A defensive tirade from invasion biologists

Pesticide use by land managers in California.  Source California Invasive Plant Council
Pesticide use by land managers in California. Source California Invasive Plant Council

An international team of invasion biologists has just published a defense of their academic turf, invasion biology.  (1) Daniel Simberloff, an American member of the team, is the most relentless defender of the crusade to eradicate all non-native species, wherever they are found, all over the world.  Their publication acknowledges the mounting criticism of this crusade and attempts to respond to that criticism, but what is most notable is what is missing from their attempt to defend their opinions.  They make no mention of the harmful methods used to eradicate non-native species:

Keep these damaging methods in mind as we visit the hypocritical and contradictory arguments used to justify the projects for which these invasion biologists advocate.  They set up “novel ecosystems” as the straw man to which they compare the goals of invasion biology.  They define novel ecosystems as “a new species combination that arises spontaneously and irreversibly in response to anthropogenic land-use changes, species introductions, and climate change, without correspondence to any historical ecosystem.”

“Lack of rigorous scrutiny”

Their primary criticism of the concept of “novel ecosystems” is that it has not been “subjected to the scrutiny and empirical validation inherent in science” and its definition is “impaired by logical contradictions and ecological imprecisions.”   These criticisms apply equally to invasion biology.

Hypothesis n % of supporting studies % of decline in support
Invasional meltdown




Novel weapons




Enemy release




Biotic resistance




Tens rule




Island Susceptibility




Although support is strongest for the invasional meltdown hypothesis, recent studies are less supportive than early studies, indicating substantial decline in supporting evidence.  Declining evidence of invasional meltdown is consistent with the fact that exotic species are eventually integrated into the food web which reduces their populations, stabilizing their spread. There is apparently little evidence that islands are more susceptible to invasion than continents and few studies have been done to test the hypothesis.

If empirical validation and semantic precision are required to establish the credibility of scientific hypotheses, invasion biology has failed that test.

“Precautionary principle of conservation and restoration”

These invasion biologists define the precautionary principle of conservation and restoration as follows:  “we should seek to reestablish –or emulate, insofar as possible—the historical trajectory of ecosystems, before they were deflected by human activity.”  This is an unusual use of the precautionary principle, which is more typically defined as avoiding damage to the environment by not using potentially harmful methods, even in the absence of solid evidence of such harm.  The precautionary principle was not used when the following “restoration” projects were defined or implemented:

Ivy in the Conservatory in Central Park, New York City
Ivy in the Conservatory in Central Park, New York City

In 1996, Daniel Simberloff made this statement in his publication about the hazards of biological controls:  “…are there any protocols for biological-control introductions that would prevent all disasters?  Probably not…” (2) Yet, in 2013, he expressed his support for the introduction of non-native insects to control cape ivy at a conference at UC Davis sponsored by the California Department of Food and Agriculture.  Although cape ivy is despised by native plant advocates, it is not an agricultural pest and therefore causes no economic damage to ecosystems, unless money is wasted on attempts to eradicate it.

“All ecosystems should be considered candidates for restoration”

In response to those who find value in novel ecosystems, these invasion biologists find none.  They reject the possibility that there is ever a point at which it may not be possible to re-create a historical landscape.  They continue to believe that ANY and ALL radically altered landscapes CAN and SHOULD be considered candidates for restoration.  Their only caveat to this universal goal is that “damaged ecosystems…should be evaluated for feasibility, desirability, and cost-effectiveness, on a case-by-case basis, so that informed and science-based policy decisions can be made, in consultations with scientists, restoration practitioners, stakeholders, and advisors.”

These criteria for potential “restoration” have nothing to do with reality:

  • Most projects in the San Francisco Bay Area have not provided cost estimates when they were planned. The public demanded cost estimates for the projects of the Natural Areas Program in San Francisco, but these demands were ignored.  Therefore, “cost-effectiveness” is not usually considered when these projects have been shoved down the public’s throat.
  • We consider the public to be “stakeholders” in decisions to radically alter our public open spaces. We are the visitors to these areas and our tax dollars pay for their acquisition, maintenance, and “restoration.”  Yet, managers of public land are consistently making those decisions without taking the public’s opinion into consideration.  Most projects are planned and executed without any public participation.  In the few cases in which there are environmental impact reviews, the projects are implemented regardless of overwhelming opposition of the public.

 “Human-damaged ecosystems can be at least partially restored”

The demonstrated futility of “restoration” projects is one of many reasons why there is waning public support for attempting them.  Yet, invasion biologists who authored this diatribe claim that “restored sites recovered on average 80-86% of biodiversity and ecosystem services…and showed improvements of 125-144% over degraded ones.”  This claim is contradicted both by other scientific studies and by experience with local projects:

  • “…this paper analyses 249 plant species reintroductions worldwide by assessing the methods used and the results obtained from these reintroduction experiments…Results indicate that survival, flowering and fruiting rates of reintroduced plants are generally quite low (on average 52%, 19%, and 16% respectively). Furthermore, our results show a success rate decline in individual experiments with time.  Survival rates reported in the literature are also much higher (78% on average) than those mentioned by survey participants (33% on average).” (3)
  • Dunnigan Test Plot, Augusst 2011.  The result of an eight-year effort to restore native grassland.  Does it look "biodiverse?"  ecoseed.com.
    Dunnigan Test Plot, August 2011. The result of an eight-year effort to restore native grassland. Does it look “biodiverse?” ecoseed.com.

    There is frequently a discrepancy between the success rates claimed in papers and those actually observed. For example, Cal-Trans gave researchers at UC Davis $450,000 to restore 2 acres of non-native annual grassland to native grassland.  UC Davis researchers spent 8 years and used multiple methods to achieve this transition.  When they ran out of money, they declared success in their published report.  They defined success as 50% native plants which they expected to last 10 years before being entirely replaced by non-native annual grasses again.  Do you consider that a success?

  • On a more anecdotal level, we watch established landscapes that have required no maintenance in the past being transformed into weedy messes by failed “restoration” projects. Then, adding insult to injury, we hear those who are responsible for these failures tell us how successful they are.

“Inadequate political will”

The authors of this publication conclude:

“No proof of ecological thresholds that would prevent restoration has ever been demonstrated.  Often the threshold that obstructs a restoration project is not its ecological feasibility, but its cost, and the political will to commit to such cost.” (1)

We are reminded of an old football adage:  “The best defense is a good offense.”  In other words, invasion biology is under fire, but the reaction of invasion biologists is to demand more….more money, more effort, and the commitment of public land managers to “restore” all ecosystems, regardless of what the public wants.  And in support of that aggressive strategy, they refuse to acknowledge the damage that is being done to the environment and the animals that live in it, by the projects they demand.

The authors of this defensive tirade have hammered another nail in the coffin of invasion biology.

  1. Carolina Murcia, James Aronson, Gustavo Kattan, David Moreno-Mateos, Kingsley Dixon, Daniel Simberloff, “A critique of the ‘novel ecosystem’ concept,” Trends in Ecology and Evolution, October 2014, Vol. 29, No. 10
  2. Daniel Simberloff and Peter Stiling, “How Risky is Biological Control?” Ecology, 77(7), 1996, pp 1965-1974
  3. Sandrine Godefroid, et. al., “How successful are plant species reintroductions?” Biological Conservation,   144, Issue 2, February 2011

15 thoughts on “A defensive tirade from invasion biologists”

  1. This post highlights the pathetic nature of invasion biology at its core. it is the same type of thinking that is trying to destroy phragmites on the shores of the Great Lakes. The destruction has no value and will not make a better world. Foolish.

  2. It is horrific seeing the increasing of plant killing in the Bay Area, leaving empty, barren land with more “invasive” grasses spreading. When they kill the trees that our native wildlife so love and need, they are supporting other “invasives.”

    I will believe the “nativists” (non-native to the Americas themselves) are sincere, when they first kill every fruit tree, vegetable garden, or rose or other non-native ornamental in their OWN yards, and then call for the eradication of all the non-native species that are in our cities as street trees and other landscaping. Most people don’t even know that the trees cities and businesses plant are primarily non-native. No more hypocrisy!

    This is a wonderful post, but my only objection is that Hedera Canariensis IS the main serious problem I see in the Bay Area with an introduced plant, where the ivy is covering redwoods and every plant they can climb. It is extremely easy to stop this, with cutting at the base of the ivy in the trees, but CalTrans or whoever takes care of the freeway plantings would rather cut down more beautiful trees than control the ivy. I think this problem is added to in their fanaticism in killing exquisite ice plant along freeways.

    Along 580 and HWY 13 in Oakland, you can see ivy covering and killing trees, from tall redwoods to our beautiful smaller plums.

    1. I have been told by several arborists, who also cited scientific studies, that ivy cannot kill trees because there is a limit to how high it can climb. Occasionally, it appears otherwise when a tree that dies then leans at an angle can be completely covered in ivy. I understand your concern. I used to take ivy off the trees in my local park because I was worried that it would kill the trees. Once I was reassured by several arborists, I started to pay closer attention and I believe they are right about that.

      1. I don’t know what real arborists would say that because we can easily see ivy covering quite tall, old redwoods who are still very much alive, though not much longer at the rate that ivy grows, on 580 and 13. Keep watching and when those trees are completely covered, when they are deprived of the light they need to live, smothered, then they die. Ivy doesn’t climb dead trees for long since they fall over.

        Ivy has already killed a lot of the smaller trees like plums who bloom so beautifully in spring. 580 on the east side, between 35th Avenue going north and west, is like a death zone of ivy killing trees. Some are still struggling, but will be completely covered soon.

        I’ve called CalTrans for thirty plus years about this, and they never do anything, It’s so easy to cut the ivy at the base, though I’ve seen some ivy so thick you’d need a saw. It’s maddening to know we can’t save those trees, when it’s so simple. They have the money to spray poison, but not save the redwoods and other trees they planted.

        I have never seen a limit to the height ivy goes, easily covering 80 foot, a 100 foot redwoods. deodar cedars, etc. The only thing that stops them is the height of the tree, and redwoods can reach 300 feet. When ivy is at the top, it spreads out to other trees it can reach, or just keeps adding weight and depth.

        How are these people arborists?

        No one has to be an expert. We can all see it happening and trust our senses. If there’s any doubt, watch the growth over the next year on each tree, and as the years pass, the tree, unable to get light, dies.

        I’m willing to show examples if anyone doubts this, but the evidence is everywhere in the Bay Area.

  3. I’m still in shock over this. When you see Hedera Canariensis covering a redwood or other tall tree, you still can usually see the top of the live tree, desperately trying to survive. That is what is so heartbreaking — trees are being killed now who could be saved by simply cutting where the ivy starts to climb the tree. (The ivy then dies, though the weight of it is still a terrible burden on the trees.)

    Most of the tall trees, and the many smaller ones, and shrubs, etc. who are being killed by ivy could be saved if people would just do something. It should be CalTrans’ or a state worker’s job to save the trees along the freeways. Eventually, every one of those redwoods and other trees will be dead. It’s even more tragic along Highway 13. And I keep mentioning those places because I see them when I drive, but this is happening everywhere that ivy is allowed to kill plants.

  4. The Cape Ivy discussion is interesting to me. This may be completely off-base, but I have a (armchair psychologist) theory about the situation. Here are two people who are concerned about the urban ecosystem we occupy. Two people who are practical-minded about its future.

    Even so, the pernicious philosophy of “human=bad,” which is a fundamental tenet of the nativist cult, keeps these two nice people from saying something that is perfectly fine to say: It is not inherently “immoral” for humans to alter the world around them. All animals do it. It takes a minute to feel comfortable saying it out loud, because we have had it drilled into our heads that we are a plague on the planet. This is sad and untrue.

    How this idea applies here:

    We can oppose cutting down trees we like in pursuit of some 18th century fantasy world. At the same time, we CAN support eradicating plants we DON’T like. Just because we don’t like them. Because we are sane, we don’t consider urban ecosystem management to be a moral crusade, and are realistic about the impossibility of total eradication.

    Cape Ivy covers trees and looks ugly, like kudzu in the South. So kill it as much as possible. Because it is ugly and covers trees we find beautiful. Yes, human desire and aesthetic sensibility are just as valid as the pseudo-science produced by invasion fanatics.

    I can’t be certain this is the exact dynamic at work here, but I do often sense good people feeling reticent to support killing ANY “non-natives” because it might somehow weaken their position. I say it doesn’t.

    Thoughtful post as always.

    1. That is an excellent point and I thank you for making it. Advocacy can be a trap that can box us into a corner and prevent us from accurately perceiving reality. We must be constantly vigilant to avoid falling into that trap. Thanks for taking the time to remind us of the dangers of advocacy.

  5. Yes, we must not lose common sense about some things. West Nile Virus isn’t native. More for the corvids than us, it’s good to try to eliminate the mosquito vector with NEVER any spraying since no amount of pesticide is ever safe. But the more practical way to think about it is that it’s better if everyone just get what seems inevitable and then are immune, and most won’t even know they had it.

    But my concern about Hedera Canariensis/Algerian Ivy is for the plants and animals, not esthetics. It KILLs everything it covers, and the smaller trees die faster. It’s been painful to see those trees slowly being killed, while the people maintaining the freeway landscaping will not save the trees, yet keep wasting time and money spraying poison.

    I want as much plant diversity as possible and this area is wonderful for many species being able to live. The fanatical nativists though seem happy with their own yards and the city landscapings of exotics, even while they want to destroy the parks for the native animals and us. (I keep meeting people who have no idea that vegetable gardens, most roses, fruit trees, etc. are all introduced and should be killed according to the fanatics).

  6. I appreciate your differentiation between aesthetics and pestilence as motivation. My point was that both can be acceptable. The harm I see is allowing ourselves to be indoctrinated with the idea of nature as a moral topic.

    I don’t know whether Cape Ivy actually kills trees. But I don’t have to know. Indeed, it isn’t necessary to prove that it does for it to be a candidate for eradication. It could be a factor in deciding how to manage a particular site. But the fact that it blankets trees I find magnificent is just as legitimate a factor.

    I may not be conveying my point very well… The fact that “native” plant enthusiasts use hyperbole and moral terminology (eucalyptus: weeds, invasive, dangerous, unnatural, they kill surrounding vegetation, they greedily drain ground water, they are health hazards, etc.) should make rational people wary. If nativists were honest and admitted just how much they are actually motivated by PREFERENCE, it could be a more productive discussion.

    Your discussion with Milliontrees just reminded me how “urgent need/moral imperative/preventing harm” type arguments receive disproportionate attention, when an equally valid, and simpler case can be made that doesn’t play into the fanatical tendencies of some of our more… ummm… passionate(?) fellow citizens. (Girdling eucalyptus in Bayview in secret, as though it were a holy mission, for example.)

    Finally, I think one statement deserves attention, because the sentiment is fairly common and potentially harmful. It is emphatically not true that “no amount of pesticide is ever safe.” Visit the website in my avatar for a clear scientific explanation (“Making Sense of Chemical Stories”) of why that isn’t true. The explanation of why the point is important is simple: “pesticide” should not be a four letter word. Eliminating everything that term includes would needlessly doom a large percentage of the world’s population to death by starvation and infectious disease. It is a discussion for another time and place, but important enough to mention in a setting where critical thinking is valued.

  7. Also, I just want to say again how amazed I am at the amount and breadth of research that is done for this blog. For no apparent financial gain (not much grant money for “Ecological Sanity Restoration Projects,” I’m guessing…) scholarly articles and expert opinion that I would never otherwise encounter are regularly linked to and discussed. It is a labor of love with an admiring emphasis on “labor.”

    1. Thank you, TBTG. I have learned a lot of interesting things. That is my reward. And, for the moment, I must say my only reward. Although the science is moving along nicely in the right direction, it is having no visible impact on public policy. I fear that soon there will be no trees left to fight for.

  8. I’ve been confused as to why my comment about Algerian Ivy — Hedera Canariensis — became a discussion of “Cape Ivy,” which I had never heard of before as a gardener for over forty years. i was assuming that it was a second common name, but actually they are two completely unrelated plants.

    Delairea Odorata, which was previously included in the genus Senecio as Senecio mikanioides, and is known as Cape Ivy in some parts of the world and German-ivy in others, is actually in the Asteraceae or daisy family.

    Hedera Canariensis, like its English cousin, Hedera Helix, is true ivy and is in the Araliaceae family. Algerian ivy is far faster and stronger than English Ivy or the mis-named Cape Ivy, and indeed can cover and kill trees over a hundred feet tall. There is no end to how high it can go. Anyone in doubt can see the redwoods along Highway 13 being covered and killed, or similar devastation on east 580 between 35th Avenue and Harrison St.

    I am completely against killing non-native plants, but this is the only one that is actually killing trees and anything it can cover, so I choose the plants it’s killing.

    1. Along the highways in Michigan and in peoples yards people remove native wild grapes and Virginia creeper all the time. Is that bad? Not really. From an aesthetic point of view it may be something they are trying to uncover that they prefer. The Hedera helix that grows here also knows no bounds and grows to the tops of sugar maple trees. It becomes part of the sugar maple at some point. I’ve noticed some of the ivy infested trees appear healthier with less limb damage. Arborists should investigate this. If you could manage the highways vegetation in this nation like it really matters you could have people easily improve the quality of the plants that grow along and yes remove vines. But for now, no one cares. It is get out the herbicide approach that is always used. Millions of milkweed plants are destroyed along the I-94 corridor from Detroit to Chicago because it happens to be a broadleaf plant and it too is in the cross hairs. It is unfortunate the environmental groups support these policies and have no clue the monster that they have let loose. Once again, no one cares. It’s the roadside. Thank you Million Trees for standing up.

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