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  • From: Toby Hemenway <toby@patternliteracy.com>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: Re: [permaculture] Toby's post on Autumn olive
  • Date: Wed, 17 Jun 2009 07:48:00 -0700


Hey, Rain: It seems incendiary to me to label a species as invasive with no knowledge of context, and it's almost guaranteed that I'll come lurching out of my cave to counter that sort of "risky generalization." And here I thought I was the one bringing balance to the often-unfounded bias toward natives! Virtually no species is simply invasive; there usually is disturbance or change in nutrient availability (AKA pollution) or some other shift in the environment first. And if you'll notice, I was careful to qualify my statements with things like "almost never," as there is, as you point out, rarely a "never" in nature.

The word native changes its usage to suit the circumstances, as Theodoropoulos has documented. That's one reason he calls invasion biology a pseudoscience. Usually the working definition for "native" is "a species that we think belongs here," and that makes little ecological sense. Mostly, we call a species native if it was there when Western scientists arrived.

Doug fir did not evolve in the US Northwest. It came from somewhere else, just like autumn olive and kudzu. If others will use "native" in many ways, so can I. Just use a larger timeframe, 4000 years instead of 500. I think it neatly illustrates the problems with the label "invasive."

Before 4000 years ago in the US NW (long after humans arrived), Doug fir was restricted largely to the wetter uplands, while the dry lowlands held prairies. A moistening climate allowed Dougs to move into valleys and low hills, and to hugely expand their range. However, fir was suppressed by humans via burning, to maintain, in spite of climate change, the prairies that indigenous people preferred. When the takeover by whites stopped the burning, Doug firs quickly overran the prairies, which were no longer suited to the moist environment. Why isn't that called invasive? Simply because we weren't there to see the carnage. We take a snapshot of a dynamic landscape and call it "the way it should stay."

Nearly every species "invaded" its current habitat (due to shifting climate and continents). We just weren't there for the disruptive decades before they developed functional relationships with the other species there.

And that's really what native means: species that have functional relations with others in a place. That develops naturally over time. Kudzu hasn't reached that yet in the US SE. Purple loosestrife is doing it nicely, reducing pollution and providing excellent habitat for local birds and insects, in some cases better than the "native" flora. So lets call autumn olive an incipient native species. It will surely remain here, and will form more functional relationships in the near future--it's already preferred by many native birds over native berries, and it's building depleted soils.

I just read an article describing how the mink, an introduced species in Britain, has shifted its feeding habit away from fish, letting it not compete directly with the "native" otter and polecat. So there's another invasive species that's quickly creating relationships with the species already present via resource partitioning. It's becoming native.

Toby
http://patternliteracy.com



Rain Tenaqiya wrote:
I don't know if Toby is trying to reignite the fiery debate on invasive
plants, but I would argue for a more balanced approach to the topic. Saying
that Douglas-fir is not native to Cascadia is to redefine the term. It was
there long before people were, as far as I've ever heard.
Also, making broad generalizations about plant succession is risky, whether invasive plants are involved (usually are) or not. To say that invasive exotic plants do not displace natives without humun disturbance is to deny the chaotic and wondrous process of ecological succession. Natives displace natives, so why can't exotic plants displace natives? I see it frequently, without humun disturbance. Sometimes, native plants displace exotic plants, too. It's all a dance.
Rain


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