How do you tell an invasive species from a natural colonizer?


By now, you’ve probably heard of the 66-foot-long, 7-foot-tall, 188-ton “tsunami dock” that washed ashore near Newport, Ore., this summer – perhaps the most dramatic chunk of debris to reach the West Coast in the aftermath of last year’s tsunami in Japan. You’ve probably heard that state workers sliced it up like a giant block of concrete cheese in August with a diamond-studded wire before hauling it away in more manageable chunks. You may have also heard that, beforehand, state officials painstakingly scraped the entire thing clean. Not to keep the works from getting gummed up, mind you, but to remove and safely bag potential invasive species – 13 pounds of them per square foot, and an estimated 100 tons overall.

We think a lot about invasive species here at High Country News – in part because we’re the sort of nerds that bring floss and GRE word books on backpacking trips, and in part because, in our intractably mixed up world, scientists are beginning to think differently about how they apply limited resources to rearranged ecosystems. (For examples, see Nick Neely’s recent HCN cover, "The Salt Pond Puzzle"  and stay tuned for online editor Stephanie Paige Ogburn’s upcoming feature examining the ongoing fight against cheatgrass, the invasive scourge of Western rangelands).

The Pacific Coast, in particular the Bay Area, is an especially invaded ecosystem, thanks to international shipping ports and the number of people that traffic through by air, sea, car and foot. It’s understandable that scientists are alarmed by the prospect that, say, a seaweed like wakame – a tsunami dock hitchhiker which has made some “worst invaders” lists and already has a foothold in SoCal and San Francisco Bay – might colonize waters off the Northwest Coast.

The blitzkrieg reaction to the dock is interesting, though, because a species transported by a natural disaster or event is, in our ecological lexicon, perceived much differently than one that hitches a ride on a boat hull or in ballast. Islands were and are colonized by species naturally in part thanks to such events, which may transport trunks, seeds and other natural debris from one place to another, along with whatever takes shelter upon them. North America was the same, thanks to Ice-Age-prompted sea-level retreat and the emergence of the Bering Land Bridge (people were among that wave, of course). In fact, many of the plants we now know as native in the Intermountain West moved in from elsewhere after the last Ice Age.

To be fair, much of the tsunami debris (and marine debris in general) headed this way is man-made and more buoyant than natural debris (pdf), increasing its chances of reaching our coast. But it does raise interesting questions about what our priorities are when it comes to “protecting” our environment. Are we really managing for a nature defined by human values – including the notion that ecosystems have a correct “balance” based on a specific window in time – rather than managing for the dynamic nature that is?

On the flipside, I wonder if it’s even possible to distinguish “natural” colonization from human-abetted invasion these days. After all, we can expect more frequent severe storms and surges thanks to climate change, and many animals are already moving northward and upward into habitats made more hospitable by climate change, sometimes pushing out the “natives” that make their home there.

Sarah Gilman is HCN's associate editor

Image of tsunami dock on Oregon coast courtesy Flickr user Wolfram Burner

Image of wakame seaweed in Japan courtesy Flickr user Roberto De Vido

Charlie Hohn
Charlie Hohn
Sep 11, 2012 06:01 PM
I think 'Invasive' is best used as a term for an ecological phenomena where one species, because it is introduced to a new environment or its environment is severely altered, begins expanding to the point that it excludes other species, causing a decline in biodiversity, ecosystem complexity, and sometimes harmful impacts to humans.

It doesn't really matter where it's from. The fact is that most invasive species are non-native, but it's also true that most non-native species never become invasive... and sometimes native species do.

There have always been occasional instances of invasive species, as long as there have been ecosystems. But, now that humans have other huge impacts on their surroundings, and introduce literally hundreds of ruderal species at once that become invasive, it creates big problems. Just like other disturbances that we increase or decrease the effect of - floods, fires, erosion, etc - introducing hundreds of invasive species to an ecosystem causes problems. This is why we should care - not because they aren't native. Because they are invasive.

I think, as you mention in the article, that a giant floating mass of concrete is far from natural. I'm sure redwood logs got washed into the ocean after tsunamis hit California, and likewise with trees from Asia, but it was surely rare. When the logs reached shores with intact ecosystems unaffected by colonial post industrial humans, species either were usually either absorbed into the ecosystem or were outcompeted and died.

You ask "Are we really managing for a nature defined by human values ... rather than managing for the dynamic nature that is?"

I would argue that we can and should do both at the same time. It's impossible for us as humans not to manage for one human value or another, and doesn't really make sense to try. But, its to the best interest of ourselves and our own values to manage for dynamic and complex ecosystems.

That's a very different thing from releasing tamarisk, brome, and emerald ash borer into ecosystems and then walking away with a 'hands off' attitude after the fact.
Bill Gore
Bill Gore Subscriber
Sep 13, 2012 04:06 PM
This is a useful discussion to have. Very useful. Orthodox environmentalists and their allies in academia spill a lot of ink, grant money and effort in trying to determine, and then enforce or restore, biometric baselines. Since the beginning of the Pliestocene the only constant has been change. Hotter, then colder. Drier, then wetter. Pine trees, then scrub, then pine trees again. Overpopulated, then desolate for a few hundred years. Then a new group moves in and thrives for a while. The geologic, botanical and archeological record of the West is a continuous sine wave of change. That does not mean we throw up our hands in existential surrender and let the landscape we love be over run by red brome or tamarisk or shopping malls, but it does give us some breathing room. We are simply one short chapter in a very long book that is prepping new chapters as we speak. All chapters are fascinating reading. Whether we (european americans) are given a subsequent role in the dramas of the future is, I'm sure, of little intrinsic interest to the landscape. We need the landscape a lot more than it needs us, or mammoths or giant sloths. Normalcy bias makes us absurd. "We want to live forever, and we have to die"-Joko Beck.
Arnie Peterson
Arnie Peterson
Sep 18, 2012 12:46 PM
I heard a story that in the past in the Hawaiian islands about one new species crossed the ocean to the islands every hundred years or so, but now with ships and airplanes arriving daily, there are about ten new species every year. The actual numbers may be wrong, but the magnitude of the problem is the same. This is the new “dynamic” “management” of nature by humans. Humans move species about more than in the past. In one day a new pretty flower / new species of mosquito / new cold virus can travel from Europe to New York to Los Angeles. And with all of the recent new species that have come to this country, even if we stop all new invaders today, it will probably be a hundred years or more before the environment is again stable or balanced. The result may not be as we expect or desire. I feel certain that I will never see the great expanses of chestnut forest across the east coast – those trees are mostly gone. I am in favor of trying to stop as many new human-abetted invading species as we can, because we don’t know in advance which is the next tamarisk. There is a grey area between purely nature driven and human caused, but in this instance if we go too far, if a storm blowing a dock is natural, are we causing harm by removing the new species? If people move ten species a year, yet we stop the one natural moving species in one hundred years, are we really stopping the dynamics of nature? We need to acknowledge that the world is changing, that some species are moving northward with global warming, and accept that tomorrow the forest may look different than it does today. We can not preserve the world of our grandparents. But we also need to be aware of how our actions may be harmful to the environment. Stopping all of the human spread of new species may not be an attainable goal, but we can decrease the spread greatly, and even then the rate will likely be much higher than natural.
Chas S Clifton
Chas S Clifton Subscriber
Sep 18, 2012 02:42 PM
When an invasive species is introduced through human action (kudzu, ice plant, tamarisk) or carelessness (cheatgrass, tumbleweed), and then it proceeds to create its own little monoculture, we should fight it to preserve biodiversity -- even if the baseline is moving.

A friend went to Uzbekistan and came back with photos of tamarisk there -- it looked totally different in its original habitat than it does along the the Colorado or Arkansas rivers, for example.