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.

Source: US EPA, 2018

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
PFTFire Resistance (%)
Woody
Tropical broad-leaved evergreen12.0
Tropical broad-leaved raingreen50.0
Temperate needle-leaved evergreen12.0
Temperate broad-leaved evergreen50.0
Temperate broad-leaved summergreen12.0
Boreal needle-leaved evergreen12.0
Boreal summergreen12.0
Grasses
C3 grass100.0
C4 grass100.0

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 21st 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

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.

Bird migration routes

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:

  1. “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.

  2. “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.

  3. “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.

Doug Tallamy’s Nature’s Best Hope denies the value of hybridization

In Nature’s Best Hope, Doug Tallamy concedes that there is no evidence of extinctions of native plants being caused by the introduction of non-native plants in the Continental US.  However, he accuses non-native plants of something more nefarious:  “There is one biological phenomenon associated with some plant invasions that is so pernicious, even continental scales are not protecting natives from invasive species.  I speak of…introgressive hybridization, where the invasive species hybridizes with a closely related native, and then through repeated backcrosses and directional gene flow, the gene pool moves closer and closer to that of the invader.” 

Jake Sigg calls this phenomenon, genetic pollution.  Both Tallamy and Sigg consider such hybridization a loss of the native species and, indeed, it can be the end of localized variants of a species.  However, hybridization is often instrumental in the creation of a new species, one that is often superior to its ancestors because it is better adapted to present environmental conditions.

In a recently published study of the evolution of oaks, scientists traced the 56 million year evolutionary history of roughly 435 species of oak across 5 continents where they are found today.  Oaks are wind-pollinated, leaving pollen fossil records of their presence where they may no longer live.  Using DNA analysis of fossil pollen, scientists tell us when and where oaks have lived.  Their presence or absence was determined by changes in climate that created or eliminated land bridges between continents enabling movement of plants and animals, as well as providing the climate conditions in which oaks can survive.

Hybridization was instrumental in the formation of oak species and the ability of oaks to survive in different climate conditions.  The article in Scientific American about the genetic study of oak species concludes:  “A firm grasp of when, where and how oaks came to be so diverse is crucial to understanding how oaks will resist and adapt to rapidly changing environments. Oaks migrated rapidly as continental glaciers receded starting around 20,000 years ago, and hybridization between species appears to have been key to their rapid response. The insights we can gain from elucidating the adaptive benefits of gene flow are critical to predicting how resilient oaks may be as climate change exposes them to fungal and insect diseases with which they did not evolve.”  

In fact, a recent study suggests that assisted species migration and intentional hybridization are necessary to prevent the extinction of plants in Arctic regions, where the climate is warming the fastest.  Intentionally planting species from warmer regions into colder regions in anticipation of climate warming is called assisted migration.  It is not a new concept.  The study acknowledges that intentional hybridization is a radical suggestion that contradicts conventional wisdom:  “Traditionally, hybridization is viewed as negative and leading to a loss of biodiversity, even though hybridization has increased biodiversity over geological times.  This study acknowledges the role that hybridization plays in increasing biodiversity.

In the Bay Area, we are surrounded by examples of hybridization, some intentional and tolerated and some natural, but not tolerated:

Sycamore. Selectree.

  • Sycamores are the most common street tree in the United States and we have many here in the Bay Area. They are a hybrid of London Plane Trees and our native Sycamore.  The California native was intentionally bred with the London Plane Tree to increase its drought tolerance.   Sycamore street trees are one of the most popular because they are extremely hardy and tolerant of challenging conditions in urban settings.  They are also the host trees of one of our native butterflies, Western Tiger Swallowtail.  The Tiger Swallowtail probably used our native Sycamore in the past, but made a seamless transition to the hybrid.

Update:  I learned about the hybrid origins of our local Sycamore street tree in an urban forestry class at UC Berkeley.  Peter Del Tredici has sent me this correction: “The london plane tree, Platanus x acerifolia is generally considered to be a hybrid between the european species, P. orientalis and the eastern species, P. occidentalis. the west coast species, P. racemosa is not part of the mix.”   

Western tiger swallowtail. Wikimedia

  • Spartina alterniflora is a marsh grass that is native on the East Coast. It grows taller and denser than our native marsh grass, Spartina foliosa that also dies back in winter, unlike the East Coast native that does not.  In other words, non-native spartina is superior protection from winter storm surges compared to native spartina.  Yet, non-native spartina is being eradicated using herbicides along the entire West Coast of the country because it hybridizes with the native spartina species.  The herbicide used for that purpose has been sprayed for about 15 years, which is probably why attempts to plant native spartina as a replacement have been unsuccessful.  The result of the eradication project has been bare mud that provides no protection from erosion caused by rising sea levels and more intense winter storms.  In other words, if non-native spartina were permitted to hybridize with native spartina on the West Coast, the result would be a new species that is better adapted to face the threats of rising sea levels and intense storm surges.

Doug Tallamy’s closing photo of his keynote speech to the California Native Plant Society Conference, 2018

Fear of hybridization is akin to fear of mongrelization–the mixing of races–by racists and xenophobes.  It is closely related to the fear of non-native plant and animal species, a short-step away from the fear of human immigrants.  Concern about racial purity is not far from fear of “genetic pollution.”  State laws in the US prohibiting interracial marriage were not repealed until 1967, when the US Supreme Court ruled in Loving v. Virginia that such laws were unconstitutional in the 16 states in which these laws still remained.  These are cultural fears, not grounded in biological science. 

In conclusion

Doug Tallamy’s intended audience is home gardeners.  Although he urges his readers to remove invasive species, he does not endorse the use of herbicides.  Unfortunately, his work is used by public land managers to justify their eradication projects that usually use herbicides.  If Tallamy’s work stayed in its home gardening lane, it would do less damage to the environment.

Eradication of marsh grass on East and West Coasts doesn’t make sense

New York State agencies have been trying to destroy the Piermont Marsh since 2013, because most of the marsh grass is not native. Piermont Marsh is adjacent to the small village of Piermont on the west side of the Hudson River, less than 30 miles north of New York City.

The community of Piermont organized to prevent the destruction of their marsh for two reasons:

  • They believed that the marsh had protected them from the devastating storm surge caused by Hurricane Sandy in 2011. The village sustained damages of $11.8 million in that storm, but villagers believed it would have been much worse without the protection of the marsh.
  • The initial plan to eradicate 200 acres of non-native phragmites proposed the use of herbicides to kill the marsh grass. The villagers were concerned about large quantities of herbicides being sprayed into their waterways.

The Piermont Marsh is also very beautiful.

I have followed the attempt to save the Piermont Marsh because it is nearly identical to our West Coast version of the same issue.  Non-native spartina grass has been nearly eradicated on the entire West Coast using herbicides over the past 15 years.  After witnessing the unintended consequences of the eradication of spartina, I was sympathetic to the community of Piermont and hopeful that their organized resistance might be successful.

Opposition to the proposed project to destroy the Piermont Marsh has accomplished a great deal.  The first round of public comment and negotiation resulted in a reduction in the size of the project from 200 acres to 40 acres.  The Piermont community was also given a commitment to conduct an analysis of the damage done to the village by the destructive storm surge in the 2011 hurricane Sandy to determine the role the marsh played in protecting the village from even greater damage.

The scientist who conducted that study reported the results of the study in July 2020.  He concluded that “the presence of the Marsh is estimated to have avoided $902,000 worth of property damage and loss.” (1) He made other significant observations:

  • The native marsh grass that the project wishes to restore does not provide as much storm protection in the spring: “Typha [the native species of marsh grass] shows far more seasonal variation than phragmites.  Unlike phragmites, which maintains its height and density year-round, Typha is shorter and sparser in the spring.” (1)
  • The scientist predicted that by 2100 the Piermont Marsh will likely be overwhelmed by sea level rise. Whatever vegetation is at the Piermont Marsh, it will be gone within 80 years.

For the moment, the Piermont Marsh project is on hold:  “[The plan] will be redrafted and the new draft should be presented to the public in 2021.” (1) Meanwhile, herbicides will not be used in the marsh and experiments will be conducted to kill marsh grass by covering it with a geotextile that deprives the vegetation of light.  However, project managers have not made a commitment to avoid herbicides in the future.

Based on my experience with opposition to such destructive projects,  delays are often ultimately victories.  Funding priorities often change and more scientific information becomes available to inform a better decision.  For example, the current draft plan contains outdated information about glyphosate.  It claims that “Glyphosate is a non-selective, systemic herbicide that controls weeds by inhibiting a specific pathway for amino acid synthesis that is unique to plants and not present in animals.”

We now know that the claim about a “unique pathway” for glyphosate existing only in plants is not true.  In 2020, plaintiffs in a class-action suit against Monsanto alleging that it falsely advertised that the active ingredient in Roundup only affects plants were awarded $39.5 million.  The settlement also requires that the inaccurate claim be removed from the labels of all glyphosate products: “…[plaintiff] says Monsanto falsely claimed through its labeling that glyphosate, the active ingredient in Roundup, targets an enzyme that is only found in plants and would therefore not affect people or pets. According to the suit, that enzyme is in fact found in people and pets and is critical to maintaining the immune system, digestion and brain function.”

In defense of phragmites

According to a study conducted in 2017, phragmites is playing the same ecological roles as their native predecessors:

“An invasive species of marsh grass that spreads, kudzu-like, throughout North American wetlands, may provide similar benefits to protected wetlands as native marsh grasses. According to new research from North Carolina State University, the invasive marsh grass’s effects on carbon storage, erosion prevention and plant diversity in protected wetlands are neutral… studies have shown that Phragmites may help reduce shoreline erosion in marshlands and store carbon at faster rates than native grasses…The team found no significant differences between ecosystem services of the marshes they studied, indicating that Phragmites’ effect was largely neutral.” 

Land managers and contractors have been trying to eradicate phragmites in the Delaware River and its estuary for nearly 40 years.  Although the contractors are still committed to that project, critics are getting louder and scientists are finding more evidence of the benefits of phragmites.  It is no longer clear that eradicating phragmites is possible, nor is it clear that it would be beneficial.

Rising sea levels as ice melts in warmer temperatures are bringing the benefits of phragmites into focus:  “Some scientists have been arguing that phragmites…could be a key line of defense against rising sea level, particularly in areas like the Mid-Atlantic where land is sinking while water continues to rise… Research from 20 years ago found that phragmites help marshes elevate faster than some other plants…”

The herbicides used to kill phragmites are aerial sprayed from helicopters, killing both native and non-native plants, resulting in barren mudflats that are more vulnerable to erosion:  “The herbicide treatment of phragmites can also mean other native plants become casualties in the process, leaving an unvegetated landscape behind. With no plants to hold sediment in place, an open mudflat can be extremely vulnerable to flooding in the face of storms or unsuccessful regrowth… ‘You know, the Phrag marsh is certainly a whole lot better than no marsh,’ [a Rutgers scientist] said.”

Trying to eradicate phragmites no longer makes sense.  So why is it continuing to happen?  A Rutgers marine biologist explains:   “Well, might I say…there’s a whole army of environmental consultants that get paid to remove phragmites and don’t get paid to leave it alone.”  That is really the heart of the matter.  The projects are designed to create jobs and apply for government funds, not to protect the environment.

The West Coast version of marsh grass eradication

If the word “spartina” is substituted for the word “phragmites” the Piermont Marsh project and the questions it raises apply to similar projects on the West Coast.  For over 15 years, non-native spartina marsh grass has been eradicated using herbicides along the entire West Coast.  The result of spartina eradication projects on the West Coast is also barren mud shoreline that is poisoned with herbicide and miles of coastline that is vulnerable to rising sea levels and erosion.

The Ridgway Rail was collateral damage of the spartina eradication project. The population of this endangered bird plummeted because its nesting habitat was destroyed.

There is another similarity between the East Coast and West Coast versions of eradicating marsh grass.  Like the native typho (cattail) that is the goal of the East Coast project, native spartina that was the goal of the West Coast project is inferior protection of the coastline against storm surges.  The native species of spartina on the West Coast that was the theoretical goal of the eradication project is shorter and less dense than the non-native species.  It also dies back in the winter, unlike the non-native species that persists throughout the year.  In other words, the native species does not provide the same protection for the shoreline that is provided by the non-native species.  In any case, plantings of the native species failed in the poisoned ground, so its benefits claimed by the project are entirely irrelevant.

These eradication projects don’t make any more sense on the West Coast than their mirror image on the East Coast. 


  1. The Piermont Marsh Alliance Report on July 16 Webinar regarding Piermont Marsh

“Restoration” projects in the Bay Area are more destructive than constructive

I began studying the native plant movement and the “restoration” projects it spawned over 20 years ago when I learned about a proposal to change my neighborhood park in San Francisco in ways that were unacceptable to me.  Virtually all the trees in the park were non-native and the original proposal would have destroyed most of them.  The trees provide protection from the wind as well as a visual and sound screen from the dense residential neighborhood.  A treeless park in a windy location is not a comfortable place to visit.

The original plans would have made the park inhospitable to visitors for several other reasons, particularly by reducing recreational access to the park.  The prospect of losing my neighborhood park turned me into an activist.  I eventually learned there were similar plans for most major parks in San Francisco.  My neighborhood organized to prevent the destruction of our park and to some extent we succeeded.  However, we were unable to prevent the city-wide plan from being approved in 2006, after fighting against it for nearly 10 years.

When I  moved to the East Bay, I learned that similar projects are even more destructive than those in San Francisco,  I have spent the last 20 years informing myself and others of these plans, visiting those places, and using whatever public process that was available to oppose the plans.  The following paragraphs are brief descriptions of the projects I have studied for over 20 years.

Tree Destruction Projects in the East Bay

East Bay Municipal Utilities District (EBMUD) is the public utility that supplies our water in the East Bay.  To accomplish that task, EBMUD manages 28,000 acres of watershed land.  Like most open space in the Bay Area, the vegetation on EBMUD’s land is a mix of native and non-native species.  EBMUD destroys non-native trees which it believes to be a fire hazard.  EBMUD uses herbicides to “control” non-native vegetation, but it does not use herbicides on tree stumps to prevent resprouting.  EBMUD reports using 409 gallons of herbicide and 6 gallons of insecticide in 2019.  Of the total amount of herbicide, 338 gallons were glyphosate-based projects.  EBMUD says “minor amounts of rodenticide were applied by contractors.”

The East Bay Regional Park District (EBRPD) approved the “Wildfire Hazard Reduction and Resource Management Plan” and its Environmental Impact Report in 2009.  This plan is removing most eucalyptus, Monterey pine, and acacia from several thousand acres of parkland.  Forests are being thinned from an average density of 600 trees per acre to approximately 60 trees per acre.  These plans are being implemented and funding for completion of the project has been secured.  Herbicides are used to prevent the trees from resprouting and to destroy vegetation deemed “invasive.”

UC Berkeley clear-cut over 18,000 non-native trees from 150 acres in the Berkeley hills in the early 2000s.  UCB applied for a FEMA grant to complete their clear-cutting plans.  The FEMA grant would have clear cut over 50,000 non-native trees from about 300 acres of open space in the Berkeley hills.

Frowning Ridge, UC Berkeley, 2010

In 2016, FEMA cancelled grant funding as a result of a lawsuit and subsequent appeals from UCB were defeated several years later.  In 2019, UCB revised its original plans.  With the exception of clear-cutting ridgelines, the revised plan will thin non-native forests.  Herbicides will be used to prevent the trees from resprouting.

The City of Oakland applied for a FEMA grant in collaboration with UC Berkeley to clear cut non-native trees on over 120 acres in the Oakland hills.  That FEMA grant was cancelled at the same time UC Berkeley lost its grant funding.  Oakland has also revised its plans for “vegetation management” since the FEMA grant was cancelled.  The revised plan will thin non-native forests on over 2,000 acres of parks and open space.  The plan is undergoing environmental review prior to implementation.  Herbicide use to implement the plan is being contested.

Tree Destruction Projects in San Francisco

The Natural Areas Program (now called Natural Resources Division) of the City of San Francisco has destroyed thousands of trees in 32 designated areas of the city’s parks since the program began in 1995.  The management plan for the Natural Areas Program was approved in 2006, after 10 years of opposition.  The plan proposes to destroy an additional 18,500 trees over 15 feet tall and untold numbers of smaller trees that the plan chooses not to define as trees.   Herbicides are used to “control” non-native vegetation and prevent trees from resprouting after they are cut down.

Sutro Forest 2010

University of California at San Francisco (UCSF) began its effort over 20 years ago to destroy most non-native trees on 66 acres of Mount Sutro.  UCSF applied for a FEMA grant to implement those plans based on their claim that the Sutro Forest is a fire hazard.  UCSF withdrew the grant application after FEMA asked for evidence that the forest is a fire hazard.  San Francisco is cool and foggy in the summer, making fires rare and unlikely.

Sutro Forest with resprouts of destroyed trees. November 2019

UCSF’s plans to destroy most trees on Mount Sutro were approved in April 2018.  Many trees on Mount Sutro have been destroyed since the project was approved and more will be destroyed before the project is complete.  UCSF made a commitment to not use pesticides in the Sutro Forest.  Many of the trees that have been destroyed have therefore resprouted.  Unless the resprouts are cut back repeatedly, the forest is likely to regenerate over time.

  Tree Destruction Projects on Federal Lands

The federal government is one of the largest landowners in the Bay Area.  Golden Gate National Recreation Area (75,500 acres), Point Reyes National Seashore (28,800 acres), and Muir Woods National Monument are operated by the National Park Service.  The Presidio in San Francisco is a National Park that is presently controlled by a non-profit trust.  These parks have engaged in extensive tree-removal on the public lands they control.  Information available on their websites does not enable us to quantify the acres or number of trees that have been removed or are planned for removal in the future.  Therefore, we will describe those projects in the broad terms available to us.

There are two main categories of tree-destruction projects on these federal lands.  There are many large-scale “restoration” efforts that have required the removal of all non-native vegetation, including trees.  These attempts to eradicate non-native plants are based on a misguided belief native plants will magically return.  Herbicides are used by National Park Service to destroy non-native vegetation, although specific information is difficult to obtain because NPS is not responsive to inquiries and the federal public records law can take years to respond.

Eradication efforts fail regardless of method used

In “Lessons learned from invasive plant control experiments:  a systematic review and meta-analysis,” scientists analyzed 355 studies of attempts to eradicate non-native plants from 1960 to 2009.  The scientists determined the methods used and the efficacy of those methods.  More than 55% of the projects used herbicides, 34% used mechanical methods (such as mowing, digging, hand-pulling), 24% burned the vegetation, and 19% used all three methods.  The study found that herbicides most effectively reduced “invasive” plant cover, but this did not result in a substantial increase in native species because impacts to native species are greatest when projects involve herbicide application.  Burning projects reduced native coverage and increased non-native coverage. In other words, it doesn’t matter what method is used, eradicating non-native plants does not result in the return of native plants.   We didn’t need a study to tell us this.  We can see the results with our own eyes.

Flammability of plants is unrelated to nativity

The other, larger category of tree-removal projects on these federal lands are the so-called “fuel management projects.”  The flammability of non-native plants and trees is exaggerated in order to justify their destruction.   Native plants are not inherently less flammable than non-native plants.

In fact, native vegetation in California is fire adapted and fire dependent for germination and survival.  The California Native Plant Society recently revised its “Fire Recovery Guide. The Guide now says, “California native plants are not inherently more likely to burn than plants from other areas.”  This statement is the mirror image of what defenders of our urban forest have been saying for 25 years:  “Non-native trees are not inherently more flammable than native trees.”  Both statements are true and they send the same message: flammability is unrelated to the nativity of plants.  “Think instead about characteristics of plants,” according to the CNPS “Fire Recovery Guide.”

There are undoubtedly many other similar projects of which we are unaware.  I report only on projects that I have direct knowledge about and that I have visited.

Why I opposed these projects

The San Francisco Bay Area was nearly treeless before early settlers planted non-native trees.  Non-native trees were planted because they are better adapted to the harsh coastal winds than native trees.  The treeless grassland was grazed by deer and elk and burned by Native Americans to promote the growth of plants they ate and fed the animals they hunted.  Grazing and burning maintained the grassland, preventing natural succession to shrubs and trees.

Native Americans setting grass fire, painting by Frederic Remington, 1908

Modern land use and management policies have suppressed fire and reduced grazing in the Bay Area.  Consequently grasslands are naturally converting to chaparral and scrub.  Although managers of public lands often describe these changes in the landscape as “invasions,” Jon Keeley (Ph.D. biologist, USGS) considers them a natural succession“These changes are commonly referred to as shrub invasion or brush encroachment of grasslands.  Alternatively, this is perhaps best viewed as a natural recolonization of grasslands that have been maintained by millennia of human disturbance.” 

Early settlers planted trees to protect their residential communities and their crops from wind.  The urban forest also provides sound and visual screens around parks that are surrounded by dense residential neighborhoods.  Urban forests are storing carbon that is released as greenhouse gas when they are destroyed. They also reduce air pollution by filtering particulates from the air.

When trees are destroyed, the unshaded ground is quickly colonized by weeds that are then sprayed with herbicide.  Even environmental organizations that support the destruction of non-native trees agree about the results of these projects:

  • The California Native Plant Society predicted the post-project landscape in its written public comment on the Draft Environmental Impact Statement (DEIS) of the FEMA project in the East Bay hills with this rhetorical question: “What mechanism is being instituted by FEMA in this DEIS to guarantee a commitment of money and personnel for management of greatly increased acreages of newly created annual weedy grassland?”
  • The Audubon Society predicted the post-project landscape in its written public comment on the DEIS: “There is no support for the conclusion that native vegetation will return on its own.  This plan may not result in an increase in native trees and plants…Heavy mulching will delay or prevent the growth of native species.”

To summarize:  I am opposed to destroying our urban forests because they perform many important ecological functions, including providing habitat for wildlife.  Furthermore, the herbicides used to destroy the forest and control weeds that thrive in the absence of shade, damage the soil and create unnecessary health hazards to humans and other animals.

Deforestation and Climate Change

Climate change is the environmental issue of our time.  The fact that the climate is warming is indisputable and the consequences of the changes are becoming more evident.  Much of California has warmed over 3⁰ F since 1980.

Source: NASA

Consequences of Climate Change

The impact of climate change on biotic and abiotic realms has been far-reaching:

  • Sea Level Rise:  Temperatures in Polar Regions have increased the most because the ice is melting and sunlight that was reflected by the ice is now absorbed by the darker surface.  Melting ice has raised sea levels between 1993 and 2017 on average 3.1 mm (1/8th inch) per year at an accelerating rate.  The Intergovernmental Panel on Climate Change (IPCC) predicts that sea levels will rise .8 meter (2.6 feet) by the end of the century.  Coastal cities are flooding during high tides and storm surges.  Islands are disappearing.
  • Warming Ocean:  Marine life is dying in warming waters and coral reefs are dying because the water becomes more acidic as it absorbs more carbon dioxide (CO₂).
  • Extreme Weather Events:  The increase in the frequency and severity of droughts, hurricanes, tornados, heat waves, etc. is attributed to climate change.  These events kill plants and animals.  Extreme temperatures will eventually make some places in the world uninhabitable for most life.
  • WildfiresIncreased frequency and intensity of wildfires all over the world are caused by global warming and associated drought.

Given the life-threatening conditions created by the warming planet, it seems a small quibble to argue about whether or not the landscape must be transformed into some semblance of what it was in the 14th century, prior to global explorations and colonization by Europeans.  We are doing next to nothing to address the causes of climate change, yet we are spending approximately $25 billion per year on such “restorations” of historical landscapes.  When these projects kill trees, they make climate change worse.  California is considered a leader in addressing climate change in the US.  Yet, when calculating carbon loss to meet stated targets for reduction, California does not include carbon loss in the trees that are destroyed.

Causes of Climate Change

There is nearly universal agreement in the scientific community that climate change is caused by greenhouse gasses emitted by the activities of humans.

Note that “forestry” (more accurately described as “deforestation”) contributes more greenhouse gas emissions than transportation.  In both cases, carbon dioxide (CO₂) is the specific greenhouse gas that is emitted by these sectors of the economy.  In the case of transportation cars, airplanes, ships, etc. are using fossil fuels that emit CO₂ when burned.  In the case of deforestation, the CO₂ that is stored by trees during their lifetime is released into the atmosphere as a greenhouse gas when the tree is destroyed and its wood decays.  And the loss of the trees means there will be less carbon storage in the future. Even if new trees were planted, less carbon would be stored because carbon storage is largely a function of biomass; that is, bigger trees store more carbon:

Carbon Storage and Sequestration in San Francisco’s Urban Forest

d.b.h. = diameter at breast height, is the standard measure of tree size.  The bigger the tree, the more carbon it stores.  Source:  US Forest Service inventory of San Francisco’s urban forest, 2007.

Forests cover 31% of the land area on Earth and annually 75,700 square kilometers (18.7 million acres) of the forest is lost as a result of wildfire, clearing for agriculture and grazing, and logging for timber.  For the past 25 years, we have also been destroying trees just because they aren’t native.  In California we destroy eucalyptus, Monterey pine and cypress outside their small native range, and a few other non-native species.  In the Southwest we destroy tamarisk trees that were planted to control erosion.  On the East Coast we destroy ailanthus (tree of heaven).  In Florida we destroy malaleuca trees.  Native plant advocates call these trees “invasive,” but a more accurate description is that they are successful trees, well adapted to current climate conditions.  There are probably many other non-native trees on the long hit list of native plant advocates.

Other benefits of trees

Trees are valuable members of our communities for many reasons in addition to storing carbon.

  • Trees provide the windbreak that makes our parks and open spaces comfortable in windy coastal locations.
  • Trees are a visual and sound screen around our urban parks and residential properties.
  • Trees remove particulates from the air, reducing the air pollution that makes urban environments unhealthy.
  • The San Francisco Bay Area is very foggy during summer months.  Tall trees condense the fog, which falls to the ground as rain, adding 10 inches of annual precipitation in East Bay eucalyptus forests and 16 inches of annual precipitation in San Francisco’s eucalyptus forests.
  • Forests transpire water from their leaves that falls back to earth as rainfall.  Where forests are destroyed, rainfall decreases significantly.
Transpiration is the process by which moisture is carried from tree and plant roots to the leaves, where it changes to vapor and is released to the atmosphere. Interestingly, a large oak tree can draw 40,000 gallons of water a year up through the roots and evaporate that moisture through the leaves.  Source:  USGS
  • Trees stabilize the soil with their roots, preventing erosion on steep hillsides that become unstable when trees are destroyed.
  • The roots of trees absorb rainfall that would otherwise run off the land without being absorbed into the soil.  The run off washes the top soil away, clogging rivers and streams and reducing the fertility of the soil.

Case Studies

We don’t need to speculate about the consequences of destroying trees because there are many specific examples of the negative impact of destroying large numbers of trees.  Here are two examples, one modern and one historical.

The island nation of Comoros, off East Africa, once had an extensive cloud forest, a forest in which trees are often surrounded by low-level cloud cover. Cloud forests, such as the eucalyptus trees shrouded in fog on Mount Sutro in San Francisco, condense large amounts of moisture out of the clouds that then falls onto the ground. Fog drip in San Francisco’s eucalyptus forests adds sixteen inches of rainfall each year in those forests.

Eucalyptus canopy on east side of Glen Canyon Park, taken from Turquoise Way December 2012, before tree destruction began. Courtesy San Francisco Forest Alliance

The delicate ecosystem on Comoros was disrupted when the cloud forests were cleared to make way for farmland. Between 1995 and 2014 about 80% of the remaining forest was cut down. The loss of trees disrupted the rainfall cycle on the islands. The moisture that the cloud forest was condensing from the fog was lost to the ground when the trees were destroyed. That ground moisture was then no longer transpired back into the air by the trees that had been destroyed, resulting in less rainfall. The disruption caused waterways to dry out, and left once-fertile soil exposed to erosion, with the loss of nutrients in the soil that remains. Comoros has lost 40 permanent rivers in the last 50 years. There is no longer enough water for agriculture or the daily household needs of the population.

Restoring forests is a challenge, and cloud forest can be particularly difficult. “It’s impossible to replace it,” said a cloud forest specialist at the University of York in England. “You need to save them before they’re gone.” Comoros could be a lesson for those who want to cut down the cloud forest on Mount Sutro and elsewhere in the Bay Area. Disrupting the rainfall cycle could make our drought even more extreme.

Sutro forest on a typical summer day. Courtesy Save Sutro Forest.

Icelanders appreciate their trees because they have few of them.  Iceland was heavily forested, mostly with birch trees, when the Vikings arrived in the 9th century.  Within 100 years, settlers cut down 97% of original forests to build housing and make way for grazing pastures.  Now only 0.5% of the Iceland’s surface is forested, despite extensive reforestation efforts since the 1950s.  Lack of trees means there isn’t vegetation to protect the soil from erosion and to store water, leading to extensive desertification.

Reforestation efforts in Iceland did not attempt to restore native birch forests because they store little carbon and they are not useful for timber.  Seeds of pine and poplar from Alaska were introduced, but growth has been slow because the soil is nitrogen poor and the climate is very cold.  The growth rate is estimated to be only one-tenth of the growth rate of tropical forests in the Amazon.

Both of these examples illustrate that when forests are destroyed, they are not easily replaced.  Much like the historical landscape, we can’t go back.  Nature is dynamic.  It moves forward, not back.

Consequences of deforestation in San Francisco Bay Area

San Francisco has one of the smallest tree canopies—only 14%–of any major city in the Country:

Source:  Data from Urban Forestry Plan, SF Planning Department, 2016. Graphic by San Francisco Forest Alliance

The small urban forest in San Francisco is storing carbon that would otherwise be released into the atmosphere as greenhouse gas, contributing to climate change.  “Carbon sequestration is the process by which atmospheric carbon dioxide is taken up by trees, grasses, and other plants through photosynthesis and stored as carbon in biomass (trunks, branches, foliage, and roots) and soils. The sink of carbon sequestration in forests and wood products helps to offset sources of carbon dioxide to the atmosphere, such as deforestation, forest fires, and fossil fuel emissions.”  (US Forest Service)

Carbon capture by above ground vegetation is proportional to biomass. Because Blue Gum eucalyptus is the largest and most common tree in San Francisco, most carbon storage in San Francisco’s urban forest is in eucalyptus trees, according to an inventory done by the US Forest Service, as illustrated by this graph of the inventory.

Carbon storage by tree species in San Francisco

Source: US Forest Service

All other trees in San Francisco inventoried by US Forest Service are also non-native because there are few native trees in San Francisco.  There are few native trees in San Francisco because they are not well adapted to challenging conditions.  The wind is strong and constant.  The soil is sand, rock, or clay.  It doesn’t rain for 7 months of the year.  The trees that were planted in the San Francisco Bay Area in the 19th century by European settlers were non-native because they were the species that could survive these harsh conditions. 

The non-native trees that are being destroyed by public land managers in the San Francisco Bay Area will not be replaced because the goal of the land managers is to restore grassland that existed prior to the arrival of Europeans at the end of the 18th Century.  All the benefits of trees and forests, including carbon storage will not be replaced.

Forests store more carbon than grassland

Native plant advocates defend the destruction of our urban forest by making the inaccurate claim that grassland stores more carbon than trees.  While it is true that more carbon is stored in the soil than in above-ground vegetation, it does not follow that the soil in grassland contains more carbon than the soil in forests.  The US Department of Agriculture report, “Considering Forest and Grassland Carbon in Land Management” (2017) graphically illustrates that forests in the US store far more carbon per hectare than any other land type and grasslands store the least amount of carbon per hectare of undeveloped land in the Western United States:

The differences in carbon storage per hectare in Western and Eastern United States are caused by differences in climate, soil, and specific vegetation types.  The USDA report also makes these statements about the value of forests for carbon storage:

  • The conversion of forest to non-forest should be avoided to preserve carbon storage, “Because mature forest stands are more likely to be carbon rich from the high volume of tree biomass and recovery takes a long time through afforestation…Further, soil carbon generally declines after deforestation from accelerated decomposition of organic matter such as litter and tree roots.”
  • “Across forest systems, the ‘no harvest’ option commonly produces the highest forest carbon stocks.  Managed stands have lower levels of forest biomass than unmanaged stands…”  In other words, from the standpoint of maximizing carbon storage, leave the forest alone!
  • “Fuel-reduction treatments lower the density of the forest stand, and, therefore, reduce forest carbon.”  Again, the message is leave the forest alone!
  • “…carbon emissions from prescribed fire, the machinery used to conduct treatments, or the production of wood for bioenergy may reduce or negate the carbon benefit associated with fuel treatments…”

Misplaced priorities

I am mystified by the obsession with native plants.  Still, I respect everyone’s horticulture preferences.  If you prefer native plants, by all means, plant them.  We make just one request:  quit destroying everything else because the loss of our urban forest is contributing to climate change and depriving our communities of the many benefits of trees and forests.

Nativism in the Natural World

Invasion biology is the scientific discipline that spawned the native plant movement.   Charles Elton published a book in 1958 that is considered the origin of the modern version of invasion biology, although there are precursors centuries earlier.  These are the basic tenets of modern invasion biology:

  • Plants and animals that are “native” to a specific location are considered members of an ideal ecosystem that have co-evolved over thousands of years so that members of the community are dependent upon one another.
  • Plants and animals introduced to an ecosystem by humans are assumed to disrupt the equilibrium balance of the community and threaten its existence because introduced plants and animals do not have predators that would control their spread.  All introduced plants and animals are therefore considered potentially invasive.
  • Animals are believed to be dependent upon the plants with which they evolved—and only these plants–and these mutually exclusive relationships are disturbed by the introduction of new plants and animals. 
  • Adaptation and evolution of introduced plants and animals is believed to be too slow for introduced plants and animals to successfully enter the food web.
  • Native members of the ecosystem are presumed to be inherently superior to introduced plants and animals.  Invasion biology does not acknowledge that introduced plants and animals are often functional members of the ecological community.
  • Native ecosystems are said to be in “balance” and introduced species are presumed to cause “imbalance.”  Introduced species must be eradicated to restore balance to the ecosystem, presumed to be the ideal for a particular location.

Hundreds of empirical studies have been conducted since the 1960s to test these assumptions.  Little scientific evidence has been found to support them. Current knowledge of ecology explains why the assumptions of invasion biology are mistaken. 

What is native?

The native plant movement defines native as the plant species that lived in a specific location prior to the arrival of Europeans.    In the San Francisco Bay Area, “native” is defined by native plant advocates as the plants and animals that lived here prior to 1769 when Europeans first laid eyes on San Francisco Bay.  When Europeans arrived, the San Francisco Bay Area was already occupied by indigenous people who had arrived approximately 10,000 years earlier. 

The arbitrary selection of the pre-European settlement period to define the ideal landscape was based on the mistaken assumption that the indigenous human population had not radically altered the land. Anthropological and paleontological research informs us that the landscape was essentially gardened by the indigenous population to provide food and cultural implements. 

Pomo gathering seeds, 1924. Smithsonian photo archive

The landscape found by Europeans at the end of the 18th century was not “natural.”  It was altered by humans to serve humans who lived as hunters and gatherers.  Since modern society no longer hunts and gathers for its food and shelter, the landscape that served that lifestyle cannot be maintained without mimicking the land management practices of native people such as frequent burning of the landscape and grazing by animals.  Indigenous people in California did not have domesticated animals (except dogs), but the grassland was grazed by wild deer, elk, and antelope. 

Plants and animals have migrated around the world without the assistance of humans since life began.  The seeds of plants are carried in the stomachs of migrating birds and on the winds of storms.  Animals, including humans, move to wherever they can find what they need to survive.  Migration is natural and often necessary for survival.  Making a distinction between species moved by humans and those moved by natural forces is pointless and usually impossible to distinguish. 

Climate change renders the concept of “native plants” meaningless because when the climate changes, the vegetation changes.  The plants that live in tropical climates will not survive in arctic cold and vice versa.  Introduced plants are often better adapted to current climate conditions than their native predecessors because the climate has changed and it will continue to change. 

Mistaken assumptions about evolution

Animals rarely depend upon a single plant species for survival.  Such mutually exclusive relationships rarely exist in nature because they are evolutionary dead-ends. Animals can, and often do, adapt quickly to changes in the environment.  Transitions from native to introduced plants are routinely made by animals, including humans.  Indigenous hunter/gatherers quickly incorporated plants introduced by European settlers into their diets.  Plants in the same family and genus are often chemically similar, making the transition more likely. 

Native plant advocates assume that evolution only occurs slowly, over thousands of years, but evolution can be faster than they assume.  Rapid environmental change accelerates the speed of evolution because extreme weather events caused by climate change increase the speed of natural selection, the primary tool of evolution.  When cataclysmic events such as hurricanes, droughts, floods, extreme temperatures kill many members of a species population, these are selection events in which the fittest members survive to breed and the next generation inherits the genetic traits that helped their parents survive.  The classic example of this principle is the finches in the Galapagos Islands who died if they didn’t have big enough beaks to eat the seeds of the only plant that survived extreme drought.  The next generation of finches had bigger beaks. 

Darwin’s finches are an example of rapid evolution

Evolution occurs when genetic changes enable future generations to inherit the genetic change.  Adaptation occurs when animals respond to environmental challenges by changing behaviors that aren’t necessarily inherited by the next generation.  Adaptation to changed environmental conditions is even more rapid than evolution and equally effective to ensure survival. Genetic changes are not required for an insect to make the transition from a native host plant to a chemically similar introduced plant.   Extreme temperatures require that plants and animals move to more temperate climates.  “Native” ranges must change to survive changes in the environment.  A plant or animal that cannot survive extreme heat will migrate (if it can) into regions where temperatures are not as warm.  They should not be prevented from doing so. 

Adaptation to Climate Change. IPCC

Plant and animal species with large populations and short lives, such as insects, evolve more quickly.  This more rapid pace of evolution enables a more rapid transition from native host plants to closely related introduced plants.

soapberry bug made transition from native to non-native balloon vine in 20-50 years. Scott Carroll, UC Davis

Nativism and the native plant movement

The native plant movement is based on the belief that native plants are superior to introduced plants, that native plants are somehow “better” than immigrant plants.  That assumption of superiority is the definition of nativism.  It is as specious an assumption in the natural world as it is in human society and it is equally dangerous. 

There are pros and cons to everything living in the natural world and there is no right answer to the question of which species is “best.” When evaluating introduced plants, nativists consider only the negative aspects. They refuse to acknowledge that there are also advantages and a death verdict should take both into consideration.  For example, native plant advocates want all eucalyptus trees in California cut down because they were planted here after European settlement.  This negative judgment of eucalyptus does not take into consideration that 75% of monarch butterflies who spend the winter in California use eucalyptus trees for their safe haven. Also, eucalyptus blooms in California from November to May, providing nectar to butterflies, hummingbirds, and bees at a time of year when native plants are not blooming.  Eucalyptus trees are also nesting homes of owls and other raptors.  Cutting down eucalyptus trees simply because they are not native in California ignores the many benefits they provide to wildlife. 

Monarch butterflies over-winter in California’s eucalyptus groves

Confusing cause and effect

The native plant movement mistakenly assumes that the mere existence of introduced plants threatens the existence of native plants.  They believe that native plants will magically emerge if introduced plants are eradicated.  They have spent 25 years eradicating non-native plants and do not seem to have noticed that native plants have not returned.  They make this mistake because they do not acknowledge the changes in the environment that make non-native species better adapted to current environmental conditions. 

Many of the changes in the environment that are inhospitable to native species are caused by structural changes made to accommodate human activities, not by introduced species.  For example, all the major rivers in California have been dammed to prevent floods and store water for use during the dry season.  These dams have fundamentally altered the ecology of our rivers.  There are no longer cleansing spring floods that clear rivers of accumulated mud and vegetation.  Channeled rivers are deeper and warmer.  Salmon can no longer get to their spawning grounds past the dams.  The altered structural conditions are more hospitable to bass than to trout.  Aquatic plants from tropical regions become invasive in warmer water.  None of these conditions are reversed by spraying aquatic plants with herbicide or killing introduced bass.

Butterfly bush (buddleia) is now being eradicated by nativists.. butterflybush.com

Wherever “invasions” are observed, no thought is given to why.  Instead, a convenient plant or animal scapegoat is found and poisoned.  That death sentence doesn’t reverse the underlying reason for the invasion.  Therefore, the invasion persists.  Society is unwilling to make the sacrifices, even inconveniences, needed to address the underlying cause of the “invasion.”  We have done little to address the causes of climate change.  We are unwilling to destroy the dams and the system of supplying water to serve agriculture needs.  Invasions are the symptom, not the cause of the changes in nature.

Conservation Sense and Nonsense

You are receiving this announcement of our changed focus and new name because you are a subscriber to our original Million Trees blog.  This is our revised mission for the Conservation Sense and Nonsense blog:

Conservation Sense and Nonsense began in 2010 as the Million Trees blog to defend urban forests in the San Francisco Bay Area that were being destroyed because they are predominantly non-native.  In renaming the Million Trees blog to Conservation Sense and Nonsense, we shift the focus away from specific projects toward the science that informed our opposition to those projects. 

Many ecological studies have been published in the past 20 years, but most are not readily available to the public and scientists are often talking to one another, not to the general public.  We hope to help you navigate the scientific jargon so that scientific information is more accessible to you.  If this information enables you to evaluate proposed “restoration” projects to decide if you can or cannot support them, so much the better.

Anise Swallowtail butterfly in non-native fennel. Courtesy urbanwildness.org

Since 2010, we have learned more about the ideology of invasion biology that spawned the native plant movement and the “restoration” industry that attempts to eradicate non-native plants and trees, usually using herbicides.  We have read scores of books and studies that find little scientific evidence in support of the hypotheses of invasion biology.  We have studied the dangers of pesticides and the growing body of evidence of the damage they do to the environment and all life. 

Meanwhile, climate change has taken center stage as the environmental issue of our time.  Climate change renders the concept of “native plants” meaningless because when the climate changes, vegetation changes.  The ranges of plants and animals have changed and will continue to change to adapt to the changing climate.  Attempting to freeze the landscape to an arbitrary historical standard is unrealistic because nature is dynamic.  Evolution cannot be stopped, nor should it be.

Destroying healthy trees contributes to climate change by releasing stored carbon into the atmosphere.  Both native and non-native trees store carbon and are therefore equally valuable to combat climate change.  Native vegetation is not inherently less flammable than non-native vegetation.  There are advantages and disadvantages to both native and non-native vegetation. 

The forests of the Earth are storing much of the carbon that is the primary source of greenhouse gases causing climate change.  Deforestation is therefore contributing to climate change.  By destroying healthy trees, the native plant movement is damaging the environment and its inhabitants.

Housekeeping

All of the articles on the Million Trees blog are still available in the archive on the home page.  The search box on the home page will take you to specific subjects of interest.  Visit the pages listed in the sidebar of the new home page for discussion of each of the main topics by clicking on the links above.  Readers who subscribed to the Million Trees blog will receive new articles posted to Conservation Sense and Nonsense unless they unsubscribe.  Thank you for your readership.  Your comments are welcome and will be posted unless they are abusive or repetitive. 

Doug Tallamy speaks…Art Shapiro responds…Million Trees fills in the gaps

Smithsonian Magazine published an interview with Professor Doug Tallamy, the entomologist who is committed to the eradication of non-native plants and most influential with native plant advocates in the United States.  The Smithsonian article gives Professor Art Shapiro an inadequate opportunity to respond to Tallamy’s assertions about the superiority of native plants.  Million Trees steps up to fill in the gaps in response to Tallamy.

  • The Smithsonian article says, “As a scientist, Tallamy realized his initial obligation was to prove his insight empirically. He began with the essential first step of any scientific undertaking, by applying for research grants, the first of which took until 2005 to materialize. Then followed five years of work by relays of students.”

The first study that Tallamy conducted is not mentioned in this article because it disproved his hypothesis:  “Erin [Reed] compared the amount of damage sucking and chewing insects made on the ornamental plants at six suburban properties landscaped primarily with species native to the area and six properties landscaped traditionally.  After two years of measurements Erin found that only a tiny percentage of leaves were damaged on either set of properties at the end of the season….Erin’s most important result, however, was that there was no statistical difference in the amount of damage on either landscape type.” (1)

  • The Smithsonian article says, “… insects tend to be specialists, feeding on and pollinating a narrow spectrum of plant life, sometimes just a single species. ‘Ninety percent of the insects that eat plants can develop and reproduce only on the plants with which they share an evolutionary history’…:”

Anise Swallowtail butterfly in non-native fennel. Courtesy urbanwildness.org

A “specialist” insect is rarely confined to using a single plant species.  Mutually exclusive relationships in nature are very rare because they are usually evolutionary dead-ends.  The study in which this claim about “specialization” originated, actually concluded:  “More than 90 percent of all insects sampled associate with just one or two plant families.”* There are over 600 plant families and thousands of plant species within those families.  Most plant families include both native and non-native plant species.  An insect that uses one or two plant families, is therefore capable of using both native and non-native plant species.  For example, there are 20,000 plant members of the Asteraceae family, including native sagebrush (Artemisia) and non-native African daisy.  In other words, the insect that confines its diet to one family of plants is not very specialized.

  • The Smithsonian article says, But he [Tallamy] thinks this [transition of insects to non-native plants] is likely to take thousands of generations to have an impact on the food web. Shapiro maintains he has seen it occur within his own lifetime.”

There are many empirical studies that document the transition that insects make from native to non-native plants within generations.  Professor Tallamy provides a few examples of such rapid transitions in his first book, Bringing Nature Home:  wooly adelgids from Asia have had a devastating effect on native hemlock forests in the eastern United States; Japanese beetles introduced to the United States are eating the foliage of over 400 plant species (according to Professor Tallamy), some of which are native (according to the USDA invasive species website).

Soapberry bug on balloon vine. Scott Carroll, UC Davis

The soapberry bug made a transition from a native plant in the soapberry family in less than 100 generations over a period of 20 to 50 years. The soapberry bug-balloon vine story is especially instructive because it entailed very rapid morphological as well as behavioral change; the beak length was quickly (a few years) selected for the dimensions of the fruit of the new host. (2)

  • Doug Tallamy claims that Art Shapiro’s findings are “anecdotal.” They are not.  Art Shapiro’s published study is based on nearly 40 years of data. (3)

Monachs in eucalyptus, Pacific Grove Museum

In a recent NY Times article about declining populations of monarch butterflies on the West Coast, an academic scientist explains how he used Professor Shapiro’s data set to study the decline:  “The monarch’s decline is part of a larger trend among dozens of butterfly species in the West, including creatures with names like field crescents, large marbles and Nevada skippers, said Matt Forister, an insect ecologist at the University of Nevada, Reno, whose conclusions are based on a nearly 50-year set of data compiled by Art Shapiro, a researcher at the University of California, Davis. “The monarch is very clearly part of a larger decline of butterflies in the West.”  Clearly, other academic entomologists do not consider Professor Shapiro’s data “anecdotal.”

The Burghardt/Tallamy study (4) does not contradict the findings of Professor Art Shapiro because Professor Shapiro is studying butterflies (not moths) in “natural areas” that have not been artificially created by choosing a limited number of plant species, as Tallamy’s study did.  In other words, the adult and larvae stages of butterflies that Professor Shapiro studies have more options, and when they do they are as likely to choose a non-native plant as a native plant for both host plant and food plant.  You might say, Professor Shapiro’s study occurs in the “real world” and the Burghardt/Tallamy study occurs in an artificially created world.

Dismissing observations as anecdotal is a well-worn rhetorical device.  Creationists often claim that evolution cannot be proven because the theory is based on millions of observations, rather than empirically tested by experiments. Yet, virtually all scientists are firm believers in the validity of evolutionary principles.

  • Tallamy dismisses climate change as a factor in plant and animal extinctions, preferring to place the blame solely on the mere existence of non-native plants.

This claim is contradicted by a multitude of studies, such as a collection of studies recently reported by Yale E360 that concludes:  “A growing number of studies show that warming temperatures are increasing mortality in creatures ranging from birds in the Mojave Desert, to mammals in Australia, to bumblebees in North America. Researchers warn that heat stress could become a major factor in future extinctions.”

Climate change is the environmental issue of our time.  When the climate changes, the vegetation changes.  When the vegetation changes, wildlife adapts or dies.  Non-native plants are one of the consequences, not the cause of climate change or plant and animal extinctions.

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*Professor Shapiro has provided a caveat to this definition of specialization of insects in a private communication, published with his permission:  A couple of observations: Hardly any insects feed on entire plant families. Rather, they feed on specific lineages within those families, typically defined by secondary chemistry (which is the necessary releaser for oviposition and/or feeding behavior). The relationship was summed up symbolically by A.J.Thorsteinson half a century ago: feeding=presence of nutrients+presence of required secondary chemicals-deterrents-antifeedants-toxins. Thus the Anise Swallowtail species-group feeds on the carrot family, Apiaceae, but NOT on Apiaceae lacking the proper chemistry.But they DO feed on some Rutaceae (including Citrus) that, though unrelated, are chemically similar. That was worked out by Vincent Dethier in the 1940s and further developed by John Thompson at UC Santa Cruz. A whole slew of things require iridoid glycosides as oviposition and feeding stimulants. Most plants containing these were in the family Scrophulariaceae before DNA systematics led to its dismemberment, but one whole branch of Scrophs is chemically unsuitable. Milkweed bugs eat milkweed, but they also eat the Brassicaceous genera Erysimum and Cheiranthus, which are chemically similar to milkweeds but not to other Brassicaceae…and so on. Native vs. non-native has nothing to do with it.”  (emphasis added)

  1. Tallamy, Doug, “Flipping the Paradigm:  Landscapes that Welcome Wildlife,” chapter in Christopher, Thomas, The New American Landscape, Timber Press, 2011
  2. Carroll, Scott P., et. al., “Genetic architecture of adaptive differentiation in evolving host races of the soapberry bug, Jadera haematoloma,” Genetica, 112-113: 257-272, 2001
  3. SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433
  4. Karin Burghardt, Doug Tallamy, et. al., “Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities,” Ecosphere,November 2010