Invasives - Rant Right Back At Ya

Last week was National Invasive Species Week, noted by our friends at Beautiful Wildlife Garden and also at this post at Andrew Revkin's  New York Times DotEarth blog. And honestly, I thought enlightened gardener agreed. I thought we welcomed both well-behaved natives and exotic plants, and we'd deal sternly with invasive exotics. When exotics spread into the wild, they displace natives, offering less optional habitat for native bugs, which are preferred by native birds and so on up the food chain.

Then I came across this post on Garden Rant (one of my favorite garden blogs, actually), where Amy Stewart interviews Jeff Gillman about his new book. Amy started the interview with this summary/quote from Jeff's book:

You quoted someone as saying that no plant species in the United States has ever been driven to extinction by an invasive plant.

And Jeff proceeds to explain that we're lacking data.

Well, if a plant is doing well in a location then the perception is that it is pushing other plants out.  If we see what appears to be a monoculture of what we know to be an alien plant then we tend to just assume that plant is displacing natives – often without much data. 

And he continues to bemoan the fact that we really don't have enough data. The ecosystem is disturbed, but we don't know what that really means. 

Thinking of the problem with pampas grass we have in California -- it's costing tax payers a pretty penny, here are some articles -- I almost left a snide comment on the post. "Interesting, but hardly relevant". But I did not. Instead, let me pose some questions:

  • How can we know which plants have been driven to extinction? The statement that "no single plant species has been pushed to extinction by invasive plants" should be, instead, we cannot scientifically prove that a species has been pushed to extinction. The first settlers did not keep careful records?  Yep. we lack data, but that doesn't mean it hasn't happened. And it certainly doesn't mean it can't happen soon. Is the only acceptable proof that a species has gone extinct? Doesn't close enough count?
  • Can a one-dimensional analysis fit  a system? The whole thread of the interview, with its emphasis on SCIENCE and DATA reminded me a lot of the scientific studies about nutrition that Michael Pollen so eloquently disassembles in his book In Defense of Food. In my mind, California meadows as they once were have been driven to extinction by non-native grasses (and also by food crops, and suburban developments). 
  • Do you really think the battle is plant against plant? Dare I say American chestnut? Sure, the European chestnut has not driven out the American chestnut, it just so happened that the fungus that drove them out came from the European chestnut. It's also highly likely that the Sudden Oak Death fungus California oaks are succumbing to in alarming numbers came in with shipments of rhododendron from China, and that the oaks are more susceptible because of the invasive annual grasses surrounding them that hold water differently than native bunch grasses.

Here's how the interview ends:

AMY:  And yet, as you point out in the book, it continues to be an ecosystem that functions in some way. I mean, England is obviously capable of supporting life -- plant life, human life, animal life.
JEFF: But what they have is completely different from what they would have had if humans had never entered the scene.  Nature has a way of finding its own balance.  New plants change the balance, but that doesn’t mean that the balance ceases to exist.

And sure, England is capable of supporting life, but a limited palette. A diverse ecosystem is, for many reasons, preferable to an ecosystem with a limited number of species. For me, it's been a revelation and a joy to come from the quite impoverished ecosystems in Europe to much richer systems in America. I've truly enjoyed the wild places that still exist here. And I don't believe nature is in balance if high percentages of native plants (such as the native oaks) are dying. I applaud nurseries that do not sell invasive species, and I wish the government did more to prevent their import and sale.

I still believe that as gardeners, we can make things worse if we plant invasives. And I believe that    we can make a difference for the better if use a diverse plant palette, if we include well-behaved exotics and natives, if we care.


ryan said…
That interview just seems like a stupid strawman argument to me. Why would extinction be a worthwhile benchmark? Invasives cause tons of scientifically measureable problems. For instance, annual broom and eucalyptus are fire hazards. People died and homes burned in the Oakland fire in part because of the fuel created by those monocultural species.
I'm glad you posted a rebuttal. Maybe Garden Rant should have you guest post it.
Anonymous said…
I have but one word on this...Kudzu.
Donna said…
bravo...I hope to post on this very topic next week...we have to be so careful to be good stewards of the land and it is not just plants that are affected but animals, insects etc...and there is scientific evidence on this...
Anonymous said…
Good thoughtful piece, Mouse! I'm no scientist, but I make my own decisions based on what I've read. I have more trouble fighting invasive non native species and some Mexican Primrose I planted myself, (Arrghhh, live and learn), than I do planting natives. So, I do both, hoping that will generally improve the garden, resigned to keeping the dogtail grass, non native, but everywhere and chop out sweet broom which is along the roadsides, sometimes drifting down the hill to my place.
An interesting piece, but it goes beyond plant vs. plant. It's not an either or scenario. Everything in the ecosystem is tied together. We have native wildlife species that are dependent on particular plant species (for food, shelter, reproduction etc.) existing in their environment. Yes, animal species can and do adapt, but often, in the context of human incursion, they simply don't have TIME to adapt.

Also, plants don't have to displace other plant species to be problematic in the environment. Take French Broom. This species in our area has been shown to restrict/alter animal movements in areas where stands are dense. Quail for example will avoid areas of dense broom growth. This invasive plant doesn't cause quail to go extinct, but may affect survival due to altered patterns of movement.

I honestly think this chap is oversimplifying the issue. Looking at it too broadly. Yes, over time, things change. Nature isn't constant. Even without humans around, Nature isn't constant. However, throw humans in the soup, and we can be downright, albeit often inadvertently, destructive. We accelerate change. As such, I will remain on my 'rip out the invasives' tirade :P
Diana Studer said…
Water hyacinth, pretty flowers, is an invasive alien in South Africa. I have seen them removing HUGE truckloads from the Liesbeeck river. Then I was appalled that another SA garden blogger wrote that she just BOUGHT water hyacinth at a nursery. But NIMBY rules, not a problem in MY pond.

Waiting hopefully for rain, and our Oxalis to green up and flower up our garden ;~)
Susan Tomlinson said…
Salt cedar--big problem for arid regions because it is a water thief.
Gillman should work harder to collect the data he claims does not exist.

I have plenty of examples of how invasive species have crowded out weaker natives. I'll bet every good gardener does.

Plus, it goes much deeper than that. Kudzu, as Frances mentioned. Asian Milfoil, for me, that turned a lovely lake cabin into a worthless piece of property.

And what about the animals who originally depended on native plants? My horses stand in knee deep greenery in their corrals in summer, greens they cannot eat. New weeds, taking over that have crowded out the good grasses and are not edible for horses....

Thanks for a great post.
Unknown said…
Anyone who thinks invasives aren't driving native plants to extinction is welcome to join me on a weeding party at the Antioch Dunes National Wildlife Refuge. A few hours of pulling vetch away from our endangered primrose should clear up the misconception.
I want to hug each and every person who commented on this.

I'll admit it: I can't read Garden Rant. It makes me crazy.
Anonymous said…
Thanks for writing this. I haven't had a chance to read the Garden Rant piece carefully -- but I believe my quick skim of it did raise my blood pressure to unhealthy levels! I just want to echo Clare's (Curbstone Valley) comments above. I think Americans have a particularly difficult time thinking systemically because of the strong individualist emphasis in our culture. This is also a problem with conventional science approaches that isolate one variable at a time for study. The study of systems -- be they social systems or ecosystems -- requires a much more complex way of thinking and doing scientific analysis. -Jean
I don't even think I am going to read what sounds like a totally thoughtless post. I run a volunteer invasive plant program on a small island 7 miles off the coast of Maine. Invasive plants are taking over the island and displacing all the native plants. Do we wait for extinction and then decide there's a problem? Yes, the earth will adjust. It will jettison the human race just like the dinosaurs and survive just fine without us. It is humans that can't survive without native ecosystems not the earth.
Town Mouse said…
Thanks everyone for reading and commenting. Getting feedback like this gives me hope and is one reason why I have a blog (or maybe half a blog).

As for GardenRant, I do love them. I think being irreverent is good. And I find it amusing their tendency to be just a little overawed when someone with a degree has something to say amusing.
Gail said…
Well said by you and your commenters.
Christine said…
Sigh... I don't even know where to begin with this, but I appreciate all the commenters clear-headed responses. I'll second Lisa's hug offer.
James said…
Nice post. The interviewee made me pretty steamed under the collar. If we've paved over 95% of many of our landscapes how could it NOT take out a number of species, especially when what's left is too often choked with weeds.