re-establishment of wild and free wolves.

Growing to 60 feet, the American Chestnut was formerly a dominant tree throughout our eastern forests, until a blight hit it early in the 20th century. The culprit? -- a variety of chestnut brought here from Asia that had resistance to the blight. Scientists are working to develop resistant strains of our native tree in hopes of restoring the chestnut to its former place as king of the forest. Doing so could have a substantial impact on mitigating climate change.

It is sobering when I consider not only changes I've witnessed in a half century of outdoor wanderings, but just recently. This past spring I saw infestations of garlic mustard in shady glens along the Potomac, choking out trillium, mayapples (see photo left), jacks in the pulpit, and other delicate native wildflowers that were flourishing only a few springs ago.

From my childhood, I remembered the path at Cunningham Falls State Park as a magical tunnel formed by the delicately needled branches of eastern hemlock trees. Wanting to get an early start on sharing my love of nature with my grandson, I took him there when he was only one year old. The magic remained. While perhaps not as plentiful, the hemlock branches still drooped gracefully above us like tiers of shyly lowered eyelashes. My grandson is now almost five years old. On a recent solitary visit, I felt like a survivor on a battlefield. The skeletons of eastern hemlock trees littered the forest floor or stood gray and silent like ghosts.

In this heavily used park, where biodiversity has already been severely diminished by grazing white-tailed deer, I suspect the hemlocks may have been even less resistant to the Wooly Adelgid-an introduced aphid-like pest. To add insult to injury, Japanese Stilt Grass was making rapid headway in crowding out native Lady ferns. (Where's Waldo the fern?) The overall effect was one of barren sterility.


Young families walked past me as I stood shell-shocked. They were blissfully unaware of what they had missed. But I knew, and mourned their loss. Especially on behalf of the children.

At my feet, a huge black beetle scurried at a surprising pace across the path to avoid being trampled. He frantically pulled some leaf litter over his head and body, obscuring not only himself but his own vision. Although tempted, I didn't disturb him. I knew how he felt.

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