native plant movement – Page 3 – Conservation Sense and Nonsense

When ideas remain unexamined and unchallenged, they intimidate ©

My last article of the year is a guest post by Marlene A. Condon, the author/photographer of The Nature-friendly Garden: Creating a Backyard Haven for Plants, Wildlife, and People (Stackpole Books; information available HERE.) You can read her blog In Defense of Nature.

Merry Christmas !

Million Trees

A birds-eye view of the University of Virginia (UHall seen in first photo) in Charlottesville, Virginia, makes clear that there are plenty of native trees to be found in developed areas.

The novelist E. L. Doctorow, in a 1989 conversation with PBS journalist Bill Moyers, said, “When ideas go unexamined and unchallenged for a long enough time, they become mythological and very, very powerful. They create conformity. They intimidate.”

He could have been speaking about the current environmental narrative regarding so-called invasive plants. Anyone who speaks out feels the wrath of the folks pushing their fictional environmental manifesto; I’ve lost jobs because of these people.

Most neo-scientists and -environmentalists, having arrived late to the party, have no clue as to why some alien plants exist in profusion along roadways, in former farm fields, and along trails in forests. The popular notion that native plants would otherwise be filling those areas is easily accepted by people who don’t possess knowledge of soil science, or who lack experience with gardening and/or closely observing the natural progression of plants in unmanaged, disturbed areas.

Knowing the prior history of the land is essential to understanding why particular nonnative plants fill some areas. Road building discomposes soil. Trail development/use and cows/farming-equipment moving over the land compact soil. Only “colonizer plants”—those capable of thriving under the altered and nutrient-poor conditions of these sites—can grow there.

Usually such areas, after many years, support a mix of native and nonnative pioneers, but sometimes alien plants outnumber the natives because they are best suited to the constraints imposed by the physical attributes of the site. Anyone (no Ph.D. required) can verify this statement by taking the time to observe the progression of plants in an area not revegetated by people. Doing so would make clear that alien plants do not “push out” native plants by “invading” and “taking over”, but rather, they fill disrupted areas where few native plants can successfully grow.

Yet, the desire by scientists and environmentalists is so great to get folks to remove supposedly invasive plants from the environment that we now have tall tales being spread. Herewith a sampling of some of the most egregiously untrue declarations regarding alien plants.

Johnny Randall, Director of Conservation Programs at the North Carolina Botanical Garden (University of North Carolina at Chapel Hill) wrote a New Hope [North Carolina] Audubon blog post called “Invasive Plants Are NOT for the Birds.”

He writes that, “The scientific literature on invasive plants and bird-dispersal is moderate but growing, and almost all of the research warns that this is a serious and multi-layered phenomenon. First off – birds either do not discriminate between native and invasive plants or often prefer invasives over natives. One reason for this is that a large proportion of invasives are high in carbohydrates, whereas the natives are often higher in protein and lipids/fats. Birds are consequently (pardon the analogy) choosing candy bars over cheeseburgers, which could affect bird nutrition, particularly during fall migration”.

The suggestion that birds are choosing “autumn olive berries [that] are sugary sweet treats, the junk food of the bird diet” is echoed by many people. This quote, from a letter to the editor of The Crozet Gazette by Susan A. Roth, William Hamersky, and Manuel T. Lerdau, Ph.D., is supposedly based upon a study published by the Wilson Journal of Ornithology in March, 2007, entitled “Fruit Quality and Consumption by Songbirds during Autumn Migration”.

Yet this study states that “Most common fruits on Block Island [where the study took place in Rhode Island] contained primarily carbohydrates…and little protein…and fat.” As the research paper’s authors were mainly speaking of native plants, this statement directly contradicts that of Mr. Randall that natives are often higher in proteins and fats than so-called invasives.

Additionally, the research paper’s authors state that “fruit selection by birds on Block Island was not simply related to differences in macronutrient composition between fruits…studies of wild and captive songbirds have shown that some species preferentially select high-fat fruits…or high-sugar fruits…”, which hardly implies that Autumn Olive fruits are a necessarily inferior food choice, as declared by Roth, et al.

A variety of foods exists to serve a variety of purposes. Turning sugar into something “bad” for birds comes as a result, perhaps, of this same application to human nutrition. But sugar is not in and of itself, “bad”. A runner in need of glucose who eats some jelly beans gets a quick burst of energy to continue exercising. There’s absolutely nothing wrong with that.

Sugar is only a problem if it’s eaten in excess, as might be done by children. But birds are not children; if they feel the need for protein and fat, they will search for insects and fruits that offer what they need.

Furthermore, Director Randall wrote that “Researchers have also shown that many invasive plants have fruits that persist longer than do native plant fruits into the fall and winter. The invasives are therefore available when our natives are not.”

In a world of disappearing habitat for wildlife because of human development, the fact that fruits on invasive plants are available when native-plant fruits are depleted should be seen as a positive rather than a negative.

Charlottesville, Virginia, residential area, has so many trees that you can’t see the roadways interspersed among them. In other words, insects and birds aren’t disappearing because alien plants have replaced native trees.

“Recent research published by Narango et al., in the October 22, 2018, issue of the Proceedings of the National Academy of Science demonstrates that native plants are best for birds. The research showed that yards landscaped with the usual garden center plants, which are mostly nonnative ornamentals, could not support a stable population of chickadees. Yards where native plants composed at least 70 percent of the plantings were able to do so. This is because native plants host more insects than non-natives and therefore provide the necessary high-protein food that birds need to feed their chicks.” [from a letter to the editor of The Crozet Gazette by Susan A. Roth, William Hamersky, and Manuel T. Lerdau, Ph.D.]

Narango’s study cannot be generalized to all birds, although many people have made the mistake of claiming it can. This study applies only to chickadees and certain other birds that inhabit forest because such species are dependent upon the native plants (trees) that comprise our forestland. In other words, if you want forest birds to reproduce in your yard, your yard must be forest. For a fuller explanation, please read “Chickadee Chicanery” at In Defense of Nature.

“These invasive species not only impact our forests, wetlands and streams, but also our economy, health and safety. They kill the trees that shade our homes and that our kids play hide-and-seek around. They increase the presence of other disease-spreading species like ticks. They diminish visibility along trails where safety is important”. [quote from an article from the Central Ohio Partnership for Regional Invasive Species Management at a Nature Conservancy-sponsored website]

The only “forests” where you will see alien-plant species are those that are either managed improperly (overly thinned and thus allowing too much sunlight to reach the ground under the trees) or those that are actually “woods” in the process of succession (transforming from a field to a forest that has not yet reached maturity). “Invasive” plant species are sun-loving and therefore do not inhabit shady mature forests.

As for killing trees, if “they” refers to vines (a common complaint in the eastern U.S.) one must ask, why was the homeowner unable (or unwilling) to keep a vine from killing a tree in his yard that his “kids play hide-and-seek around”? However, if “they” refers to nonnative animals and/or diseases killing trees, that is a different situation altogether, which is not the point of this article. It’s unfortunate the writer did not make clear what “they” referred to. As far as I can tell, there’s no proof that “invasive” plants, in general—as stated above—increase the presence of organisms such as ticks. A study published in Environmental Entomology

purportedly shows that barberry-infested plots support more mice and thus ticks than plots in wooded areas with no barberry.

However, the “no barberry” plots were severely browsed by deer and thus “little understory vegetation was present.” In other words, these scientists compared two completely different habitats, which explains the greater number of ticks in the shrubby (Japanese Barberry) area that provided “questing habitat [for] blacklegged ticks [whereas] little other suitable vegetation exist[ed] in [the] severely browsed forests.”

“Questing habitat” refers to plants upon which ticks can wait at the appropriate height to grab onto an animal that comes by. Obviously, ticks are not going to be found in an area with little understory vegetation as they have nowhere to sit and wait for their quarry.

And we’re to believe “invasive” plants diminish visibility along trails, and native plants don’t? It sounds more like the folks who are supposed to be maintaining the trails have been derelict in their duties!

It’s clear that scientists and journalists are doing everything they can to assure that government and the general public view so-called invasive plants in a negative light. Yet, to my knowledge, no study condemning “invasive plants” exists that has the least bit of merit.

Marlene A. Condon

Addendum by Million Trees

Nativism turns a blind eye to climate change

“Reflexive demonization of alien species ignores the beautiful but complex truth that nature fights to find a way—and for a planet navigating the pressures of climate change and overpopulation, that just might be our saving grace.” – Marianne Willburn, Garden Rant

Margaret Renkl writes an opinion column for the New York Times that I usually enjoy because she frequently writes about nature, often based on observations of wildlife in her own garden. She lives in her childhood home in Nashville, Tennessee. Much of her garden was planted with non-native plants and trees decades ago by her deceased mother. Yet, in a recent column, Ms. Renkl blames non-native plants for a variety of crimes against nature.

She suggests that non-native trees are blooming earlier than native trees, which she says has “skewed our experience of spring.” She is apparently unaware that spring does indeed arrive earlier than it has in the past because of climate change. Warmer weather arrives earlier, triggering the blooms of spring, not vice versa. Both native and non-native plants are blooming earlier than they did in the past.
She suggests that gardens planted with non-native plants are “blooming wastelands where the flowers feed nobody at all,” yet her columns are usually filled with the wildlife that lives in her own garden, with introduced plant species.
Although she does not use pesticides in her own garden, she believes that her neighbors’ non-native gardens require them to use pesticides that kill wildlife. She says, “The typical suburban yard is actually worse than a wasteland. It’s a death trap.” She does not seem to know that most herbicide is used to kill non-native plants, not native plants nor does she seem to realize the contradiction in her indictment of gardening with non-native plants. If there are more insects living in native gardens than non-native gardens, why would more pesticide be needed in non-native gardens? If people could learn to love the clover, dandelions, and English daisies in their lawns as much as I do, they would use less “weed killers” on their lawns.

Ms. Renkl’s misperceptions about non-native plants seem to be based on a mistaken belief in their origins. She says, “Ambulatory and omnivorous, human beings are a migratory species. That’s not true for the vast majority of plants.” In fact, plants are just as mobile as animals, including humans. Plants are carried by birds, animals, wind, ocean currents, etc. They come and go as the climate changes, as it has many times in the past 500 million years that plants have existed on Earth. Plants now considered non-native existed here in the distant past, in a different climate. Here are a few examples of such dispersals; most occurred before humans even existed:

Although Dawn Redwoods are now considered non-native in California, there is fossil evidence that they lived here 40 million years ago.
Pollen remains of rhododendron now being eradicated as an “invasive” alien in the United Kingdom, indicate that they lived there over 30,000 years ago.
The oldest known fossils of eucalyptus are 52 million years old. They were found in Argentina, where eucalyptus no longer grows naturally. Eucalypts were planted in Argentina by Europeans as agricultural crop protection and more recently for pulp, as they were in many countries all over the world.
This is a map from a study, showing pre-historic oceanic dispersals of plants from one continent to another: (1)

The ability to migrate is essential to the survival of plant and animal species. As the climate changes, this survival strategy is quickly becoming even more important. When we demand that plants be restricted to their historical “native” ranges, we doom them to extinction because when the climate changes, the vegetation must change.

Where did Ms. Renkl learn these myths?

Ms. Renkl’s cites Doug Tallamy’s Nature’s Best Hope as one of the sources of her mistaken beliefs. Tallamy considers the existence of non-native plants the root of all evil in nature. He calls them “ecological tumors.” He blames non-native plants for declining populations of both native plants and insects, and by extension to declining populations of birds that eat insects.

In Nature’s Best Hope, Tallamy says, “…we must not use climate change as an excuse to do nothing. Most species of plants and animals are far more resilient to climate variability than we give them credit for. Besides, increasing the number and biomass of the plantings in our yards and public spaces is one of our most accessible and convenient tools to fight climate change.” The problem with Tallamy’s dogma is that it inspires the public and land managers to eradicate established landscapes that are not native based on Tallamy’s claims that non-natives are “crowding out” native species and depriving wildlife of food. All native plant “restorations” begin by eradicating non-native plants, usually with herbicides that retard new growth. In other words, the native plant ideology is causing the loss of vegetation and therefore the loss of stored carbon and the reduced capacity for carbon sequestration in the future. The native plant ideology is not increasing biodiversity, nor is it “fighting climate change.” It is more destructive than constructive.

I’m not looking for “an excuse to do nothing.” On the contrary, I believe every effort must be made to stop or at least slow down the inexorable advance of climate change. The most basic effort we can make is to stop destroying functional vegetation, especially trees. Then, there is a lengthy list of what we should be doing to reduce greenhouse gas emissions, which is another, equally important topic.

Native plant advocates consider climate change irrelevant because they believe the existence of non-native plants is the sole culprit of all problems in the environment. They see every environmental issue through the narrow lens of their dogma. This comment on an article about the value of non-native plants by Marlene Condon published in [Chesapeake] Bay Journal is an example of such a misinterpretation of an environmental issue:

“English ivy is an evergreen, non-native, invasive groundcover that has demolished undisturbed natural areas…In salmon country that’s the difference between clean, cold streams and warmer streams filled with sediment.”

Eradicating ivy on stream banks is likely to produce more sediment because it will take some time for replacement vegetation to cover the ground, especially if herbicides are used to eradicate the ivy. Water is warmer in streams because of climate change and because there is less water due to water diversion and droughts. There are many other reasons for declining populations of salmon, particularly dams that prevent salmon from reaching their spawning grounds upstream.

Treat the cause, not the symptom

The native plant ideology ignores the underlying causes of changing ecosystems. Most changes are caused by the activities of humans, such as agriculture, development, water diversion, and pesticides. Climate change is the underlying cause of some changes in nature and it will steadily become a more important factor. Eradicating non-native plants will not reverse any of those changes nor will it prevent changes in the climate.

Alan de Queiroz, “The resurrection of oceanic dispersal in historical biogeography,” Trends in Ecology and Evolution, 20 No. 2, February 2005

Photo credit for featured photo: Garden Rant, Marianne Willburn

Computer models predict the future? Garbage in, garbage out

Computer modeling is an increasingly popular tool used in ecological studies. The rapidly changing climate is putting pressure on scientists to predict the trajectory of the change and the impacts those changes will have on the environment. However, a computer model is only as predictive as the assumptions used to build it. In other words, “garbage in, garbage out.”

That sets the stage for a study published in 2018 that predicted that “grassland may be a more reliable carbon sink than forests in California.”(1) The study was quickly adopted by native plant advocates as a weapon in their battle to destroy non-native trees in favor of grassland they prefer. (2) They prefer grassland because it was the pre-settlement coastal landscape. They don’t acknowledge that burning by Native Americans and grazing by native ungulates were the primary reasons why grassland did not succeed to shrubs and forests prior to settlement. Pre-settlement grassland was as much a human creation as any modern landscape.

Most carbon storage is below ground, in roots and soil. That is true of both grassland and forests. If the forest burns, the carbon it has stored in soil remains, just as the below ground carbon sink of grassland remains.

The study (1) that claims grassland may be a more reliable carbon sink than forests reaches its erroneous conclusion by comparing below ground carbon storage in grassland with above ground carbon storage in forests. It’s a classic case of inappropriately comparing apples with oranges to the disadvantage of forests. It seemed such an unlikely comparison that I asked the study’s authors to confirm they had compared below ground carbon storage in grassland with above ground carbon storage in forests. They confirmed that they did, indeed, make that inappropriate comparison.

The study also bolsters its mistaken conclusions by erroneously claiming that forests are more likely to burn than grasses:

“The fire resistance for grasses is 0.5 while that of trees range from 0.1−0.3, making grasses more resistant to wildfires than trees, which is roughly consistent with field-observations since in the event of a wildfire, when compared to trees, a smaller fraction of the biomass of grass is damaged.” (1)

However, the study cited as the source of this statement (3) says exactly the opposite:

“The fraction of individuals killed depends upon the prescribed PFT fire resistance, which represents the PFT survivorship during a fire (see Table 1). In the fire model, grasses and litter are fully consumed.” (3)

Table 1 PFT parameter values for fire resistance
PFT	Fire Resistance (%)
Woody
Tropical broad-leaved evergreen	12.0
Tropical broad-leaved raingreen	50.0
Temperate needle-leaved evergreen	12.0
Temperate broad-leaved evergreen	50.0
Temperate broad-leaved summergreen	12.0
Boreal needle-leaved evergreen	12.0
Boreal summergreen	12.0
Grasses
C3 grass	100.0
C4 grass	100.0

Table 1 is consistent with this statement in the abstract of the cited study: “Estimated litter moisture is the main driver of day‐to‐day fire probability.” (3) Forests retain more moisture in the soil and leaf litter because of the shade provided by the tree canopy. I wrote to the study author again, asking “where is the source of your statement that grasses are more fire resistant than trees?” He did not reply.

If a study doesn’t seem to make sense, or it contradicts other sources of information, it is worthwhile to look under the hood. What is driving the model? Is it fueled by hot air? Is it serving an activist agenda? Are cited studies accurately quoted?

Some truth emerges from the model’s black box

Despite the erroneous assumptions of the computer model used by this study, there is some truth in the conclusions it reaches. Vegetation type conversions are occurring now and they will continue as the climate continues to change because when the climate changes, the vegetation changes. We are presently witnessing the transition of native conifers at high altitudes to lower altitude hardwood trees. Although these changes will occur gradually and there will be many intermediary transitions, the fact is that grassland is more likely to survive than forests in a warmer, drier climate in the long run.

The Guardian has published a comprehensive report about the loss of forests all over the world. In the Rocky Mountains, one-third of places where trees burned 20 years ago are now occupied by shrubs and flowers. About 15% of forests in the Rocky Mountains are not expected to grow back if killed by fire because the climate is no longer suitable for them. About half of existing forests in Alberta, Canada are expected to vanish by 2100. The “megadrought” in south-western US is expected to convert 30% of forests to shrubland or another type of ecosystem.

In the short run, the loss of forests can be mitigated by reforestation with tree species that are better adapted to a warmer, drier climate. The study (1) acknowledges the potential for mitigation to preserve forest ecosystems: “Factors such as species traits, biodiversity, rapid evolution, and human management intervention could alter our model-based findings from the projections provided here. Consequently, our results indicate the potential direction of change as opposed to predictions that consider the full ensemble of ecological, physiological and management factors that can alter pathways and responses of ecosystems to climate change.”

From the standpoint of carbon storage, it is not good news that grassland is likely to inherit hot, dry lands previously occupied by forests. Forests and wetlands store more carbon than grasslands, as the above chart in a USDA publication about carbon storage shows. Sustaining below ground carbon sinks will depend on carbon sequestration by above-ground plants and trees. Because above-ground carbon sequestration is primarily dependent upon the biomass, forests will always do a better job than grassland in the long run. In the short-run, grassland will grow back more quickly than forests, but it will never achieve comparable biomass.

Forests are presently absorbing about one-quarter of all human carbon emissions annually. Forests make a significant contribution to reducing carbon emissions, but planting trees is not a panacea as long we continue to burn fossil fuels to generate energy. The loss of carbon-sequestering capabilities of forests will exacerbate climate change in the long-run. It’s one of many dreaded feedback loops that are reaching tipping points: the impacts of climate change are destroying the mechanisms that mitigate climate change.

The study (1) acknowledges that by the end of the 21^st Century, under current climate conditions (warming limited to 0.3⁰ – 1.7⁰ Centigrade) forests will have removed 5 times more net carbon (carbon storage minus carbon loss) per hectare from the atmosphere than grassland in California. See Table 1 in the study (1). Thus, the study agrees that forests store more carbon than grassland.

From the standpoint of wildlife, it is not good news that grassland is likely to replace forests in a warmer climate. The insects, birds, and animals that live in the forest will lose their habitat. Forests are home to over 80% of terrestrial species. We will lose our shade in a warming climate and our windbreak.

Not an argument for destroying forests

This study (1) is unfortunately being used by the native plant movement to advocate for the preemptive destruction of healthy urban forests that are not more likely than native forests to burn in wildfires. Virtually all wildfires in California occur in native vegetation. There is no advantage to destroying healthy forests that are expected to live for another 100-200 years. We don’t amputate our limbs to avoid breaking them. Nor should we destroy our forests before they die.

(1)“Grasslands may be more reliable carbon sinks than forests in California,” Pawlok Dass, Benjamin Z Houlton, Yingping Wang and David Warlind, 10 July 2018, Environmental Research Letters, Volume 13, Number 7

(2) “Importance of Grasslands for Carbon Storage,” Yerba Buena Chapter of California Native Plant Council, Quarterly Newsletter, March 2021, page 6.

(3) “The role of fire disturbance for global vegetation dynamics: coupling fire into a dynamic global vegetation model,” Thonicke K, Venevsky S, Sitch S and Cramer W 2001, Glob. Ecol. Biogeogr.10 661–77

Nobody cares where a pretty wildflower is from

The feel-good ending of the local news broadcast on Channel 7 (ABC) on February 17, 2021, featured this video of a huge field of oxalis (Bermuda buttercup, Oxalis pes-caprae) blooming on the roadside of Highway 1 in Santa Cruz County. People were stopping along the road to admire the bright yellow blooms of spring and photograph them. No one said anything about where the plant “belongs,” and no bad words were spoken about this useful plant that native plant advocates love to hate.

Click on the picture to activate the video

Despite its beauty and utility, oxalis is sprayed with one of the most toxic herbicides on the market in public parks and open spaces in the Bay Area. San Francisco’s Recreation and Parks Department has been spraying oxalis in several public parks for over 15 years. San Francisco Forest Alliance (SFFA) published a brilliant article about this pointless and destructive crusade that was republished by Conservation Sense and Nonsense in 2015. That article about the many benefits of oxalis is one of the most popular articles on this blog; it has been viewed by over 10,000 readers and many more on the SFFA website. We invite you to visit it and we summarize it briefly here:

Oxalis blooms briefly in early spring and dies back before summer begins, leaving the ground to other plants. It does not kill other plants, rather it co-exists briefly during its annual bloom.
Oxalis is very useful to pollinators and its tuberous roots (bulbils) are eaten by ground dwelling animals such as gophers.
Oxalis is called sour-grass because of its pleasant-tasting tang and it is often eaten by children.
Triclopyr is the active ingredient in the herbicide that is used on oxalis during its blooming season. It damages the soil by killing beneficial fungi and microbes, and it is toxic to many animals.

The annual poisoning of oxalis on Mount Davidson was recently videotaped by Ron Proctor and published by the San Francisco Forest Alliance. A crew of 5 men was hired to do the deed. Ironically, this spraying of oxalis on Mount Davidson in San Francisco was taking place at the same time that tourists were admiring oxalis in a neighboring county.

Oxalis is not an isolated example of a non-native plant that is admired by the public, but hated by native plant advocates and public land managers who do their bidding. As a member of the Sierra Club, I receive emails alerting me to opportunities to advocate for the protection of the environment. The most recent email featured a picture of a yellow wildflower in the foreground of a photograph of a Bay Area landscape:

The yellow wildflower in the foreground is Black Mustard (Brassica nigra). I responded to the Sierra Club’s email:

“The plant in the foreground of your photograph appears to be Brassica nigra: ‘Brassica nigra, or black mustard, is an annual plant cultivated for its black or dark brown seeds, which are commonly used as a spice. It is native to tropical regions of North Africa, temperate regions of Europe, and parts of Asia.’ Wikipedia

“I hope the use of this photo in this Sierra Club email to its members means that the Sierra Club is finally prepared to accept the reality of the presence of non-native plants in our public parks and open spaces. The Sierra Club’s support for unnecessary and destructive eradication projects has been regrettable, particularly because they require the use of harmful herbicides. I hope this email is an indication that the Sierra Club is finally ready to reconsider this futile crusade.”

I received this disappointing reply from the Sierra Club: “The staffer who puts together our newsletter isn’t a plant buff and wouldn’t have known the difference. But I am a plant buff and review the newsletter and know the difference between a mustard and a native plant. I somehow just overlooked that photo entirely. Thanks for bringing it to my attention. I’ll be more careful in my review of the newsletter in the future (look more carefully at the photos). And we’ll change the online version.”

The beauty and resilience of weeds

Dandelion by Mona Caron. Click on the picture to see more murals by Mona Caron. Mona is a Swiss artist who became a muralist in her adoptive hometown San Francisco, California. She is best known for her multi-story murals celebrating the rebellious resilience of weeds.

The Bottom Line

The general public doesn’t care where plants came from. The public recognizes and values beauty wherever it is found. Unfortunately, our public lands are in the death grip of the native plant movement and environmental organizations that should be objecting to the use of herbicides in our public parks and not promoting that destructive agenda. The crusade against non-native plants has been responsible for spraying our public lands with dangerous pesticides for over 20 years. They have little to show for their toxic crusade, perhaps because the herbicides damage the soil and make the survival of native plants even less likely.

The featured photo at the top of this article was taken in Glen Canyon, another public park in San Francisco where oxalis has been sprayed annually for many years. The copyright photo of a coyote in a field of oxalis was taken by Janet Kessler and is shown with her permission.

Fact vs. Fiction: The real threats to native plants in California

The enduring fiction of the native plant movement is that the existence of non-native plants threatens the existence of native plants by “crowding out” native plants. If that were true, we should expect to see some evidence of such a causal relationship after 250 years of steadily increasing numbers of non-native plant species. But we don’t.

Marcel Rejmanek (UC Davis) is the author of the most recent report on plant extinctions in California, published in 2017. At that time there were 13 plant species and 17 sub-species native to California known to be globally extinct and another 30 species and sub-species extirpated in California but still found in other states. Over half the globally extinct taxa were reported as extinct over 100 years ago. Although grassland in California had been converted to Mediterranean annual grasses by grazing domesticated animals decades before then, most of the plants now designated as “invasive” in California were not widespread over 100 years ago.

Most of the globally extinct plant species had very small ranges and small populations. The smaller the population, the greater the chances of extinction. Most of the globally extinct plants were originally present in lowlands where most of the human population and habitat destruction are concentrated. Although there are many rare plants at higher altitudes, few are extinct. Plants limited to special habitats, like wetlands, seem to be more vulnerable to extinction. The primary drivers of plant extinction in California are agriculture, urbanization and development in general.

Non-native plants are the innocent bystanders to disturbance

“Invasive species” are mentioned only once in the inventory of extinct plants published by California Native Plant Society and only in combination with several other factors. However, the identity of this “invasive species” is not clear. Rejmanek suggests that the “invasive species” rating refers to animal “invasions” by predators and grazers. He says, “Indeed, one needs quite a bit of imagination to predict that any native plant species may be driven to extinction by invasive plants per se.” (1)

Although climate change is not cited as the cause of any of the known plant extinctions in California, Rejmanek predicts that climate change is likely to be a factor in the future, not only because of the impact of drought and higher temperatures, but also because non-native plants may be better adapted to changed conditions.

There are over 1,000 naturalized non-native plant species in California. Their presence is associated with human disturbance. Naturalized non-native plants are a symptom of disturbance, not the cause. The impact of non-native plants on native plants cannot be separated from other factors that created the conditions for success of non-native plants.

Specialized insects are exaggerated

Another popular fiction among native plant advocates who love to hate non-native plants is that specialized insects—especially pollinators—require specific native plant species. Again, the record of plant extinctions in California does not support that myth: “…there is no indication that the loss of pollinators was an important factor in plant species extinctions in California. [For example, one of the native plant species extirpated in California] has many documented non‐specialized pollinators. There does not seem to be any particular dispersal mode associated with presumably extinct plants in California.” (1)

Putting plant extinctions into context

Mediterranean Climates are found in coastal temperate zones. Mediterranean climates are characterized by hot dry summers and mild wet winters.

Setting sub-species aside, there are 5,280 identified native plant species in California and 28 known extinctions of native plant species, including 15 plant species known to still exist in other states. Only .53% of California native plants are known to be extinct in California, about one-half of one-percent. Does that seem like a lot? Rejmanek compared the extinction rate in California with other Mediterranean climates. The extinction rate of native plants in California is similar to those in the European Mediterranean Basin, South Africa, and Australia, but a little greater than the rate in Chile, where there are fewer endemic plants that exist only in Chile. Endemism is associated with small native ranges and small populations that are more vulnerable to extinction.

Why are there many endemic plants in California?

About 40% of native plant species in the California Floristic Province are endemic, found only in California and in most cases only in small areas within California, including our off-shore islands. Their small populations in isolated geographic areas, sometimes within unique ecosystems, such as alkaline sinks, make them particularly vulnerable to extinction.

The evolutionary history of endemic plant species explains why there are so many in California. Endemic plants are close relatives to plants that exist elsewhere and are sometimes plentiful where they came from. For example manzanita is a genus of chaparral shrub that is plentiful in California, but there are also many rare endemic manzanita species that occur only in small areas and small populations. There are several endangered manzanita species in the Bay Area (pallid, Raven’s, Franciscan).

Franciscan manzanita is one of 2 endangered manzanita species in San Francisco. There is one individual plant left of each of these two manzanita species. There are many endemic plants and insects in San Francisco and several are now extinct. San Francisco has a complex, diverse geology and topography and it is surrounded on 3 sides by water, creating many small, isolated microclimates in which many endemics have evolved.

The geography of California explains why the evolution of a plant species diverged from its plentiful ancestors to become an endemic species in a small geographic area. Plants move around in a wide variety of ways, most natural, without the aid of humans. Their seeds are dispersed by animals and birds that eat them or inadvertently carry them to another location. Sometimes their seeds are carried on the wind or brought to islands by storms and currents.

When a plant arrives in a new location that is isolated from its original home and therefore cannot mate with its relatives, it begins its own, independent evolutionary history. Each successive generation is reacting to its new environment, rewarding its fitness with its new home with a successful new generation. Each generation rolls the genetic dice, its genome drifting away from its ancestors in a random way. Occasionally a mutation will occur that alters the evolutionary trajectory. Eventually, the plant in its new home is sufficiently genetically distinct that taxonomists are ready to call it a separate species. Naming a new species is a judgment call, often questioned by some taxonomists, called “lumpers” as opposed to the “splitters” who are ready to name it a new species.

The factors that result in endemic species are many, but broadly speaking they are mobility and, ironically, isolation. California is one of the most geographically diverse states in the country, with corridors for mobility, but many barriers that create isolation. Gordon Leppig describes California’s geographic diversity in Beauty and the Beast: California Wildflowers and Climate Change, published by California Native Plant Society: “The state’s natural wonders include five deserts, the highest and lowest points in the continental United States, the third-longest state coastline (about one thousand miles), the most national parks (nine), the most federally designated wilderness areas (more than 140), the highest percentage of wilderness in the contiguous United States (14%), the most diverse conifer assemblage outside the Himalayas, the most federally listed species….” The multitude of different ecosystems with unique microclimates produces one of the most diverse floras in the world.

Click on the picture to watch the movement of tectonic plates over one billion years. Watch California slowly emerge as the jigsaw puzzle takes shape. California is the edge of two tectonic plates that collide and grind past one another perpetually, uplifting and dropping the land into fractured geomorphic pieces.

Human activities penetrate the barriers that created genetic isolation in the past. Our roads become corridors for the biological exchange that threatens small, isolated pockets of rare plants. Trade and travel has ended the isolation of off-shore islands. Our roads and dams also create new barriers for mobility. In other words, we are altering pre-settlement corridors and creating new ones. We should expect consequences for our ecosystems for the changes we have made.

Given the number of rare and endemic plants in California and the changes in the environment required to accommodate nearly 40 million human Californians, it seems that extinction of less than one-half of one percent of native plants is a surprisingly small loss.

(1) Marcel Rejmanek, “Vascular plant extinctions in California: A critical assessment,” Diversity and Distributions, Journal of Conservation Biogeography, 2017

Migration: Life on the move

Sonia Shah’s recently published book, The Next Great Migration: The Beauty and Terror of Life on the Move, takes a deep dive into the past to trace the ancient history of migrating life on Earth. For as long as life has existed on Earth, life has been on the move, as needed to survive the constantly changing environment in which all plants and animals live.

1 Homo sapiens
2 Neanderthals
3 Homo erectus

Shah’s is an ambitious attempt to tell this story, not confined to human migration, but encompassing plants and animals as well because all of these migrations are connected. Scientists speculate the earliest migrations of human ancestors, some 100,000 years ago out of Africa, were in pursuit of the migrating animals that humans hunted. On balance, the movements of plants and animals are beneficial to life on Earth because they are necessary to survive. When they aren’t beneficial, the problems are usually short-lived and humans are usually unable to stop them because nature is more powerful than we are.

Click on map for animated movement of animals in response to changing climate conditions.

Migrations are even more frequent at a time of rapid and extreme climate change. As crops fail in the withering heat and drought caused by global warming, farmers are abandoning their farms to find the food they need to survive. Hence, Shah’s prediction that we are about to witness the “next great migration” because of the challenges of climate change. When the climate changes, the vegetation changes. When the vegetation changes, animals must move to find the food they need. Humans wish to put ourselves in a special category that denies our kinship with animals. But we are as dependent upon our food as any animal and the changing climate will challenge our existence as much as other forms of life.

Shah also traces the brief history of human knowledge of migrations about which little was known before the development of the scientific tools to study it. Paleontology could dig up fossils that would raise more questions than answers about the residents of deep time, but it wasn’t until the development of molecular analysis that fossils could inform scientists of the evolutionary history of and close relationships among plants and animals that reflect migrations in the distant past. New technology is capable of tracing the movements of animals that were unknown in the distant past, when animals seemed to mysteriously disappear at the end of one season and returned at the beginning of another season.

Invasion Biology is based on ignorance of migration

The fact that animal migration was largely unknown led to some fundamental misunderstandings about nature, including the unfortunate rise of nativism in the natural world that was spawned by the mistaken hypotheses of invasion biology. Shah explained the consequences of inadequate knowledge of migration in a recently published article in New York Times Magazine:

“When scientists considered movements across barriers and borders, they characterized them as disruptive and outside the norm, even in the absence of direct evidence of either the movements themselves or the negative consequences they purportedly triggered…Influential subdisciplines of biological inquiry focused on the negative impact of long-distance translocations of wild species, presuming that the most significant of these occurred not through the agency of animals on the move but when human trade and travel inadvertently deposited creatures into novel places. The result, experts in invasion biology and restoration biology said, could be so catastrophic for already-resident species that the interlopers should be repelled or, if already present, eradicated, even before they could cause any detectable damage.”

In turn, Invasion Biology spawned pointless and destructive eradication projects

Conservation Sense and Nonsense has followed the destructive and futile attempts to eradicate plants and animals that nativists say “don’t belong here:”

Hawaii is an extreme case of attempts to eradicate non-native plants and animals: frogs, owls, egrets, seals, fruit trees, mangroves, parrots, etc. These eradication projects often do more harm than good. The “logic” for these projects is muddled, partly because the Hawaiian Islands emerged from the sea as barren volcanoes. The question of “what belongs there” is a matter of opinion and debate in Hawaii and elsewhere.

Non-native plants that produce berries which are eaten by birds are being eradicated because the birds carry the seeds of the plants where nativists have decided “they don’t belong.” Obviously, birds don’t benefit from the loss of important sources of food.
Plants are eradicated with herbicides that are harmful to animals. Many of the plants that are eradicated are valuable food and cover for animals. Animals are the collateral damage of these destructive projects.
The native plant movement cannot or does not make a distinction between natural succession and “invasion.”
Plants and animals are often scapegoated when the underlying reason for a so-called “invasion” is not understood. The attempted eradication doesn’t fix the problem, because the scapegoat isn’t the cause of the problem. Until the underlying cause is addressed, it is pointless to focus on the symptoms.

Migration enables survival

I hope that improved knowledge of migration will help people understand that migration is a natural phenomenon that is essential to the survival of all life on Earth. Migration enables life to adapt to changes in the environment, facilitating evolution and reducing frequency of extinction.

Doug Tallamy’s Blame Game

The fact that insect populations are declining in many places around the world is well known, but the reasons for the decline are not well known. Where there is uncertainty, there is speculation and where there is speculation, there is debate.

Doug Tallamy recently stepped into that debate by publishing a review article about insects and their use of plants. The article is a mind-numbing list of studies that find both positive and negative relationships between insects and non-native plants.

Tallamy contends those studies add up to support for his belief that non-native plants are bad for insects and native plants are good for insects. He suggests that declining populations of native plants should be considered one of the reasons for declining populations of insects, but then he goes one step further. Tallamy suggests that non-native plants are responsible for declining populations of native plants. It follows that Tallamy blames non-native plants for the disappearance of insects.

My interpretation of the studies in Tallamy’s review is different. The studies tell me that there is too much variation in insect-plant relationships to generalize about the relative value of native vs. non-native plants to insects. A more accurate conclusion would be that sometimes insects make a successful transition from a native to a non-native plant—especially in the absence of a native in the same lineage—and sometimes they don’t…or at least they haven’t yet.

Anise swallowtail butterfly is one of many insects that have made a successful transition from a disappearing native plant to an introduced non-native plant in the same lineage. Prior to that transition, swallowtails were able to lay eggs only once a year, when the native was available. The introduced non-native is available year around, which enables the swallowtail to lay its eggs year around. Courtesy urbanwildlife.org

Since evolution is a process and not a historical event, these insect/plant relationships will continue to change. There are many studies that document such transitions and Tallamy cites some of them in his review. Tallamy assumes insects will be forever handicapped, if not killed, by whatever deficiencies there are in the non-native substitute. I assume the insect is more likely to adapt and eventually evolve to cope with those deficiencies. Both our assumptions are just guesses. Tallamy considers nature immutable, while I consider it dynamic. Where Tallamy sees doom and gloom, I see opportunity.

Professor Art Shapiro’s (Distinguished Professor of Evolution and Ecology, UC Davis) assessment of Tallamy’s review article is less equivocal than mine. Keep in mind when reading his assessment that he is far more knowledgeable than I am:

“There is little evidence known to me of alien plants (‘invasives’) competitively displacing natives in ‘communities’ except in highly disturbed environments, except in the case of ‘ecological engineer’ species like Japanese honeysuckle, Himalayan Blackberry, climbing fern in Florida, Purple Loosestrife, etc. — things that drastically alter the ground rules for structuring the vegetation by smothering or prompting fire.
“The use of natives and non-natives by insects has a long and venerable history, going back to T.R.E. Southwood and his comparisons of insect faunas on British trees to Godwin’s history of the British flora, Azevedo’s student study at SF State, etc. — demonstrating overall that enemies accumulate in time on naturalized aliens, but it may be a very slow process if there is no phylogenetic or chemical bridge to their colonization. Experiments using haphazardly-selected species to examine acceptability are basically silly, and very easy to ‘stack’ if one knows one’s phytochemistry.
“As I have repeatedly pointed out, ‘weed’ eradication would lead rapidly to the extirpation of nearly all of the non-tree-feeding urban and suburban butterfly fauna in lowland California (and many other places).”

Why are insect populations declining?

A 2017 study revealed a shocking 76 percent decline in the biomass of flying insects over 27 years in protected areas in Germany. The German study does not offer specific explanations for the significant decline in insects, but it speculates about probable cause: “Agricultural intensification (e.g. pesticide usage, year-round tillage, increased use of fertilizers and frequency of agronomic measures) that we could not incorporate in our analyses, may form a plausible cause. The reserves in which the traps were placed are of limited size in this typical fragmented West-European landscape, and almost all locations (94%) are enclosed by agricultural fields. Part of the explanation could therefore be that the protected areas (serving as insect sources) are affected and drained by the agricultural fields in the broader surroundings (serving as sinks or even as ecological traps). Increased agricultural intensification may have aggravated this reduction in insect abundance in the protected areas over the last few decades.” Presumably “protected areas” in Germany are not landscaped with non-native plants, rendering the use of this study to corroborate Tallamy’s hypothesis irrelevant.

A comprehensive review of 73 reports of declining insect populations around the globe was published in 2019. These studies report the reasons for declining populations: “The main drivers of species declines appear to be in order of importance: i) habitat loss and conversion to intensive agriculture and urbanization; ii) pollution, mainly that by synthetic pesticides and fertilisers; iii) biological factors, including pathogens and introduced species; and iv) climate change. The latter factor is particularly important in tropical regions, but only affects a minority of species in colder climes and mountain settings of temperate zones.” The “introduced species” are usually insects rather than plants.

In a Yale e360 article about Tallamy’s review, one commenter offers his opinion that the over-population of deer and their preference for eating native vegetation is likely a greater threat to native plants than the existence of non-native plants that provide an alternative source of food for deer, thereby reducing predation of native plants. Tallamy seems to agree that deer are a problem for native plants, while rejecting deer as a greater threat to native plants than the existence of non-native plants.

The list of reasons for declining insect populations is long and will probably get longer as more research is done. If the existence of non-native plants is on that list, it is unlikely to be higher on a prioritized list than the pesticides that are being used to eradicate non-native plants. The more herbicide that is used to eradicate non-native plants, the more harm is done to insects.

EPA Biological Evaluation of glyphosate is a black eye for native plant “restorations” that use herbicide

The Environmental Protection Agency has finally published its Biological Evaluation (BE) of the impact of glyphosate products (all registered formulations of glyphosate products were studied) on endangered animals (mammals, birds, amphibians, reptiles, fish, invertebrates) and plants. The BE reports that 1,676 endangered species are “likely adversely affected” by glyphosate products. That is 93% of the total of 1,795 endangered species evaluated by the study. Of the total of 792 critical habitats of endangered species, 759 (96%) were “likely adversely affected” by glyphosate products. Most of those critical habitats probably contain predominantly native plants that are clearly not benefiting from herbicides used to kill their competitors.

Both agricultural and non-agricultural uses of glyphosate products were evaluated by the BE. Although only endangered plants and animals were evaluated by the BE, we should assume that all other plants and animals are likewise harmed by glyphosate because the botanical and physiological functions of plants and animals are the same, whether or not they are endangered. Herbicides, specifically glyphosate products, are used by the majority of projects that attempt to eradicate non-native plants. As a result, the crusade against non-native plants is undoubtedly a far more important factor in the decline of insect populations than their mere existence.

Why are native plant populations declining?

There are many reasons why native plant populations are declining, but there is little evidence that non-native plants are the cause of declining populations of native plants. Many of the causes of declining insect populations are also causes of declining populations of native plants. A recent study reports that 65 taxa of native plants in the US and Canada are thought to be extinct. The study did not report a single case in which the extinction was caused by the existence of non-native plants. Sixty-four percent of extinct plants were single-site endemics. The same drivers cited by recent insect studies appear on the list of causes of plant extinctions. Nearly half of the extinctions occurred more than 100 years ago, long before introduced plants were considered an issue.

Butterfly bush is a host plant of Variable checkerspot butterflies. It is also an important source of nectar for butterflies and bees. It is being eradicated on public land because it is not a native plant. butterflybush.com

My New Year’s Wish

Nature is too complex to be reduced to a single cause for changes in the environment. Human knowledge is insufficient to identify all of the causes. That’s why we make many mistakes when trying to fix a perceived problem in nature. Our own priorities influence our evaluation of changes in the environment. We should not automatically assume that a change is a problem or that it must be reversed.

The existence of novel ecosystems is a case in point. They can as easily be seen as positive as negative. If a native plant or animal is no longer adapted to changes in the environment, such as climate change, we should be grateful that a non-native substitute is capable of tolerating the change. Where some see enemies, others see friends.

I wish you all a very happy New Year in 2021. I can’t wish 2020 a fond farewell. I can only say good riddance! I am hopeful for a more peaceful year, one in which we befriend our enemies and work together for a better world for nature and for humanity. I am grateful for your readership.

Re-upping on Reality

Marlene A. Condon is the author/photographer of The Nature-friendly Garden: Creating a Backyard Haven for Plants, Wildlife, and People (Stackpole Books 2006; information at www.marlenecondon.com). Please visit her blog, In Defense of Nature. You can reach her at marlenecondon@aol.com

To the farmer’s eye, Eastern Redcedar trees “invade” his cow fields where he would prefer only grass to grow. To the ecologist’s eye, the trees signify the need for soil remediation. Photo credit Marlene A. Condon

Prefatory Comments

When I was a student in the mid-1970s at Virginia Tech, small farms surrounded the town of Blacksburg. I spent time at many of the cow farms, where I constantly heard complaints by agriculturalists about the Eastern Redcedar (Juniperous virginiana) perpetually invading their fields.

After getting my degree in physics, I moved north to Charlottesville, a 140-mile highway drive through rural areas. In the ensuing decades, numerous small farms were abandoned as it became more difficult for farmers to make a living from them.

On frequent trips back to Blacksburg, I watched as the forsaken cow fields began to fill with cedar trees. Then, as time went on, Autumn Olive (Eleagnus umbellata) shrubs began to show up as well. It took decades for those fields to become a forest of cedars, olives, or a mix of both; succession was a slow process because the soils had been emptied of their nutrients, and they were compacted by the generations of half-ton animals that had trod upon them.

What the farmers didn’t understand in the 70s, and what most people still don’t understand today, is that Mother Nature tries constantly to replenish degraded areas by sending in colonizers—plants capable of growing in and enriching exhausted soil. Because very few kinds of plants can perform this natural restorative work, their presence in an area is a sure sign of impoverished land.

Virginia Cedar, Virginia Pine (Pinus virginiana), and Broomsedge (Andropogon virgincus) comprise the most-common native species that move into old Virginia cow fields, sometimes accompanied by Black Locust (Robinia pseudoacacia) that is somewhat beyond its original range. But Autumn Olive, from Asia, is a far superior restorer. It not only enriches the soil with nitrogen, an essential nutrient for plant growth, but also provides for wildlife far better than these other plants. I can’t think of another species that feeds such an abundance of pollinators in the spring with its fragrant blooms, and birds and mammals in mid-to-late summer with fruits and again in late winter by way of its buds.

Yet Autumn Olive is one of the most despised plants of people going after so-called invasive-plant species, the presence of which in our environment they don’t understand and have misinterpreted. For example, University of Delaware entomology professor Doug Tallamy starts Bringing Nature Home (published in 2007) with an explanation of how he came to write his book: He and his wife had moved seven years earlier to 10 acres in southeastern Pennsylvania where he found “at least 35 percent of the vegetation on our property (yes, I measured it) consisted of aggressive plant species from other continents that were replacing what native plants we did have.”

Despite his knowledge that the area “had been farmed for centuries before being subdivided and sold to people like [him and his wife]”, this entomologist clearly had no clue about the full story of the landscape he had bought. The presence of Multiflora Rose (Rosa multiflora), Autumn Olive, and other much denigrated alien species that occupied about a third of his property revealed a prior history that Dr. Tallamy and other invasion proponents ignore.

The farmer’s land had obviously stood idle for some years, giving the variety of plants mentioned plenty of time to move in to rehabilitate the soil. These alien species didn’t suddenly appear and grow to full size overnight; we know the plants had been growing for a long time because the author tells us: “In places on [his] land, bittersweet…was supported at the base by vines with six-inch diameters.”

They weren’t “taking over the land” by “push[ing] out any existing natives,” as Dr. Tallamy erroneously asserts. Ecological succession is defined as “a gradual and orderly process of change brought about by the progressive replacement of one community [herbaceous plants to woody shrubs] by another until a stable climax [forest] is established.” (1) If Professor Tallamy truly understood how the natural world works, he would realize he can now grow his preferred climax community of native trees only because the alien “invaders” prepared the site for him to do so.

It’s unfortunate that Doug Tallamy’s false version of nature has been given much credence and publicity. Thanks to conservationists and governments at all levels rallying around his contrived version of reality, huge areas of well functioning habitat have been, and continue to be, destroyed throughout the United States. Adding insult to injury, the “mission” to get rid of supposedly invasive plants has usually been accomplished with the use of herbicides deadly to wildlife.

Book review of Wild Urban Plants of the Northeast by Peter Del Tredici

The natural world would currently be in far better shape if years ago the press had instead taken note of urban ecologist and Harvard botanist Peter Del Tredici’s book, Wild Urban Plants of the Northeast (first published by Cornell Press in 2010, with an expanded version out this year). Unlike Dr. Tallamy, Dr. Del Tredici recognizes the substantial modifications to our environment wrought by development and climate change, such as soil degradation that goes hand in hand with construction, and drought that is more severe and more frequent due to climate warming.

Anyone knowledgeable about plants should recognize that these changes are quite consequential for these organisms. Perhaps Professor Tallamy doesn’t “get it” because he’s focused only on insects and knows very little about animal/plant relationships. For example, he erroneously writes (2) that the Tulip Poplar tree (Liriodendron tulipifera) “is one of the least productive forest species in terms of its ability to support wildlife—insects and vertebrates alike.” He doesn’t know Tulip Poplar blooms feed a myriad of insects along with hummingbirds, and its seeds are taken by the Eastern Gray Squirrel and other rodents, as well as birds like the Carolina Chickadee, the mascot for his cause célѐbre.

It’s a shame that Wild Urban Plants of the Northeast is referred to as a field guide on its cover and in advertisements. People are bound to think this book is mainly for identification of plants growing in urban areas, but it is so much more. Conservationists and gardeners throughout the entire country—and certainly students learning about plants—would do well to read the 29-page “Introduction”.

The true value of this work lies in the author’s explanatory text about why the 268 covered species show up in the cracks and crevices of city sidewalks and deserted parking lots, as well as from the walls of decrepit buildings. It’s an ecology lesson that is far more illustrative than the dry text you might read in a book devoted to the subject for the classroom.

An urban Krakatoa. This sea of urban blacktop is like a volcanic lava flow, and the plants that grow here, including mullein (Verbascum thapsus) , chicory (Cichorium intybus), New England hawkweed (Hiercium saubadum), and white heath aster (Symphyotrichum pilosum), can tolerate extreme heat and drought. Courtesy Peter Del Tredici

For example, in Wild Urban Plants, the reader views a photo of an abandoned building with its fissured parking lot in which a variety of wildflowers grow. The caption likens the “sea of urban blacktop” to “a volcanic lava flow” where plants must be able to tolerate extreme heat and drought. What a superb metaphor! It conveys the environmental conditions to which these plants are subjected while also making very clear to the reader why only certain plants germinate and survive well in such places.

Princess Tree (Paulownia tomentosa) colonizing an abandoned building in New London, Connecticut. From the plants’ perspective, a decaying brick wall is just a limestone cliff. Courtesy Peter Tredici.

In Wild Urban Plants, Princess Tree (Paulownia tomentosa) is seen growing out the side of a neglected painted-brick building in New London, Connecticut. The caption informs us that, “From the plants’ perspective, a decaying brick wall is just a limestone cliff.” How marvelously enlightening!

The urban glacier leaves a trail of compacted glacial till in its wake. Courtesy Peter Del Tredici

Perhaps the most unique metaphor of all can be found in the picture of a backhoe sitting atop a hill of dirt. The author tells us “The urban glacier [referring to the backhoe] leaves a trail of compacted glacial till in its wake.” A conglomerate of unsorted broken rocks, till does not provide amenable growing conditions for very many species of plants.

The author doesn’t go into this subject, but moss is often the first colonizing organism to move in. It secretes organic acids that break down the rocks into soil, paving the way for plants with the ability to fix nitrogen to come in, and over time, as plants die, the soil is enriched via their nitrogen, allowing other kinds of plants to live here. An understanding of this process is sorely lacking among those conservationists who insist that “invasive” plant species serve no useful purpose in the environment. In fact, it’s a darned good thing they are here, given their ability to flourish under present environmental conditions. This is the explanation, after all, for their apparent invasiveness.

Dr. Tredici’s “Introduction” should be required reading for everyone involved in conservation. With a better comprehension of how the natural world works, people should be able to realize that the United States is wasting many millions of taxpayer dollars every year to remove alien plants. And annually putting millions of pounds of herbicides into our environment (according to a 2012 Environmental Protection Agency report (3)) manifests a horrendous crime against nature.

This counterproductive war on nonnative plants must be stopped quickly; far too much damage has already been done. Spread the word about this book to everyone you know.

References:

https://www.thefreedictionary.com/Plant+succession
Bringing Nature Home, Doug Tallamy
https://www.epa.gov/sites/production/files/2017-01/documents/pesticides-industry-sales-usage-2016_0.pdf

Observations of the Blue Ridge Naturalist

I’ve been a nature writer/photographer in Crozet, Virginia, for more than 25 years. My freelance articles have been published in numerous national and state magazines and newspapers, and I’ve written nature columns for many newspapers, as well as Virginia Wildlife, the magazine of our state wildlife department. My yard was featured on Virginia PBS stations in 1994 and again in 2005, and is the basis of my book, The Nature-friendly Garden: Creating a Backyard Haven for Plants, Wildlife, and People (Stackpole Books, 2006). In all of these venues, I discussed nonnative plants, including some considered “invasive”, without suffering much, if indeed any, blowback.

Home of Marlene Condon in Crozet, Virginia. Photo credit Marlene Condon

However, over the past quarter century, there has been more-and-more of a push by native-plant societies to get government entities and environmental groups to rid the natural world of so-called invasive plants, including even native plants considered “thugs” because their growth is exuberant. Because I was concerned about the destruction of habitat and the often-extensive use of pesticides to accomplish their mission, I started writing explicitly about this movement, as in the article below.

After the publication of this article last year, nativists mounted a smear campaign against me personally, a sure sign of how weak their invasive-plant arguments are. The lead writer never even publicly disclosed her affiliation with the Blue Ridge PRISM, a group “targeting common invasive plants in the Blue Ridge”, which would have allowed readers to question whether her comments about me were suspect. My editor certainly was duped, placing a headline of “Blue Ridge Naturalist–NOT!” over their comments. And perhaps not coincidentally, shortly thereafter, he fired me, even though I’d written for–and received high praise from–him for 11 years.

Since then, I’ve found it virtually impossible to write openly about any nonnative plants. Media and environmental groups are cowed by these people, thanks to their numbers and involvement with various organizations and governments (local, state, and federal). Sadly, this movement is highly detrimental to our natural world that is already in very bad shape and can hardly withstand yet more negative impacts upon it. Folks who understand the senselessness of destroying functioning habitat and poisoning the Earth with pesticides must speak out publicly for the benefit of nature.

Marlene Condon, Blue Ridge Naturalist

FEBRUARY 2019
The Blue Ridge Naturalist
© Marlene A. Condon

Bees and other kinds of insects obtain nourishment from the blooms of Weigela, a spring-blooming shrub native to Asia. Photo credit Marlene Condon

Ecologists Recognizing Value of Alien Plants

Scientists are either waking up to what I’ve been saying for years, or finally becoming brave enough to speak out against the wide-spread invasive-plant movement. In an opinion piece signed by 19 ecologists in the journal Nature, they argue that “policy and management decisions must take into account the positive effects of many invaders.”

Recognizing that “It is impractical to try to restore ecosystems to some ‘rightful’ historical state”, they go on to point out that eradicating or drastically reducing the abundance of invasive plants is “an impossible goal.”

Critical thinking is a must for deciding invasive-plant policy to avoid harming wildlife and wasting millions in tax dollars. A situation in California illustrates the foolishness of blindly pushing an agenda without giving any thought to the real-world consequences of doing so.

In the name of “saving” the environment from so-called invasive plants, a movement has sprung up to remove Eucalypt (Eucalyptus globulus) trees from California. These trees, brought in from Australia, now serve as the most frequented overwintering sites for the western Monarch butterfly population.

Monarchs originally roosted in native conifer stands of Monterey Pine (Pinus radiata), Monterey Cypress (Cupressus maculatum) and Coast Redwood (Sequoia sempervirens). Sadly, extensive development, logging, and poor land-management decisions have reduced the number of these native-tree stands, leaving the butterflies to rely upon non-native Eucalypts.

Ignoring the fact that overwintering Monarchs are very much dependent upon isolated stands of these trees, government plans are mandating removal of them. Does this make environmental sense? Absolutely not; eradication of the Eucalypts means no wintering habitat for Monarchs, which means they will die.

In other words, this deliberate destruction of habitat is taking place because of ideology, an illustration of the danger posed by people who have been led to believe they are part of an environmentally moral crusade. Native-plant folks out west have managed, as they have here in the East, to convince environmental organizations and government entities at every level that it is a moral imperative to remove plants deemed invasive.

But, the whole point of conservation of the environment is conservation of wildlife, without which the environment cannot function properly. Yet, absolutely no thought is given to how much so-called invasive plants support wildlife or serve important environmental functions in degraded areas.

Thus, for example, in the city of Waynesboro, Virginia, the Parks and Rec department decided it had to remove Japanese Knotweed (Fallopia japonica, formerly known as Polygonum cuspidatum) from growing along the South River greenway (Waynesboro News Virginian, March 9, 2018, “War on Weeds”). The main reason given for the removal of these plants was that they are preventing native plants from growing, but this statement is nothing more than invasive-plant folklore that gains credence by the act of repetition.

Read about virtually any “invasive” species and you will find that these plants are typically growing in disturbed areas where man or a weather event destroyed the original soil profile. As a result, the plants that had been growing there previously did not come back because they could not handle the altered physical conditions of the site. It’s why you see so-called invasive plants mainly along roadways, in parks, and along river trails—all areas easily seen by people who then mistakenly believe the exotic plants pushed out native species.

The newspaper stated that knotweed is a “formidable culprit to the river’s health”, but the true threat lies in its removal. This plant has superbly performed erosion control of soil in which native plants struggle to grow; feeds numerous kinds of pollinators when it blooms; and provides wonderful cover and nesting sites for numerous species of birds and the non-herbivorous insects that feed them. One need only to walk the trail with open eyes and an open mind to ascertain the truth of this statement.

Additionally, park employees would use herbicides to kill the knotweed. How can poisoning the Earth be less harmful than allowing alien plants to grow in areas where they are currently the most suited to thrive and thus provide badly needed habitat for wildlife?

You might wonder how the invasive-plant movement became so entrenched in environmental and governmental circles. The answer lies in the treatment of it as a moral cause in which those who agree with removing “bad” plants are virtuous; those who disagree must be bad like the plants themselves. Under these circumstances, it is difficult for folks to take a stand in opposition; no one wants to be considered immoral.

However, this undertaking is deeply flawed. Rather than critically analyzing each situation and dealing with it in the most appropriate manner, plant nativists (people who practice a policy of favoring native plants over nonnative) take the simplistic approach that demands removal of every plant designated as “invasive”, no matter what function it is fulfilling in the local environment or how well it fills what would be an otherwise empty ecological niche.

Earlier this year, for example, someone removed a Leatherleaf Mahonia (Mahonia bealei) that was growing in a swath of red dirt along the road where I exercise. It was one of the few plants that had survived the highway department’s installation of a new guardrail. No native plants had been able to grow in the poor, dry soil exposed a few years earlier by construction, leaving an area several feet wide and long mostly devoid of plants to assist wildlife.

The Mahonia (a native of China) would have provided a very early source of nectar desperately needed by the first pollinators to become active in spring at a time when native plants in bloom are very few. Its fruits would later feed birds, such as Cedar Waxwings and American Robins. Now, not much exists in this area to feed either insects or birds, making the land a wasted resource.

Native or not, plants provide habitat whereas bare ground does not. Nativists disregard the reality that native plants struggle to survive under the adverse conditions of road salt, mowing, drought, and disturbed, compacted, and depleted soil. They would do better by the environment if, instead of pulling and pesticiding, they focused on eliminating the actual causes of alien-plant spread.

Removing the Mahonia near the bridge resulted in no benefit to the environment, whereas it very much negatively impacted ease of survival for many insects and birds. And in California, removing Eucalypts may well doom the wintering Monarch butterfly population.

Contradictions of the native plant movement

In a recent article in Bay Nature, the author tells the story of two California native trees and proposes to answer the question, “Now the question is, where do [these trees] belong?” It’s a thorny question and one that illustrates one of the contradictions of the native plant movement.

The definition of “native” in California is based on the arrival of Europeans near the end of the 18^th century, specifically 1769 in the San Francisco Bay Area. Wherever plants or animals lived in 1769, they are considered native in the Bay Area. If they were introduced or arrived after 1769, they are considered non-native, and in many cases designated as “invasive.” Status as “invasive” makes them targets for eradication.

Monterey pine is a case in point. It has a small native range around Monterey, California, just 115 miles south of the East Bay. It was widely planted in the Bay Area by early settlers because the climate is similar to Monterey and much of the Bay Area was treeless. It is well adapted to conditions and thrives here. Yet, it is being eradicated by most public land managers in the Bay Area because it is, strictly speaking, non-native according to the official classification of non-natives.

Bird’s eye view of San Francisco in 1868. US Library of Congress. About half of San Francisco was treeless sand dunes before early settlers planted the non-native trees that now live there.

There is fossil evidence that Monterey pine has lived along the coast of California many times in the past, far outside its small present “native” range. The evidence of its prehistoric past in the Bay Area has not saved it. It wasn’t here in 1769, so it’s gotta go to suit the purist agenda of our public land managers.

But, wait! Maybe our public land managers don’t have such a purist agenda. The same public land managers who are eradicating Monterey pine in the Bay Area are also planting Torrey pines and Catalina ironwood, which are native to the Channel Islands, off the coast of Southern California. These tree species weren’t here in 1769, nor were they here in the distant past. In Monterey, where Monterey pines are native, Torrey pines are considered “invasive,” according to the interview with a tree advocate in Monterey who is quoted by the Bay Nature article.

Torrey pine, Torrey Pine State Reserve. By Richard O. Barry from San Diego, California:

Catalina ironwood – Catalina Island. Wikimedia Commons

Where I have observed Torrey pines and Catalina ironwood being planted by East Bay Regional Park District and other public land managers, they seem to be doing well. Therefore, I have no objection to their being planted here, although they are not “native” as defined by local native plant advocates. I have one straight-forward criterion for “where trees belong:” they belong where they will survive.

The author of the Bay Nature article demurs, “Should we view Monterey pine as unwanted and possibly damaging invaders or welcome them as neo-natives? I couldn’t decide.” That seems to me an easy question to answer: It makes no sense to destroy healthy Monterey pines that have lived in the Bay Area many times in the past, while simultaneously planting trees that have never lived here. If trees are adapted to present environmental conditions, they should be welcome here.

Nativist Dilemmas

The native plant movement is fraught with conundrums such as the vexing question of where Monterey pine and its close relative, Torrey pine, belong.

There are many unresolved debates about exactly where native ranges are. The rusty crayfish is “probably the most reviled crayfish species in North America,” yet there are as many opinions about its native range as there are publications about the species. Pike is eradicated in Ireland, yet a recent genetic study revealed that there are actually two pike species, one of which is likely native and unique to Ireland. (1)
There is little agreement among invasion biologists about the difference between non-native and “invasive.” Some consider all non-native species potentially invasive, some do not. (1) The California Invasive Plant Council recently designated nearly 100 plant species as invasive (in addition to 200 plants already on the list), despite the admission that they are not invasive in California. Given that the behavior of plants depends to a great extent on local climate conditions, we cannot assume they will be invasive in California. When a plant is designated as “invasive” it becomes a target for eradication. It is therefore a designation that should be used sparingly.
Public land managers in the Bay Area kill as many native plants as non-native plants because of their goal of recreating the landscape that existed here prior to the arrival of Europeans. That goal requires that early-succession native shrubs be killed when they naturally encroach on grassland if it is not burned periodically or grazed by animals. Native coyote brush is eradicated as often as non-native broom when it “invades” grassland. Are we trying to preserve native species or historical landscapes? Those are different goals and they are often contradictory.

Invasion biology is an ideology, not a science

These—and many other—contradictions are symptoms of a pseudoscience, struggling to make sense, but failing to do so. Invasion biology made the initial mistake of picking a specific point in time to define the “ideal” landscape. Because nature is dynamic, in response to a constantly changing environment, the arbitrary selection of a static landscape will always be a source of contradictions. The environment has changed radically since 1769 and even more radically since the 400-year baseline used on the East Coast. We cannot expect to recreate that historical landscape because we cannot recreate the environment in which it existed.

C. Guiasu, C.W. Tindale, “Logical fallacies and invasion biology,” Biological Philosophy, Sept 2018, 33(5)

Tag: native plant movement

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