Bill (and all): interestingly, it has been proven that ecosystems with a large
degree of biodiversity (read: "healthy ecosystems") have more varieties of
invasives present than those ecosystems that have less biodiversity. I can dig
up the studies, if anyone is interested.
There is always the question of what good do invasive species (particularly
plants) do in an ecosystem? Yes, here I go again, playing Devil's
Advocate...but consider for a moment how some of these rampant,
densely-populated plant colonies effectively fix carbon from the atmosphere,
alter the soil chemistry and hence the soil zoology and biology (potentially
for the better?), and some even filter toxic chemicals from the soil. For
example, Japanese knotweed (Fallopia japonica, Polygonum cuspidatum) appears to
thrive in old mines, being quite adept at leaching out copper from the soil. I
think that a lot of ecological thought can be turned on its ear by thinking
outside one's paradigm, looking at the bigger picture. But Bill is right in
that so very many people make abolishing invasives their life's work...their
sole raison d'etre. Invasive = Evil, no ifs, ands or buts. That is simply not
a scientific approach, not is it realistic or pragmatic. Other scenarios and
paradigms must be recognized and considered in order for respectful and honest
discussion can take place.
Working with knotweed in Vermont,
Kelly Stettner, Director
Black River Action Team
Springfield, VT
www.blackriveractionteam.org
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Date: Fri, 16 Nov 2007 10:18:47 -0000
From: William Silvert
Subject: Re: ECOSYSTEM Health Alien invasions persistence decline limits
control Re: semi-silly question from John Nielsen
I'll pick up on two of Wayne's points. One is that "some aliens that do
little harm" -- this is true, and some aliens are introduced deliberately.
Mustangs are alien to N. America, and are widely appreciated. Many
ornamental plants are deliberately introduced. My mother was a member of the
Florida Native Plants Society, and felt that they were fighting a losing
battle against the imports. An interesting downside is that often introduced
plants in dry areas require lots of water and this creates problems.
As for the comment that healthy ecosystems resist invasion, this depends on
whether they have had a chance to immunise themselves by past experience.
Because mammals were unknown in Australia, their introduction was impossible
to resist. The same is often true when snakes or mosquitos arrive in regions
where nothing similar has every been present. Often the best defence against
an invading species is a predator that can control it, but if such predators
are not already present, it may take a few million years for them to evolve.
Sometimes man has tried to counter one alien invasion by introducing another
alien species to control it -- which brings into action the Law of
Unintended Consequences. It's a tricky game to play.
Bill Silvert
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