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Rethinking Invasive Plants

December 27, 2017

Beyond the War on Invasive SpeciesFor several years, I have been concerned about the issue of invasive plants, and particularly about the challenge this poses for gardeners. (See, for example, Invasive Plants: What’s a Gardener To Do and Invasive Plants.)When I talk about invasive plants, I am not talking about “garden thugs,” plants that run riot in your garden. I am talking about non-native plants that escape from gardens, naturalize in the wild, and harm native ecosystems by out-competing native plants. In other words, invasive plants are not defined by how they behave in your garden, but by how they behave when they get out of your garden.

Most invasive plants were introduced into local environments intentionally, often by gardeners. For this reason, invasive plant programs try to prevent the introduction and propagation of problem plants through public education and through legal prohibition on the sale and propagation of the most problematic invasives. Invasive plant initiatives typically also go beyond prevention by trying to restore ecosystems  that have already been invaded and harmed by aggressive exotic plants.

This is a widely shared understanding of invasive plants, and it underlay my recent efforts to get my local Conservation Commission involved in an invasive plant project. But then I read Tao Orion’s Beyond the War on Invasive Species (Chelsea Green Publishing 2015), which challenged everything I thought I knew about invasive plants. Orion is a permaculture designer whose training is in agroecology and sustainable agriculture. She makes a very persuasive case for rethinking our approach to invasive species, and the key tenet of her argument is that invasive species are not a cause of damage to native ecosystems, but a symptom or effect of that damage. For exotic plants to take hold and naturalize in an ecosystem, she argues, there must be an available ecosystem niche, and the existence of that vacant niche is a sign of disruption in the native ecosystem.

But Orion does not stop at this fundamental challenge to current thinking about invasive species. She goes further by challenging the assumption that invasive plants contribute little or nothing to ecosystem services. For example, she notes that many invasive plants obtain an ecological advantage from being able to photosynthesize more than do native plant. Since atmospheric CO2 is a key ingredient in the process of photosynthesis, these invasive plants may be mitigating the effects of rising CO2 levels by removing CO2 from the atmosphere and sinking it in the ground.

Orion lives and works in the western United States, and many of her examples are from western ecosystems. One powerful case study is her analysis of salt cedar (Tamarisk), widely considered an invasive scourge in western riparian ecosystems where it is seen as outcompeting native willows and cottonwoods that are key to those ecosystems. She argues that salt cedar spreads aggressively where willows and cottonwoods are already in decline. And why are they in decline? Because of dams and other flood control measures that disrupt the cycle of periodic flooding on which willows and cottonwoods depend. What’s more, in river systems where river waters have been diverted for agricultural irrigation and are subject to increasing salinization because of agricultural fertilizer runoff, salt cedar plants perform the ecosystem service  of  “absorb[ing] salty water through their roots, acumulat[ing] salt within their tissues, and transpir[ing] freshwater through their leaves. Transpiration releases moisture into the atmosphere, and little by little, the salty water that other plants’ roots come in contact with is rendered less salty.” (p. 72)

Is Orion arguing that we should stop worrying about invasive species? Not at all. The presence of invasive plants is a sign of  trouble in an ecosystem. But she is arguing that, in order to understand both the effects of invasive plants and their control, we must “think like an ecosystem.” Simply killing off all the invasive plants, by whatever means necessary, will not restore the native ecosystem to its previous state. We must understand the disruption that created an ecological niche for the invasive plant, and we must also understand that ecosystems are always in the process of transition and the role of particular invasive plants in the processes of ecosystem succession. Orion is particularly concerned about the widespread use of herbicides in invasive plant eradication, and she provides a compelling analysis (chapter 1) of the harm done by so-called “inert” ingredients in popular herbicides.

In the last chapters of her book, Tao Orion considers the implications of her analysis for projects to control invasive species and restore native ecosystems.

One of the reasons we’ve been so misguided in our approach to managing invasive species is because managing them effectively requires something far more challenging and more powerful than the business-as-usual approach of aggressive, extensive annihilation of “offending” plants and animals. Effective management requires that before anything else – before we develop a plan or reach for the herbicide – we have to first teach ourselves to think differently…. [I]f we are to embrace the true meaning of ecological restoration as repairing degraded ecosystems, then we must move beyond short-term and short-sighted invasive species eradication measures and begin the necessary process of engaging the critical task of restoration on all fronts, from our homes and neighborhoods, to farms, forests, and the economic systems that support them – as well as restoring our own way of thinking. (p. 165)

And just as I was feeling overwhelmed by the magnitude of this charge, I turned to Orion’s final chapter, which provided a step-by-step practical guide to putting these principles into action.

Beyond the War on Invasive Species has challenged me in ways that are both disquieting and exhilarating.  Not since Doug Tallamy’s Bringing Nature Home have I read a book that so powerfully changed my thinking about the complex ecosystems around me and my relationship to them.

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10 Comments leave one →
  1. GARY permalink
    December 28, 2017 11:40 am

    Interesting viewpoint Jean. It’s good, I believe, to not get so caught up in native restoration that one becomes militant against any other ways of looking at nature and landscaping.

    • January 4, 2018 8:22 pm

      Gary, I’ve never been a native plant purist, but I was sure that invasive plants were harming native ecosystems. Now I think it’s more complicated than that.

  2. Charles F. Emmons permalink
    December 28, 2017 1:18 pm

    This is really interesting. I have had some amorphous thoughts like this in the back of my mind, and this articulates some of it and removes some of my confusion. Well summarized, I might add.

    • January 4, 2018 8:24 pm

      Thanks, Charlie. I realized I had a pretty good understanding of this book’s basic argument when I tried explaining it to a friend who’s a plant ecologist.

  3. December 29, 2017 1:07 am

    Fascinating. Always good to learn and think out of the box. Really, the author is speaking of systems thinking, isn’t she . . . looking at the whole, rather than just the parts. We’re all clothed in a single garment. Always easier said than done. Thanks for sharing this important treatise.

    • January 4, 2018 8:25 pm

      Bruce, I thought I *was* taking an ecosystem approach to thinking about invasive plants, but this book argues for backing up and taking a much wider view of the system.

  4. December 29, 2017 12:10 pm

    Hello Jean, there’s food-for-thought, I hadn’t thought of the point-of-view of invasive plants as a symptom of troubled eco-systems but I’m not convinced that’s always the case. A balanced eco-system can be disturbed by a non-native introduction that would never have naturally occurred due to geographical isolation. Similar habitats and conditions that are geographically spread can end up with very different eco-systems, some may be more fragile than others when it comes to external change or disruption.

    • January 4, 2018 8:27 pm

      Sunil, I agree, and I think Tao Orion might too. A big part of her argument is that we need to look at each invasive species and its ecological relationships rather than assuming one view works for all.

  5. January 4, 2018 4:14 pm

    Jean, As someone in the Southeast living amidst Kudzu, known as ‘the plant that ate the south’, I found this view very interesting. Kudzu was introduced to stop soil erosion, but in its native country, goats on the mountainsides kept it in check. In the south we don’t have goats roaming the hillsides, so it is an invasive plant. Does it stop soil erosion? Oh yes, along with covering everything in its path, including huge oaks and other hardwoods. I don’t have any Kudzu on my property, but I do have lots of other invasive plants such as Chinese privet, Japanese holly and honeysuckle, which I have given up trying to eradicate. These plants are tenacious, refusing to go. Great post!

    • January 4, 2018 8:30 pm

      Kathy, I know there are places where utility companies and highway departments hire goats to graze in areas where vegetation needs to be controlled. I think Orion would argue that bringing in a goatherd and goats to graze the Kudzu would be a better management approach than spraying it with herbicide.

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