We received a comment from a reader in Wales that prompted us to visit her website, Clegyr Boia. She tells a story that contains an important lesson for us: to observe the performance of plants in our gardens and to base our evaluation of them on actual experience rather than preconceived judgments.
Eucalyptus leucoxylon ‘Rosea’ Wikimedia Commons Jean Tosti
In retelling this story, we shall call the owner of Clegyr Boia by the location of her property. Clegyr Boia’s favorable opinion of eucalyptus trees is based on her visit to Australia in 1980. As we did, she could see the beauty of the eucalyptus forest in Australia.
When she bought her property in Wales, she viewed it as an opportunity to develop an artistically beautiful landscape that she knew would include eucalyptus trees. She planted eucalypts around one of her art installations because the blue color and graceful curves of their leaves enhanced her rock sculptures. She planted other species of eucalypts in areas of the garden to shield them against the wind.
Soon after she began to plant eucalypts on her property, she was visited by friends and neighbors who were concerned about the introduction of eucalypts to their area. They warned against the invasive properties of eucalyptus. They claimed that nothing would grow under the eucalypts and that they would not provide food for wildlife.
Clegyr Boia’s initial response was to remove the eucalypts she had planted. Then she had second thoughts. She realized that her garden was full of non-native plants that were thriving and were providing valuable food for the denizens of her home, including her. Since much of the food we eat is non-native, she decided that nativity is not a suitable criterion for banning a plant from her garden. She decided to observe the eucalypts closely and decide based on their actual performance in her garden if they needed to be removed.
Some years later, she considers the eucalypts in her garden important contributors to its beauty. They have demonstrated that other plants are welcome in the shelter of their canopy and that insects make good use of them. They have also been remarkably resilient in salty, windy conditions. When they have died back after heavy storms, they have soon resprouted. Everything in her garden must make its own way, including the eucalypts, thereby proving their sustainability in this harsh setting.
Native blackthorn grows next to eucalyptus. Photo courtesy Clergy Boia
We invite our readers to visit the Clegyr Boia website for the complete story, as well as a historical review of the migration of eucalypts all over the world and speculation about why they have acquired a negative reputation.
We tell this story because we admire Clegyr Boia’s commitment to her trees. She listened to her neighbors, but she also made the commitment to her trees to watch their behavior in her garden. She based her ultimate judgment of their suitability on their actual performance in her garden. They have rewarded her patience with their success.
We received a comment on our “Wildlife” page from “entomologist” that deserves a comprehensive response.
Conversation with “entomologist”
“entomologist:” “Adaptation to exotic species by specialist herbivores is unusual. Those butterflies that switch to exotics tend to be generalists already.”
Webmaster: “Entomologist” is mistaken that the butterflies now using non-native plants are generalists, by which we assume he means that they use many plants, rather than a specific species. According to Professor Art Shapiro (UC Davis), 26 of the 82 species of California butterflies now feeding on exotic plant species, are using only one plant species. In other words, nearly one-third of California butterflies presently using exotic plant species are not generalists.(1) When butterflies have made the transition from a native to a non-native plant, the plants are usually chemically similar.
Anise Swallowtail, Sutro Forest, March 2010
The Anise Swallowtail is a conspicuous example of a California butterfly that is now dependent upon a particular exotic plant, fennel. This relationship between a specific native insect and a specific non-native plant is one of the reasons why the Million Trees blog was created. Non-native fennel is being eradicated by every native plant “restoration” in the Bay Area.
Over ten years ago, a park advocate in San Francisco became enraged by the eradication of fennel in his park because he was aware of the dependence of the Anise Swallowtail upon the fennel. He made every effort to convince the so-called Natural Areas Program to stop destroying the fennel in his park. He enlisted the help of Professor Art Shapiro in that effort. His efforts were ultimately unsuccessful. The Natural Areas Program considered the non-native origins of the fennel sufficient reason to eradicate it, regardless of the needs of a native butterfly. They continue those eradication efforts to this day.
It is such mindless destruction of non-native plants, regardless of their benefit to fauna (or other benefits) that has made the Natural Areas Program so unpopular with people with a broader view of nature. We value the Anise Swallowtail butterfly as much as any theoretical benefit from eradicating a non-native plant.
“entomologist:” “This idea that exotic plants are as good for wildlife as natives is just plain pathetic, especially for anyone who knows about herbivory patterns on native and exotic plants.”
Webmaster: By “pathetic” we assume “entomologist” means that he does not believe that insects eat non-native plants. He is mistaken that insects do not eat non-native plants. Returning to Professor Shapiro, he reports that 82 of 236 (35%) total species of California butterflies feed on non-native plants.
Damselflies (probably Common Blue) mating on non-native ivy in Glen Canyon Park.
We also use our eyes when we walk in our parks. We often find insects in non-native plants. Those non-native plants are often targets for eradication. The damselflies in a San Francisco park are another example of the contradictory strategies of the Natural Areas Program. They have made several attempts to reintroduce the rare Forktailed Damselfly to one of the parks in San Francisco. Although those attempts have not been successful, we see other species of damselflies in that park, using the non-native plants that are repeatedly sprayed with herbicides by the Natural Areas Program. We wonder if the herbicide use in that park is contributing to the failure of attempts to reintroduce the Forktailed Damselfly. Does the right hand know what the left hand is doing?
“entomologist:” “Insects eating plants are at the base of the food chain and native plants have more insect herbivores and support more native birds.”
Webmaster: We can agree that many birds eat insects and those that do are likely to benefit from greater populations of insects. But, there is substantial evidence that insects are as likely to be found in non-native plants as in native plants and we trust that the birds know where to find them. However, unlike “entomologist” we are as interested in the welfare of non-native birds as we are in native birds.
“entomologist:” “Doug Tallamy’s work shows this in the eastern US conclusively.”
Webmaster: Professor Tallamy’s (University of Delaware) publications do not seem to be available on-line, which prevents us from reading his publications. However, since he studies the insects on the east coast we don’t think whatever he reports trumps the studies that we have cited of insect populations here in the Bay Area.
“entomologist:” “I certainly feel for the loss of trees, but the alternative is that we accept a homogenized set of urban-tolerant plants and wildlife. Maybe that’s ok if you don’t know the difference, but for those of us who actually pay attention it is profoundly sad.”
Webmaster: We don’t see the logic of “entomologist’s” vision of a “homogenized” ecology. If we destroy non-native plants and animals, our ecology will be less diverse. And we hope that the readers of Million Trees will agree that we are, indeed, “paying attention.”
The Big Picture
We suggest that “entomologist” and other native plant advocates step back from their deeply-seated prejudices against non-native plants and consider the big picture. The fact is that insects are particularly vulnerable to climate change because they live in relatively narrow temperature ranges. (3) Although they are adjusting well to changes in vegetation, they are not likely to be able to make an equally successful adjustment to changes in temperatures. Therefore, if our top priority is insects, we would be wise to reconsider destroying millions of non-native trees that are sequestering millions of tons of carbon, contributing to greenhouse gases and thereby to climate change.
(1) Arthur M. Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110, 413-433, 2003
(2) Dov Sax. “Equal diversity in disparate species assemblages: a comparison of native and exotic woodlands in California,” Global Ecology and Biogeography, 11, 49-52, 2002.
(3) “Mountain plant communities moving down despite climate change, study finds,” Los Angeles Times, 1/24/11
One of many doom and gloom scenarios used by native plant advocates to frighten the public into accepting their destructive “restoration” projects is the claim that “non-native species are the second greatest threat to the survival of species in peril.”(1) Although the statement originates with a scientific study published in 1998, the context in which it was originally reported has long since been lost as it has been cited more than 700 hundred times in scientific studies according to Mark Davis.(2)
The original 1998 article in BioScience by Wilcove et.al. clearly states that the claim is not based on any actual data:
“We emphasize at the outset that there are some important limitations to the data we used. The attributes of a specific threat to a species is usually based on the judgment of an expert source, such as a USFWS employee who prepares a listing notice or a state Fish and Game employee who monitors endangered species in a given region. Their evaluation of the threats facing that species may not be based on experimental evidence or even on quantitative data. Indeed, such data often do not exist.”(3)
This caveat is rarely repeated when the claim is invoked by native plant advocates to justify their crusade against non-native plants and animals. In fact, since the statement was originally made over a decade ago, it is now repeated without reference to the original source. It has acquired the status of a mantra amongst native plant advocates that requires no citation to substantiate its “truthiness.”
The Wilcove et.al. article in BioScience in which this statement was made was heavily influenced by selecting a geographic area which is not representative of the United States as a whole. Although Hawaii is a part of the United States its rates of extinction are not typical of the contiguous states of the union. Rates of extinction are substantially higher on islands because they contain many more endemic (unique) species that do not occur elsewhere. These endemic populations are small and vulnerable to the introduction of competing species. Native populations on islands are not supplemented by immigrations as they are elsewhere.
Coqui frog is being eradicated in Hawaii. USDA photo
If Hawaii is removed from the anecdotal information in the Wilcove article, the rates of extinction are comparable to those in Canada where introduced species are considered the least important of six categories of causes of extinction (habitat loss, over-exploitation, pollution, native species interactions, and natural causes such as storms) identified in a similar article in 2006(4). This list doesn’t include climate change, which is now considered a serious threat for extinction. Similar studies in the continental United States have reached similar conclusions.(5)
At the time the Wilcove et. al. article was published there was no evidence of a single extinction (or even local extirpation) of a native plant in the continental US resulting from competition from an introduced species of plant. Clearly, the authors of this study were guilty of exaggeration.(6)
Although native plant advocates have misused this publication by taking it out of context, the authors were complicit in its misuse by selecting a geographic area that is not representative of the United States. Non-native species are NOT the second greatest threat to the survival of endangered native species. In fact, they probably aren’t the third, fourth, or fifth greatest threat to native species.
We wish that native plant advocates would examine the origins of their assumptions more carefully. We believe if they did so they would modify their destructive projects to reflect a more inclusive view of nature.
(1) Wilcove, DS, Rothstein, D., Dubrow, J., Phillips, A., and Losos, E, “Quantifying threats to imperiled species in the United States,” BioScience, 48, 607-615, 1998.
We encourage native plant advocates to comment on our posts because we learn from them. We learn more about their ideology and the assumptions that support it.
These dialogues with native plant advocates are embedded in our posts and are therefore not as accessible to our readers as they often deserve to be. Occasionally, we will create a post from these exchanges so that all of our readers can benefit from them. In so doing, we hope not to discourage native plant advocates from posting comments, as they are essential to improving our mutual understanding of the complex issues we are debating.
Name Here: “Since you don’t have the confidence to post your identity, I thought it only fitting to return the favor. Your argument would have much more strength if you were not anonymous.
You claim on your home page to provide citations, yet in this article you fail to tell us who “We had the privilege of meeting the ecology consultant who designed the plant palette for the living roof for the academy and many other institutions around the world.” is referring to. The “ecology consultant” does not have a name? By then throwing out Peter Del Tredici’s name it would appear as though you wish your reader to assume that he was the “ecology consultant” you refer to.”
Webmaster:The ecology consultant for the living roof on the Academy was Paul Kephart of Rana Nursery. He is the person we are quoting in our post about planning for the living roof. Our readers can confirm Mr. Kephart’s role in the design of the roof by reading this article: “High Maintenance Superstar,” Linda McIntyre, Landscape Architecture, August 2009. This article is not available on-line, but the edition of the magazine in which it was published can be purchased on-line. However, Mr. Kephart’s statement quoted in our post was made in a lecture to a group and does not appear in this publication.
Our post did not state, nor did it imply that Peter Del Tredici was the ecology consultant for this project. He is a scientist who has published articles about native plant “restorations,” particularly in urban settings. We quote him in our post because his observations about native plant gardens are directly relevant to the living roof.
Name Here: “On another note, you mention this third predominant species on the roof as “a moss” and then tell us it is non-native, yet offer no proof of this. Citing another blog with no standard of journalistic integrity is not a valid source. You might want to present the scientific name of this moss to prove your point, though I do not believe, judging by your writing, that you actually know the name, or you would have presented it.”
Webmaster: At the time that we published our posts about the living roof, we did not know the names of the mosses on the roof, which is why we quoted the “From the Thicket” blog. The author of the “From the Thicket” blog, Heath Schenker, is Professor of Landscape Architecture at UC Davis. Her background and credentials are described on her blog. She wrote her post about the living roof at the California Academy of Sciences after attending a symposium at the Academy about their monitoring project. Our readers can judge for themselves if this was a credible source of information to document our post at the time it was published.
Name Here: “There are many different species of mosses out there, some native, some non-native. Many moss are very cosmopolitan in their range and therefore may occur natively all over the world. The actual quote from InTheThicket is as follows: “Nobody knows where the mosses came from, but they appear to be varieties of early-succession mosses, the types that commonly show up in disturbed soil.” I challenge you to show me where this says they are non-native.”
Webmaster: After we published our post, the Academy made their monitoring report available on-line: http://www.calacademy.org/pdfs/living-roof-project-results.pdf. The report contained the names of the mosses on the roof: Bryum sp., Rosulabryum sp., Ceratodon purpureus, Leptobryum pyriforme. We took that list to the Jepson Herbarium at UC Berkeley to confirm that our description of the mosses was accurate. The staff at the Herbarium looked up those mosses for us and described them as “cosmopolitan,” which means they are widespread and cannot be considered either native or non-native. Since these mosses were not amongst the 9 species of native plants originally planted on the roof, we felt comfortable with our original description of them. They are clearly “volunteers,” not part of the original roof top planting.
Name Here: “I think it is important for anyone reading this blog to be reminded that it is just that, a blog. It is written by an anonymous source who can say whatever they like with no fear of reprisal other than these comments, and with no need to live up to journalistic standards of any kind.”
Webmaster: Yes, the Million Trees blog is “just a blog.” However, I invite our readers to consider the difference between this accusatory comment from “Name Here” and the information we present. We provide citations for most statements we make. Those citations are usually of publications by academics at major universities, published in peer-reviewed journals or journalistic articles about their publications. We often resort to journalistic articles because they are easier for non-scientists to comprehend.
We know that we are confronting firmly held beliefs in the community of native plant advocates. Therefore, we cannot expect to challenge their assumptions without providing well-documented information. And since we have often been on the receiving end of ad hominem attacks by native plant advocates, we do our best to protect ourselves from such attacks by standing on firm scientific ground and by remaining anonymous. (One wonders what “reprisals we should fear” for providing information with which “Name Here” disagrees.)
In contrast, “Name Here” questions our credibility without providing any evidence to substantiate his claim that we are fabricating information. Therefore, his comment seems more an attempt to discredit than to illuminate.
We have had over 200 comments from readers, most in support of our perspective on the native plant movement, but many critical of our approach to this issue. We have posted most, but not all of the critical comments.
This comment is typical of those few that we chose not to post: “This entire website is essentially just a cesspool of misinformation.” We responded to that reader: “If you would be more specific, we might post your comment. You should also cite your sources as we do on Million Trees. At the moment, your comment contains no information.” He did not respond, so we did not post his comment.
Most native plant advocates who post comments are more specific, but they have never provided references for the generalizations that are the underpinnings of the native plant movement, such as:
Native grassland stores more carbon than forests (Since carbon storage is proportional to biomass, this is a physical impossibility.)
Native plants produce: “Better soil function resulting in improved air quality and hydrology and pollination” (We have seen no scientific evidence to support any of these claims.)
Wildlife prefers native plants (Most wildlife has adapted to non-native plants and is sometimes dependent upon them)
We responded to these comments with scientific references that contradict these claims and we invited the authors to provide us with scientific references that support their view. We did not receive any replies to these requests for information about the sources of their statements.
In one case, we had a long email dialogue with a native plant advocate who filled pages with such generalizations. We repeatedly asked him to cite his sources. Finally he sent us a 12 page bibliography, none of which he claimed to have read. Nor did he make any connection between this lengthy bibliography and the statements he made in support of his arguments. That was the end of the dialogue.
We conclude that these unsupported generalizations about the superiority of native plants are symptomatic of the native plant movement, which is an ideology, not a science. The ideology persists because it is a victim of incestuous amplification, the sharing of misinformation by a group that isolates itself from dissenting views. They hear their assumptions repeated so often that the assumptions are eventually transformed from fiction into fact in their minds.
Unlike native plant advocates, we read all available literature on the subject, particularly publications in support of the native plant movement, such as the newsletters of the California Native Plant Society, Nature in the City, as well as Jake Sigg’s Nature News. When we see new claims of the benefits of native plants, we research those claims by comparing them to the scientific literature.
It is our research of the scientific literature that gives us hope that the native plant movement is losing its credibility. In the past few years, more and more scientists have published their research refuting many of the assumptions of the native plant movement. We have reported on Million Trees the research of some of these scientists: Mark Davis, Peter Del Tredici, Hugh Raffles, and Dov Sax. The publications of these scientists have enabled us to provide our readers with the evidence that many of the assumptions of the native plant movement are unsupported by scientific research.
Thank you to the readers of the Million Trees blog for visiting and commenting. We invite our readers to correct any misstatements of fact, as we try our best to avoid the incestuous amplification that can accompany advocacy. We provide citations of scientific literature whenever possible to avoid that trap. We renew our appeal to native plant advocates to supply us with the scientific literature that they believe supports their ideology and we commit ourselves to reading and reporting such evidence.
Our inclusive view of nature: native and non-native plants at Oyster Bay
For the record, we repeat Million Trees’ primary appeal to native plant advocates: please plant native plants if that is your preference, but quit destroying non-native plants, trees and animals.
Conservation Sense and Nonsense 