Invasive plants, fungi and animals are a perennial bugbear of environmentalists in America. In their efforts to preserve and enhance the biota of North America, they find that these invaders threaten to push out unique species unable to compete with them, often taking advantage of an ecosystem already disrupted by humans.
The sad fact is that much of the damage done so far is irreversible. Vigorous weeds such as plantain, dandelions, mullein, chicory, Queen Anne’s Lace, kudzu, purple loosestrife as well as a host of others are now too widespread to eliminate.
The chestnut blight, accidentally introduced when Asian chestnuts were brought into the country, killed billions of native chestnuts, forever altering the East Coast ecosystem. Dutch Elm disease wiped out 80 percent of the trees here. As a child, I can remember all elms in my home town, one by one, having the sticker attached, warning the tree was infected. One by one they were all cut down, nearly all gone by the time I graduated high school.
Insects such as the Emerald Ash borer and Hemlock Woolley Adelgid are making inroads on these trees as well, though it’s still up in the air as whether ash trees and hemlocks will go the way of the chestnut and elms.
Birds like the starling were deliberately brought here by individuals apparently homesick for birds from their native lands. The result is 150 million starlings, who hog nesting sites favored by bluebirds and other native species. English or house sparrows, brought over to control a linden tree pest, also compete with native birds, their aggressive behavior often giving them an edge.
Plant invasives were deliberately brought in by bumbling well-meaning humans. Kudzu was introduced as an ornamental as well a high protein plants for cattle to forage on. Instead, without any natural enemies to control it, the kudzu vine went berserk, transforming into the ‘vine that ate the South’.
Interestingly enough, not all invasives come from other countries, so they don’t need any human help getting a foothold. Virginia Creepers, a vining plant with foliage which turns a garnet red in the fall as well as dusty blue berries favored by birds was for a long time confined to the south.
But over the past 30 years, it has begun appearing here in New Hampshire, its seeds spread by birds, particularly turkeys, by passing through their digestive tracts along with a nice little package of fertilizer. This is a vigorous plant which spreads tendrils up trees and along the ground, quickly dominating the area. I’m constantly pulling the darn stuff up. I like to refer to it as the kudzu of the north.
A bird which has begun spreading throughout the south from Central and South America is the black-bellied whistling duck.
I’m not sure if they quality as invasives, but they’ve not only been expanding into southern states, but there have been confirmed breeding in states such as Illinois and Arkansas, with fringe sighting as far north as Canada. Wikipedia reports their current population as between 1 and 2 million, with indications it is increasing. They often use nest boxes and tree cavities for nesting so there is the potential for them to displace wood ducks though I haven’t found any reports of that yet.
Other animals have been deliberately brought into the US as well, though whether they will ever become invasive is really debatable.
One surprise is the zebra. A feral herd of zebras live in southern California. These animals are the descendents of a herd once kept by William Randolph Hearst at Hearst Castle as part of a private zoo he had. After financial hard times came during the Great Depression, most of the animals in his zoo were donated to other zoos, but the zebras were turned loose to fend for themselves. There are estimated to be about 120 animals who seem to survive just fine in the southern California climate. Because the population is so small, it’s not likely their numbers will explode to troublesome levels. But you never know.
Another import from Africa is the oryx. In the early to mid 1970’s New Mexico Fish and Game brought in 95 captive-bred animals for release on the White Sands Missile Range for big-game hunters. Since the area is very similar to the Kalahari Desert they came from, they did well and their population has expanded to between 3000 and 6000 animals, possibly more (the exact number is unclear).
The concern now is to keep them from expanding beyond the area Fish and Game intended. They eat the same browse as native deer and pronghorn. Their size, between 300 and 500 pounds, along with simitar like horns, makes them a formidible animal, easily outcompeting the much small pronghorn who is a much more delicate 75 to 100 pounds. Limited hunting of about 1500 animals a year is permitted.
Their size keeps some native predators at bay. They’re too big for coyotes. Wolves, existing in small populations in New Mexico, would have a hard time tackling an adult, unless it was ill or aging. Calves might be a better bet. But cougars, weighing at 100 to 200 pounds can take an adult. Reports indicate some of the big cats are in fact willing to tackle oryx. One enterprising cougar is reported to have taken 29 oryx with the animals making up to half of his (or her) diet.
What will the future bring? Given the small size of the zebra herd in California, they are not likely to really expand very much. But the oryx is more likely to succeed and become a permanent part of North America. Kudzu, dandelions and other imports are also here to stay. The environment will eventually reshape around them. And life goes on.
Have a happy September.
