An invasive species is one which is not native to a given area and which by means of aggressive growth when once introduced acts to diminish or choke out local species to the detriment of the ecosystem. The consequences of this intrusive behavior can be severe. To quote a USDA Forestry Service web site, these consequences may include:
“loss and destruction of forage and habitat for wildlife, loss of available grazing land, diminished land values, lost forest productivity, reduced groundwater levels, soil degradation, increased risk of devastating wildfires, and diminished recreational enjoyment.”
That is severe. The northeast United States, like almost every corner of the world has its share of invasive plant species. In no particular order, here are a few of the worst offenders.
Garlic mustard, or Alliaria Petiola, is a plant native to Europe but was not known before 1868, when it was first reported on Long Island in New York State. It is believed to have been deliberately introduced; the leaves make a quite acceptable green vegetable and the plant was believed to have medicinal properties as well.
It is now present throughout most of the northeast with the exception, for now, of Vermont, New Hampshire and Maine. It is most dense east of the Mississippi but can be found as far west as Washington State and British Columbia.
Garlic mustard is a perennial which produces seeds in vast numbers in its second year of growth; these seeds have been shown to be viable for at least five years in the ground. It has few natural enemies; even deer only feed on it sparingly, being perhaps put off by its garlicky odor and, when raw, bitter taste.
Not only does it choke out most native species, it also releases toxins into the soil which seem to inhibit the growth of other plants.
The only effective counter are non-specific herbicides which must be used with care to avoid killing desired species, and hand pulling and bagging, which must be continued for at least a five-year period to have effect.
Japanese knotweed, or Fallopia japonica, is a similarly devastating invader all along streams, ditches and other damp places throughout the country, but especially throughout the northeast. Growing rapidly each spring, it can attain a height of nine to 12 feet and grows so densely as to crowd out virtually every other plant.
The bamboo-like plant was brought to the States in the late 1800s because of the attractive flowers which it produces.
It spreads underground through the growth of very aggressive rhizomes and quickly establishes a single-plant environment to the detriment of all other life, plant and animal, in the area. It can significantly reduce the aquatic life of nearby streams and impoundments by completely disrupting the traditional food chain.
Knotweed is extremely difficult to eradicate once established. There are some potent herbicides that can suppress it, but they will also harm nearly everything else that grows. If cut short a half dozen times a season, every season for years, eventually the rhizomes will die off, but vigilance must be maintained to avoid re-occurrence.
Giant hogweed is not as prevalent as either garlic mustard or Japanese knotweed, but it is on the move. It is not merely an environmental hazard; it is dangerous to humans and animals.
Of Middle Eastern extraction, the plant was, like knotweed and garlic mustard, brought to the United States for its ornamental value. It has spread throughout 16 northeastern states, mostly along waterways, next to which it will flourish, the seeds in fact being carried by the current.
Heracleum mantegazzianum is related to the carrot, the wild parsnip and also to Queen Anne’s lace, but the difference is hogweed’s toxic sap. Once pierced, the plant exudes a sticky sap that contains compounds which cause burns on the skin, usually with permanent scarring. Discomfort and discoloration can last for months and, when presumed healed, be reactivated by sunlight.
The sap can, and has, caused blindness.
Giant hogweed is referred to as giant for a reason. It can grow 15’ tall with gigantic yard-long leaves. It is topped by umbrella-like white flowers that are also nearly a yard wide.
Weed whacking this invasive giant would have catastrophic consequences.
Most states have in their agricultural departments specially trained and equipped teams to deal with this threat, and they have had a good deal of success in reducing the number of sites where it flourishes. Homeowners who detect hogweed are cautioned to call these professionals; the plant is simply too dangerous.
These three illustrations should serve to demonstrate the magnitude of the damage that invasive species can cause, not to mention the outright danger that some, like the giant hogweed, can pose to unaware or careless humans.