nature – Page 2 – Conservation Sense and Nonsense

Defining “Success” so “Success” can be achieved

I always attend the conferences of the California Invasive Plant Council (Cal-IPC) and the California Native Plant Society because I feel obligated to understand their viewpoint so I can accurately report on the controversies of invasion biology. Ironically, the more I learn about the native plant movement and the “restoration” industry it spawned, the less sense it makes. The October 2024 Symposium of the California Invasive Plant Council has provided more evidence that attempts to eradicate well-established non-native landscapes and replace them with native plants are futile.

Tricks of the “restoration” trade

Every Cal-IPC Symposium has wrestled with the question of whether or not it’s possible to convert non-native grassland to native grassland. A study of 37 grassland “restorations” in coastal California addresses that question. (1) It’s really quite simple. All you need to do is define success as 25% native plants after “restoration” and limit post-project monitoring to 5 years or less: “Monitoring is done ≤5 years after project-implementation, if at all, and rarely assesses the effects of management practice on project success.”

It also helps if public land managers in charge of the projects won’t allow the academic researcher to enter the land to conduct a survey of the results. 43% of the projects that were studied were “statutory,” i.e., they were mandated by laws such as county general plans or legally required mitigation for projects elsewhere that Environmental Impact Reports determined were harmful to the environment. 30% of the managers of the statutory projects would not allow the academic researcher to survey their projects.

It is also easier to achieve success if the project goal is downgraded mid-project as were many of the statutory projects because they weren’t able to meet the original goal.

Project managers can also reduce their risks of failure by planting a small number of native species that are particularly easy to grow: “Ninety-two percent of restoration managers preferentially use one or more of the same seven [native] species.” Seven projects planted only one native species.

According to the study, the result of planting only a few hardy native plants is “biotic homogenization.” Call it what you will, but this risk-averse strategy is inconsistent with claims that the goal of native plant restorations is to increase biodiversity.

The study did not ask project managers about the methods they used to eradicate non-native plants or plant native plants. The study tells us nothing about the methods that were used or whether or not some methods were more effective than others. Since results of the projects were all very similar, should we assume that the methods that were used didn’t matter?

The presentation of this study concluded with this happy-face slide. (see below) It looks like a cartoonish marketing ad to me:

Harmless aquatic plants being pointlessly eradicated

A USDA research ecologist stationed at UC Davis made a presentation about the most effective way to kill an aquatic plant with herbicides, but that wasn’t the message I came away with.

Jens Beets told us about a species of aquatic plant that is native to the East and Gulf coasts of the US, but is considered a “noxious weed” in California, solely because it isn’t native. He said the plant is considered very useful where it is native. (see below)

Where Vallisneria americana is native, it is considered a valuable plant for habitat restoration because it is habitat for vertebrates and invertebrates and it stabilizes soil and water levels. The canvasback duck is named for this plant species because it is preferred habitat for the native duck that is found in California during the winter.

Vallisneria americana looks very similar to other species in the genus considered native in California. For that reason, native species of Vallisneria have been mistakenly killed with herbicide because applicators didn’t accurately identify the target plant as native. Jens Beets recommended that genetic tests be performed before plants in this genus are sprayed with herbicide.

This story probably sounds familiar to regular readers of Conservation Sense and Nonsense. The story is identical to the pointless and futile effort to eradicate non-native species of Spartina marsh grass in the San Francisco Bay. The species being eradicated in California is native to the East and Gulf coasts, where it protects the coasts from extreme storm surges and provides valuable habitat for a genus of bird that is plentiful on the East Coast, but endangered in California. The 20-year effort to eradicate non-native Spartina has killed over 50% of the endangered bird species in the San Francisco Bay.

Throwing good money after bad

Because the hybrid is indistinguishable from the native species of Spartina on the West Coast, 7,200 genetic tests have been performed in the past 12 years before hybrid Spartina was sprayed with herbicide. Taxpayers have spent $50 million to eradicate Spartina over 20 years. Recently, California state grants of $6.7 million were awarded to continue the project for another 10 years. A portion of these grants is given to the California Invasive Plant Council to administer the grants.

Plants are sprayed with herbicide because they aren’t native, not because they are harmful. Even if the target species is needed by birds and other animals, it is still killed and animals along with it. The target species looks the same as the native species and only genetic testing can identify it is as a non-native. The non-native is the functional equivalent of the native. It is only genetically different because natural selection has adapted it to the conditions of a specific location.

Pesticide regulation in the US is a hit or miss proposition

The final session of the symposium was a carefully orchestrated apologia for herbicides, a defensive tirade that suggested Cal-IPC believes its primary tool is in jeopardy. Two presentations were made by employees of regulatory agencies. Their assignment was to reassure the public that pesticides are safe because they are regulated by government agencies.

The fact that many countries have banned pesticides that are routinely used in the US does not speak well for our regulatory system. America’s pesticide regulators rarely deny market access to new pesticides. A recent change in policies of California’s Department of Pesticide Regulation made a commitment to the continued use of pesticides for another 25 years.

In 1996, Congress ordered the U.S. Environmental Protection Agency (EPA) to test all pesticides, used on food, for endocrine disruption by 1999. The EPA still doesn’t do this today. Twenty-five years later, the EPA has not implemented the program, nor has it begun testing on 96% of registered pesticides. In 2022, an organization that represents farm workers sued the EPA to conduct the legally mandated evaluation of chemicals for endocrine disruption. The lawsuit has forced the EPA to make a commitment to conduct these evaluations of chemicals for hormone disruption.

The Cal-IPC presenters got some badly needed push back from attendees. One attendee informed the audience that all the testing of herbicides is bought by the manufacturers, not the regulators who don’t do any testing. Another attendee pointed out that herbicides have not been evaluated for the damage they are doing to the soil, damage that makes it difficult to grow native plants in the dead soil. The “pesticide regulator” agreed with those observations.

Fire safety or native plant restoration?

The Interim Deputy Director of the Laguna Canyon Foundation was the final presenter for the Symposium, speaking on a Friday afternoon at 4:30 pm, when there were less than 100 attendees left of the 690 registrants. His presentation was about the blow back that his organization gets from the public about herbicide applications. Criticism of herbicides escalated after a wet year that increased vegetation considered a fire hazard. This photo (below) is an example of the visible effects of fuels management by Laguna Canyon Foundation using herbicides.

It seems likely that a fuels management project was selected for this presentation because it’s easier to justify herbicide use for fuels management than for eradicating harmless plants solely because they aren’t native.

I recently supported Oakland’s Vegetation Management Plan that will use herbicides for the first time on 300 miles of roadsides and 2,000 acres of public parks and open space in Oakland. Previously, herbicide applications were only allowed on medians in Oakland. I tracked the development of the Vegetation Management Plan for 7 years through 4 revisions to avoid nativist versions of fuels management such as leaving dead thatch after herbicide applications on grassland or destroying non-native trees, while leaving highly flammable bay laurel trees behind or destroying broom, while leaving more flammable coyote brush behind.

However, using herbicides for the sole purpose of killing non-native plants is much harder to justify. The irrational preference for native species has put us on the pesticide treadmill. Every plant species now targeted for eradication with herbicides should be re-evaluated, taking into consideration the following criteria:

Is it futile to attempt to eradicate a plant species that has naturalized in an ecosystem?
Will the attempt to eradicate the plant species do more harm than good?
Is the targeted plant species better adapted to current environmental and climate conditions?
Is the targeted non-native plant making valuable contributions to the ecosystem and its animal inhabitants?

If these questions cannot be satisfactorily answered, the bulls-eye on the targeted plant should be removed. Limiting the number of plants now being sprayed with herbicide is the only way to reduce pesticide use. If the plant isn’t a problem, there is no legitimate reason to spray it with herbicide.

Pot calls kettle black

The Cal-IPC presentation was a detailed criticism of the public’s complaints about herbicides used in their community. The intention of the presentation was to arm herbicide applicators with defenses against the public’s complaints. Herbicide applicators were encouraged to recognize these arguments (below) and participate in the “education” of the public about the righteousness of their task.

The presenter then showed a series of slides making specific accusations, such as these: (see below)

Those who object to the pointless destruction of nature can also cite distortions and misrepresentations of facts (AKA lies) by those who engage in these destructive projects;

Nativists fabricated a myth that eucalyptus kills birds to support their demand that eucalyptus in California be destroyed. There is no evidence that myth is true.
Nativists also fabricated a myth that burning eucalyptus in the 1991 firestorm in the East Bay cast embers that started spot fires 12 miles away from the fire front. There is no evidence that myth is true .
Nativists exaggerate the success of their projects by setting a low bar for success, conducting no post-project monitoring, and restricting access to their completed projects.
The EPA justified the dumping of rodenticides on off-shore islands by inaccurately claiming that the rodenticides do not end up in the water, killing marine animals. There is ample evidence that island eradications have killed many marine animals because rodenticide lands in the water when applied by helicopters.
USFWS justified the killing of 500,000 barred owls in western forests by claiming they are an “invasive species.” In fact, barred owls migrated from the East to the West Coasts via the boreal forests of Canada. These forests were not planted by humans and have existed since the end of the last Ice Age, some 10,000 years ago. The arrival of barred owls on the West Coast was a natural phenomenon. Barred owls are therefore not “invasive species.” In a rapidly changing climate, many animals must move to survive.
Nativists claim that most insects are “specialists” that require native plants. That claim is a gross exaggeration of the dependence of insects on native plants, which are sometimes confined to a family of plants containing thousands of both native and non-native species.
Pesticide applicators also complain about “personal attacks.” They are not alone. I (and others) have been called “nature haters,” “chemophobes,” and “climate change deniers.” Pesticide applicators feel abused. So do I.

I could go on. The list of bogus claims of the superiority of native plants and animals is long and getting longer as more and more public money is available to conduct misnamed “restorations.” Suffice to say, there is plenty of misinformation floating around invasion biology and most of it is used to defend destructive “restoration” projects. The war on nature is also a war of words.

(1) Justin Luong, et.al., “Lessons learned from an interdisciplinary evaluation of long-term restoration outcomes on 37 coastal grasslands in California.” Biological Conservation, February 2022.

The program for the Cal-IPC 2024 Symposium is available HERE. Abstracts and presentation slides have not yet been posted to the website, but they will eventually be available to the general public.

Dana Milbank: The evolution of a native plant advocate

Dana Milbank is a political columnist for the Washington Post. Like many Americans, Milbank moved his family from urban Washington D.C. to a derelict farm in the foothills of the Blue Ridge Mountains in Virginia, seeking refuge in nature from urban confinement imposed by the Covid pandemic. So began his war on nature, dictated by native plant ideology.

In a series of columns, WaPo readers observed how his battle against non-native plants developed:

The first installment of his “restoration” saga described the over-grown property that he believed he was obligated to tame: “an entire civilization of invasive vines and weeds had cruelly exploited the inattention [of previous elderly owners].” The vines were “murdering defenseless native trees.” He hired a crew to clear brush, until the cost challenged his budget. Then he bought equipment and tried to do it himself. He concluded that he could not “restore order” to his land without using herbicides. Even then, he was doubtful of ultimate success: “Clearly, I won’t be defeating these invaders. At best, I’ll battle them to a temporary truce, holding them at bay until I lose the will to fight them.” Like many city-slickers, Milbank has an unrealistic vision of what nature looks like when allowed to take its course.

Kaweah Oaks Preserve, Visalia, CA. November 2013. California Wild Cucumber, also called manroot (Marah fabacea), climbing over a native valley oak. Both native and non-native plants can be “invasive.”

In the second episode of Milbank’s battle plan, deer were his target: “I will be wielding my gun against a brutal foe—one that destroys our forests, kills our wildflowers, sickens humans and threatens the very survival of birds, mammals, insects and amphibians. I am becoming a deer hunter.” Where top predators, such as wolves and bears, have been eliminated by humans, there is an over-population of deer who browse vegetation, depriving other animals of the food and cover they need. Again, Milbank has his doubts about the effectiveness of hunting deer on his property: “I can’t pretend that my hunting will make a dent in the deer population.”
After taking Virginia’s Master Naturalist Program, Milbank’s third episode expresses his regrets as a gardener: “I’ve been filling my yard with a mix of ecological junk food and horticultural terrorists” and he warns urban and suburban gardeners that their gardens are “dooming the Earth.” He takes aim at cultivars in general and many specific species of introduced plants. Conservation Sense and Nonsense explains why most of these accusations are exaggerated, if not, patently false.
In Milbank’s column, “How I learned to love toxic chemicals,” he expresses frustration about how hard it is to eradicate non-native plants: “I was losing, badly, to the invasive vines and noxious weeds…I’d cut them back, but they would return in even greater numbers.” He fully embraces the use of herbicides to escalate his war on nature: “I have become a reluctant convert to chemicals.” He acknowledges that glyphosate is toxic, but he claims that the cut-stump application method he uses is “surgical.” He wears protective clothing, including a respirator, which is not required by the product label or California law for glyphosate applications. He is encouraged by Doug Tallamy, who calls herbicides “chemotherapy.” Conservation Sense and Nonsense explains why herbicides are doing more harm than good to the environment and everything that lives in it.

Throwing caution to the winds

In the latest installment of Milbank’s crusade against non-native plants, he tosses caution about herbicides aside. He hires a drone to spray a hayfield with glyphosate in preparation for creating a meadow of native grasses and forbs:

“To save the birds, I brought in this big bird: a 10-foot-square, Chinese-made drone with 8 propellers, capable of carrying 10 gallons of fluid, in this case glyphosate, to kill the grass in my hayfield. (It might seem counterintuitive to douse a field in herbicide to help nature, but conservationists broadly endorse the practice.)”

Herbicides are often sprayed from drones to eradicate non-native plants considered “invasive.” Source: https://www.researchgate.net/figure/Spray-drone-used-to-treat-a-patch-of-invasive-Lepidium-latifolium-on-Suisun-Marsh-The_fig3_372867398https://www.researchgate.net/figure/Spray-drone-used-to-treat-a-patch-of-invasive-Lepidium-latifolium-on-Suisun-Marsh-The_fig3_372867398

Milbank has abandoned his cautious use of herbicide and is now aerial spraying from a drone 30 feet over his head, while he watches, without wearing any protective gear:

“Shanley, in shorts, sneakers and fishing shirt, plopped in a lawn chair in the shade of my barn and, using a control pad with two joysticks, sent the drone into the sky… In a moment, the beast was airborne and, from a height of about 30 feet, spraying death on my hayfield. It sprayed the fescue. It sprayed the Johnson grass. It sprayed the foxtail. It returned, flew over the barn — and sprayed me with glyphosate. Programming error. “Sorry about that,” Shanley said. My eyes burned for two days.”

If he had been wearing safety goggles, as required for glyphosate applicators in California, he would have been spared. Milbank has the right to poison himself, his land, and the animals that live on his land. Although the applicator may be breaking laws (he would be in California) by not wearing any protective equipment, Milbank isn’t doing anything illegal.

If I weren’t reading his story in the mainstream media with a national following, I wouldn’t be writing about what he’s doing. I’m writing about Milbank’s dangerous use of herbicides because he has a big audience and his audience displays their ignorance of the dangers in over 1,400 comments.

The reader comments on Milbank’s latest article are uniformly positive, as were comments on his earlier installments about his war on nature. Most comments are short expressions of unqualified praise, such as “You are doing holy work,” or “God bless you.”

A handful of comments (including mine) express concern about the indiscriminate use of glyphosate. The few dissenting readers are blasted by Milbank’s supporters. Some of their responses betray ignorance of herbicides:

“It’s not Round Up; it’s a safe herbicide.” In fact, Milbank says he’s using glyphosate, which is the active ingredient in Round Up.
“He said nothing about dousing. It looks like a selective approach. In some cases, there is no practical alternative.” In fact, Milbank says explicitly that he’s spraying 10 gallons of herbicide 30 feet over the ground from an aerial drone. Does that sound selective?

The reader comments claiming that glyphosate is harmless brought to mind a recent article about the army of paid apologists for pesticides. The pesticide industry, in collaboration with the US government, has “established a ‘private social network’ to counter resistance to pesticides and genetically modified (GM) crops in Africa, Europe and other parts of the world, while also denigrating organic and other alternative farming methods. More than 30 current government officials are on the membership list, most of whom are from the US Department of Agriculture (USDA).”

The most common defense of Milbank’s herbicide spraying was that it only needs to be done once, with an occasional follow up prescribed burn. Milbank doesn’t actually claim that herbicide only needs to be sprayed once, but his supporters wish to believe that. Here are a few actual attempts to convert non-native grass to native grass that illustrate that such a conversion is unlikely to be possible, even after a persistent, long-term attempt.

Dunnigan plot in August 2011, after 9 years of effort, described below. Source: https://www.ecoseeds.com/road.test.html

A team of academic scientists at UC Davis attempted to convert non-native grasses to native grasses on 2 acres of roadside. At a cost of $450,000, they tried every available method (herbicides, plowing, plug planting, mowing, burning) for 9 years. When they ran out of money, they declared success, which they defined as 35% native grasses that they expected to last for no more than 10 years. (See above)
The Invasive Spartina Project in the San Francisco Bay has been trying to eradicate non-native spartina marsh grass with herbicide for 20 years at a cost of $50 million. The project was recently granted another $6.7 million to continue the project for another 10 years. The project has killed over 600 endangered birds (Ridgway rails) in the San Francisco Bay because of the loss of habitat.
One of the presentations at the 2022 conference of the California Native Plant Society was about a 20-year effort at the Santa Rosa Plateau Ecological Reserve to convert non-native annual grassland to native grassland, using annual prescribed burns. Many different methods were used, varying timing, intensity, etc. The abstract for this presentation reports failure of the 20-year effort: “Non-native grass cover significantly decreased after prescribed fire but recovered to pre-fire cover or higher one year after fire. Native grass cover decreased after prescribed fire then recovered to pre-burn levels within five years, but never increased over time. The response of native grass to fire (wild and prescribed) was different across time and within management units, but overall native grass declined.” The audience was audibly unhappy with this presentation. One person asked if the speaker was aware of other places where non-native grass was successfully converted to native grass. The speaker chuckled and emphatically said, “NO. I am not aware of any place where native grasses were successfully reintroduced.”

This map of the San Francisco Bay shows where herbicides have been sprayed on non-native marsh grass for 20 years. It is a BIG project!

Anyone with a little knowledge of how herbicides work, would know that glyphosate kills only the top-growth of an actively growing plant. Glyphosate won’t kill the seed bank of Milbank’s hayfield, which he says has been growing there for decades, perhaps as long as 100 years. That’s why glyphosate must be applied annually as the seed bank continues to produce new top-growth annually. If Milbank plants native plants after the initial spraying, they will be killed by subsequent spraying because glyphosate is a non-selective herbicide, which kills whatever it touches, both native and non-native plants. Perhaps Milbank knows this, but his readers don’t. It might explain why Milbank is not particularly optimistic about the prospects of achieving his goal of a native meadow: “Will it work? I have no idea. It could become the field of my dreams…Or it could be a costly and time-consuming failure.”

Only two of Milbank’s readers mention the damage that herbicide does to the soil, making future plantings even less likely to survive. One of those comments is from a farmer who has reason to know this important information:

“The number of things you screwed up, from possibly destroying that old man’s life, family, and farm, to messing up the winter food supply with a cascading effect for farms in your region, to obliterating a small farm, were appalling until you got to the part where you killed your soil microbes with poison. You actually killed topsoil with the idea you were going to grow healthy plants! If I were to write a caricature of a [sub]urbanite transplanted to a farming community and with the best intentions absolutely destroying everything, couldn’t have done any better than you have with your self-congratulatory actions. Farms are complex systems embedded in even more complex natural systems. Farms interact with and depend on each other. It’s where food comes from. When you kill one, you hurt all the others. You also hurt animals and plants that depend on the farm. Creating a farm, and a farming community, is hard. Destroying one is easy, and you just did it.”

This comment brought to mind a recent study about the damage that pesticides do to the soil. A meta-analysis of 600 studies “…published in the journal iScience found that soil pollution was the leading cause of declines among organisms living underground. The finding has surprised scientists, who expected farming intensification and climate change to have much greater impacts.” The co-author of the study said, “Above ground, land use, climate change and invasive species have the greatest impact on biodiversity, so we assumed that this would be similar below ground,” Victoria says. “Our results show, however, that this isn’t the case. Instead, we found that pesticide and heavy metal pollution caused the most damage to soil biodiversity. This is worrying, as there hasn’t been a lot of research into the impacts of soil pollution, so its effects might be more widespread than we know.”

A familiar story

Dana Milbank’s plans to transform a derelict farm into a native plant garden are the mirror image of the native plant movement in the San Francisco Bay, the region where I live and have observed failed native plant “restorations” for over 25 years:

Native plant “restoration” projects in the Bay Area began over 25 years ago based on the mistaken assumption that if non-native plants were destroyed, native plants would magically emerge without being planted. In other words, nativists originally believed that the only obstacle to native plants was the mere existence of non-native plants.
After 25 years of applying herbicides repeatedly, there are no more native plants in the San Francisco Bay Area than there were 25 years ago. The soil has been poisoned by herbicides and climate change and associated drought makes native plants progressively less well adapted to current environment conditions.
Despite the obvious failure of these “restoration” attempts, they continue unabated because vast sums of public money are available to keep them going. Dana Milbank will run out of money eventually, but the public coffers are never empty. Milbank is 56 years old. When he gets too old to do the work or when he dies, whatever he has accomplished will quickly revert to its previous unmanaged state. Nature will prevail and his brief conceit that humans can control nature will be history.
The public is unaware of how much herbicide is used by public land managers because application notices are not required for most pesticides. In California, for example, if the manufacturer of the pesticide claims that the pesticide will dry within 24 hours, application notices are not required by law. Glyphosate is one of many herbicides for which application notices are not required. Some land managers post application notices anyway, but many do not. The public is also ignorant of the damage that pesticides do to the environment and everything that lives in it.

The Light Eaters: Plants will find a way to survive…if we let them

“Life finds a way, if given a chance.” – The Light Eaters

The Light Eaters was written by Zoë Schlanger, a science journalist who covered climate change before writing Light Eaters. (1) She explains her pivot to botanical science as a retreat from the oppressive gloom of climate change. It proved a wise choice, as she found much to cheer us in the remarkable capabilities of plants to adapt to challenges, defend themselves against their predators and competitors, and collaborate with their plant and animal neighbors.

Ms. Schlanger believes that botanical research has lagged behind other biological inquiry partly because of a detour unwisely taken by journalists in the 1960s and 70s that projected human traits onto plants, such as intelligence and consciousness. Humanizing animals and plants is considered a dangerous source of bias by scientists. When scientists described plant behavior in human terms, they were often ridiculed by their colleagues and their research projects weren’t funded. Researchers of the capabilities of plants have been trained to avoid anthropomorphic terms to describe plant behavior. Although Ms. Schlanger tried to observe that rule, I will give myself more leeway because most of my readers are not scientists.

Plants don’t have the mobility that enables them to fly or run away from threats. We might think of them as handicapped compared to the mobility of animals. But what they lack in mobility, they more than make up for with their ability to make they own food from sunlight by photosynthesizing. And with the energy that sunlight provides, plants can create the food—such as pollen, nectar, and fruit—that entices insects and other animals to help them reproduce. So how do plants protect themselves without fleeing from their predators? That’s what Light Eaters is about.

I don’t know the source of this photo. It was sent to me in an email by someone who found it on Facebook.

How do plants perceive threats and react to them?

Plants can sense that they are being attacked by an insect in a variety of ways. They can sense the vibration of the chewing, which is closely related to how animals hear. The attack can also trigger an electrical impulse which can travel throughout the entire plant.

Plants emit chemicals in response to the attack on their leaves and roots. The chemicals can repel the insect by making the plant unpalatable. In a sense, the plant is producing its own pesticide, which has the potential to replace synthetic pesticides.

The chemicals are also wafted into the air to serve as warning signals to their plant neighbors, who can then produce their own chemicals in preparation for attack. Some plants can distinguish between an attack that threatens individuals and those that threaten the entire community. They can tailor their warning messages accordingly, to send messages only to their relatives or to the entire plant community. When plants are sprayed with herbicides, these chemical messages are masked by herbicides. (2) Likewise, pollution can also muddle the chemical messages of plants and reduce their ability to perceive and respond to threats. (3)

Plants sometimes demonstrate a preference for their relatives in other functions as well. They can make room for the roots of close by relatives and move branches to avoid shading their relatives. They can also vary these accommodations depending on available resources, making room when there is plenty of water, nutrients, and light, but not when there’s not enough.

Such warning signals can also be sent via the underground root network, which connects plants in a community to one another through the network of mycorrhizal fungi that attach themselves to plant roots. That network is also used by the community of plants to share resources, such as moisture and carbohydrates produced by photosynthesis. The fungal network enables both communication and sharing of resources. Herbicides that are carried to the roots of trees damage the fungal network, depriving trees of the nutrients they need to survive. (4) The widespread use of these herbicides by native plant “restorations” is one of many reasons why these projects rarely result in new landscapes of native plants.

Can plants hear?

One of the first discoveries of the ability of plants to find what they need is the ability of tree roots to grow in the direction of water sources. Mycorrhizal fungi attached to the roots of plants are clearly involved in guiding that connection. Over 450 million years ago, the evolution of fungi enabled plants to move from water to land by delivering moisture from soil to roots of plants, greatly increasing abundance and diversity of plants. About 80% of plants today receive much of their nutrients and moisture through mycorrhizal fungi. (5)

Now there is evidence that plants may also be able to hear the sound of water to direct the growth of roots. The researcher who made that discovery encased the roots of a plant in plastic pipe so that the roots could not sense the availability of moisture. The plastic pipe formed a “Y” to give the roots the option of growing in one direction or the other. The researcher played a recording of running water at the end of one pipe. The roots grew in the direction of the recording of running water. This is still a controversial discovery, because other researchers have found it difficult to replicate.

The replication of breakthrough scientific discoveries is one of the ways that science moves forward. It is a not a reliable method of confirming or rejecting a new discovery because there are always many variables operating simultaneously that are difficult to control, particularly in field studies, and researchers have rarely identified all the variables involved in the phenomenon they are observing.

The academic career of David Rhoades is an example of the dangers of being too far ahead of your academic colleagues and a reminder of the conservatism inherent in academic science. Rhoades was a chemist at University of Washington and the author of a study that made the first report of warning signals that plants under attack send to their neighbors via volatile chemicals in the atmosphere.

The forest on Rhoades’ campus was being killed by tent caterpillars. He studied the spread of the caterpillars until the insect infestation was stopped by the chemicals that the unaffected trees infused into their leaves. The chemicals killed the caterpillars and the spread of the insect in the forest was stopped. Backed by a mountain of carefully accumulated data, Rhoades concluded: “This suggests that the results may be due to airborne pheromonal substances!”

Rhoades was met with resistance to this new information from his colleagues. Then he had trouble replicating his original study. When his grant applications were rejected, he gave up. He left academia and taught chemistry in a local community college to make a living. Years later, other researchers figured out why he was unable to replicate his original study. The airborne chemicals that trees produce are seasonal. Rhoades’ original study was done in the spring and Rhoades was trying to replicate the study in the fall. The scientists who eventually confirmed Rhoades’ finding did so in the laboratory where conditions are easier to control.

Plants collaborate with animals to protect themselves and reproduce

The Light Eaters reports many remarkable observations of interactions of plants and animals. Here is a sampling of these stories:

If bumblebees emerge from hibernation before plants begin to bloom, the hungry bee bites the plant’s leaves to trigger the bloom that delivers the nectar the bees need.
Plants must use their limited resources to make pollen and nectar. Some plants can ration the delivery of the pollen and nectar that attracts their pollinators by timing the delivery with the anticipated arrival of the pollinator. The plant estimates the time of arrival of the insects based on its memory of past visits.
Bats find the plants they pollinate by using echolocation sonar to locate them in the dark. Some plants that are pollinated by bats have evolved saucer-like petals that act like a satellite dish to receive the sonar ping to help bats find them.
Some corn, cotton, tomato and tobacco plants can emit chemical distress signals to summon tiny parasitic wasps to kill caterpillars such as tobacco budworm and corn ear worm.
Many orchids are pollinated by wasps. Some orchids attract wasps by mimicking the chemical pheromones of the female wasp. The orchid is pollinated by the attempt of the male wasp to mate with what he supposes is a female wasp.
Some plants form partnerships with ants by secreting a sugary substance that feeds the ants, who eat the insect predators of the plant.

Can plants see?

The observation that plants are capable of mimicking animals and other plants is not new. In the early 1900s, a Russian agronomist observed that weeds in food crops have sometimes mimicked the food crop and thereby evaded the hand-weeding that was the method used by farmers to eliminate competition for their crop. Rye, oats, and lentils were initially considered weeds of wheat and rice. Over time, they evolved the seed heads that qualified them as food crops.

More recently, weeds that are killed by herbicides within crops that have been genetically modified to be resistant to the herbicide have engaged in mimicry at the biochemical level to also become resistant to the herbicide. Those who engage in chemical warfare against plants do not seem to understand that it’s a war they can’t win because evolution will enable plants to develop resistance to their poison.

Like many of the remarkable capabilities of plants, scientists can observe the phenomenon, but they are rarely able to explain the mechanism that makes it possible, beyond the evolutionary force of natural selection, which achieves a better adapted plant or animal through a series of mutations and genetic and epigenetic drift. Each change in the species is a trial balloon. If the change works, it’s a keeper. If it doesn’t, it’s in the dustbin with some 99% of the estimated 5 billion species that have lived on Earth. The dominant evolutionary force is random, irrepressible, complex change. The notion that humans are capable of stopping evolution is absurd.

In 2014, a Peruvian ecologist discovered a vine in the Chilean rain forest that is capable of quickly taking on the shape of almost any plant that it grows beside. Nicknamed the chameleon plant, many tests proved that the vine can mimic many different species of plants. Presumably this mimicry enables the vine to become invisible in the sense that it blends in with whatever plants it grows amongst. It’s a disguise, if you will, that protects the plant from its predators.

The chameleon vine is able to mimic plants that are native to their locations as well as plants that are foreign to the region. In other words, mimicry is not the result of a long evolutionary co-existence. This finding is another blow to the nativist myth that plant and insect associations are the result of co-evolution that makes insects dependent on native plants. The associations between plants and insects evolved long before the plants and insects moved into new regions. Plants and insects retain that association as they change in response to their new environment and as the result of mutations and genetic drift.

Until recently, there was a debate among scientists about how the chameleon plant morphs itself into an entirely different shape. One school of thought speculates that plants have an organ that performs much like our eyes. Another school of thought is that horizontal gene transfer (6) from the bacteria inhabiting the plant being copied to the plant doing the copying achieves this transformation.

A study (7) published in 2022 seems to support the hypothesis that some plants have some type of organ that functions like our eyes. The study found that the chameleon vine was capable of mimicking an artificial leaf. The plastic leaf contains no chemicals or bacteria.

In conclusion

The Light Eaters reports many other capabilities of plants that aren’t covered in this article. If it’s a topic of interest to you, the book is well worth reading. It’s well researched and well written. It is also thoughtful because it asks us to ponder the philosophical question of whether or not this new(ish) knowledge of plants adds up to intelligence, consciousness, and agency. Ms. Schlanger dodges that question by reminding us that there is not consensus agreement about what any of those descriptions actually mean.

Now we must add a few caveats that we hope will put this important topic into perspective:

Not every plant species has all of the capabilities described in The Light Eaters.
Those that do have such capabilities may not consistently use them because every plant is responding to a specific environment in a specific place. Plants are inseparable from their environment. A plant that has plenty of water and plenty of light behaves differently than plants with less resources. Sweeping generalizations about plants are usually ridiculous. For example, it makes no sense to claim that native berries are more nutritious than non-native berries. (8)
Plants have the potential to develop such capabilities, depending on their specific circumstances.
Without a brain or a nervous system, plants seem to organize a response to stimuli by functioning as a decentralized network.

The Light Eaters says as much about science as it does about plants. There are fads in science, just as there are fads in every human endeavor. Presently, much scientific investigation of botanical phenomenon is focused on genetics, which has misled the public to underestimate the plasticity of plants and animals. In fact, the genome of a species is a flexible repertoire, with many genes unexpressed until triggered by a change in the environment in which the plant lives. For many characteristics of species, the environment is a more powerful influence than genes.

Science is better at observing than it is at explaining. Explaining requires speculation and academic science studiously avoids speculation. The reader of scientific studies is often left in a quandary. Conclusions are often a contradictory list of maybes with a plea for funding for further investigations. That’s one of many reasons why science journalism is important to the general public’s understanding of scientific issues. Ms. Schlanger goes out on a limb for us by speaking in comprehensible terms that many scientists refuse to use. Thank you, Ms. Schlanger, for helping the public understand the plant world.

Shortly before publishing this article and after I had drafted my article, I received the following review of The Light Eaters from Arthur M. Shapiro, Professor Emeritus of Ecology and Evolution, UC Davis. He has given permission to add his review to my article.
– Conservation Sense and Nonsense

“Elizabeth Kolbert has a collective review of Schlanger and two other, similar books–“The Nation of Plants” by Gregory Conti and “Planta Sapiens” by Calso and Lawrence–in the new NY Review of Books (Oct.3). Her review is only lightly snarky because it’s clear she doesn’t know quite what to make of the “plant neurobiology” fad.

“When I read Schlanger (I haven’t read the others) I dug back into my library to find my copy of “The Secret Life of Plants” by Peter Tompkins and Christopher Bird (1973). I doubt that Kolbert realizes that the current fad is a rerun of the 70s! Unlike Schlanger and perhaps the others reviewed by Kolbert, Tompkins and Bird is packed with overt woo-woo and makes little attempt to be “science-based.” The frank woo-woo is very 70s. But the underlying motivation for both waves is the same: philosophical panpsychism, the notion that consciousness is ubiquitous in Nature.

“There is nothing in the actual data discussed by Schlanger that obliges one to embrace panpsychism. The main reason to do so is that one WANTS to. That is, for some (many?) people it is very reassuring to believe that at least the biosphere, if not the entire universe, is sentient. (This has resonances with the Gaia Hypothesis.) This notion is an integral part of a number of cultural cosmologies, of which the most familiar to most Americans is probably Native American, broadly speaking. In the 70s many hippies embraced the Native American notions of “tree people,” “stone people,” etc. Some still do.

“Remember that I have taught community ecology for some 50 years, with an emphasis on coevolution. Things like inducible anti-herbivore defenses (chemical or morphological) and communicable defensive messages (plant pheromones, if you will) come as no surprise. Rather, they are predictable consequences of natural selection: if something can evolve, it probably will. There is no logical necessity to invoke intelligence or consciousness to account for them. If you want to, go right ahead. But don’t call it science!

“I have never had a chance to pull up a mandrake plant. In the Middle Ages it was widely believed that if you did it would shriek, and the sound if heard would drive one mad. Thus one must cover one’s ears when doing so. Now, that is framed as a testable hypothesis!

“Are you familiar with the walking fern? If not, Google it. I am very fond of it, but never for a moment would I claim it has the property of wanderlust.“

Arthur M. Shapiro, Professor Emeritus of Ecology and Evolution, UC Davis

Zoë Schlanger, The Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth, Harper Collins, 2024. The Light Eaters is the source of information in this article unless otherwise noted.
Behrend*, J.E., & A.L. Rypstra (2018) Contact with a glyphosate-based herbicide has long-term effects on activity and foraging of an agrobiont wolf spider. Chemosphere 194:714-721 doi: 10.1016/j.chemosphere.2017.12.038
“Polluted Flowers Smell Less Sweet to Pollinators,” New York Times, February 16, 2024
K. Hage-Ahmed, “Arbuscular mycorrhizal fungi and their responses to pesticides,” Pest Management Science, September 25, 2018
Thomas Halliday, Otherlands, A Journey Through Earth’s Extinct Worlds, Random House, 2023
Conservation Sense and Nonsense, “All Life on Earth is Related”
Jacob White and Felipe Yamashita, “Boquila trifoliolata Mimics leaves of an artificial plastic host plant,” Plant Signaling Behavior, 2022
Conservation Sense and Nonsense, “Baseless Generalizations in Doug Tallamy’s Nature’s Best Hope”