Native vs. nonnative – can’t we all just get along?

Probably the most contentious gardening topic I deal with online is the native vs. nonnative plant debate. This, unfortunately, is a debate that is more based in emotion than science, and I don’t intend to stir that pot again. We’ve discussed it on this blog before (you can find a list of them here), and I’ve published both a literature review and a fact sheet on the science relevant to tree and shrub selection. What I want to do in this post is compare two research papers, both in peer-reviewed journals, that come up with dramatically different conclusions.

The first has been getting a lot of publicity on the web and in social media. It was published just two days ago, but because of widespread PR prior to release it appears over 37,000 times in a Google search. The title “Nonnative plants reduce population growth of an insectivorous bird” – and much of the prerelease publicity about the article spell doom and gloom. It’s a message that gets traction.

The second was published a year earlier and is entitled “Native birds exploit leaf-mining moth larvae using a new North American host, non-native Lonicera maackii.” It appears 194 times in a Google search, even though it’s been available for over a year.

Amur honeysuckle (Lonicera maackii)

The reason I’m singling out these two articles is they have completely different messages – and one of them is not being heard as loudly as the other. The first focuses on a single bird species, the Carolina chickadee (Poecile carolinensis) and its diet in urban landscapes. Their conclusion: “…properties landscaped with nonnative plants function as populations sinks for insectivorous birds.” Thus, any gardener who happens to use introduced ornamental plants in their landscape is made to feel guilty for starving their insect-eating birds. (As an aside with my manuscript reviewer hat on – this statement has no business being in an abstract as it overextrapolates the research on one species to include ALL insectivorous birds.)

Carolina chickadee (Poecile carolinensis)
Black-capped chickadee (Poecile atricapillus)

 

 

 

 

 

The second article has a different focus. It reports the feeding of black-capped chickadees (Poecile atricapillus) on the larvae of a leaf-mining moth (Phyllonorycter emberizaepenella). While leaf miners are common food items for chickadees, the point of this article was to document the host of the leaf-miner – a nonnative and particularly invasive species of honeysuckle (Lonicera maackii).

Honeysuckle leaf miner (Phyllonorycter emberizaepenella)

 

Honeysuckle leaf miner damage

 

 

 

 

 

Chickadees as a group are particularly adept at finding and consuming leaf miners, whose tunnels normally protect them from insectivorous birds. Chickadees move along branches,“examining leaves both above and below them; the chickadees sometimes scanned by hanging upside-down.” This makes it easier to find and extract leaf-miners, as the underside of the leaf is easier to tear open than the surface. And in fact this behavior is reflected among other species of chickadee and leaf-miner: “Similarly, in 15 years of study, Connor et al. (1999) never observed species other than Carolina chickadees (Poecile carolinensis) feeding on the larvae of the gracillarid Cameraria hamadryadella [oak leaf miner].” While these are not the same species of leaf miner studied in this paper, the point is that chickadees eat leaf-mining insects. And leaf-miners can obviously adapt to new food sources, including introduced plants. This is basic ecological science.

Oak leaf miner damage
Oak leaf miner (Cameraria hamadryadella)

 

 

 

 

 

 

Neither Craves’s article (the second of these two articles) nor that by Connor et al. (cited within Craves’s article) are cited by Narango et al. (2018 – the first article), even though both are certainly pertinent to the topic. But they don’t fit the narrative – which is that introduced plants are not good food sources for the insects that chickadees eat. So they are left out of the discussion, which by default is now biased – not objective. Not science-based.

And I don’t have a good answer to the obvious question – which is why we continue to demonize noninvasive, introduced plants in the absence of a robust body of evidence supporting that view.

 

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Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and an Associate Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

12 thoughts on “Native vs. nonnative – can’t we all just get along?”

  1. Good post. Forgive me if you have covered this already, but the University of Kentucky has done extensive research, which is ongoing, on pollinator plant preferences. You can read more at this link: https://uknow.uky.edu/research/uk-entomology-research-reveals-list-bee-friendly-plants
    Essentially, the research is revealing that preferences are all over the map, native AND non-native. Some are very attractive, some are not, and it has little to do with whether the plant is native. One of the highest scoring trees is Seven Son Flower. I have heard so many times that native pollinators only like native plants. Research is showing otherwise. As per your post, you could certainly pick out one non-native in this research and say it is not all that attractive to pollinators, but you could also pick out one native and do the same!

  2. I completely agree with the theme of your post and we have the same blinkered thinking and pro native propaganda over here in the UK
    Your post encapsulates a difficulty I have with gardening needing to be science and research based – the problem is which science?

    1. As I tell people during my seminars on scientific literacy – any paper that contradicts the existing body of science must clear a high bar and is therefore subject to close scrutiny. Science does evolve. But strong, incontrovertible evidence is required to overturn working hypotheses. In this case, the science strongly supports the use of trees and shrubs that provide habitat to wildlife regardless of provenance.

  3. Often the most difficult task in science is in figuring out what is the most important question to ask. It seems to me an important question for gardeners is how to design a garden that promotes insect diversity and wildlife habitat. What are the principles? You cannot answer this by doing countless studies of individual species or cultivars. You need to consider habitat structure, layering, microclimates and relationships with surrounding habitats. This is more of an ecosystem question than an individual plant question. We know that native ecosystems with diverse structures and species tend to promote high insect diversity. We don’t know very well how to create this with small gardens or restored habitats. It’s important to know as you point out that there is a lot more to the story than just looking at native vs non native. If you want to promote diversity in a garden then it’s important to first think about the garden not as an odd collection of plants but as an ecosystem that is part of a larger landscape. Whether or not a given plant is going to help promote insect diversity will depend not only on the chemistry & nutrition of its leaves and structure but also what grows around it. Always a good thing to encourage people to think about this! The fact that a chickadee can utilize insects in an invasive honeysuckle doesn’t necessarily tell us whether it is better to plant this species vs. a native honeysuckle or a diverse native ecosystem if your goal is to promote wildlife diversity.

    1. Actually, your comment that “We know that native ecosystems with diverse structures and species tend to promote high insect diversity” is not accurate. My literature review on the topic (mentioned in the blog) demonstrates that landscape structure and plant function is more important than nativity. Please read that article, which is hotlinked in the post.

      1. The comment “We know that native ecosystems with diverse structures and species tend to promote high insect diversity” is accurate. It does not imply that ecosystems must be native to promote diversity. It merely states that such native ecosystems tend to promote high insect diversity, and they do.

        1. Let’s not be silly. Ecosystems with introduced plants with diverse structures also promote high insect diversity. The subjective label “native” is unnecessary and suggests that nonnative systems wont’ do the same thing.
          Why not just say landscapes with diverse structures promote high insect diversity?

          1. Linda, please take a deep breathe and actually read what wrote. We agree. All I wrote was that it is true that native landscapes generally promote high insect diversity, and they do. There is plenty of research supporting that. There is also an increasing body of research which strongly suggests such diversity can be achieved in non-native or hybrid landscapes with diverse structures I referenced that in a previous reply. This is being demonstrated at many locations, including the Cincinnati Zoo and Botanical Gardens. CZBG is actively conducting counts to document insect diversity in such plantings and is publishing those results on an ongoing basis. The two statements are not contradictory and can be simultaneously true. So, I agree that “landscapes with diverse structures promote high insect diversity.” That could be a native landscape, a non-native landscape, or a hybrid landscape. Can’t we all just get along?

  4. The more the structure, the more diverse the insects that will come, should also be couched with an asterisk on plant function, as plant function varies by species. For example, some pollinator-dependent plants have high sugar content in their nectar, but low mineral nutrients, and vice versa. They co-evolved along with the local pollinators. Safe to say non-native plants are no different when it comes to function. If your garden-planted non-native gets munched by insects, or its berries get eaten clean by birds, then it’s serving some function other than just structure i.e. cover, though many gardeners intuitively don’t want to select plants that get heavily munched and instead select plants that look/stay relatively pristine all growing season. It’s the “invasiveness” by growing regions that gardeners should be concerned about. Non-natives that are invasive in a particular climate, while providing structure, can essentially be a biological desert when it comes to function due to their lack of “palatability”. Pair Lonicera maackii’s allelopathic leaf character trait with it’s seed productivity and you have a shrub that is spreading rapidly across both urban and rural eastern United States. Your comment “The subjective label “native” is unnecessary and suggests that nonnative systems wont’ do the same thing” [as native systems] for insect diversity is also subjective as it will also depend on the details of the component plants to determine if the individual insect diversity is interacting with an ecologically functional environment or merely attracted to the structure itself. Not black and white for sure tho! Thanks for the food for thought!

  5. Finding non-native plants in the forest near by home is disheartening. They shade-out and take-over a variety of habitats to the detriment of local ecosystems. Surely whether a non-native can support insects and this birds is not the only consideration.

    1. You’re talking about invasive species, which I am not including in my comments about nonnatives. Only a small fraction of introduced plants become invasive and degrade natural areas. Noninvasive, nonnative species are not a detriment to landscapes. You need to read the fact sheet that I linked to in the post. It discusses this issue in detail.

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