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.
Click on picture to activate the video.
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.
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
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.
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.
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.
The draft Environmental Impact Report (DEIR) for Oakland’s Vegetation Plan (OVMP) has been published. When the DEIR is approved and funding is identified, implementation will finally begin after a process that began four years ago. The plan and its EIR are available HERE. The deadline for public comments on the DEIR is January 22, 2021. The email address for submitting public comments is DEIR-comments@oaklandvegmanagement.org
The primary purpose of the plan is to reduce fire hazards in High Fire Hazard Zones in Oakland by reducing fuel loads on about 2,000 acres of public land and 300 miles of roadside. Although there were many issues, the primary battle lines were drawn by these issues at the beginning of the process and they remain:
On one side, some people were concerned by the scale of tree removals that were considered and the herbicides that would be needed to control the resprouts of the trees after removal. If the plan as proposed is approved, herbicides will be permitted in places where they were prohibited in the past.
On the other side, some survivors of the 1991 Oakland wildfire and native plant advocates who are their allies, want all non-native trees to be destroyed and replaced with native plants. They are not satisfied with plans to thin trees around structures and roadsides.
The consequences of destroying Oakland’s urban forest
The survivors of the 1991 fire in Oakland asked that the OVMP be radically revised at a public hearing about the OVMP DEIR on December 16, 2020. They called their version of a vegetation management plan Alternative 5. It is an alternative that does not exist in the DEIR. These are the major elements of what they asked for:
They ask that all non-native trees be destroyed everywhere in the treatment areas. They ask that the trees be clear-cut rather than thinned, as proposed by the plan. They ask that tree removals not be confined to defensible space around structures, as proposed by the plan.
They ask that removed trees and non-native vegetation be replaced with native trees and vegetation.
They ask that roadside clearance of vegetation occur 100 feet from both sides of the road rather than 30 feet as the OVMP proposes.
They expressed concern about dead trees. They are apparently unaware of the epidemic of Sudden Oak Death that has killed 50 million native oaks in the past 15 years and is spreading rapidly.
The OVMP DEIR is responsive to some of these concerns.
The OVMP DEIR makes a commitment to seeding areas that are steep and barren after vegetation removal with seeds of native plants. The purpose of this seeding is to minimize the potential for erosion.
The OVMP DEIR makes a commitment to replant trees removed in riparian areas as required by Oakland’s ordinance to protect creeks.
The OVMP makes a commitment to remove all dead trees in treatment areas. Sudden Oak Death (SOD) is the probable cause of the dead trees described at the public hearing. SOD has been found in many treatment areas in the plan: Garber Park, Shepherds Canyon, Dimond Canyon Park, Joaquin Miller Park, Leona Heights Park, Knowland Park, and Sheffield Village. (OVMP DEIR 3.4-87)
Increasing roadside clearance to 100 feet would increase the acreage of roadside tree removals and vegetation required by the OVMP by 233%.The consequences of such extensive removals can be seen on Claremont Ave, west of Grizzly Peak. These removals were done by UC Berkeley. Catastrophic erosion after intense rainfall looks inevitable.
Claremont Ave, West of Grizzly Peak Blvd. November 2020
Huge piles of wood chips and logs must be disposed of. Such piles of wood chips are known fire hazards until they are spread or disposed of. The wood chip piles resulting from roadside clearance on Claremont Ave cannot be spread because the quantity exceeds available land. UC Berkeley has made a commitment to build a biofuels plant to burn the wood chips to generate electricity for campus facilities. The OVMP does not make a commitment to build a biofuels plant to properly dispose of wood chips and it mandates a limit of 6 inches of wood chip mulch on the ground. Please look at these pictures of some of the wood debris created by clearcutting less than one mile of roadside on Claremont Ave. Then consider that the OVMP proposes to treat 300 miles of roadside. Multiply these piles of wood chips and logs by 300 to consider the consequences of “Alternative 5.”
Update: Since publishing this article, I have learned that UC Berkeley has NOT built a biofuels plant to dispose of the wood debris to meet Cal Fire grant requirements for reducing greenhouse gas emissions. Nor does UC Berkeley intend to build a biofuels plant. The disposition of the wood debris from this project has not yet been determined. This is the final paragraph of my formal complaint to Cal Fire about this project: “In conclusion, the grant application for this project makes a commitment to reducing greenhouse gas emissions that is based on the assumption that a biofuels plant will generate electricity from the wood debris. Such a plant has not been built and UC Berkeley apparently does not intend to build such a plant. Other claims made in the grant application about carbon storage are based on inaccurate claims about carbon storage. Grant guidelines state, “Failure to meet the agreed upon terms of achieving required GHG reduction may result in project termination and recovery of funds.” In other words, Cal Fire should terminate this project and recover any funds that have been remitted to UC Berkeley. The project is a misuse of grant funds because it will increase fire hazards and increase greenhouse gas emissions. Without imputing motives, on the face of it, the grant application looks fraudulent.” The full story of how this project has violated grant guidelines as well as the description of the project itself in the grant application is told HERE. January 18, 2021
One of many piles of wood chips, Claremont Ave, November 2020One of many piles of logs, Claremont Ave., December 2020. Photo by Doug Prose, courtesy Hills Conservation Network.
Oakland does not want a biofuels plant because it will significantly increase pollution. Sierra Club Magazine reports that “The manufacturing of biomass-energy wood pellets requires drying the logged material in a wood-fired process, then pressing the dried wood into pellets—and every step emits significant amounts of air pollution. According to the Environmental Integrity Project study, the emissions from the facilities include fine particulate matter, nitrogen oxides, carbon monoxide, and volatile organic compounds. Wood-pellet manufacturing emits a form of soot and dust called PM 2.5, which can pass deep into the lungs and depress lung function, worsen asthma, and cause heart attacks. Volatile organic compounds, when exposed to sunlight, transform into ozone, which is especially dangerous to children and the elderly.”
This aerial view of the clear cut on Claremont Ave makes it clear that this is a native plant “restoration,” not fire hazard mitigation. The north side of the road has been clear cut 100 feet from the road where the trees were non-native. There has been no comparable clearance on the south side of the road where the trees are native. The native trees are predominantly native bay laurels that are known to be highly flammable. The leaves of bay laurel contain more oil than the leaves of eucalyptus and the branches grow to the ground, providing a fire ladder to the tree canopy. If fire hazard mitigation were the goal of this project, both sides of the road would have been treated the same.
This picture of the Claremont Ave project was taken from the west December 2020. Photo by Doug Prose, courtesy Hills Conservation Network.
The cost of Alternative 5 would be prohibitive. The plan would need to be rewritten and a new EIR prepared. The first plan took four years to prepare; the second will take nearly as long after new funding is secured for it. Funding for implementing the OVMP has not been identified. The City of Oakland is currently running an annual budget deficit of $62 million. Budget cuts are planned to address the deficit, including 10 mandatory furlough days for police and firemen.
One of many reasons why I love my home, Oakland, is its deep commitment to equity. If Oakland had the resources to fund restoration of approximately 2,000 acres of public land and 300 miles of roadside to native vegetation, it is unlikely to spend those resources in the wealthiest communities in Oakland on a project that would bring little benefit for the poorest communities in Oakland. Oakland’s Equitable Climate Action Plan (ECAP) is a case in point. Its forestry section is devoted to planting trees in the poorest neighborhoods that suffer the most air pollution and have the fewest trees, as it should be.
I am sympathetic to the survivors of the 1991 Oakland fire as well as to those who have been injured by chemicals to which they were exposed. Fire survivors have had a traumatic experience that has irrevocably altered their perception about the causes of wildfire. There are also other survivors of the 1991 fire who watched native redwoods and oaks burn. Their understanding of wildfire is therefore different, but it is more consistent with the wildfires of the past 5 years that have occurred in predominantly native vegetation. Native vegetation in California is fire adapted and fire dependent. Non-native vegetation is not inherently more flammable than native vegetation.
Public Policy requires compromise
Thinning of non-native forests and herbicide treatment to prevent resprouting is not without risks. We will lose some of our protection from wind. The trees that remain will be more vulnerable to windthrow. There may be some erosion in steep areas. The herbicide that is usually used to prevent resprouts (triclopyr) kills tree roots by traveling from the freshly cut stump through the roots of the tree. The roots of trees are intertwined with the roots of their neighbors that are often damaged by the herbicide and sometimes killed. The herbicide kills mycorrhizal fungi that live on the roots as well as microbes in the soil. Their loss reduces the health of the soil, handicapping the survival of remaining and new plants. This damage to soil is one of many reasons why native plant “restorations” are frequently unsuccessful after scorched earth eradications. Both triclopyr and imazapyr are on the list (California Code of Regulations 6800) of pesticides that have “the potential to contaminate groundwater” because they are very mobile and persistent in the soil.
I accept these risks in the interests of reducing fire hazards. I have asked for a few tweaks to the plan, including continuing to prohibit foliar spraying of herbicides in public parks and open spaces. These are the compromises that must be made to make public policy. We cannot paralyze ourselves by letting the perfect be the enemy of the good. Oakland needs a Vegetation Management Plan that is effective, affordable, and safer than other alternatives. That’s what the Oakland Vegetation Management Plan is.
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 or 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.
Earlier this year, several comments on the Garden Rant website drew my attention to the Conservation Sense and Nonsense blog. The well informed scientific based comments of the Conservation Sense webmaster resonated with me – our gardening should be built on fact and best practice, not dogma or belief. I garden in England, the United Kingdom – and here we just don’t have the same intensity of debate surrounding native plants and restoration projects. Instead, we have a rich diversity of plants, drawn from all over the world; and our gardens are based on the principles of freedom of expression and individual design.
There is an emerging movement here, advocating the use of sustainable plant communities, taking design to the next level by creating functional ecological plantings – for nature, not just human enjoyment. This is a natural progression, utilising suitable plants from anywhere in the world, already growing in the equitable English climate. That said, our weather has been more challenging over the last few years, with increasing volatility and unpredictability; which makes appropriate plant selection even more important.
To encourage the use of a wide range of well-chosen plants, I decided to share my knowledge and experience in a short book, called “Grasses and Perennials – Sustainable Planting for Shared Spaces,”available from Amazon in print and digital download. The book is the culmination of fifteen years professional landscaping, working to establish plant communities that hold a person’s interest, if only for a few moments – the difference between the forgettable, and the noteworthy. My passion is planting spaces that the public see and work at every day; but the principles in the book apply equally well to domestic gardens, as do all the plants I’ve listed. The book also brings science and reason to the debate around the use of native plants, and gives practical hints and tips for managing successful, sustainable plantings.
Here is a taster quote from Chapter 3 – Functional Space:
“Rather than relying on plants considered native to the British Isles, I will use any plant with potential, from anywhere, provided it will establish within a community of compatible plants. There is currently a mistaken assumption that native plants (as opposed to non-native plants, often labelled as exotics), are ideally suited to geographic region of origin and pollinators, without question. In reality, native plants may succumb to freshly introduced pathogens and react poorly to a swiftly altering climate.
“The insistence by some designer’s on using solely native plants, is effectively a determination that a given moment in time (usually in the past), is somehow ecologically superior – and overlooks the positive and scientific arguments for planting non-natives. There is little point constructing plantings based solely on region of origin, rather than usefulness and resilience. Plant communities alter all the time and nature is never static; and the definition of native plants is also somewhat subjective – we cannot know for certain how plants were moved and used by early humans. Can we safely assume that a plant is native to a given environment simply because a plant hunter happened to discover it there – probably quite recently in terms of our evolution?”
We recently published an article in defense of hybridization, inter-breeding of two different species. Conservation Sense and Nonsense defends hybridization because it is under fire from the native plant movement. Many projects that needlessly destroy non-native plants (or one locally perceived as such) do so to prevent them from hybridizing with a native plant, which has the potential to cause a localized loss of a variant of a native plant species.
This classic California poppy is eradicated in the Presidio in San Francisco because of fear it could hybridize with a sub-species of poppy that is considered “native” to the Presidio.
We are revisiting the topic because The Economist magazine recently published a comprehensive article about recent discoveries of the prevalence of hybrids among both plants and animals. Until the advent of DNA analysis in the 1970s, the extent to which plant and animal species were the result of inter-breeding was largely unknown. Also, conventional wisdom was that such inter-breeding was usually an evolutionary dead-end because offspring were often sterile, as exemplified by mules, the offspring of horses and donkeys. In general, the consequences of hybridization were assumed to be negative.
Recent advances in DNA analysis have largely disproved these assumptions. Hybridization is not only common, it can result in the creation of new species more rapidly than other forces of evolution, such as mutation and natural selection: “Hybridisation also offers shortcuts on the long march to speciation that do not depend on natural selection at all.” (1)
Both the positive and negative effects of hybridization are real. In plants, the effects of hybridization are often beneficial because of plants’ unusually flexible genetics. Plants, for instance, are frequently polyploid—meaning that each nucleus contains genomic copies in greater multiples than those of animals. Polyploidy provides spare copies of genes for natural selection to work on, providing additional possibilities for selection.
Polyploidy confers another advantage. It creates a barrier to breeding with either parent species. That gives a new, emerging species a chance to establish itself without being reabsorbed into one of the parental populations. Recent evidence suggests that hybridization between two plant species in the distant past, followed by a simple doubling of the number of chromosomes in their offspring, may be responsible for much of the diversity in flowering plants that is seen today.
Plants seem to benefit from hybridization more often than animals. “For many animals, however—and for mammals in particular—extra chromosomes serve not to enhance things, but to disrupt them. Why, is not completely clear. Cell division in animals seems more easily confounded by superfluous chromosomes than it is in plants, so this may be a factor. Plants also have simpler cells, which are more able to accommodate extra chromosomes. Whatever the details, animal hybrids appear to feel the effects of genetic incompatibility far more acutely than do plants.” (1)
The Economist provides many important examples of hybridization among animal species, most notably the history of hybridization of our species, Homo sapiens. We are now the sole surviving species of genus Homo. Our genome contains the relicts of the genes of other members of our genus that are now extinct, which indicates hybridization with other hominoid species. The modern human genome contains 1-4% of Neanderthal genes.
The Economist article concludes, “This is a more complex conception of evolutionary history, but also a richer one. Few things in life are simple—why should life itself be?” Keep your eyes and your mind open to new scientific knowledge that improves our understanding of life.
The bottom line
Biodiversity is the mantra of the native plant movement. Native plant advocates claim that the primary purpose of saving native plants is preserving biodiversity. But is it? When non-native plants are eradicated, aren’t we depriving native plants of the opportunity to breed with a hardy new comer? Are we preventing the creation of a new species by eliminating potential mates? Are we dooming the native plant that is not adapted to survive the changing climate by depriving it of the opportunity to improve its survivability?
There is a community of birders in Central Park in New York City who are famous around the country because the New York Times often reports on significant events in their community. If you are a birder you know that the arrival of a rare bird in your vicinity generates a lot of excitement. In the case of the barred owl, its arrival in Central Park was such an event. Ironically, elsewhere in the country, the barred owl isn’t unusual because it is a species that is rapidly expanding its range and becoming a target for eradication where it is perceived as an “invader.” The article in the New York Times was oblivious to this irony, so I took on the task of telling NYT readers about it. Here is the dialogue that my comment generated in NYT.
[My Comment] Oakland, CA Nov. 17
Barred owls are expanding their range. Good thing this barred owl didn’t show up here in the San Francisco Bay Area where barred owls are being shot because they are considered competitors with a rare, legally protected bird. The legally protected owl is so rare that logging was stopped in many western forests. The timber industry figured out how to place the blame on the barred owl. They hired someone to conduct a study to prove that the mere presence of the barred owl was correlated with the dwindling population of the rare owl. The study resulted in a program to shoot barred owls and the timber industry was once again allowed to log in the forests where the rare owl used to live. Here on the west coast, barred owls are one of the scapegoats that enable the fiction that endangered species are being protected. [1]
[Response]
Vancouver, BC
The “rare owl” is the Spotted Owl. When mates are scarce it will actually interbreed with the Barred Owl – another threat to its continued existence. Of course the scarcity of the Spotted Owl is human-caused as you point out – the presence of Barred Owls just accelerates their disappearance
[My First Reply] Oakland, CA Nov. 17
Yes, I know the species that is legally protected. Ironically, spotted owls would benefit greatly by hybridizing with barred owls because it is a hardier species. Hybridization is a natural, evolutionary process that often improves the survivability of the species that are breeding with more common species in order to breed. Advances in molecular analysis are reporting that hybridization is more common than previously thought and that it results in better adaptation to the environment, increasing chances for survival. Nativist attempts to prevent hybridization is futile and harmful. We can’t stop evolution, nor should we try,
[Second Response]
Vancouver, BC Nov. 17
You didn’t originally mention what the “rare owl” is called. Other people might like to know what you were talking about. Extensive hybridization with a far more numerous species will not “strengthen” the spotted owl as a species. On the contrary it will lead to the disappearance of the spotted owl as a separate species, as its genetics are swamped by those of the larger population. That’s what happened to the southeastern Red Wolf in the 1960s – when their numbers dropped very low, they began mating with coyotes, the last act in their genetic disappearance as a wolf species. “Nativism”, a political concept, has zero to do with this biological phenomenon. You say, “Hybridization is a natural, evolutionary process that often improves the survivability of the species” Well yes, in the face of human disturbance and habitat destruction, animals better adapted to the disturbed/replaced habitat will survive better… but the more sensitive species may eventually disappear, one way or another. Pigeons and rats are models of survivability – they’re highly adapted to commensal life with people – they thrive in human-altered landscapes. I wouldn’t casually class human-caused extinction as “evolution”, i.e. as a natural phenomenon and no cause for concern.
[My Second Reply]
Oakland, CA Nov. 17
The expanding range of barred owls is not caused by humans. It is also a natural phenomenon. The purpose of shooting barred owls is to enable the continued timber harvesting in the forests where spotted owls lived in the past. In other words, if “natural” processes are your goal, you might want to start by stopping the harvesting of the forests that spotted owls lived in. Spotted owls are choosing barred owls as their breeding partners. What’s more “natural” than that? Here is an article in Economist Magazine about the evolutionary value of hybridization: The Economist, “Match and mix, hybrids and evolution,” October 3-9, 2020, page 67-70. It’s not an idea that originates with me. Many articles like it are based on molecular analysis that traces the evolutionary history of hybridization for 500 million years of life on Earth.
You say, “’Nativism’, a political concept, has zero to do with this biological phenomenon.” I disagree. Nativism begins with a human prejudice against plants and animals (including humans) perceived as foreign. It becomes political when it becomes government policy and law, as it has in the case of shooting barred owls. That program was initiated and administered by US Fish and Wildlife. Likewise, attempts to abolish all forms of human immigration to the US is a policy of the federal government. I seem to have attracted the attention of members or admirers of the “restoration” industry. I’m glad. You should know that your deadly projects are not universally admired. They are misguided and they are usually based on specious reasoning masquerading as “science.” When they kill animals and use pesticides to kill plants, they are damaging the environment and the animals that live in it.
Barred owls moved north and west in the late 20th century because of the forestation of what was historically prairie and other treeless habitats. That’s about as clearly “caused by humans” as anything.
[And receives assistance from Vermont]
Middlebury, VT Nov. 18
Yellow Barred Owls only occur on the West Coast because Europeans planted trees across the great plains as windbreaks and parkland, allowing the owls to spread across the formerly treeless region. Prior to that, the species was confined to the East Coast–their expansion to the Pacific is entirely the result of human interferance in the ecosystem. They should not be in the West and their removal, along with strong habitat protection, is the best hope for the Northern Spotted Owl to survive as a species.
[I got the last word]
Oakland, CA Nov. 18
The forests in which barred owls live along the West Coast were not planted. They are native conifer forests. As for pre-settlement prairie now occupied by forests, they are the result of natural succession from grassland to shrubland and ultimately forests in the absence of indigenous burning and grazing by native ungulates. They weren’t planted either. In the view of the “restoration” industry, natural processes such as succession, hybridization, and evolution are not consistent with the goal of re-creating a pre-settlement landscape. It’s a fool’s errand, even in the absence of a rapidly changing climate which makes it delusional. The only thing constant about nature is change. There’s nothing natural about humans killing animals they have decided “don’t belong there.”
According to this map of barred owl distribution, the route the barred owl took from the East to the West Coast was via the boreal forests of Canada. Source: Cornell Ornithology Lab
Addendum: The barred owl is the pin-up photo for the January page of Audubon’s 2021 calendar. Here’s what Audubon says about the conservation status of the barred owl: “The rich baritone hooting of the Barred Owl is a characteristic sound – one that some birders may already hear less of due to loss of parts of the bird’s southern swamp habitat to climate-related threats, including wildfires, spring heat waves, and urbanization. Audubon is passing clean energy legislation in the South, including landmark solar energy bills in Arkansas and South Carolina, ensuring a healthier future for these states and birds, like the Barred Owl, that depend on them.”
We often find contradictions between the national policies of environmental organizations such as Audubon and their local chapters. In this case local Audubon chapters are actively engaged in shooting barred owls that are expanding their range into cooler, northern climates, while the national organization understands that the barred owl must change its range to survive climate change. Well-meaning people often don’t have the big picture when making conservation decisions and they are resistant to changes in nature. The instinct seems to be to freeze nature into place. Nature won’t stand for that. January 2021
[1] Green Diamond Resource Co, a lumber company managing timberland in Humboldt, Del Norte and Trinity counties, is the author of the plan to “manage” barred owls in their forests. (“Managing” or “removing” barred owls is the euphemism used to describe the killing of barred owls by shooting them.) Lowell Diller, a biologist and contractor for the Green Diamond Resource Co., was responsible for the “study” that resulted in the “management” plan. He designed the study and literally executed it by shooting barred owls. When interviewed by the Bay Area News Group, Green Diamond Resource Co. explained, “When you can protect and sustain a business and jobs and also conserve the northern spotted owl,” he said, “why not do it?” (source: “California biologists shoot scores of bully owls to protect endangered spotted owls,” East Bay Times, August 15, 2016)
Daniel Simberloff gave the keynote address to the symposium of the California Invasive Plant Council (Cal-IPC), entitled “Invasive Species Denialism and the Future of Invasion Management.” Simberloff is the most vocal academic defender of invasion biology. His presentation to Cal-IPC contains interesting clues about more effective strategies for the critics of invasion biology, of which I am one. In a nutshell, Simberloff dismisses critics easily with a few waves of his hand, but he stumbles when faced with the economic and ecological costs of the methods used to eradicate so-called “invasive species.” He can defend the theoretical hypotheses of invasion biology, but he finds it difficult to defend the “restoration” industry that invasion biology spawned, specifically the use of pesticides.
Simberloff opened his presentation with this rogue’s gallery of the critics of invasion biology. Some readers will recognize some of these “deniers.” If not, you might recognize some of the many books the “deniers” have published.
Simberloff categorized the criticisms of invasion biology then flipped them off, one by one. Keep in mind as you read Simberloff’s summary that it does not do justice to the actual criticisms of invasion biology.
Critics say that most non-native species aren’t harmful.
Simberloff says we don’t know how harmful non-native species are because few are studied, their impacts are often subtle, and there is often a time lag before they become harmful. He believes that all non-native plants are potentially harmful to ecosystems.
Critics say that some non-native species are beneficial.
Simberloff says that critics only report the benefits, while ignoring the negative impacts of non-native species. (Actually, most critics are proposing a cost/benefit analysis that acknowledges both positive and negative impacts.)
Critics say that invasion biology is xenophobic.
Simberloff says that if you’re looking for xenophobia, you often see it. He calls this the “law of instrument” or if your instrument is a hammer, everything looks like a nail. (Frankly, I didn’t understand the point he was trying to make, but I have tried to describe it accurately based on what he said.)
Critics say that trying to eradicate non-native species is futile.
Simberloff says this argument ignores the progress that has been made in the technology of eradication methods. He used the “early detection and rapid response” strategy as an example of progress in eradicating non-native plants. That strategy focuses on small populations of non-native plants, basically acknowledging the futility of trying to eradicate large areas of well-established non-native plants.
Much of Simberloff’s presentation was devoted to describing many developments in genetic engineering, such as CRISPR to drive species to extinction and gene silencing. All of the examples of such developments were aimed at killing insects (such as mosquitoes) and animals (such as rats and mice), with one exception. He was particularly enthusiastic about island eradications of which there are hundreds, and hundreds more on the drawing boards. Only one gene-editing project on plants is trying to develop a genetic method to eradicate phragmites.
Things finally became interesting, when Simberloff took questions: “Dan, you mention the “futility” argument, but what about the notion that the cost in environmental damage (e.g, pesticide use and nontarget impacts) is too high for some well-established invaders?” Simberloff’s answer to this question was surprising and encouraging to critics of pesticide use to kill non-native species:
“Absolutely, it’s a huge problem, not only on non-target species, but also the fact that evolution of resistance leads to greater use of pesticides before they are useful and leads to greater impact on non-target species. I didn’t talk about this, but yes, of course the cost both economically and ecologically might be too great even if management eradication is feasible. But that’s not what denialism is about. Denialism willfully denies that there are impacts or they confound arguments about values as if it is an argument about science.”
The Executive Director of Cal-IPC recognized the dangers of Simberloff’s answer because pesticides are the primary tool used by the “restoration” industry and much of the conference was devoted to telling over 650 employees of the “restoration” industry about new developments in pesticide use. Those new developments are not good news to those who are concerned about the dangers of pesticides. For example, a new “drizzle” technique increases the concentration of the active ingredient and lowers the volume of the application, increasing toxicity of the application. Another alarming presentation described the use of drones to spray herbicides on hundreds of acres of phragmites in the Suisun Marsh.
The absence of good alternatives to pesticide use in eradication projects is another source of pressure on the “restoration” industry and therefore on Cal-IPC:
Jon Keeley’s presentation about the interaction of fire, fire prevention, and plant invasions included the observation that using prescribed burns to eradicate non-native plants results in more non-native plants, not more native plants.
A land manager in Southern California acknowledged that pressures to reduce pesticide use threaten the future of his project: “Natural herbicides result in more time intensive and costly weed control, with less confidence of success. Where herbicide application is completely restricted, other weed control methods like hand weeding or mowing can be implemented successfully, but they often fall short of herbicide in effectiveness. This resulting reduction in effective weed control must be taken into account in future plans for habitat restoration and management, and our existing programs will have to reevaluate the proposed efforts, cost of those efforts, and expectations for success, both short and long term.” (Scott McMillan, abstract)
Finally, with the exception of a few timid questions from participants, no mention was made about the threat of climate change on the future of native ecosystems. Simberloff likened critics of invasion biology to “climate change deniers.” In fact, it’s fair to say that those who demand that we replicate native ranges existing 250-500 years ago are more accurately called climate change deniers.
The Executive Director of Cal-IPC tried to save the day by portraying those who oppose pesticides as extremists, based on what he considers “unscientific” studies. But Simberloff wouldn’t take the bait. He wasn’t willing to dismiss the concerns about pesticides. Instead, Simberloff passed the buck:
“I’ll beg off on answering that question on grounds that I’m not a social scientist or psychologist. This is not my area of expertise. There is some reason for the extremists because Monsanto has sometimes lied to us and there have been problems associated with pesticides. I leave this question to policy scientists.”
Simberloff reveals the flaw in the “restoration” industry
As a critic of invasion biology and the use of pesticides, I have always been frustrated that critics of invasion biology do not use the damage done by eradications as a reason for their criticism. With the exception of Tao Orion’s Beyond the War on Invasive Species, none of the books written by critics have used this argument. It is a missed opportunity and Simberloff’s presentation to Cal-IPC is an indication that it is the strongest argument against eradication projects that are inspired by invasion biology.
Invasion biology is a theoretical construct. It does no harm to ecosystems until it justifies the use of harmful methods to eradicate non-native species. I humbly ask that critics of invasion biology wake up to this opportunity. Pesticides are a winning argument against “restoration” projects that eradicate non-native plants. Any cost/benefit analysis of new eradication projects should include the ecological and economic costs of pesticides in the equation.
Beyond Pesticides points the way forward
I try not to leave the field without offering a compromise because opposition without solutions is not constructive. I offer this sage advice from Beyond Pesticides about case-by-case evaluations of weed invasions that will reduce damage to ecosystems. Beyond Pesticides responded to this question: “I’m working on a pesticide policy in my community and am interested in how you might suggest we deal with “invasive” species. Can you point us in the right direction? Martin, Boston, MA.” This is BP’s thoughtful answer:
“It’s Beyond Pesticides position that invasives, or opportunistic species, should be dealt with on a case-by-case basis, with established priorities and a plan. With any unwanted species, there needs to be an understanding of the ecological context. We need to be asking the right questions: What role is the plant currently playing in a landscape—what niche is it currently filling? If we remove this plant, what will fill that niche? Will we be replanting the right native species to fill that niche? What are the detrimental impacts of letting it spread? Is there a way we can isolate it to stop its spread? Can we ever remove this plant altogether, or will we be working at control indefinitely? These are important questions that we need to be asking before we even consider management methods. Regarding policy, requiring an individualized invasive species management plan seems to be the right answer, though unfortunately many pesticide reform policies sidestep the issue and simply exempt invasives to avoid opposition. Just like all organic approaches, we’ll want to place a focus on prevention and working with ecological systems, rather than against them, making even least-toxic pesticide use a last resort. There is a strong potential to undermine the stability of an ecosystem if we simply go in and immediately break out the strongest tools in the toolbox without a plant replacement strategy. On a turf system with common weeds a simple answer is grass plants. But, in forested areas already subject to intrusion (from construction/logging, etc.), rights-of-way, and urban areas, the focus is on alternative vegetation or ground cover. Sometimes, little should be done except simple mechanical cutting to keep these species in balance. This is an interesting and, at times, contentious issue that environmentalists grapple with, so there is certainly room for fresh ideas on how to approach opportunistic species without the use of toxic pesticides. For more information, we encourage you to watch the talk given at Beyond Pesticides 37th National Pesticide Forum in New York City by Peter Del Tredici, PhD, senior research scientist at Harvard’s Arnold Arboretum (www.bp-dc.org/ invasives).”
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 ofWild 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.
