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.

_______________________________________________

*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

Forest Action Brigade: “Oakland’s Vegetation Management Plan is significantly improved”

The City of Oakland began the process of developing a Vegetation Management Plan (VMP) over three years ago.  The purpose of the VMP is “to evaluate the specific wildfire hazard factors in the Plan Area [2,000 acres of city-owned parks and open space and 300 miles of roadsides] and provide a framework for managing vegetative fuel loads…such that wildfire hazard is reduced and negative environmental effects resulting from vegetation management activities are avoided or minimized.” (revised VMP, page 3)

The first draft of the VMP was published in June 2018.  There were significant issues with the first draft that were described by Million Trees HERE.

The VMP was revised and published on November 1, 2019.  It is available HERE.  Written comments can be submitted until December 12, 2019. Scoping comments may be submitted by email (arobinsonpinon@oaklandca.gov) or by mail to Angela Robinson Piñon, 250 Frank H. Ogawa Plaza, Suite 4314, Oakland California 94612.  “Scoping” is the first step in the process of preparing an Environmental Impact Report (EIR). The purpose of scoping is to identify the issues that must be evaluated by the EIR.

The Forest Action Brigade accepts the revised VMP because fire hazards are real and compromise is needed to address them.  Public comments submitted by the Forest Action Brigade regarding scoping for the EIR explain our reasoning. See below. We believe the revised VMP will reduce fire hazards in Oakland without destroying more trees than necessary and limiting herbicide use primarily to preventing trees from resprouting after they are removed.  It is counterproductive to destroy more trees than necessary because climate change has made wildfires more frequent and destructive and carbon sequestered by mature trees is one of the most effective means of reducing greenhouse gas emissions causing climate change.

TO: Angela Robinson Pinon, Oakland Fire Department
arobinsonpinon@oaklandca.gov
FROM: Forest Action Brigade
RE: Oakland’s Vegetation Management Plan, Scoping Comments for EIR

The revised Vegetation Management Plan is a significant improvement over the first draft.  We accept the revised Vegetation Management Plan for the City of Oakland because:

  • Standards for creating and maintaining defensible space around structures, along roadsides, and on ridgelines are reasonable and consistent with both fire science and State law.
  • Forests will be thinned, but “broad based tree removal is not proposed.” Mature trees will be retained, which reduces carbon loss.  Fire ladders to tree canopies will be eliminated.
  • Forest canopy will be retained so the forest floor is shaded and growth of flammable understory grasses and shrubs is suppressed. Density of the canopy will be reduced, but the canopy will be intact.
  • Herbicide will be used to prevent resprouts of trees that are removed, but foliar spraying will be “minimized.” The VMP acknowledges that vegetation killed by foliar spraying is left in place and becomes dry, easily ignited fuel.
  • Best Management Practices for herbicide use require that all applications be done by certified applicators and requests for herbicide application be approved by a licensed pest control advisor.
  • The revised VMP acknowledges that the flammability of plants and trees is unrelated to the nativity of the species. The VMP classifies some species of both native and non-native plants and trees as “pyrophytic.” Non-native plants are not inherently more flammability than native plants.  Flammability is related to the physical and chemical characteristics of plants, not their nativity.
  • The VMP clearly states that the implementation of the VMP is the responsibility of the Oakland Fire Department. OFD is not obligated to respond to the wishes of advocacy organizations unless their proposals are consistent with fire hazard mitigation.

The revised VMP will reduce fuel loads and risk of ignition.  The revised VMP is a fire hazard reduction project with one exception:  the VMP continues to propose the destruction of individual non-native trees within stands of native trees.    However, that proposal is ranked as Priority 3 and is therefore unlikely to be funded. Oakland’s Tree Services Division is inadequately funded and severely understaffed.  Tree Services does not have the resources to remove trees unless they are dead or pose a hazard to the public.  Neither Tree Services nor this VMP is responsible for landscape type conversion: “This VMP does not propose vegetation type conversion as an end goal or strategy…” (Page 1)  Moreover, such unnecessary removal of mature trees damages the surrounding environment, especially in riparian areas, and increases carbon loss, contributing to climate change.

If the VMP is ultimately funded by renewal of the parcel tax for fuels management, revenues should not be used to hire contractors to destroy individual non-native trees within stands of native trees because that would not reduce fire hazards.  The previous parcel tax was cancelled by voters partly because it was misused to fund native plant projects that conflict with fire hazard mitigation.  When native plant advocates plant rare, protected plants in Oakland’s parks and open spaces (which they do), they then oppose fuels management that threatens the plants they prefer.  It is not possible to mow a meadow of grass to prevent ignition without simultaneously destroying individual plants in that meadow.  We saw that principle at work at the public hearing by the Planning Commission on November 20, 2019.  The parcel tax that we would vote for would explicitly prohibit the use of the revenue for vegetation type conversion that is incompatible with fire hazard mitigation.

Scoping Issues

These issues must be addressed by the Environmental Impact Report for the revised VMP, as required by CEQA State law:

  • Carbon loss resulting from tree removals must be estimated. Mitigation for carbon loss must be proposed or negative environmental impact must be acknowledged and estimated. Carbon loss contributes to climate change and climate change is making wildfires more frequent and intense.  Therefore carbon loss increases wildfire hazards and must be estimated by the EIR for this project.
  • The EIR must identify the herbicides and estimate the quantities that will be used to implement the VMP. The amount and impact of pesticides to be used in the VMP should be compared with Oakland’s current levels of herbicide use in the city, including roadside applications. Known hazards of the herbicides that will be used should be acknowledged by the EIR, such as collateral damage to non-target trees and vegetation, damage to the soil, risks to wildlife and human health, mobility and persistence in the environment, etc.  The EIR should mitigate for the increased herbicide use by providing mechanisms for accountability to the public, such as a yearly publicly accessible report on pesticides used in this project, including brand names, location, date, method of application, and quantities. Prohibition of herbicide applications by “volunteers” who are not employees or contractors of the City of Oakland should also be added to Best Management Practices to prevent unauthorized herbicide applications in Oakland.
  • CEQA requires that alternative plans must be considered by an EIR. Typically, “no project” is one of the alternatives.  A third alternative should be less destructive, not more destructive than the proposed project.  For example, an alternative to destroying only non-native trees, as proposed by the VMP, would be to destroy bay laurels that are also a pyrophytic species, as well as vectors for Sudden Oak Death that has killed 50 million oaks in California since 1995.  In 2019, the rate of SOD infection increased from 1% to 12% in one year in sampled trees between Richmond and San Leandro.   Source:  https://www.sfchronicle.com/environment/article/Sudden-oak-death-spreading-fast-California-s-14815683.php?cmpid=gsa-sfgate-result

There are several advantages to thinning bays and Monterey pines rather than eucalyptus:

  • Every dead oak becomes fuel. Therefore, reducing SOD infections prevents oaks from becoming fuel.
  • Bays branch to the ground, providing fuel ladders that are difficult to eliminate because the tree trunk often sprawls on the ground.
  • Removing bays instead of eucalyptus also reduces carbon loss because bays are smaller trees and they have shorter lives than eucalyptus trees, which are expected to live another 200-300 years in the Bay Area based on their longevity in their native range.
  • Monterey pine has a shorter lifespan than eucalyptus and it is a soft-wood tree. Therefore, removal of Monterey pine will result is less carbon loss than destruction of eucalyptus. Furthermore, Monterey pines do not resprout after destruction.  Therefore, they will not require herbicide treatment to prevent resprouts as eucalyptus does.  Many Monterey pines in the East Bay are nearing the end of their lives because of when they were planted as well as pine pitch canker infection.
  • “We ask that a 4th alternative be considered by the EIR.  A “no pesticides” alternative would acknowledge the public’s concerns about the potential for increased pesticide use in Oakland that could be enabled by the completion of the EIR.  That alternative must propose a method of preventing tree resprouts without using herbicides.  There are precedents for such methods.  East Bay Municipal Utilities District does not use herbicides to prevent resprouts.  UCSF does not use any pesticides in the Sutro Forest where thousands of trees have been destroyed and thousands more will be destroyed in the future.”  Addendum 12/2/19
  • CEQA requires that cumulative impacts of similar projects be identified by the EIR. Fuels management projects similar to the VMP are being implemented all over the East Bay. Tree removals by PG&E should be included. The cumulative impact of all fuels management projects in the East Bay must be acknowledged by the EIR.

We hope the revised VMP will survive the public process required to bring it to fruition because we believe it will reduce fire hazards in its present form.  We believe that fire hazards are real and that compromise is needed to address them.  We congratulate the consultants who prepared the VMP and OFD for shepherding it to completion. Those who were involved in its preparation listened patiently and were responsive to the public’s concerns.  We are grateful.

Forest Action Brigade

Tilden Park, October 2016. East Bay Regional Park District has thinned this area to distances of 25 feet between remaining trees. The forest floor is still shaded because the canopy is intact.

Study design determines study findings

Million Trees can never resist a response to misinformation we find in Jake Sigg’s Nature News. (In this case, the statement originates with one of Jake’s readers, not Jake himself.)

“This study takes some of the life out of Art Shapiro’s ecological fitting theory:  Non‐native plants supported significantly fewer caterpillars of significantly fewer specialist and generalist species even when the non‐natives were close relatives of native host plants.”  “Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities” by Karin Burghardt, Doug Tallamy, et, al. (Ecosphere, November 2010).

We’ll get to the study later, but first let’s address the statement about ecological fitting.  Ecological fitting is more accurately described as an observation, rather than a theory or hypothesis and it does not originate with Art Shapiro.  The first observation of ecological fitting was recorded by Dan Janzen in 1980 and described by other ecologists as “the process whereby organisms colonize and persist in novel environments, use novel resources or form novel associations with other species as a result of the suites of traits that they carry at the time they encounter the novel condition.” (1) Ecological fitting is an alternative to the view that relationships between plants and insects and parasites and hosts are the result of co-evolution.  It is consistent with the observation that adaptation to new arrivals in an ecosystem often occurs without evolutionary change and can occur more rapidly than co-evolution would require.

The Colorado potato beetle readily devours an introduced relative of its Solanum hosts as a result of ecological fitting.  (Hsiao, T. H. (1978). “Host plant adaptations among geographic populations of the Colorado potato beetle”. Entomologia Experimentalis et Applicata. 24 (3)) USDA photo

Ecological Laboratory Science

The Burghardt/Tallamy study is a laboratory experiment in the sense that it creates an artificial environment by planting a garden in which it chooses the plant species and then inventories the insect visitors to the garden.  In one garden, native plant species were paired with a closely related species of non-native plant in the same genus (called congeners).  In another, distant garden, native plant species were paired with unrelated species of non-native plants.  The insect visitors that were counted are specifically the larvae stages (caterpillars) of lepidoptera (moths and butterflies).  The adult stage of the caterpillars (moths and butterflies) were not inventoried, nor were members of the other 28 insect orders.

Source: handsontheland.org

The study considers caterpillars “specialists” if they feed on three or fewer plant families.  The authors make this determination based on scientific literature and on observations of their artificially created garden.  Using scientific literature, 30% of visiting caterpillar species to the experimental garden were specialists.  Using actual visits to their experimental garden, 64% of visiting caterpillars were specialists.  The difference is as we should expect because the scientific literature is based on the behavior of caterpillars in the field, but the study confines the choices of the caterpillars to a few specific plant species chosen by the authors of the study.  In other words, caterpillars in the experimental garden had fewer choices of plant species.

The inventory of caterpillars was conducted over two summer months in 2008 and three summer months in 2009.  Findings were very different in the two years of the study:  “We found no difference between the total Lepidoptera larvae supported by native plants and their non-native congeners in 2008, but found over three fold more larvae on natives in 2009.  In 2008 there was no difference in the abundance of generalists on native and non-native congeners, but natives supported more than twice as many generalists as non-natives in 2009.” (2) Similar results were reported for species richness (number of different larvae species).  When paired with unrelated non-native plants, caterpillars showed a significant preference for native plant species, as we should expect because the plants were not chemically similar.

Caterpillar of Anise swallowtail butterfly on its host plant, non-native fennel. Berkeley, California

Although on average, native species attracted more caterpillars than the non-native congener with which they were paired, the strength of that difference varied significantly.  One matched pair attracted eight times as many caterpillars to the native plant compared to the non-native plant.  Another matched pair attracted slightly more caterpillars to the non-native plant compared to the native plant.  

The study authors interpret the significant differences between findings in the first and second years as an indication that caterpillars accumulated more rapidly on native plants than on non-native plants.  They speculate that a longer study would have found even greater preferences for native plants compared to non-native congeners.  Given that adaptation to introduced species occurs over time that is a counter-intuitive prediction.  In fact, many studies find that insects have made a successful transition from native to non-native hosts within a few generations.

Limitations of laboratory studies

The Burghardt/Tallamy study is often cited by native plant advocates in support of their belief that insects require native plants for survival.  This generalization is not supported by the results of the Burghardt/Tallamy study because:

  • The study results are not relevant to all insects.  The findings apply only to the larvae stages of moths and caterpillars.  The adult stages of moths and butterflies also require nectar and pollen from a much broader range of plants than their host plant, where the adult lays its eggs and caterpillars feed before becoming flying adults.  At the adult stage of their lives, they become pollinators.  Studies of the preferences of pollinators consistently find that a diverse garden that prolongs the blooming period is most useful to them. 
  • The study does not support the claim that caterpillars consistently choose native plants in preference to closely related non-native plants over time.  In fact, other studies find such preferences fade over longer periods of time.
  • Statements made by native plant advocates about the degree to which caterpillars are “specialized” are often exaggerated.  When a diverse landscape is available to caterpillars, scientific literature reports that specialization to a few plant families is found in only 30% of the 72 caterpillar species identified by this study. 
  • The Burghardt/Tallamy study was conducted on the East Coast where the climate is different than California.  It snows in the winter and it rains during the summer, unlike most of California.  Our native plants are therefore different from natives on the East Coast.  The Burghardt/Tallamy study was conducted in the summer months from June to August.  Native plants in California are no longer blooming and many are dormant during summer months unless they are irrigated.  The findings of the Burghardt/Tallamy study are therefore not applicable to California unless they can be replicated here.
This is the Serpentine Prairie in Oakland. It is one of the native plant “restorations” done by East Bay Regional Park District. About 500 trees (including native oaks) were destroyed to return the prairie to native grassland. This is what it looks like in June.

Comparison of laboratory with field studies

The Burghardt/Tallamy study 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.  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. 

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

The credibility and relevance of Professor Shapiro’s studies are also based on 47 years of visiting his research plots at least 250 days per year, that is, year around.  During that period of time, he recorded his observations and they were statistically analyzed for the study he published in 2003. (3)  His study is of particular interest as the climate changes rapidly because the length of the study also enables us to observe the impact of climate change on our butterfly population in the Bay Area.  In contrast the Burghardt/Tallamy study was conducted in a total of 5 months over a total of two years.  Population trends cannot be determined from such a short study.

Burghardt/Tallamy study is consistent with mission of Million Trees

The Burghardt/Tallamy study does not contradict anything Million Trees advocates for.  Decisions to plant a particular species and the decision to eradicate a particular species are entirely different.  Gardeners should plant whatever they prefer, in my opinion.  When planting decisions are made for public land, I prefer that plants be capable of surviving current local and climate conditions.  When my tax dollars are being spent, I prefer that they not be wasted. Besides, I hate watching plants and trees die in the parks I visit.

This study is consistent with my view that non-native plants don’t threaten the survival of insects unless they replace native plants that insects prefer.  The Burghardt/Tallamy study quite rightly does not say that they do.  Local experience in the Bay Area informs me that they rarely do.  To the extent that they have replaced native plants, they are better adapted to current conditions in a specific location.  Eradicating them rarely results in native plants successfully replacing them.  As the climate continues to rapidly change, the failure of native plant “restorations” is inevitable because vegetation changes when the climate changes.

Site 29 on Claremont Blvd in Oakland is one of the places where UC Berkeley destroyed about 19,000 trees about 14 years ago. Non-native weeds thrive in the sun where trees were destroyed. Poison hemlock and thistle are 8 feet tall where not sprayed with herbicide. Site 29, May 2016.

The Burghardt/Tallamy study does not justify eradication of non-native plants because it does not take into account the damage done by the methods used to eradicate non-native plants.  Since most eradication projects use herbicides, we speculate that more harm is done to insects by herbicides than by the existence of non-native plants.

The decision to eradicate non-native plants must also take into consideration whatever benefit the plants may provide, such as food for wildlife.  For example, even if a plant species isn’t a host plant, it might be a food plant. Butterfly bush (Buddleia) is an example of a plant that is very useful to pollinators, including butterflies, but native plant activists advocate for its eradication. 

Monarch nectaring on butterfly bush. butterflybush.com

Many thanks to Jake Sigg for creating this opportunity for dialogue with native plant advocates.  I am grateful for the window into the community of native plant advocates that Jake’s Nature News provides.

  1. Agosta, Salvatore J.; Jeffrey A. Klemens (2008). “Ecological fitting by phenotypically flexible genotypes: implications for species associations, community assembly and evolution”. Ecology Letters11 (11): 1123–1134. 
  2. “Non-native plants reduce abundance, richness, and host specialization in lepidopteran communities” by Karin Burghardt, Doug Tallamy, et, al. (Ecosphere, November 2010).
  3. SD Graves and AM Shapiro, “Exotics as host plants of the California butterfly fauna,” Biological Conservation, 110 (2003) 413-433

Happy New Year and Farewell

The Million Trees blog is folding its tent and moving on because most of the projects in the San Francisco Bay Area that I have followed for 20 years have been approved, funded, and are being implemented.  Every public land manager in the Bay Area has made a commitment to destroying most non-native trees and using pesticides for that purpose.

If you wish to continue following the development of these projects, I recommend these websites:  San Francisco Forest Alliance Defend East Bay Forests, Save the East Bay Hills, and Hills Conservation Network.

For the record, this is a brief summary of my beliefs about the environment:

If I return to the blogosphere in the future, the title and mission of a new blog would change.  The focus would be the science that informs my commitment to the cosmopolitan landscape that exists, rather than the fantasized landscape of the past.  I will also continue to inform readers of new studies that find evidence of the damage that pesticides do to the environment and its inhabitants.  If you are a subscriber to the Million Trees blog, you will be informed if I publish a new blog.

Thank you for your readership.

Million Trees