Baseless generalizations in Doug Tallamy’s Nature’s Best Hope

Doug Tallamy’s latest book, Nature’s Best Hope, continues his crusade against non-native plants.  He now calls invasive plants “ecological tumors.”  You might be tempted to respond that invasive plants are a small subset of non-native plants until you realize that Tallamy calls 3,300 plant species in North America “invasive.”  There are approximately 6,500 species of native plants in California, which reminds us that introduced plants are often a significant portion of our urban landscapes.  The title of Tallamy’s book is a misnomer.  Nature is not confined to native plants, as Tallamy wishes it to be.

Tallamy makes no meaningful distinction between “invasive” and “non-native.”  The classification of berry-producing non-native plants as “invasive” is a case in point.  Although Himalayan blackberries are invasive, most other berry-producing non-natives in California are not.  Cotoneaster, pyracantha, and holly are a few examples of berry-producing plants being eradicated in the Bay Area that are not inherently “invasive.”  They spread because birds eat the berries and deposit the seeds elsewhere.

Cedar Waxwings in crab apple tree. Wikimedia Commons

Eradicating berry-producing plants deprives birds of an important source of food.  If herbicides are used to kill the plant, the birds are also exposed to harmful chemicals, known to reduce reproductive success and cause other sub-lethal health issues in wildlife. In the case of Himalayan blackberries, they are frequently eaten by children and adults, who are then exposed to the herbicides used to kill the shrubs that are often widespread in our parks and open spaces.  San Francisco’s Recreation and Park Department sprayed blackberries in San Francisco’s parks and open spaces 23 times in 2019.

Tallamy and his nativist allies claim that native plants are beneficial to wildlife, especially birds.  How can they claim that eradicating berry-producing plants benefits birds?  They do so by claiming that native berries are more nutritious than non-native berries.  In particular, they claim that native berries contain more fat than sugar and that migrating birds require berries with high fat content.   Tallamy cites one study in support of that claim, a study that compared fat and sugar levels in the berries of 9 species of plants in the Northeast, 5 native species and 4 introduced species.  They found that the native species they analyzed had more fat content than the introduced species they analyzed. (1)

Generalizations unsupported by evidence

From that single study of nine plant species, Tallamy generalizes that berries of plants that are considered native in Asia are less nutritious for migrating birds than the berries of native plants in North America are. (None of the nine plant species studied occurs in California.)  Does that generalization make sense?

  • Tallamy does not provide any evidence that there are fewer migratory birds in Asia, or that the nutritional needs of migratory birds in Asia are different than those in North America. In fact, looking at the migratory patterns of birds confirms that migratory routes of birds span several continents.  The intercontinental flights of birds sometimes span both Asia and North America.  There is no logical or evidentiary explanation for berries of native plants in Asia being uniformly less nutritious than native plants in North America.
  • However, Tallamy offers evidence of the similarity between plants in Asia and closely related plants in North America. Wooly adelgids quickly made a transition to native hemlocks when they arrived in North America from Asia because its native host in Asia is closely related to the American native.  The adelgid has “all but eliminated hemlocks” in America, according to Tallamy.  The emerald ash borer has killed millions of ash trees in America when it arrived from Asia, where its native host was closely related.  On one hand, Tallamy claims that native plants in America are unique, completely different from plants in Asia, yet he recognizes that insects from Asia rapidly adapt to closely related host plants in America.
  • Asian species are not so foreign to America as Tallamy wishes us to believe. There are relicts of vegetation that extended completely around the Northern Hemisphere about 50 million years ago that were broken up by a combination of mountain-building and climate change. Tree of Heaven, Gingko, and Dawn Redwood, now considered introduced trees from Asia, occurred here naturally during that geologic period.  Tallamy says we must confine our choices to plants that “share an evolutionary history.”  In fact, many plants now considered non-native shared an evolutionary history with plants now considered native. Trees are time travelers, marching to the beat of the Earth’s geologic and climate drum.  Now they must be on the move to survive our changing climate.  We should not stand in their way.

Such generalizations unsupported by evidence are typical of Tallamy’s work.  In “Native plants improve breeding and foraging habitat for an insectivorous bird,” Tallamy and his collaborators conclude, “We demonstrate that residential yards dominated by nonnative plants have lower arthropod abundance…that function as population sinks for insectivorous birds.”  The data provided do not support such a broad generalization.  They studied one species of bird, in one geographic location, in a short period of time.  They inventoried arthropods for two years in a single month time-frame.  They quantify only one variable (plant foliage biomass) in addition to the nativity of plants, the abundance of insects, and the breeding success of one bird species.  They have not taken into consideration intervening variables such as variations in temperature, rainfall, pesticide use, etc.  The bird species studied is abundant within its range.  Its conservation status is “Least Concern.”  The abundance of this bird species does not justify the dire predictions of Tallamy’s study.

In conclusion

I have focused on just one of the many controversies discussed in Doug Tallamy’s new book.  I haven’t touched on the two most fundamental errors in Tallamy’s work:

  • Tallamy underestimates the speed of adaptation and evolution. There is ample evidence of rapid adaptation to non-native vegetation, including Tallamy’s examples of wooly adelgid and emerald ash borer making a quick transition to North American native trees after arriving from Asia.
  • He exaggerates the degree of specialization among insects. For example, he claims that 30% of native bees are “host-plant specialists,” yet Bees of the World (Michener, Johns Hopkins University) estimates a global average of 9% of bee species use plants within the same genus and it is “exceedingly rare” for bee species to be confined to only one plant species.

We have explored those issues in Tallamy’s work in previous articles:

  • Doug Tallamy claims that insects eat only native plants, yet his own study proves otherwise: HERE
  • Doug Tallamy claims that non-native plants are “ecological traps for birds.”  HERE is an article that disputes that theory.
  • Doug Tallamy claims that native and non-native plants in the same genus are not equally useful to wildlife, but he is wrong about that.  Story is HERE.
  • Doug Tallamy advocates for the eradication of butterfly bush (Buddleia) because it is not native.  He claims it is not useful to butterflies, but he is wrong about that.  Story is HERE.
  • Doug Tallamy publishes a laboratory study that he believes contradicts field studies, but he is wrong about that.  Story is HERE.
  • Doug Tallamy speaks to Smithsonian Magazine, Art Shapiro responds, Million Trees fills in the gaps:  HERE

(1) B. Smith, et. al., “The value of native and invasive fruit-bearing shrubs for migrating birds,” Northeastern Naturalist, 2013, 20(1): 171-84.

16 thoughts on “Baseless generalizations in Doug Tallamy’s Nature’s Best Hope”

  1. What comes to mind is Darwin’s book the Beak of the Finch. As I recall the finches would rapidly evolve their beak shape according to the proliferation of certain types of seed producing plants.
    Bird watching has been a family trait for generations. The birds don’t seem to check the passport of the berries and seeds they eat. But they can’t eat the food sources that have been cut down or poisoned.
    one thing about “native” that has always bothered me is who exactly determines the range. If a plant is “native” in say 100 square miles but it supplies food for “native” birds and mammals that range for thousands of miles how is that determined?

    1. Beak of the Finch (by Jonathan Weiner about finches in the Galapagos identified by Darwin) was also very helpful to me to understand natural selection and how rapidly it can occur in a rapidly changing environment. Here’s one of my articles about Beak of the Finch: https://milliontrees.me/2012/08/28/darwins-finches-an-opportunity-to-observe-evolution-in-action/

      Native ranges are defined by invasion biology and the native plant movement based on where plants and animals lived prior to the arrival of Europeans. On the East Coast, that’s about 400 years ago. Here in the Bay Area the magical date is 1769, the first record of Spanish explorers in this area. Unfortunately, nativists are ignoring that the ranges of native plants have changed and will continue to change. When native plants and animals migrate into new territories, they are often killed. The barred owl is an example of a bird that is being killed because it is trying to expand its range.

  2. “Ecological tumors”?!!!!! Wow, that man must spend a significant portion of his time thinking up these kinds of comments to catch people’s attention. I’d say “invasive” plants are more like ecological cures for being able to withstand tough environmental conditions (that are perhaps the main reason for their seeming invasiveness) and thus they are helping our wildlife to survive.

  3. Regarding (again) Tallamy’s suggestion that “invasive plants [are] ecological ‘tumors’”:

    Tallamy’s tumor metaphor has only one purpose: to metastasize throughout peoples minds a manipulative message of fear of, and hatred for, these plants. But while the word “tumor” immediately brings to mind “bad” and a call to action to do something to get rid of it, in reality there are benign tumors that are not a problem. It’s critical to know when to act and when it’s not necessary. In other words, people shouldn’t take Doug Tallamy’s comments at face value; they should get a second opinion, just as one should do when a medical diagnosis can bring serious consequences.

    For example, a dermatologist once told me I had a cancerous spot on my leg and prescribed a $1200 (!!) cream for me. A second opinion saved me from dishing out that enormous sum of money (serious monetary consequences, in this case) for a problem I didn’t actually have.

    Unfortunately, invasive-plant activists don’t question Tallamy, whose information they believe to be inerrant–but it’s actually chock full of errors. When people follow his seriously uninformed advice, they bring harm to the environment.

    It’s easy to know the truth about the natural world: just go out there and observe it for yourself.

    Sincerely,
    Marlene

  4. This article is simultaneously alarming and amusing. It is clear that the author had no intent of representing Tallamy’s views accurately. In _Bringing Nature Home_, Tallamy literally states that some native generalist herbivores seem to show a preference for certain nonnative plants, citing Parker and Hay 2005 (pp. 53-54; ch. 5). He then goes on to elaborate on research he is performing to test his own theory and outlines his preliminary findings.
    Tallamy never says that all nonnatives are invasive; in his lectures, he emphatically draws a distinction between the two, and even suggests that property owners use nonnative species (e.g. _Lagerstroemia indica_) without guilt. He contends that the plant communities we use in our home landscapes should primarily consist of species that are actively participating in the ecosystem, and contends that natives tend do a better job of it. This is radically different from the claim you put into his mouth by quote-mining.
    I hope we can have a civil discussion about this, but given your propensity to misrepresent Tallamy (who I disagree with on many things), I have reservations.

    1. The article on which you are commenting is about Tallamy’s latest book, Nature’s Best Hope in which he says specifically that there are 3,300 “invasive” plant species in North America. In 2018, USDA reported that there are 6,275 non-native plant taxa (that would include sub-species, a larger number than exclusively species) established in the contiguous US. https://pubs.usgs.gov/of/2018/1156/ofr20181156.pdf That suggests that Tallamy considers over half of non-native plant species “ecological tumors” (a literal quote from Nature’s Best Hope). I am not “quote-mining.” I am quoting from his most recent book, which you are not quoting.

      The article on which you are commenting is about a specific claim in Nature’s Best Hope that berry-producing non-native plants are less nutritious for birds than native berries based on a single study of 9 plant species, comparing 5 natives and 4 non-natives. The point of the article is that this is insufficient evidence that the plants in question are inherently “invasive.” This is a specific example of the mislabeling of non-native plants as “invasive” that are not, in fact, invasive. Not only are these plants being pointlessly eradicated with herbicide (of which Tallamy himself does not approve), their loss is a loss for birds who eat them. This is an example of plants that are “actively participating in the ecosystem” and should not be eradicated.

      1. Just curious as to how much time milliontrees have spent outdoors calculating and documenting just in Maine, just as a starting point. Along the roadways, the highways, the towns, the neighborhoods, the fields, along the shores, and more…Maine is being smothered by “invasive plants”. Invasive plants/species are now known and seen by everyday eyes as a large contributor to the loss of birds and insects. Our food chain and our food webs. Our critical food shortages. This destruction of our biodiversity and ecosystems is happening so fast it is real-time and damage and demise of the economies of our natural resources, all documented over many years. Our extinction crises are as critical and severe as our climate emergency. The crisis is so severe that children notice as well as the millions who do not have any specific training. Thank you.

        1. Your observations are consistent with mine. Non-native plants thrive and outcompete native plants on disturbed land, such as roadsides. This article published by Bay Journal, serving 100,000 readers in 6 states around Chesapeake Bay explains: https://www.bayjournal.com/opinion/forum/let-invasive-plants-do-their-job-so-the-natives-can-take-over/article_7387fc70-93c6-11eb-a929-03fb0e9b107b.html

          The success of non-native plants is a symptom of changes in the environment, not the cause. As this article explains, non-native plants prevent erosion of barren ground and restore damaged soil by fixing nitrogen in depleted soils. They provide wildlife habitat after vegetation has been lost to development.

          In the long-term non-native plants that are adapted to changes in the climate will be the landscape of the future. When the climate changes, the vegetation changes. This natural sequence of events has been demonstrated repeatedly for millions of years. When we try to eradicate non-native plants with herbicide, we are exacerbating the damage that has created opportunities for plants that can tolerate disturbance.

          Ironically, the author of the Bay Journal article begins her article just as you begin your comment, by inviting people to use their eyes while putting their dogma aside and opening their minds to the reality of changes in the environment caused by human activities, not by non-native plants.

      2. The underlying point to Tallamy’s books is that the non-native plants do not support the foundation of the ecosytem: the insects. Sure, birds can eat berries and seeds from non-natives. Butterflies can get pollen from some non-native plants. But most bees can access only certain colors and shapes of flowers. Buterflies and other insects have evolved with the native plants, and only recognize them for laying eggs on, and the caterpillars can only digest the leaves of their specific host plants due to the chemicals plants produce in the leaves. Birds need those caterpillars to feed their chicks (it takes about 6,000-9,000 caterpillars to raise one brood of 5 chickadees) long before they can eat non-native berries.
        Invasive plants can still “invade” by natural means. Oriental bittersweet is literally out of control in the Northeast, spread by birds eating the berries and pooping out the seeds. The eat the berries because the bittersweet has crowded out, shaded out, or strangled out other sources of food, but they contain little fat to help the birds survive the winter, and are so indigestible the berry is mostly intact when it is excreted, which spreads the plant. Other invasives put out leaves earlier than our natives, which denies them light to grow.
        Frankly, this article missed, and misrepresented, the entire point of the book. The negative effect non-native plants, whether invasive or simply foreign, have is directed on the insects that pollinate the planet, break down plant and animal waste, spread seeds, and are food to many other animals. Birds might find adequate nutrition from certain non-native plants, but if they can’t find enough insects, mainly native caterpillars (we have invasives there, too!), to feed their chicks, then there will be no chicks. It’s all interconnected and the keystone is native plants to feed our native insects.

        1. Well said! And true. I’ve been gardening with both native plants and non-natives since the 1970s, so I’ve seen in my yard the points he is making.
          It’s not clear from this site which commercial interests are fueling this windy, slanted critique against Tallamy, who signed my copy of his book with this advice, “Garden as though life itself depend on it.” But slanted they are with “explanations” that omit facts an skew the argument.
          Reveal yourselves, please.

          1. There are no “commercial interests” in this blog. I derive no economic benefit from my website. I don’t sell books or make paid presentations to the public. I don’t use my name on my website because of the personal attacks I have experienced.

            I must use my name when I write or speak at hearings about projects on public lands, so I have experience with the name-calling and personal attacks that those provoke. I have been chased down the hallways of city hall. I have had a rock thrown through my car window. I have had threatening letters delivered to my home.

            I am a member of the general public who has 20 years of experience with native plant projects in public parks and open space in the San Francisco Bay Area. These projects have used hundreds of gallons of herbicide for over 20 years and they continue to apply herbicides annually on the plants they don’t like that aren’t going anywhere. There are more non-native plants now than there were when they began the crusade against them.

            What you do in your own garden is entirely up to you. If you prefer native plants, by all means plant them. The focus of my advocacy is on public parks and open spaces that are owned and funded by the public. If you don’t find my blog useful, don’t read it.

            Yours is the third request for my identity in the past few weeks. The more pressure I get to give my name, the more reluctant I am to give it. If you lived in the San Francisco Bay Area, you would know who I am because I can’t participate in the public process anonymously. You have no legitimate reason to know my name and I don’t need to know yours.

          2. This reply is directed at milliontrees, but I didn’t see a reply button there. First, I’m sorry you have to put up with all that. People should know better than to use violence against people they disagree with. Judging by the fact that you’re still online answering questions, threatening you seems to be a pretty ineffective method of opposing you (in addition to the fact that it’s obviously wrong). Second, I don’t think that people should completely ignore the native/nonnative/invasive status of garden plants. They should definitely consider any plant’s effect on the ecosystem before they plant it. That doesn’t mean they have to plant all natives, but as Tallamy repeatedly emphasizes in his books, what we do with the land matters. As an activist, you obviously know that. It will make a difference for an endangered species if everyone chooses plants that support that species. It will make a difference for biodiversity if most gardens support a variety of plants and animals of all sizes. That brings me to my third point. Maybe you were a little too hard on Tallamy in your article. People might be more likely to hear you out if you also point out all the areas where you and Tallamy agree.

            The name I made up is based off of your name (I’m talking about milliontrees, not your real name). I hope you don’t mind.

          3. I have re-read the article on which you are commenting because I take seriously your suggestion that I am “being too hard on” Doug Tallamy. Although I am sorry that the tone seems harsh to you, my reading of the article is that it is focused on the factual inaccuracies in Tallamy’s books and studies. I am specific about those inaccuracies, so I won’t repeat them here.

            Why do I defend the need to inform the public of the facts that contradict Tallamy’s publications? Because of the consequences when public land managers justify their destructive projects by citing Tallamy’s work. Important food sources for birds and pollinators are being killed based on misinformation. Valuable habitat is lost. Sheltering urban forests are destroyed.

            Tallamy doesn’t endorse the use of pesticides (including herbicides), yet herbicides are the primary tool of all native plant “restorations” that always begin by killing non-native plants. Tallamy doesn’t specifically tell people to kill non-native plants, but that’s how his work is interpreted and used.

            I have defended our urban forest and novel ecosystems for over 20 years. Doug Tallamy’s publications are the only source of information that the promoters of those destructive projects use. Hence his work is my primary target. If he weren’t cited by every native plant advocate and public land manager, he would not be my target. I debunk Tallamy’s publications rather than attack him as person. I will continue to do so as long as his work is used to justify the destructive projects I oppose.

  5. Yes, I understand the point of Tallamy’s books. The problem is that much of what he says is inaccurate. He exaggerates the degree of specialization of insects and he underestimates the speed of adaptation and evolution. Some insects use as food and host only one or two families of plants. Plant families have hundreds, sometimes thousands of species that are chemically similar. There are native and non-native members of most plant families. Here are a few specific examples of insects that have made the transition from native to non-native host plants in a relatively short period of time. There are many other examples.
    • Milkweed is the hostplant of monarch butterflies. They use both native and non-native milkweed. This study done by UC Davis found that monarchs showed a strong preference for non-native tropical milkweed as both host and food compared to two species of native milkweed that were available to them in the same experimental garden: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=43489
    • The host plants of Anise swallowtail butterfly are non-native fennel and poison hemlock. The availability of these non-native weeds has enabled the swallowtail to breed year-around. Its native host was only seasonally available and it is largely gone because of the loss of marsh areas in the Central Valley of California. https://butterfly.ucdavis.edu/butterfly/papilio/zelicaon
    • Non-native Buddleia (butterfly bush) is the host plant of checkerspot butterflies. Arthur M. Shapiro and Katie Hertfelder, “Use of Buddleia as Host Plant by Euphydryas chalcedona in the Sierra Nevada foothills, California,” News of the Lepidopterists’ Society, Spring 2009

    Studies of the flower preferences of bees consistently report that bees are best served by diverse gardens that prolong the blooming season. Some non-native weeds and garden ornamentals are favorites with bees. Here’s a recent study that finds that non-native plants provide as much nectar and pollen as native plants: https://www.anthropocenemagazine.org/2021/03/urban-gardeners-have-a-big-role-to-play-in-protecting-pollinators/?utm_source=rss&utm_medium=rss&utm_campaign=urban-gardeners-have-a-big-role-to-play-in-

    Yes, some bee species are particularly well-adapted to specific flower shapes, but these relationships are as likely to be native as non-native plants. Bumblebees are the most effective pollinators of tomato flowers. Alfalfa bees are experts at pollinating non-native alfalfa flowers.

    Non-native plants rarely “crowd out” native plants. Non-native plants naturalize on disturbed ground such as roadsides and abandoned or fallow agricultural land. The natives are already gone when early succession non-natives colonize bare, depleted soil. They succeed in those areas because they can tolerate the disturbed conditions and the natives cannot. Would you prefer bare ground?

    There is no scientific evidence that non-native berries are inherently less nutritious than native berries. All plants are native somewhere and birds are resident and migrants in the places where they are native. Birds aren’t starving to death everywhere in the world where there are plants that you don’t consider “native.” All life on Earth is related.

    Tallamy’s dogma is not just mistaken, it is dangerous because it denies plants and animals their ability to move to find the climate conditions they need to survive. Plant nativism is a form of climate change denial. When the climate changes, the vegetation changes. The “native” ranges of plants and animals have changed and they must continue to change as the climate continues to change. This natural sequence of events has been true on Earth for 500 million years (though the current episode is man-made). You would benefit from a long-term perspective on nature.

  6. My understanding is that insects play a very important role in ecosystems and that plants should be chosen for their ability to support insects as well as other life. I plant native milkweeds (for monarch butterflies), nonnative rue (for black swallowtails), and native goldenrod (its leaves and flowers attract and support a huge variety of insects), among other things. It seems like one thing that both you and Douglas Tallamy agree on is that we should all do our best not to damage existing systems in nature. To Tallamy, this means preventing invasive species from displacing, outcompeting, and killing native species. To you, this means preventing people from destroying the nonnative plants that are already here. I believe I read somewhere else on your website that milliontrees began as an effort to protect a large number of trees that were going to be cut down because they were not native. I think that’s a great reason to start something, but I also think that Douglas Tallamy makes some pretty good points as well. He claims that insects are important, and they are. He claims that invasive species are a problem, and they are.

    I agree with you that more research is needed. What percentage of insects are able to transition to nonnative plants, and how long does this take? My best guess is that insects transitioning to nonnative plants is best modeled with a system similar to the one that describes the half lives of atoms. It would factor in the nonnative plant’s close native relations (or lack of close relations), the nonnative plant’s distant native relations, the number of insect species known to feed on those native relations, and the time since introduction. For all I know, a system like this might already exist.

    Until we have all the research we need, we should all agree not to destroy what already exists. Invasive species can be removed safely and carefully, without herbicides. Nonnative species can be left where they are, as long as they are causing more good than harm. New nonnative species should not be brought into a continent unless they are needed for agriculture, the control of some pest, or some other important reason (a desire for new and exotic garden decorations is not a good enough reason), and not before at least some research has been done to estimate their ecological impact. Native species can be left where they are— again, as long as they are causing more good than harm. People choosing plants to add to their gardens should consider the ecological role of each plant, especially its ability to provide food for other organisms. Also, for people living in a watershed, plants that require less fertilizer and hold soil together will really help with water quality. If a plant checks all or most of these boxes, plant it.

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