permaculture

[Toby Hemenway <toby@patternliteracy.com>]

On 9/4/04 2:09 PM, "David Neeley" <dbneeley@yahoo.com> wrote:

> The pattern of growth you
> suggest is typical of a so-called "clumping" variety of
> bamboo...

Actually, I did mean running bamboos. I have heard stories of the 100-foot a
year runners. Of the 30 or so tropical and temperate species I know, I've
never seen any run anywhere near that, but I'm no expert. Here's a fruitful
question to ponder: if they run 100 feet a year, why haven't they taken over
the Earth? All species encounter impediments to their spread, usually in the
form of intact ecosystems (too shady or perhaps dry for bamboo)

Rain wrote:

>streams.  These ecosystems are continually "self-disturbed" and are therefore
>open to colonization by exotic species.

Excellent example--I'm always looking for non-human causes of disturbance.
So here's my real question: why are "exotic" species considered bad, and
"natives" considered good? (I won't go into the sloppy, shifting definitions
often pasted onto those terms) What harm is done in a constantly disturbed
riparian zone when, say, several imported mazzard cherries replace some
native willows before they too are swept away by flood and replaced? Sure,
if every willow of that species were exterminated over a huge range, we'd
also lose the species that depend exclusively on the willow. But
single-species dependence is uncommon, and total species extinction solely
by an exotic is incredibly rare (AFAIK never documented, but I'm still
looking). Multiply the two frequencies and you get a very, very rare event.
Something else must explain anti-exotics fanaticism.

In the normal case where a few new species move into a disturbed landscape
and replace a moderate percentage of individuals of some of the existing
species, what harm is being done? Isn't this an increase in biodiversity?
Won't that ecosystem now be more resilient and better able to cope with
change? Won't it support a wider array of pollinators, soil organisms, and
everything else? And even if not, what damage is done? Species move around
constantly. Or does change equal damage by definition?

We need to re-evaluate our assumptions: that what we saw at one time in a
location is the only "right" species mix, that a new species is doing
something bad, that species don't naturally and constantly change their
range and composition, that "exotics" aren't perhaps a solution to
disturbance and climate change rather than a problem, and that nature is
being stupid when she allows "exotics" and "natives" to mix in exuberant
recombinant communities that cover a damaged landscape.

The great biologist Ernst Mayr researched bird populations on islands. On
every island he studied, bird species underwent complete turnover every
50,000-100,000 years. That's every single bird species on the island going
extinct and being replaced with another one, totally naturally, many times
over the course of an island's multi-million year history. That puts
human-caused species change into perspective: Purple loosestrife or tamarisk
may locally push some species out of a drainage (actually the data show
those two "invasives" support as many native animals as the vegetation they
replace), but it won't render every bioregional bird species extinct the way
nature can (I apologize for the sloppy human/plant/nature division; the
semantic niceties would take too long to parse).

50 years after Krakatau blew up, 1100 species had moved there. And how many
more species didn't survive the ocean crossing and establishment? That gives
you some idea of the huge waves of species that are constantly shuttling
around the planet. And that's across ocean; overland dispersal is far more
intense. Darwin found seeds of 12 species stuck to a single bird foot.
Multiply that by billions of birds traveling thousands of miles; do humans
spread species at that staggering rate? So species are shifting and invading
and colonizing and being pushed out all the time. If that upsets us, it is a
flaw in our thinking, not a fault in nature's program that we need to
correct by killing any plant we find outside of what we've decided is its
natural range. Invasion is the rule, not the exception.

So sure, let's identify the species truly at risk and save them. But
freaking out over the arrival of a new species and the attendant changes
that brings (or is caused by!) shows only that we are ignorant of how nature
works, and that our prejudices and xenophobia drive us to see danger where
there is merely change. If we choose to stop that change, then let's
recognize that we are imposing our own idea of order, and not putting the
land in some better, more "natural" state.

Toby
www.patternliteracy.com