Q: What are invasive species, and why are they bad?
Kudzu in Alabama...
...and in North Carolina
An "invasive species" is a plant, animal, or pathogen that aggressively
colonizes habitats. The invasive species that are bad for the environment
are usually non-native invasive species. These plants colonize habitats, and
exclude the native plants and animals. Since they decrease native biodiversity,
they are bad for the environment.
Another name for invasive species is "exotic species", because
the word exotic means something from another place.
(Sometimes people think exotic species means an
exciting or interesting plant or animal---this is because people tend to
think of things from other lands as exciting or interesting, so the
confusion has developed.) Other words for invasive species are non-natives,
aliens, or just plain weeds.
Invasive species can be merely annoying, dreadfully destructive, or anywhere in
between. A mildly annoying invasive species is the dandelion
(Taraxacum officinale). This plant is from Europe, but may be found
growing in many other parts of the world as an invasive species. Fortunately,
dandelions are little more than an annoyance. On the other hand, some
plants such as buckthorn (Rhamnus), when growing in the US instead
of its native habitat, encroach upon wetlands and make dense shade that cannot support native
species. What was once a lovely
carnivorous plant bog filled with dozens of interesting plant species becomes
over-run and dominated by just one species---buckthorn. The animals that depended upon those native
plants for food? Gone.
Some weeds, like plants in the bean family (Fabaceae) can change the
character of the soil by making it heavy in nutrients, killing the
carnivorous plants which cannot survive in that kind of soil.
Incidentally, just as noncarnivorous plants put into carnivorous
plant habitat are not good, it is not good to
introduce carnivorous plants
into places they don't belong either.
Surprisingly, invasive species are the second largest cause for extinctions
(exceeded only by direct habitat destruction)! The Nature Conservancy
has many programs focusing on combatting invasive species.
Sometimes people argue that it is OK for people to introduce invasive species to areas, because---after all---plants move
around one way or another, and we're a part of nature, so our moving plants is all just part of the natural aspect of
evolution and planetary change.
I suppose you could agree that this argument has merit. But if you did, then you'd have to turn your back on every way we are
degrading the planet: habitat destruction, pollution, and so on. Do you really think that a bulldozer ripping up carnivorous
plant habitat is natural? I don't. By the same merit, I don't think it is natural that carnivorous plant seeps in Alabama (USA) are
being obliterated by privet---a species of plant that we imported from China because we like them
in our gardens.
And if you really believe that invasive species, habitat destruction, and pollution are all part of the natural scheme of things,
for God's sake read "The Lorax", would you?
Page citations: Bossard, C., et al. 2000; Randall, J.M., and Marinelli,
J. 1996; Rice, B.A. 2006a; personal observation.
