Invasives: Friend or foe?
I
cut my teeth on the conventional theory of invasive plants and
animals --- they
outcompete native species and cause a decline in diversity.
Species like kudzu are able to run amok in our climate because they
have no native diseases and predators to keep them under control, so
they can swallow up whole hillsides. The solution is eradication
--- rip out every kudzu plant you see.
Lately, though, I've
read several thought-provoking analyses of the invasive
situation. In Edible Forest Gardens, Dave Jacke and Eric
Toensmeier assert that invasives only gain a foothold if the ecosystem
is already out of whack. According to these permaculturalists, the answer is not to spend
weeks weeding Japanese stiltgrass out of your woods, but to discover
what man-made change has made the invasive able to take over in the
first place. In their eyes, my original view of invasive control
is like sticking a band-aid on an ecosystem suffering from chicken pox.
Hugh
Raffles' recent New York Times article considers invasives in yet
another light. Raffles looks at species over a geologic time
frame and reminds us that many of our "native" plants and animals
originated elsewhere. Nature is constantly in flux, wiping out
species that aren't able to deal with changing conditions while
replacing them with hardier cousins. Taking a purely
preservationist view of the earth --- trying to turn our current
species assemblage into a static museum --- is bound to fail because
species would migrate and die out even if we hadn't stirred the pot.
I think that both of
these modern analyses of invasive species have merit...and
problems. I love the idea of looking for and trying to fix the
underlying problems that promote the spread of invasives, but what if
the problem is forest fragmentation and can't be dealt with on the
personal scale? Should we just throw up our hands and let our
biodiverse woodlands turn into a monoculture?
And
although Hugh Raffles' has a very good point about species flux over
the course of geologic time, it's also true that extinction rates are
currently at an all-time high, presumably because of human
meddling. Raffles' argument is also strongly colored by his
recent experience becoming an American citizen, and I think that he
needs to be a bit more careful about drawing parallels between people
immigrating and whole species moving in.
When it comes right down
to it, my difference of opinion with all three of these commentators is
responsibility --- I think that humanity is ethically bound to take
responsibility for the environmental devastation we've caused.
Looking at the bigger picture is always a good idea, but not if the
exercise enables us to say "that kudzu-coated hillside isn't really our
fault." We broke it, so we should do everything we can to fix it,
especially if we can come up with innovative answers like Peter Becker's
Japanese Knotweed elimination campaign.
Our chicken waterer is the POOP-free alternative
for the modern chicken coop.
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People like to chose extreme positions. Neither conveniently ignoring the negative aspect of invasive plants nor being hard line about preserving "native" plant assemblies is very productive. The middle road, wherein sensibility often lies, makes much more sense. Each situation/plant has to be examined individually to make any sense of the problem. It has to be noted though that we can't necessarily accurately predict what will happen when we introduce new plants, so I tend to advocate for caution in such matters... the precautionary principle... weigh the potential consequences and lean your position accordingly.
I fight nasty invasives on my place every year and more show up on our shoes or tires or whatever. True, many are more aggressive in disturbed environments, which any homestead has plenty of but others, like tansy ragwort, need little help and increase exponentially. Yes, someday a balance may be achieved wherein the plants slowly become part of a community through the mechanism of naturally evolving checks and balances, but that will be a long time coming in evolutionary terms and for now they continue in growing numbers to decrease total plant diversity which is often held, and justly, as the sign of health in most ecologies. I hope to blog on this subject eventually as I've butted heads with both sides on numerous occasions. Thanks for being a voice of reason!