Ministry of Controversy

Chalker-Scott on Natives and Introductions

From Sustainable Landscapes and Gardens: Good Science, Practical Applications, the hot-off-the-presses book edited and co-written by Linda Chalker-Scott, Linda's own chapter on native plants and introductions (never the loaded terms "alien" or "exotic") deserves some attention here on the Rant.  That's because as much as we appreciate plant passions, we're also big fans of science, especially when it mighLindaMainCovert just clear the air caused by all those passions.

So I'm quoting extensively in hopes that Linda's unemotional assessment will break through the relentless overgeneralizations about both native and nonnative plants, and bring some civility to the topic.  Oh, and maybe reduce the "exotic guilt" about growing, say, hostas or daylilies that we're seeing mentioned with growing frequency.  (You want guilt-inducing?  Grow up in Richmond, VA hiding your mother's maiden name – Sherman – and your family connection to the Atlanta-burner himself.  Then go to college in the North and be held to account for, well, all of Southern history.  Interesting times!)

So let's starting with definition of "native".  According to Linda, that here-before-the-Europeans thing isn't as clear-cut as we think.  For example, the Ginkgo biloba is considered an Asian plant, yet its fossils can be found in Washington State, where it grew millions of years ago.  Concludes the good hort doctor: "Defining a plant as native based on what existed in a landscape before European immigration ignores the influence that earlier human cultures, animals, natural forces, and natural selection have on plant introductions and distribution."  And " This is not a rational approach to understanding the dynamic character of landscapes either in natural or urban areas."

Benefits and Drawbacks of Native Plants  (Ever seen that header before?)
She lists the well-known benefits (see any source on the subject), but also the missing caveats in almost all discussions of native plants: "Unfortunately, many of us live in areas that no longer resemble the native landscapes that preceded development…The combination of urban soil problems, increased heat load, reduced water, and other stresses mean that many native species do not survive in urban landscapes. … When site conditions are such that many native plants are unsuitable, the choice is either to have a restricted plant palette of natives or expand the palette by including nonnative species."

Landscape Uses for Native Plants
For parks and public areas that are minimally managed, Chalker-Scott recommends selecting natives that "are easily planted and require little care once established."  Not just any native plant.

And in developed areas: "Commercial and industrial sites and planting strips along streets and highways receive little to no care and are usually environmentally hostile and unsuitable for many natives. In addition to the typical problems associated with urban environments, these areas may be overrun with nonnative, invasive plant species, contaminated with pesticides and other pollutants, and contain small root zones with little available water or nutrition. So few native species can tolerate these conditions that we must consider supplementing our plant palette with better adapted, nonnative species."

Benefits of Introduced Plants (Again, ever seen that?) Italics added.

  • "There are practical, functional, ecological, and aesthetic reasons for using introduced species. From a practical standpoint, you may not be able to find many native plant species at your local nursery. If you limit yourself to a sparse selection, you decrease the potential biodiversity of your landscape."
  • "Introduced plants can provide functions that perhaps native species are unable to do in your landscape of interest." Functions like removing pollutants from the soil, or fixing nitrogen, as clover does. "The nature of many urban sites is such that native plants are unable to establish and survive", and nonnatives have proven in many cases to provide these functions, including providing for wildlife.
  • "Similarly, native species that are locally extinct can be replaced by nonnative members of the same genus and thus increase the biodiversity of the landscape."
  • "Finally, there are the aesthetic benefits of broadening your plant palette. Though it may seem less important from a scientific standpoint, in fact studies have shown that attractive landscapes can improve human health and well-being, to the extent that healing gardens are now common in many medical facilities."  (And can I add – aesthetic benefits often mean turning homeowners into passionate gardeners like me who've filled their yards with environmentally beneficial and sustainable plants.)

Drawbacks of Introduced Plants
Here she lists again the usual warnings, starting with the chance of invasiveness.  There's also the chance that imports could contain nonnative pests, parasites, or disease – stowaways – an outcome she calls unlikely because of quarantine and inspection by the USDA. 

The last drawback is the possibility that the introduced plant doesn't have genetic resistance to local pests and diseases.  That's one more reason reason to avoid buying brand new introductions – whether imports or hybrids or whatnot.  Because you never know – the latest and greatest could turn out to be another Windows Millennium Edition.

Click here for info about the book and how to order.

Posted by on February 1, 2010 at 5:20 am, in the category Ministry of Controversy.
Comments are off for this post

27 responses to “Chalker-Scott on Natives and Introductions”

  1. vicki says:

    Thanks for this post, Susan. This type of info is one of the major reasons I appreciate GardenRant.

  2. Leave it to Linda Chalker-Scott to put into clear words concepts that bounce around inside my head and never seem to form easily expressed ideas and arguments. Thank you for posting the highlights of her arguments. I’ll take good science over impassioned arguments any day.

  3. naomi says:

    Well, you didn’t grow up in Atlanta, like my bro-in-law, who obviously is related to you (of course, on his dad side he’s related to a famous general on the opposite side). Ashes help fertilize that ground, so more grows, and since less than 12% of the plants in Atlanta are native – due to erosion caused by cotton crops – all types of transplants must be welcomed there, and here in New Orleans.

  4. Laura Bell says:

    Excellent – love hearing well-reasoned discussions rather than passionate arguments on any subject. Linda put into writing what I’ve been thinking for a while now – our urban environment barely resembles the original landscape of the region. Why stick to plants that may not work in these changed conditions ? After all, sequoias were once native to Alaska, but you can’t grow them there now.

    Adding this book to my library wish-list …

  5. Claire Splan says:

    My biggest problems with the native plant movement have been how inadequately and misleadingly the term “native” has been defined and how it ignores the very important issue of diversity. It’s nice to see these issues treated intelligently and scientifically. It’s also nice to see a rational argument for not using natives in some feeble attempt to turn back the clock. Too many proponents of natives ignore the fact that soil and climate changes have completely altered the environment and there just ain’t no going back.

  6. Gloria says:

    So Linda Chalker-Scott says do not grow native plants because there is no valid reason???

    I guess I’ll go pull out all those successfully growing for several years now plants out in the garden.
    Rain garden out
    run-off pollution flow over that lawn and into the sewer.
    Pretty native plants you should be replaced with something from elsewhere.
    Why? Because she said so.

  7. how it grows says:

    Yes, I have heard about the “benefits of introduced plants” and the “drawbacks of native plants” because that’s the convential wisdom and it has been for some time. I as I’ve pointed out before, go to any nursery and you’ll quickly see where natives stand in the scheme of things (it’s not very high up). It seems like lots of bloggers have a chip on their shoulder about natives. Why are people so defensive? It seems like if someone suggests maybe we should try a different approach to our landscapes and try to incorporate more natives, they’re portrayed as being overbearing and saying we should plant natives exclusively, don’t truly understand soil conditions or habitat, are emotional rather than scientific and make people feel ‘guilty’.

  8. Carolyn Cates Wylie says:

    Gloria: Linda Chalker-Scott clearly did not say not to grow natives, much less to pull up the ones you already have. She said there are good reasons for using natives and also good reasons for using other plants.

    how it grows: Linda Chalker-Scott doesn’t sound defensive. You and Gloria sound defensive.

  9. how it grows says:

    Carolyn, I don’t know if Linda Chalker-Scott is defensive or not-I haven’t read the book. I’m just pointing out what I see happen on garden blogs whenever the topic of natives comes up.

  10. I take the same stance on natives as Linda, because it’s certainly not sustainable to keep planting natives in urban/suburban lots that have been altered so dramatically from the original habitat that some fussy natives might not survive. I think that if a non-native plant is growing well on your lot, that it’s most sustainable to let it keep growing, as long as it’s not on the list of invasives.

    That said, I belong to the Florida Native Plant Society and certainly encourage the planting of natives where appropriate. My list of rain garden plants for Florida are all tough natives that can withstand the standing water and the drought. We have a 7-month dry season.

    A good resource for Florida gardeners who wish to introduce natives in their landscapes is Gil Nelson’s “Florida’s Best Native Landscape Plants: 200 Readily Available Species for Homeowners and Professionals.” Gil provides details about the best growing conditions and likely companion plants for each of the 200 species.

    If we all pay attention, we can increase habitat with some tough natives and make it a little easier for our butterflies and birds.

  11. John says:

    Linda Chalker-Scott, Ginny Stibolt, Jeff Gillman are all my favorite gardening gurus – the right mix of scientific fact and love of nature. I hope more people read their words and get on board.

    For all the gardeners that scream about “only natives”, “only perennials”, “only xeric” or whatever they feel like screaming about – your voice is loud and it is also shrill and not backed up by anything other than emotion.

    I’m sorry, but I find it amusing to hear a bunch of white people yelling about invasives.

    forest… trees???

  12. how it grows says:

    Re: posting by John. See what I mean?

  13. Dan Mays says:

    Yesterday I attended the Annual Winter Meeting of the Iowa Prairie Network — certainly one of the leading native plant organizations in the Midwest.

    Linda Chalker-Scott’s “new information” does not sound new to us at all. In fact, it mirrors much of the information talked about at that meeting.

    The problem is the press that gets 10% of the information and proceeds to write articles espousing 100% of the story — poorly researched and misleading at best.

    True native plant enthusiasts want the truth. They want to eliminate the misconceptions because they are detrimental to everyone.

    If only we could get the lazy press to actually do some old fashioned research instead of just regurgitating the same old garbage being parroted in an old, shallow article they are foolishly calling “reference material”. Grrrr…

    Go Linda!

  14. Matt says:

    I’ve always wondered how closely related plants need to be to the “native” version to have the same benefits. Are “domesticated” daylilies that are simply different colors really worse than the wild orange ones? Are fruiting cherry trees worse than wild black cherries? Anyone out there ever hear someone address this?

  15. donna says:

    I have both natives and introduced plants in my SoCal garden, and they seem to all get along just fine — Toyons next to roses, sages next to, well everything…

    As long as you meet the plants’ needs, they all get along pretty well.

  16. Seems naive (Drawbacks of Introduced Plants)to think that incoming inspections will prevent the introductions the author cites. Various longhorn beetles, the lily leaf beetle, viburnum beetle, emerald ash borer have a history, recent or past, of avoiding detection. Current devastation is serious.

    The discussion of labels like invasive and noxious and exotic versus natives is similarly perplexing to me. Three years ago I stopped at a very well known, well publicized nursery in the state of Washington and found giant hogweed potted for sale. I challenged the owner and was told that it’s new, it’s architectural and it sells. I won’t write what I said.

    George Africa
    The Vermont Gardener

  17. Chris Upton says:

    Regarding the second issue (drawback) with introduced plants, it’s a more common situation that there are no native pests to afflict an introduction. Generally pests and diseases aren’t “generalists”; a particular insect or disease has evolved with it’s host/victim. One of the traditional advantages of introduction is precisely that they likely won’t connect with existing pests/diseases.

    Still, though I prefer to use natives where I can, I freely admit that the vast majority of introduced plants, used judiciously, aren’t likely to harm local ecosystems.

  18. sara says:

    “Benefits and Drawbacks of Native Plants”

    It is good to see the point that the landscape is different from what it was when all the indigenous plants were thriving and doing their native plant thing. When I walk past weed-choked abandoned lots, and unkempt parks, I see a lot of French broom. Did we not create the perfect conditions for some of these invasive species to thrive?

  19. I dunno….maybe I am naive, but I don’t understand what the huge fuss is about.

    I like natives. I am trying to plant more in my garden. I think other people should consider natives. I think nurseries should offer more natives, and stop selling invasives.

    That said, I still have plenty of non-natives in my yard. And will undoubtly buy more.

    Because I like natives, and think they should be the first place we look for plants for our yards, some people seem to think I am intolerant of other people’s choices. Not so.

    I realize that there are extremists on both sides of this argument, but for most of us, we just have a love for these plants and want to share that with others.

    Again, maybe I am naive to a lot of bad blood between the two “camps” but I don’t see what is so unusual or wonderful about a writer talking about the pluses and minuses of different plants (native or non).

    And if I am naive – leave me be – I like the way my rose-colored glasses go with my hair.

  20. Bob says:

    …As for Day lilies… They aren’t native…period (whether wild or “tame”).

    They are a problem in our few remaining prairies, where they form massive clumps, displacing native vegetation.

    How to remove? Round-up, backhoes…maybe nuclear explosives:)

    There are beautiful native lilies: Michigan, Turk’s Cap, Canada… but they have been systematically removed along with most native vegetation in many areas.

    I might point out that to “go back” to the Mesozoic (Dinosaur times) to claim that Sequoias are native to Alaska is pretty silly… there have been no major changes in environmental factors in the last few thousand years that would render our native plants suddenly deficient in some way!

    The point is that there is an entire vast interconnected environmental structure in Eastern North America, Western N. America, etc… each different, each a vast complex “machine”…

    How many parts can one remove before it no longer operates? That’s not saying one can’t garden with the plants one wants’ (with some exceptions).

    But… to write-off the entire eco-structure of the continent because we’ve made changes… borders on the irrational.

  21. Hoover says:

    Here there are native plant promoters, but the general and inevitable trend is towards a solid sea of concrete punctuated by strips of asphalt.

    The most destructive and agressive invasive species is not Giant Hogweed. It’s Homo sapiens.

  22. Town Mouse says:

    What I really appreciate about the “Bringing Nature Home” book is that the author has done solid research to back up his claim that more natives result in greater biodiversity.
    I haven’t ready this book, but I don’t see the research mentioned that substantiates the information presented. Is it all educated guesses and anecdotal evidence? One wonders.
    For example, here in California, even mainstream nurseries are carrying more and more natives, and are becoming more educated about them, so you can have your natives and your biodiversity too.
    Regardless, it does sound like an interesting book, and I’m glad to see an attempt at an unemotional (if not necessarily scientific) assessment.

  23. Town Mouse says:

    What I really appreciate about the “Bringing Nature Home” book is that the author has done solid research to back up his claim that more natives result in greater biodiversity.
    I haven’t ready this book, but I don’t see the research mentioned that substantiates the information presented. Is it all educated guesses and anecdotal evidence? One wonders.
    For example, here in California, even mainstream nurseries are carrying more and more natives, and are becoming more educated about them, so you can have your natives and your biodiversity too.
    Regardless, it does sound like an interesting book, and I’m glad to see an attempt at an unemotional (if not necessarily scientific) assessment.

  24. Genevieve says:

    There’s a five part podcast at Timber Press with Tallamy of Bringing Nature Home that explains something that nobody had ever explained before and is now making me rethink everything.

    He says that the way insects decide if a plant is the correct plant to lay eggs on is by using their legs to detect the chemical composition of that plant.

    He seemed to be indicating that if it’s not THE plant it wants to reproduce on, the insect won’t reproduce, it will die. Fewer insect species, fewer birds.

    The problem with learning about natives is there’s not a set of good answers on this stuff yet, so far as I can tell.

    Can I plant a named variety of a native plant? How native is native? What about things like Ceanothus that breed wildly with one another in the wild? Can I have a naturally-occurring variety of that and still be helpful to bugs and birds, or no? Nobody knows because there hasn’t been adequate research on this.

    I’m curious as to what research Chalker-Scott draws on to make her case, and whether she discusses Tallamy’s book and the facts he brings up in there.

    Because if the bend is entirely as to whether natives function better in the landscape than other plants, then it’s missed the point of natives. I think the type of person who buys a book on natives isn’t doing so because they aren’t sure about which plant performs better, it’s because we care about biodiversity and particularly supporting bugs and birds.

    If C-Scott does discuss the facts that Tallamy brings up, then I am very interested to see all the studies she cites, because there is a decided lack of info on that and it’d be fascinating to read more.

  25. Genevieve says:

    http://www.timberpress.com/podcast/

    Download the Tallamy ones to hear what he has to say – it was really game-changing for me.

  26. There is a wealth of information from the scientific literature on insect adaptability to new food sources. Here’s the lead sentence from a recent (Dec. 2009) article: “Plant invasions represent ecological opportunities for herbivorous insects able to exploit novel host plants.” Basic botany texts talk about the coevolution that occurs between plants and insects. Plant poulations evolve strategies to discourage herbivory, and insect populations evolve abilities to overcome defenses. Basic ecology texts describe population growth curves of introduced species: growth is exponential until carrying capacity is reached. The reasons growth slows is due to competition, predation, and disease. These are not new ideas. Species are not static. Populations continue to evolve. There will always be specialist species, whose survival is more tenuous when ecosystems change. We tend to focus on these species, whether they are pandas or orchids, and ignore the vast numbers of generalists.

  27. You might be interested in some of Dr. Tallamy’s research findings (Zuefle, ME, WP Brown and DW Tallamy. 2008. Effects of non-native plants on the native insect community of Delaware. Biological Invasions 10(7): 1159-1169. Here are some direct quotes from this article:

    1) Our data did not support the hypothesis that phytophagous insects are predominantly specialists.
    2) Based on Chi-square tests, there was no difference in the ratio of specialist to generalist insects found on Native, Non-native Congener, and Alien plant species groupings (P<0.05 in all pair-wise comparisons).
    3) There was no difference in species richness among Native, Non-native Congener, and Alien plant species in either year, nor in both years combined.
    4) Aliens held more insect biomass than did Non-native Congeners

    Quick translation: Most of the herbivorous insects identified in this field study were not specialists, and "alien" plant genera supported more insects than did introduced plant species with close native relatives (i.e. are in the same genus).

  • Follow Garden Rant

    Follow Me on Pinterest RSS