permaculture

[Toby Hemenway <toby@patternliteracy.com>]

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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