Doug Tallamy speaks…Art Shapiro responds…Million Trees fills in the gaps

Smithsonian Magazine published an interview with Professor Doug Tallamy, the entomologist who is committed to the eradication of non-native plants and most influential with native plant advocates in the United States.  The Smithsonian article gives Professor Art Shapiro an inadequate opportunity to respond to Tallamy’s assertions about the superiority of native plants.  Million Trees steps up to fill in the gaps in response to Tallamy.

  • The Smithsonian article says, “As a scientist, Tallamy realized his initial obligation was to prove his insight empirically. He began with the essential first step of any scientific undertaking, by applying for research grants, the first of which took until 2005 to materialize. Then followed five years of work by relays of students.”

The first study that Tallamy conducted is not mentioned in this article because it disproved his hypothesis:  “Erin [Reed] compared the amount of damage sucking and chewing insects made on the ornamental plants at six suburban properties landscaped primarily with species native to the area and six properties landscaped traditionally.  After two years of measurements Erin found that only a tiny percentage of leaves were damaged on either set of properties at the end of the season….Erin’s most important result, however, was that there was no statistical difference in the amount of damage on either landscape type.” (1)

  • The Smithsonian article says, “… insects tend to be specialists, feeding on and pollinating a narrow spectrum of plant life, sometimes just a single species. ‘Ninety percent of the insects that eat plants can develop and reproduce only on the plants with which they share an evolutionary history’…:”
Anise Swallowtail butterfly in non-native fennel. Courtesy

A “specialist” insect is rarely confined to using a single plant species.  Mutually exclusive relationships in nature are very rare because they are usually evolutionary dead-ends.  The study in which this claim about “specialization” originated, actually concluded:  “More than 90 percent of all insects sampled associate with just one or two plant families.”* There are over 600 plant families and thousands of plant species within those families.  Most plant families include both native and non-native plant species.  An insect that uses one or two plant families, is therefore capable of using both native and non-native plant species.  For example, there are 20,000 plant members of the Asteraceae family, including native sagebrush (Artemisia) and non-native African daisy.  In other words, the insect that confines its diet to one family of plants is not very specialized.

  • The Smithsonian article says, But he [Tallamy] thinks this [transition of insects to non-native plants] is likely to take thousands of generations to have an impact on the food web. Shapiro maintains he has seen it occur within his own lifetime.”

There are many empirical studies that document the transition that insects make from native to non-native plants within generations.  Professor Tallamy provides a few examples of such rapid transitions in his first book, Bringing Nature Home:  wooly adelgids from Asia have had a devastating effect on native hemlock forests in the eastern United States; Japanese beetles introduced to the United States are eating the foliage of over 400 plant species (according to Professor Tallamy), some of which are native (according to the USDA invasive species website).

Soapberry bug on balloon vine. Scott Carroll, UC Davis

The soapberry bug made a transition from a native plant in the soapberry family in less than 100 generations over a period of 20 to 50 years. The soapberry bug-balloon vine story is especially instructive because it entailed very rapid morphological as well as behavioral change; the beak length was quickly (a few years) selected for the dimensions of the fruit of the new host. (2)

  • Doug Tallamy claims that Art Shapiro’s findings are “anecdotal.” They are not.  Art Shapiro’s published study is based on nearly 40 years of data. (3)
Monachs in eucalyptus, Pacific Grove Museum

In a recent NY Times article about declining populations of monarch butterflies on the West Coast, an academic scientist explains how he used Professor Shapiro’s data set to study the decline:  “The monarch’s decline is part of a larger trend among dozens of butterfly species in the West, including creatures with names like field crescents, large marbles and Nevada skippers, said Matt Forister, an insect ecologist at the University of Nevada, Reno, whose conclusions are based on a nearly 50-year set of data compiled by Art Shapiro, a researcher at the University of California, Davis. “The monarch is very clearly part of a larger decline of butterflies in the West.”  Clearly, other academic entomologists do not consider Professor Shapiro’s data “anecdotal.”

The Burghardt/Tallamy study (4) does not contradict the findings of Professor Art Shapiro because Professor Shapiro is studying butterflies (not moths) in “natural areas” that have not been artificially created by choosing a limited number of plant species, as Tallamy’s study did.  In other words, the adult and larvae stages of butterflies that Professor Shapiro studies have more options, and when they do they are as likely to choose a non-native plant as a native plant for both host plant and food plant.  You might say, Professor Shapiro’s study occurs in the “real world” and the Burghardt/Tallamy study occurs in an artificially created world.

Dismissing observations as anecdotal is a well-worn rhetorical device.  Creationists often claim that evolution cannot be proven because the theory is based on millions of observations, rather than empirically tested by experiments. Yet, virtually all scientists are firm believers in the validity of evolutionary principles.

  • Tallamy dismisses climate change as a factor in plant and animal extinctions, preferring to place the blame solely on the mere existence of non-native plants.

This claim is contradicted by a multitude of studies, such as a collection of studies recently reported by Yale E360 that concludes:  “A growing number of studies show that warming temperatures are increasing mortality in creatures ranging from birds in the Mojave Desert, to mammals in Australia, to bumblebees in North America. Researchers warn that heat stress could become a major factor in future extinctions.”

Climate change is the environmental issue of our time.  When the climate changes, the vegetation changes.  When the vegetation changes, wildlife adapts or dies.  Non-native plants are one of the consequences, not the cause of climate change or plant and animal extinctions.


*Professor Shapiro has provided a caveat to this definition of specialization of insects in a private communication, published with his permission:  A couple of observations: Hardly any insects feed on entire plant families. Rather, they feed on specific lineages within those families, typically defined by secondary chemistry (which is the necessary releaser for oviposition and/or feeding behavior). The relationship was summed up symbolically by A.J.Thorsteinson half a century ago: feeding=presence of nutrients+presence of required secondary chemicals-deterrents-antifeedants-toxins. Thus the Anise Swallowtail species-group feeds on the carrot family, Apiaceae, but NOT on Apiaceae lacking the proper chemistry.But they DO feed on some Rutaceae (including Citrus) that, though unrelated, are chemically similar. That was worked out by Vincent Dethier in the 1940s and further developed by John Thompson at UC Santa Cruz. A whole slew of things require iridoid glycosides as oviposition and feeding stimulants. Most plants containing these were in the family Scrophulariaceae before DNA systematics led to its dismemberment, but one whole branch of Scrophs is chemically unsuitable. Milkweed bugs eat milkweed, but they also eat the Brassicaceous genera Erysimum and Cheiranthus, which are chemically similar to milkweeds but not to other Brassicaceae…and so on. Native vs. non-native has nothing to do with it.”  (emphasis added)

  1. Tallamy, Doug, “Flipping the Paradigm:  Landscapes that Welcome Wildlife,” chapter in Christopher, Thomas, The New American Landscape, Timber Press, 2011
  2. Carroll, Scott P., et. al., “Genetic architecture of adaptive differentiation in evolving host races of the soapberry bug, Jadera haematoloma,” Genetica, 112-113: 257-272, 2001
  3. SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433
  4. Karin Burghardt, Doug Tallamy, et. al., “Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities,” Ecosphere,November 2010

11 thoughts on “Doug Tallamy speaks…Art Shapiro responds…Million Trees fills in the gaps”

  1. There is a real problem with the definition (or lack of) for the word “native”. How can any species that is migratory (which is pretty much every species) be prevented from migrating? If one follows the logic (?) of nativism it essentially insists that species stop migrating when migration is an essential part of their nature.
    If I am not mistaken species migrate by any means necessary including ships, airplanes, wind, ocean currents, other animals, etc…..

    1. In a rapidly changing climate, migration is one of the most effective strategies for survival of plants and animals. In fact, “assisted” migration is rapidly becoming a common conservation strategy. Insisting that plants and animals stay where they lived 250 years ago on the West Coast and 400 years ago on the East Coast will doom them to extinction in a rapidly changing climate.

  2. In Portland, Oregon, some native plant enthusiasts criticize the “introduction” of asclepias speciosa because they insist there is not historical data to prove it is “native” to the Portland area, and suggest Portland “could become a population sink” for monarchs, with zero data to back up that assertion. But if monarchs are to survive, they must go where the milkweed is. If milkweed will grow here, and monarchs will come here to find it, which they do, what does it matter if it was here 100 years ago? It’s native to the region. Climate change will make Portland increasingly hospitable for milkweed. Monarchs have proven themselves resilient when given half a chance. Why not give ’em the chance? The assertion that milkweed did not grow in the Portland area is disputed, but some powerful groups are on the other side of the argument.

    1. The same bizarre strategy is being used by native plant advocates here in the San Francisco Bay Area. They instruct us NOT to plant milkweed (native or non-native) anywhere where there is no historical record that monarchs lived 250 years ago, such as the entire San Francisco peninsula. That’s the magic date native plant advocates have selected to confer “native” status on plants because it’s the date when Europeans first sighted the San Francisco Bay.

      I can’t explain this policy because it doesn’t make any sense to me. I consider it an example of the senseless ideology that is trying to dictate what plants are allowed to live here. The environment has changed drastically since Europeans arrived, the climate most notably. It seems illogical to me to try to prevent plants and animals from moving in response to those changes. That’s how they will survive. It makes even less sense when herbicides are used to eradicate harmless plants that are useful to wildlife.

      Thanks for your visit. Thanks for telling us what is happening in Portland. I’m sorry to learn that Oregon is also in the death grip of the native plant movement.

  3. There is a complete lack of consideration, or perhaps understanding as well, about rapidly increasing loss of biodiversity (which encompasses diversity within and between species as well as diversity of ecosystems). Simply standing aside while native species of any kind disappear because nonnative species can compete with them for resources such as space, moisture, nutrients and light without the burden of competing with organisms that control their numbers is foolish in the extreme.

    Webmaster: The existence of non-native plants and animals is not the primary cause of the loss of biodiversity. Loss of habitat is the primary cause due to development and conversion of natural vegetation for agricultural purposes. Climate change and pollution (especially pesticides) are also important factors. Here is one of the recently published studies that identify the factors in declining insect populations:

    As we lose native habitat anywhere on Earth, we lose species dependent on that habitat and that has ramifications throughout the entire web of life. Your dogma, if widely adopted, will lead to increased simplification of the biotic pyramid that can never be nearly as stable as a highly diverse one. Let’s forget for a moment the intrinsic value of native species and native ecosystems (rather than sub-optimal habitats) in which they flourish best.

    Webmaster: As the article on which you are commenting says, there is no evidence that native species are “intrinsically” more valuable than non-native species. There are a multitude of studies that find equal number of species in native habitat compared to non-native habitat. Furthermore, if native habitat is no longer adapted to current environmental conditions, eradicating non-native habitat (especially with pesticides, as commonly done) will result in a barren landscape. In other words, eradicating non-native habitat that is adapted to current environmental conditions reduces biodiversity.

    Given human self-centeredness and the tendency for emotions to overrule reason, I’ll make an argument to appeal to those characteristics. We do not know at what point most species, including our own, may face extinction as there is a cascading effect already evident. Current rates of extinction are two orders of magnitude greater than background rates and are trending toward rates that are three orders of magnitude greater. As E.O. Wilson observed: “One planet, one experiment.”

    Webmaster: Extinctions have not been caused by the mere existence of non-native plants. Here is one study about the primary reasons for extinctions: Maria Dornelas, et. al., “Assemblage times series reveal biodiversity change but not systematic loss,” Science, April 18, 2014

    I will suggest that you visit the following link for a basic primer on the leading causes of biodiversity loss. You can then read other pertinent chapters to learn about why biodiversity loss is the real, perhaps final, crisis facing humanity. It’s quite easy for the objective thinker to connect the dots.

    Click to access document.273.aspx.pdf

    Webmaster: This document says, “Loss of habitat area through clearing or degradation is currently the primary cause of range declines in species and populations.” In other words, this document corroborates that the existence of non-native plants is not the primary cause of biodiversity loss.

    Finally, you may wish to read last the [May 2019] Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services: .

    Webmaster: Have YOU read this voluminous document? I very much doubt that it claims the existence of non-native plants is a major driver in the loss of biodiversity. If so, please provide a specific quote from this document that makes such a claim. I can’t find one.

    Here is an article about a study done in preparation the next meeting of the UN Convention on Biological Diversity (CBD) in October 2020: The scientists, led by Conservation International, used data on almost 290,000 species, to make this recommendation about reducing anticipated plant and animal extinctions: “Limiting climate change to 2 degrees Celsius and conserving 30 percent of terrestrial area could halve the risk of plant, bird and mammal extinctions compared to the consequences of uncontrolled climate change and no increase in conserved areas…” In other words, the UN Convention on Biological Diversity does not agree that the eradication of non-native plants will prevent extinctions or increase biodiversity.

    You would benefit from some reading on the subject as well. The “basic primer” for my viewpoint is Mark Davis’s Invasion Biology, Oxford University Press. My viewpoint is based on reading over 100 books and hundreds of scientific studies, attending classes, and collaborating with academic scientists. If you will read some of my articles, you will find that they are based on specific books and studies and citations are provided.

    1. Dear Walter,

      I’ve been observing the natural world for virtually all of my life, and landscaping with wildlife in mind for 50 years. The real reasons for our diminishing biodiversity is not a dearth of native plants. Rather, it’s the long list of things people overlook and prefer not to deal with: an overpopulation of deer in many areas; the ubiquitous–and usually unnecessary–lights burning everywhere; a degraded environment (soil and climate changes) that has resulted from an explosion of development due to the explosion of the human population, etc. Additionally, nonnative plants are not generally competing with natives because they fill in areas natives are not filling (two objects cannot fill the same space; hence plants come up in bare spots). As for herbivorous insects limiting the plants they feed upon: This does not happen in a properly functioning environment (the point of my book, The Nature-friendly Garden, 2006). Embracing nonnative plants–especially those deemed “invasive” only because they’re able to survive the human-caused impacts so detrimental to plants and animals–is the way to impart resilience to our environment. Refusing to recognize the new world we live in is what’s truly foolish in the extreme.

      Marlene A Condon, Author/Photographer, The Nature-friendly Garden: Creating A Backyard Haven for Plants, Wildlife, and People (Stackpole Books)

  4. Doug Tallamy sees himself as a crusader against so-called invasive plants, but he’s more like Don Quixote. He’s trying to rid the U.S. of “invasive” plant species, which equates to tilting at windmills: He’s fighting a war that’s impossible to win against an adversary he misinterprets, and his course of action is based upon a misapplied idealistic justification.

    Today’s world is not that of 50 years ago and it’s impossible to return to it. There’s been much development resulting in disturbed soil along roadsides, around houses and other new structures, and along trails in local as well as national parks. In addition, many farm fields have been abandoned.

    All these areas host numerous alien plant species for one reason: the ground is degraded (compacted and nutrient-/organic matter-poor) and inhospitable to most native plants. Only colonizer plants can grow in such areas to work on replenishing the soil for later use by native plants, but (I dare say), the native colonizers (grape vines, Redcedar, pines, Black Locust, and Broomsedge) don’t offer the diversity of benefits to wildlife that species such as Autumn Olive do.

    The assumption that certain alien plants have pushed out native plants is a myth. People who are younger than I am or who have never paid much attention to the natural world until noticing an abundance of alien plants along highways, etc., misinterpret what they see. They don’t recognize the importance of prior history of the landscape to understanding correctly what they are viewing.

    Thus, Doug Tallamy buys a former hay field filled with nonnatives and he immediately thinks these plants pushed out the native oaks he’d rather see in their place. But oaks are climax species; the field must first go through successional stages of field to shrubland, and only then—when the soil has been vastly improved—to forest.

    Everyone should, indeed, try to grow as many native plant species as possible to support those organisms that feed upon them. However, Tallamy’s push for folks to rid areas of nonnative plants that are already providing well for wildlife doesn’t help the environment. Leaf-feeding insects are not the only organisms that matter.

    At a local natural area, an entire field (yes, it was once a farm field) of Autumn Olive was destroyed, creating a huge loss for pollinators that used it when in bloom; for mammals and birds that ate its fruits, and for winter birds and squirrels that fed upon its late-winter/spring buds.

    Will native plants grow in its place? Not easily, thanks to an abundance of deer. And in suburbia where Doug Tallamy thinks everyone can go native, people would need to cage native plants, just as he admits to doing. But he’s hidden on his 10 acres; in suburbia, no one wants to look at caged plants for their home landscape.

    Then there’s climate change that has already caused years of drought coupled with temperature extremes. Most native species suffer under these conditions while nonnatives remain strong and healthy. Idealism under these circumstances is foolhardy.

    Lastly, Doug Tallamy has made people believe that so-called invasive plants cause more harm to the environment than pesticides that are poisoning our world. Herbicide usage has gone up tremendously as people fight this inane battle. Even government at all levels has gotten in on this war, wasting millions of our tax dollars on fruitless battles that don’t really change anything–other than destroying habitat being used by many species of wildlife.

    As President John F. Kennedy said (Commencement Address at Yale University, June 11 1962): “The great enemy of truth is very often not the lie–deliberate, contrived and dishonest–but the myth–persistent, persuasive and unrealistic. Too often we hold fast to the clichés of our forebears. We subject all facts to a prefabricated set of interpretations. We enjoy the comfort of opinion without the discomfort of thought.”

    Sincerely, Marlene A Condon

  5. If some insects can evolve “within generations” to use non-native plants, then convince me that means there need be no concern about those species that can’t make the “transition,” e.g., the Karner blue butterfly. There are many other examples I would be happy to furnish–and not just invertebrates but vertebrates as well.

    Webmaster: Yes, Karner blue is dependent upon lupine for its host plant—as are some other rare butterfly species such as Mission blue. Nothing in the natural world can be reduced to the absolutes you wish to impose. This website does not advocate against native plants. Rather, we object to eradicating non-native species, especially by using pesticides. Here is a description of the activities that are harmful to Karner blues. Note that none of these activities are related to the existence of non-native plants: “According to reviews and general field observations, management activities that are typically harmful to Karner blue butterflies include management that increases deer and/or grouse populations, close-cropped grazing, frequent or poorly-timed mowing, plowing, use of herbicides that kill lupine or nectar plants, and use of pesticides that are detrimental to Karner blue butterflies, ants they associate with, or pollinators of species they use for nectar.[6][7][27][32] Information on the impacts of an insecticide on Karner blue butterflies[43] and some herbicides[44] on Karner blue butterflies as well as lupine and nectar species are available.” (Wikipedia)

    And species do not “migrate by any means necessary.”

    Webmaster: I did not make that statement. My understanding of what was intended by the person who made the statement is that species move around the planet—and always have–by many different means, including methods that are unrelated to human activities. Your responses to that statement are a mixed bag of irrelevant examples of migration as well as impossible migrations. For example, coastal redwoods live within a narrow range of horticultural requirements that limit their ability to migrate on their own or when planted by humans. Here in California, where redwoods are popular, they are often planted in places that are too hot and dry, where they will not survive. Likewise, mangroves will not tolerate freezing temperatures of Cape Cod. Like all other ecological principles, assisted migration is NOT always possible. Nothing in nature is an absolute rule.

    British Columbia will not experience an in-migration of coastal redwoods; Cape Cod will not host mangroves; zebra mussels didn’t stow away on freighters to get into the Great Lakes; European starlings did not fly to North America; Burmese pythons did not sneak aboard a plane or a ship; and Asian carp did not swim to the Midwest. Many species survive in situ until human interference or a natural disaster moves, or in many cases, eliminates them.
    Assisted migration is “rapidly becoming a conservation strategy.” I would love to know more about that. Imagine moving whole, or even parts of, complex ecosystems around like pieces on a chessboard, anticipating every possible outcome given we surely must know exactly how climate change will affect every region, correct? What a golden opportunity for an entrepreneur. Now all that is needed is to find sufficient vacant space in which to install highly complex and completely functional ecosystems, then duplicate the effort many times over. Surely” if we build it, they will come.” But I imagine that since all living things are equal to similar organisms, we can afford to cut a few corners on what species we move. Maybe we’ll find the perfect new home for zebra mussels, Burmese pythons, starlings, passion flowers and butterfly bush and go from there. Oh, and yes, eucalyptus trees, this time complete with koalas. Tamarisk in the riparian areas of the Southwest has been a raving success, has it not? Or maybe we can just scatter everything about willy-nilly and see what happens. Oh, wait…we’ve already done that!

    Webmaster: Burmese pythons may not have migrated on planes, but the brown tree snakes of Guam DID arrive in the wheel casings of planes. Asian carp DID swim to the Midwest from distant places where they were introduced for aquaculture and zebra mussels DID arrive in the Great Lakes in the ballast of ships. Tamarisk is essential to the survival of the endangered Willow Flycatcher, just as eucalyptus is essential to migrating monarch butterflies in California.

    Once again you take a black and white approach to every ecological issue. Of course, assisted migration is not a universally useful strategy. Like every conservation strategy, there are pros and cons to everything we do in nature. For example, eradicating one species of non-native plant may benefit one animal species, but it will probably harm another animal species that depends on that plant. A simplistic approach to these complex issues is not possible because nature defies such generalizations. Nature cannot be put in the strait-jacket you wish to put it in.

    And yes, I did read the voluminous IPBES document to which I referred. I read science almost exclusively. I have no interest in fiction whatever, even when disguised as science.

    Webmaster: If you read the document, perhaps you can quote it as supporting your claim that non-native plants are the biggest threat to biodiversity, as I suggested.

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