History of Earth predicts its future

My interest in the native plant movement began about 25 years ago when my neighborhood park was designated as a “natural area” by San Francisco’s Recreation and Park Department.  My park was only one of 33 parks in San Francisco that were designated as a “natural area.” 

What did it mean to be a “natural area?”  As I studied the plans, my reaction was primarily to the proposed destruction of non-native plants and trees.  Later I realized that the eradication of non-native plants and trees would be accomplished with herbicides. 

Stern Grove Park in San Francisco was my neighborhood park where I began my long journey to understand why anyone would want to destroy trees in a treeless neighborhood. 

How could the creation of native plant gardens justify the destruction of our urban forest using herbicides?  I have spent the last 25 years trying to answer that question.  There are many useful lines of inquiry in the search for the answer, but the approach that has been most helpful to my understanding of the futility of the undertaking has been the study of the physical and biological forces that created Earth and its inhabitants.  Today, I will take you on an abbreviated journey of the past 4.6 billion years of events on Earth that have resulted in present-day nature, drawing from A Brief History of Earth by Andrew Knoll, Professor of Natural History at Harvard University. (1)

Gravity “created” the Earth

“Gravity is the architect of our universe.”  Gravity is the attraction of objects to one another in proportion to their mass and proximity that over billions of years accumulated the elements dispersed in Earth’s universe.  As these dispersed objects coalesced into stars, planets, moons, and asteroids, Earth was formed about 4.6 billion years ago.

Cross-section of Earth. Source: USGS

“Earth is a rocky ball.”  Its inner core is solid, composed mostly of iron.  Earth’s molten outer core moves by convection as hotter, denser material near the base rises and cooler, less dense matter toward the top sinks.  This circular motion generates electrical current that creates the Earth’s magnetic field.  The mantle is composed of the molten magma that emerges on the surface crust of Earth where tectonic plates are separating and when volcanoes erupt where tectonic plates submerge into the mantle. The crust of Earth that is visible to us is only 1% of Earth’s mass.

Physical Earth

Simplified map of Earth’s principal tectonic plates, which were mapped in the second half of the 20th century (red arrows indicate direction of movement at plate boundaries).  Source:  USGS

The crust of Earth is composed of plates that are moved on the surface of the Earth by the convection current of the mantle.  Some of the plates are moving away from one another where they meet.  As the plates separate, molten magma from the mantle is pushed through the crust, forming new crust.  The North American and Eurasian plates are moving apart in the middle of the Atlantic Ocean at the rate of about 1 inch per year. 

Since the Earth is not getting bigger, the expanding crust collides with adjacent plates.  In some places, the collision of the plates pushes up the crust into mountain ranges.  The Himalayan mountain range is the result of the collision of the Indo-Australian and the Eurasian Plates, a process that continues today.

Map of subducted slabs, contoured by depth, for most active subduction zones around the globe. Source:  USGS

In other places, the expanding crust is pushed below the adjacent plate in subduction zones, where the crust dives below the crust into the mantle.  Earthquakes are common in subduction zones and the subducting plate triggers volcanic eruptions in the overriding plate.  Earthquakes are also common where adjacent plates are grinding against one another in opposite directions, as is the case on the coast of California.

Pangea super-continent

The movement of tectonic plates has assembled and reassembled the Earth’s continents many times. The entire history of the configuration of continents is not known to us because of the cycle of the crust emerging from the mantle only to return to the mantle about 180 million years later.  We know that all continents were fused into a single continent, named Pangea, about 350 million years ago and began to break up 200 million years ago.  Much of life as we know it evolved on Earth while the continents were fused, which is one of the reasons why all life on Earth is related.  Geographic isolation of species results in more biodiversity as genetic drift and different environments result in greater speciation.  Geologists believe such continental mergers are likely in the distant future.  

Earth’s oceans and atmosphere were formed within the first 100 million years of its birth.  Continents were visible above oceans, but small compared to their present size.  The absence of oxygen in the air at that early stage was the most significant difference between present and early Earth.

Biological Earth

Life, as presently defined, requires growth and reproduction, metabolism, and evolution. (I say, “presently defined” because debate continues about defining viruses as life since they do not meet all criteria.)  The chemical components required to perform the functions of life and the natural processes to combine them (such as heat and lightning) were available on Earth for millions of years before they combined to perform the functions of life.  Precisely how and when that happened on Earth is studied intensely, but not conclusively known, although Professor Knoll describes theoretical possibilities. 

The geological record suggests that “Earth has been a biological planet for most of its long history.” Microbes may have been living on Earth 4 billion years ago.  Climate on Earth was warm at that time for the same reason the climate is warming today.  The atmosphere was composed primarily of carbon dioxide (the greenhouse gas that traps heat on the surface of the Earth) and nitrogen:  “…life emerged on an Earth barely recognizable to the modern eye—lots of water and not much land, lots of carbon dioxide but little or no oxygen…”

Oxygen Earth

Phylogenetic tree of life based on Carl Woese et al. rRNA analysis. The vertical line at bottom represents the last universal common ancestor.

Two of the three domains of life were capable of living without oxygen:  archaea and bacteria.  Archaea are single-cells without nuclei.  We are all too familiar with bacteria, as they are as much a part of our bodies as our own cells.  Oxygen was the prerequisite for the evolution of the third domain of life, eukarya.  The kingdoms of eukarya most familiar to us are plants, animals, and fungi. 

Oxygen arrived on Earth when early life forms evolved the ability to photosynthesize, the process by which plants (and some other organisms) use sunlight to synthesize food from carbon dioxide and water, generating oxygen as a byproduct.  This transition occurred about 2.4 billion years ago, as measured by the absence of iron on the seafloor after that time. 

Photosynthesis alone could not have accomplished the transformation of Earth’s atmosphere to the balance of carbon dioxide and oxygen needed to support complex life on our planet because photosynthesis also requires nutrients as well as sunlight and water.  Phosphorous weathers from rocks, a process that was initially limited by the small amount of land above sea level.  As the planet matured, more land emerged from the sea, making more phosphorous available to photosynthesizing organisms.  Photosynthesis was also enhanced when some bacteria and archaea evolved the ability to convert nitrogen gas into biologically usable molecules, a process called nitrogen-fixing.  Many plants in the legume family are capable of nitrogen-fixing today.

Extinctions of the past predict extinctions of the future

There have been five major extinction events in the past 500 million years that changed the course of evolution of life on Earth and at least 20 mass extinctions in total (2).  The first representatives of all modern animal phyla (a taxonomic classification between kingdom and class) evolved during the Cambrian Period (541-486 million years ago).  All extinction events were associated with radical changes in the climate.  Many of the changes in the climate were caused by changes in the balance of carbon dioxide and oxygen in the atmosphere.  All these catastrophic events were natural events, not caused by the activities of humans because they all occurred long before the advent of human evolution. 

The third and biggest extinction event occurred 252 million years ago at the end of the Permian geologic period, when more than 90% of marine animals and 70% of terrestrial species disappeared.  At that time, continents were fused into the single supercontinent of Pangea.  The extinction of most life on Earth was caused by the sudden and catastrophic change in the atmosphere–and therefore the climate–by an episode of volcanism in Siberia “a million times greater than any volcanism ever witnessed by humans” or our primate ancestors.  Gases emitted by volcanism at the end of the Permian period rapidly increased the carbon dioxide content of the atmosphere and oceans by several times greater than before that event.  “It would take 10 million years for life to reassemble into something approaching the complexity of the ecosystems that preceded it. The world that emerged from the volcanic dust was unlike anything that came before.” (2) The current increase of carbon dioxide in the atmosphere caused by the burning of fossil fuels by human activities is comparable to this event and is expected to cause the sixth great extinction on Earth.  

The fifth and most recent massive extinction event occurred 66 million years ago, bringing 170 million years of dinosaur evolution to an abrupt end. The entire environment of the planet was radically and suddenly altered by the impact of an asteroid 7 miles in diameter that landed on what is now the Yucatan peninsula in Mexico.  The impact engulfed Earth in a dust cloud that precipitated the equivalent of a nuclear winterkilling most vegetation and animals adapted to a much warmer climate.  As with all massive extinctions, it took millions of years for plants and animals to slowly evolve adaptations to the new environment.  Dinosaurs did not evolve again, a reminder that evolution does not necessarily repeat itself (although birds evolved from dinosaurs).  Although there were small mammals during the dinosaur age, the disappearance of dinosaurs and corresponding changes in the climate introduced the age of mammals, including the human lineage about 300,000 years ago.  When multiple animal groups disappear it creates opportunities by reducing competition between groups.

What can we learn from the history of Earth?

If a native plant advocate were reading this abbreviated history of Earth, these are the lessons I would hope they might learn from it:

  1. Andrew H. Knoll, A Brief History of Earth, 2021.  All quotes in this article are from this excellent book unless otherwise indicated.
  2. Elsa Panciroli, Beasts Before Us: The Untold Story of Mammal Origins and Evolution, Bloomsbury Sigma, 2021.

A Natural History of the Future

“The way out of the depression and grief and guilt of the carbon cul-de-sac we have driven down is to contemplate the world without us. To know that the Earth, that life, will continue its evolutionary journey in all its mystery and wonder.” Ben Rawlence in The Treeline

Using what he calls the laws of biological nature, academic ecologist Rob Dunn predicts the future of life on Earth. (1)  His book is based on the premise that by 2080, climate change will require that hundreds of millions of plant and animal species—in fact, most species–will need to migrate to new regions and even new continents to survive.  In the past, conservation biologists were focused on conserving species in particular places.  Now they are focused on getting species from where they are now to where they need to go to survive.

In Dunn’s description of ecology in the future, the native plant movement is irrelevant, even an anachronism.  Instead of trying to restore native plants to places where they haven’t existed for over 100 years, we are creating wildlife corridors to bypass the obstacles humans have created that confine plants and animals to their historical ranges considered “native.” 

The past is the best predictor of the future. Therefore, Dunn starts his story with a quick review of the history of the science that has framed our understanding of ecology.  Carl Linnaeus was the first to create a widely accepted method of classifying plants and animals in the 18th century.  Ironically, he lived in Sweden, one of the places on the planet with the least plant diversity.  Colombia, near the equator, is twice the size of Sweden but has roughly 20 times the number of plant species because biodiversity is greatest where it is hot and wet.

Global Diversity of Vascular Plants. Source: Wilhelm Barthlott, et. al., “Global Centers of Vascular Plant Diversity,” Nova Acta Leopoldina, 2005


Humans always have paid more attention to the plants that surround us and the animals most like us.  Dunn calls this the law of anthropocentrism.  We are the center of our own human universe.  Consequently, our awareness of the population of insects that vastly outnumber us came late to our attention in the 20th century.  In the 21st century we learned that all other forms of life are outnumbered by the microbial life of bacteria, viruses, and fungi that preceded us by many millions of years.  Our knowledge of that vast realm of life remains limited although it is far more important to the future of the planet than we realize because those forms of life will outlast our species and many others like us.

Tropical regions are expanding into temperate regions

The diversity and abundance of life in hot and wet tropical climates give us important clues about the future of our warming climate.  We tend to think of diversity as a positive feature of ecosystems, but we should not overlook that tropical regions are also the home of many diseases, such as malaria, dengue fever, zika, and yellow fever that are carried by insects that prey on animal hosts, including humans.  In the past, the range of these disease-carrying insects was restricted to tropical regions, but the warming climate will enable them to move into temperate regions as they warm. The warming climate will also enable the movement of insects that are predators of our crops and our forests into temperate regions.  For example, over 180 million native conifers in California have been killed in the past 10 years by a combination of drought and native bark beetles that were killed during cold winters in the past, but no longer are.  Ticks are plaguing wild animals and spreading disease to humans in the Northeast where they did not live in the cooler past. 

Human populations are densest in temperate regions“The ‘ideal’ average annual temperature for ancient human populations, at least from the perspective of density, appears to have been about 55.4⁰F, roughly the mean annual temperature of San Francisco…” (1) This is where humans are most comfortable, free of tropical diseases, and where our food crops grow best.  As tropical regions expand into temperate regions, humans will experience these issues or they will migrate to cooler climates if they can.

Our ability to cope with the warming climate is greatly complicated by the extreme variability of the climate that is an equally important feature of climate change.  It’s not just a question of staying cool.  We must also be prepared for episodic extreme cold and floods alternating with droughts. Animals stressed by warmer temperatures are more easily wiped out by the whiplash of sudden floods or drought.

Diversity results in resiliency

Diversity can be insurance against such variability.  If one type of crop is vulnerable to an insect predator, but another is not, growing both crops simultaneously increases resiliency.  That principle applies equally to crops that are sensitive to heat, cold, drought, or floods. 

Agricultural biodiversity. Source: Number of harvested crops per hectar combining 175 different crops. Source: Monfreda et al. 2008. “Farming the planet: Geographic distribution of crop areas, yields, physiological types, and net primary production in the year 2000”. Global Biogeochemical Cycles, Vol. 22.

Historically, cultures that grew diverse crops were less likely to experience famine than those that cultivated monocultures.  The Irish potato famine of the mid-19th century is a case in point.  The Irish were dependent upon potatoes partly because other crops were exported to Britain by land owners. When the potato crop was killed by blight, more than one million people died in Ireland and another million left Ireland.  The population dropped about 20-25% due to death and emigration.  The diversity of crops in the United States (where corn is the commodity crop) and Brazil (where soy is the commodity crop) is very low, compared to other countries.  This lack of diversity makes us more vulnerable to crop failure and famine, particularly in an unpredictable climate.

Change in total use of herbicides, antibiotics, transgenic pesticide producing crops, glyphosate, and insecticides globally since 1990. Source: A Natural History of the Future

Instead of increasing crop diversity, we have elected to conduct chemical warfare on the predators of our crops by using biocides, such as pesticides for agricultural weeds and insects and antibiotics for domesticated animals.  The scale of our chemical warfare has increased in response to growing threats to our food supply.  This is a losing strategy because as we increase the use of biocides we accelerate evolution that creates resistance to our biocides. We are breeding superweeds, insects, and bacteria that cannot be killed by our chemicals.  This strategy is ultimately a dead end.

Evolution determines winners and losers

Inevitably, evolution will separate the survivors of climate change from its victims. Dunn reminds us that “The average longevity of animal species appears to be around two million years…” for extinct taxonomic groups that have been studied.  In the short run, Dunn bets on the animals that are most adaptable, just as Darwin did 160 years ago.  The animals most capable of inventing new strategies to cope with change and unpredictability will be more capable of surviving.  In the bird world, that’s corvids (crows, ravens, jays, etc.) and parrots.  In the animal world that’s humans and coyotes.  We aren’t helping adaptable animals survive because we are killing abundant animals based on a belief it will benefit rare animals.  Even in our urban setting, the East Bay Regional Park District contracts Federal Wildlife Services to kill animals it considers “over-abundant,” including gulls, coyotes, free-roaming cats, non-native foxes, and other urban wildlife throughout the Park District.  We are betting on evolutionary losers.


If and when humans create the conditions that cause our extinction, many of our predators are likely to disappear with us.  Bed bugs and thousands of other human parasites are unlikely to survive without us.  Many domestic animals will go extinct too, including our dogs.  On the bright side, Dunn predicts that cats and goats are capable of surviving without us.             

Timeline of the evolution of life. Source: CK-12 Foundation

However, in the long run Dunn bets on microbial life to outlast humans and the plants and animals with which we have shared Earth.  Humans are late to the game, having evolved from earlier hominoids only 300,000 years ago, or so.  The plants and animals that would be recognizable to us preceded us by some 500 million years, or so.  But microbial life that is largely invisible to us goes back much further in time and will undoubtedly outlast us.  Dunn says microbial life will give a big, metaphorical sigh of relief to see us gone and our environmental pollutants with us.  Then microbial life will begin again the long process of rebuilding more complex life with their genetic building blocks and the tools of evolution. 

Some may consider it a sad story.  I consider it a hopeful story, because it tells me that no matter what we do to our planet, we cannot kill it.  For the moment, it seems clear that even if we are not capable of saving ourselves at least we can’t kill all life on Earth.  New life will evolve, but its features are unfathomable because evolution moves only forward, not back and it does not necessarily repeat itself. 

  1. A Natural History of the Future, Rob Dunn, Basic Books, 2021

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.


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. 

California’s Urban Greening Grant Program: An opportunity to speak for the trees

In September 2016, the State of California passed a law that allocated $1.2 billion to create a cap and trade program to reduce Greenhouse Gas (GHG) emissions.  The California Natural Resources (CNR) Agency was allocated $80 million to fund green infrastructure projects that reduce GHG emissions.  The CNR Agency is creating an Urban Greening Program to fund grants to cities, counties, and other entities such as non-profit organizations in URBAN settings.  75% of the funding must also be spent in economically disadvantaged communities.

These grants must reduce GHG emissions using at least one of these specific methods:

  1. Sequester and store carbon by planting trees
  2. Reduce building energy use from strategically planting trees to shade buildings
  3. Reduce commute, non-recreational and recreational vehicle miles travelled by constructing bicycle paths, bicycle lanes, or pedestrian facilities.

Clearly, planting trees is one of the primary objectives of this grant program.  That sounds like good news for the environment and everyone who lives in it until you read the draft program guidelines which are available HERE.

Unfortunately, as presently drafted, the grant program will NOT increase California’s urban tree canopies, because the program requires the planting of “primarily” native trees.   That requirement is explicitly stated several times in the draft guidelines, but there are also places in the draft where the reader might be misled to believe the requirement applies only to plants and not to trees.    Therefore, I asked that question of the CNR Agency staff and I watched the public hearing that was held in Sacramento on October 31st.  CNR Agency staff responded that the requirement that grant projects plant “primarily” native species applies to both plants and trees.

The good news is that the grant program guidelines are presently in draft form and the public has an opportunity to comment on them.  If you agree with me that we need our urban forest, you will join me in asking the CNR Agency to revise their grant program guidelines to remove restrictions against planting non-native trees.   Public comment must be submitted by December 5, 2016.  Send comments to:  Urban Greening Grant Program c/o The California Natural Resources Agency Attn: Bonds and Grants Unit 1416 Ninth Street, Suite 1311 Sacramento, CA 95814 Phone: (916) 653-2812, OR Email: urbangreening@resources.ca.gov Fax: (916) 653-8102

Here are a few of the reasons why limiting trees to native species will not increase tree canopies in urban areas in California:

Many places in California were virtually treeless prior to the arrival of Europeans.  Non-native trees were planted by early settlers in California because most of our native trees will not grow where non-native trees are capable of growing.  According to Matt Ritter’s California’s Guide to the Trees Among Us, only 6% of California’s urban trees are native to California:


Draft guidelines for the Urban Greening grants refers applicants to the California Native Plant Society for their plant palette (see page 24 of guidelines).  If applicants use this as the source of their plant palate, they will find few trees on those lists.  This is another way to understand that if you want trees in California, most of them must be non-native.

Most California native trees are not suitable as street trees because of their horticultural requirements and growth habits. 

  • The approved list of street trees for the City of San Francisco includes no trees native to San Francisco.  There are many opportunities to plant more trees in San Francisco because it has one of the smallest tree canopies in the country (12%).  The US Forest Service survey of San Francisco’s urban forest reported that 16% are eucalyptus, 8% are Monterey pine, and 4% are Monterey cypress.  None of these tree species is native to San Francisco.
  • The approved list of street trees for the City of Oakland includes 48 tree species of which only two are natives. Neither seem appropriate choices:  (1) toyon is a shrub, not a tree and the approved list says it will “need training to encourage an upright form.”  It is wishful thinking to believe that toyon can be successfully pruned into a street tree; (2) coast live oak is being killed by the millions by Sudden Oak Death and the US Forest Service predicts coast live oaks will be virtually gone in California by 2060.



Climate change requires native plants and trees to change their ranges if they are to survive.  One of the indicators of the impact of climate change on our landscapes is that 70 million native trees have died in California because of drought, insect infestations, and disease.  The underlying cause of these factors is climate change.

  • 66 million native conifers have died in the Sierra Nevada in the past 4 years because of drought and native bark beetles that have spread because winters are no longer cold enough to keep their population in check.  Update:  A new survey of California’s trees now reports that 102 million trees are now dead.  That’s one-third of California’s trees.  62 million trees died in 2016 alone, which is an accelerating rate of death.  These trees are still standing and they pose an extreme fire hazard.  These are NATIVE TREES being killed by a combination of drought and NATIVE BARK BEETLES.  
  • 5 million native oaks have died since 1995 because of Sudden Oak Death. A study of SOD by University of Cambridge said in spring 2016 that the SOD epidemic is “unstoppable” and predicted that most oaks in California would eventually be killed by SOD. The Oak Mortality Task Force reported the results of its annual survey for 2016 recently.  They said that SOD infections increased greatly in 2016 and that infections that were dormant in 2015 are active again.  This resurgence of the pathogen causing SOD is caused by increased rain in 2016.
  • Scientists predict that redwood trees will “relocate from the coast of California to southern Oregon” in response to changes in the climate.

If you care about climate change, please join us in this effort to create a grant program that will expand our urban forests and reduce the greenhouse gas emissions that are causing climate change.  Restrictions against planting non-native trees must be removed from grant guidelines in order to increase our tree canopies in California’s urban environments. 

Update:  Final guidelines for California State Urban Greening grant applications were published on March 1, 2017, and are available HERE.  That program will distribute $76 million to cities that reduce greenhouse gas emissions by planting trees or reducing fossil fuels emissions.  The deadline for grant applications is May 1, 2017.  There will be a workshop for applicants at the Lake Temescal Beach House (6500 Broadway, Oakland) on March 27, 2017.

Final guidelines are improved from the draft guidelines.  Draft guidelines would have required applicants to plant only native trees.  The State agency received 62 public comments on the draft.  27 of those comments asked that the guidelines be revised to permit planting non-native trees as well as native trees.  One of the 27 comment letters was signed by 33 tree-advocacy non-profit organizations. 

Final guidelines reflect the public’s opposition to prohibiting the planting of non-native trees, which would have severely limited the number of trees that would survive.  Native trees have specific horticultural requirements that limit the places where they can be planted.

Final guidelines now say that only “invasive” trees cannot be planted by grant projectsIf the granting agency uses the classification of the California Invasive Plant Council to determine “invasiveness,” applicants would not be allowed to plant 15 specific tree species.  However, the California Invasive Plant Council is revising its inventory of “invasive” plants, so we don’t know if the number of “invasive” trees will be increased by that revision.

Update #2:  The California Invasive Plant Council has published the proposed revision to its list of “invasive” species.  There were about 200 plants on the existing list.  Now they propose to add another 99 species.  Ten of those species are added based on their current impacts in California.  One of the ten is a tree (glossy privet).  87 of the species are proposed for addition “based on risk of becoming invasive” in the future in California.  Twelve of the 89 potentially invasive plants are trees. 

There were 15 trees on the original list of “invasive” species.  That means that the revised list of “invasive” trees will now include a total of 28 trees that cannot be planted by Urban Greening projects that are applying for grant funds. 

The revised inventory of “invasive” plants was just published.  Public comments can be submitted on the proposed revisions by May 8.  The proposed revisions and how to make comments on the proposal are available HERE

Personally, I object to the introduction of a new category of 89 plants that are not presently having any “impact” according to Cal-IPC but are predicted to in the future.  These revisions will increase the inventory of “invasive” plants by 50%.  It represents a significant escalation of the crusade against non-native plants in the California. 

Nativist bias is not entirely absent from the revised guidelines for the Urban Greening program.  Applicants are required to explain why they plan to plant non-native trees.  However, applicants are also required to have a certified arborist or comparable horticultural expert certify that the plant list is appropriate to the planting location.  Hopefully, that will prevent the wasteful planting of native trees where they will not survive. 

Response to denier of climate change

California poppy

Last week we published an article about how plants are responding to climate change.  We received a comment from Don E that questioned the accuracy of the climate data in the study in Ohio which found a relationship between increased temperatures and earlier blooming times.  We didn’t have access to the information needed to respond to that comment, but we were unwilling to publish it without verifying its claims because we do not want to misinform our readers. 

So, we asked the author of the study in Ohio, Kellen Calinger, if she could help us verify the accuracy of the comment.  Ms. Calinger has generously obliged us with a detailed critique of the comment.  With her permission, we are now publishing her reply in its entirety.


Don E:   “There are controlled laboratory experiments to show that temperature, moisture, and CO₂ effect plant growth. The Ohio study was not a controlled study and the temperature data are questionable.”

Ms. Calinger:  There are indeed controlled laboratory experiments regarding impacts of temperature, moisture, and CO2 on plant growth and my study was not controlled.  My study falls under the broad heading of observational science.  Observational and experimental studies are both extremely common and each has pros and cons.  The pros of experiments include a high degree of control over the system allowing you to focus on impacts of your variable of interest while the cons include less realistic description of a natural system.  The pros and cons of observational studies are essentially the opposite of an experiment; I didn’t control environmental variables in my study, but it likely reflects the reality of what’s happening in ecosystems far more than an experiment.  Again, these are both accepted methods of the scientific community.

Don E:  .”USHCN makes a huge TOBS adjustment in Ohio between 1979 and 1988. The justification for this is that they claim people in Ohio switched from reading temperatures in the afternoon, to reading them in the morning. That would theoretically push measured temperatures progressively down from 1979 to 1988. The Ohio raw data does not provide any support for the TOBS theory. In the middle of a long term cooling trend, measured temperatures rose very quickly from 1979 to 1988.”

Ms. Calinger:  The TOBS adjustment (time of observation adjustment) is essentially to control for the time of day that temperature measurements were taken.  A simple example would be that if I measured temperatures at noon from 1980-1990 and the next observer measured temperatures at 6AM from 1991-2000, it would probably seem like it was cooler in the ’90’s since 6AM is typically cooler than noon.  If you don’t correct for the time of observation, the actual temperature trend would be obscured by daily variation in temperatures based on time of observation. 

The U.S. Historical Climatology Network is part of the Carbon Dioxide Information Analysis center, and they lay out exactly how they treat data on their website–here’s the link: http://cdiac.ornl.gov/epubs/ndp/ushcn/monthly_doc.html

Don E:  “In addition Ohio Valley Summer Temperatures have been plummeting for 80 years. July of 2009 was the coldest on record in the Ohio Valley, and July temperatures have been plummeting in that region since 1930. July 1934 and 1936 were both much hotter – even after NCDC adds 1.5 degrees on to recent temperatures relative to the 1930s.”

Ms. Calinger:  It seems that the commenter got this information from the following blog: http://stevengoddard.wordpress.com/2012/08/03/ohio-valley-summer-temperatures-have-been-plummeting-for-80-years/

The blog presents a plot of temperature data for the Ohio Valley that starts in 1930 and runs until 2011 that indicates an overall trend of temperature decrease by 0.19 degrees Fahrenheit per decade.  While I can’t know the intentions of the author of this blog, this seems to be a case of data manipulation to mislead.  I went to the NCDC website used by the blog author and made an identical plot of Ohio Valley temperature data for July, but I didn’t restrict my plot to 1930-2011.  Instead, I used the full temperature data set from 1895-2012 and found NO indication of temperature decrease.  An extremely common tactic among climate change skeptics is to restrict a data set to a small subset of the total data that shows a cooling trend even though this is not indicative of the long term pattern.  

You can make these graphs at: http://www.ncdc.noaa.gov/oa/climate/research/cag3/ce.html

Don E:   “I would never call anyone a denier. That is an ugly term intended to denigrate skeptics by associating them with holocaust deniers. There are many highly regarded climate and physical scientists not funded by the fossil fuel industry that don’t accept the hypothesis that CO2 is the primary cause of climate change. BTW there has been no global warming in 16 years.”

Ms. Calinger:  There is simply no debate in the scientific community about climate change.  It is accepted that climate change is occurring and that warming is predominantly caused by humans.  This blog provides a really good summary of the scientific consensus: http://www.desmogblog.com/2012/11/15/why-climate-deniers-have-no-credibility-science-one-pie-chart

Of 13, 950 scientific papers, 24 reject climate change. That’s pretty clearly an overwhelming majority.  

Also, there has most definitely been warming in the past 16 years.  This past summer was the 3rd hottest on record in the U.S. and seven of the 10 hottest summers in U.S. history have occurred since 2000.  


Webmaster:  We are grateful to Ms. Calinger for her help to respond to Don E.  We have certainly learned something from her and we hope that Don E has as well. 

We take the time and trouble to research the claims of those who choose to deny the reality of climate change because we believe that it is presently the most serious threat to our environment.  Human civilization is currently unwilling to take needed action to reverse this dangerous trend. Those who refuse to believe that it is necessary to take action are at least partly to blame for this.  We hope that if and when human civilization acknowledges climate change and its consequences, we will finally make the tough decisions that are needed.

Postscript:  The word “denier” is defined by Webster’s Unabridged Dictionary as “one who denies.”  It is not used exclusively to describe those who deny that the holocaust occurred.  In fact, it doesn’t even imply that the denier is denying something that actually exists.  It is a neutral term that applies to any person who denies anything.  For example, I deny that I am fabricating information about climate change.  Therefore I am a denier of that accusation.

Although we do not use the word “denier” in order to denigrate those who choose not to believe in climate change, we are frankly mystified by their motivation.

Predicting the future of plants in a changed climate

Despite a minority of die-hard deniers and their corporate enablers in the fossil fuel industry, most scientists have quit debating that the climate has changed and will continue to change.  Nor is there much doubt that the primary cause of climate change is the significant increase in the greenhouse gases that trap heat on the Earth’s surface.  Scientists have now turned their attention to the huge task of understanding the consequences of a changed climate and predicting its future course.  Our best hope is that such knowledge can help us to devise strategies for coping with the consequences.

In this post, we will share with our readers some of the recent research about how plants and trees are responding to climate change. 

Non-native plants are more responsive than natives to higher temperatures

The State of Ohio has one of the most complete climate records in the country.  They have had weather stations in stable locations throughout the state since 1895.  From 1895 to 2009, these weather stations reported an average increase in temperature of 1.7 degrees Fahrenheit.  All of the weather stations were outside of urban areas, so we can be confident that the data were not confused by the separate, but associated, phenomenon of the urban heat affect as population and development in urban areas increased during this period. 

These data were combined with an equally rich source of information, the herbarium of the University of Ohio which contains 500,000 plant specimens.  These two sources of information enabled a graduate student, Kellen Calinger, to assemble “one of the six-largest such data sets in the world tracking the history of the wildflower life cycle in response to climate change.” (1)

When is the California poppy blooming?
When is the California poppy blooming?

Ms. Calinger compared the bloom time of 141 species of plants with the temperature at the time of bloom.  She reports that “…46% of the 141 species showed significant advancement in flowering in response to increased temperatures.  And more of this advancement was seen in introduced species [AKA non-natives] than in native plants.”

Ms. Calinger predicts that the non-native plants that bloom before their native neighbors have a competitive advantage.  Presumably, they are growing and occupying ground prior to the natives.  If, indeed, climate change is giving non-native plants an advantage that would help to explain why attempts to eradicate non-native plants and replace them with native plants are often unsuccessful. 

However, the report of this research then enters muddy territory.  It speculates, but without offering evidence, that there may also be disadvantages to blooming earlier:

  • Is the flower blooming prior to the arrival of its pollinator thereby decreasing its reproductive success?
  • Will the early bloom only become the victim of a subsequent frost because the growing season is not yet stable?
  • Will migrating birds pass through only to find that the nectar sources they have depended upon in the past have now completed their blooming period?

What do we know about the response of plants in urban areas?

So, how does this information apply to our urban area?  In general, temperatures in urban areas are higher than in rural areas because so much of our ground is covered with buildings and hardscape that absorb and retain heat.  This is called the urban heat affect.   It seems logical to assume that what has been observed in the rural setting would be exaggerated in the urban setting.  That is, plants in urban areas are likely blooming even earlier because the temperatures are higher, although there is probably an upper threshold, beyond which there is no growth benefit.

However, there are other factors in climate change that are more important in urban areas which are also affecting the growth of plants and trees.  Greenhouse gases are greater in urban areas than in rural areas because of industrial and transportation emissions. 

Carbon dioxide concentrations have increased 24% globally since 1960.  We should assume that increase is greater in urban areas.  Carbon dioxide is the primary fuel of photosynthesis, so we should not be surprised to learn that higher concentrations of carbon dioxide are associated with faster plant growth. (2)

Are the oaks growing faster?
Are the oaks growing faster?

Kevin Griffin (Columbia University) compared the growth of the native red oak in rural New York with their brethren in New York City over a period of 8 years.  The average minimum temperature in August was 71.6 degrees at the city site and 63.5 degrees in the country.  He also found elevated levels of nitrogen in the leaves of the trees in the city.  Nitrogen is a plant nutrient.  Griffen reported that, “The urban oaks, harvested in August 2008, weighed eight times as much as their rural cousins, mostly because of increased foliage.”  (2)

Unfortunately, like most stories about climate change, this one is also a mixed blessing.  While carbon dioxide and higher temperatures may benefit plants in the city, other elements in urban air do not.  Higher levels of ozone can severely damage plant pores, which slows their growth and some trees are more susceptible to this damage than others.  Cottonwoods are particularly susceptible to ozone damage.  Ironically, ozone levels are actually higher in rural areas than in urban areas because some of the ozone is converted to oxygen in the city, while the remaining ozone “blows out to the country.”  (2)

What are the implications for readers of Million Trees?

Here’s our take-away message from these research reports:

  • The consequences of climate change are complex and are incompletely understood.
  • Climate change and air quality conditions in the urban setting are probably giving non-native plants a competitive advantage over native plants which helps to explain the frequent failures of attempts to eradicate non-native plants.
  • There are pros and cons to every change in the environment.  To call change “good” or “bad” is to over-simplify the complexity of nature.
  • Finally, our usual rhetorical question, “Do the managers of native plant installations understand the complexity of their undertaking?”  We don’t think they do. 


(1)    “Non-native plants show a greater response than native wildflowers to climate change,” October 5, 2012.  Available here.

(2)    Guy Gugliotta, “Looking to Cities, in Search of Global Warming’s Silver Lining,” New York Times, November 26, 2012.  Available here.

Biological Control: Another dangerous method of eradicating non-native species

We were recently reminded of the use of biological controls to eradicate non-native species when we learned that Australian insects may have been illegally imported to California to kill eucalyptus, which had been virtually pest free until 1983.  So, an article in the New York Times about the development of a fungus for the purpose of killing cheatgrass (Bromus tectorum) caught our attention.  The fungus has been given the ominous name, Black Fingers of Death, for the black stubs of cheatgrass infected with the fungus.

Cheatgrass, Bromus tectorum

Cheatgrass is one of the non-native grasses that have essentially replaced native grasses throughout the United States.  It was probably introduced with ship ballast and wheat seed stock in about 1850.  As we have reported, native grasses were quickly replaced by the non-native grasses which tolerate the heavy grazing of domesticated animals brought by settlers.    Native Americans had no domesticated animals.

Biological controls have frequently caused more serious damage than the problems they were intended to solve.  Therefore, we would hope that their intended target is doing more damage than the potential damage of its biological control.   We must ask if the cure is worse than the disease.  And in this case, we don’t think the damage done by cheatgrass justifies inflicting it with the Black Fingers of Death.

The track record of biological control

Biological control is the intentional introduction of animals, pests, microbes, fungi, pathogens, etc., for the purpose of killing a plant or animal which is perceived to be causing a problem.  The ways in which some of these biocontrols have gone badly wrong are as varied and as many as the methods used.

Introduced species of plants are said to have an initial advantage in their new home because their pests and competitors are not always introduced with them.  This is the “enemy release hypothesis” popular amongst native plant advocates to explain the tendency of non-native plants to be invasive.  However, this is usually a temporary advantage which is exaggerated by native plant advocates who do not seem to recognize the speed with which native species can adapt to new species, and vice versa.

Therefore, a popular method of biological control is to import the predator or competitor of the non-native species which is considered invasive.  This is only effective if the pest is selective in its host.  There are many examples of such introductions which did not prove to be selective:  “For the United States mainland, Hawaii, and the Caribbean region, Pemberton (2000) listed 15 species of herbivorous biocontrol insects that have extended their feeding habits to 41 species of native plants…” (1)  Although most of the unintended hosts were related to the intended hosts, some were not.

Similar shifts from target to nontarget species have occurred for biocontrol agents of animal pests:  “For parasitoids introduced to North America for control of insect pests Hawkins and Marino (1997) found that 51 (16.7%) of the 313 introduced species were recorded from nontarget hosts.  For Hawaii, 37 (32.3%) of 115 parasitoid species were noted to use nontarget hosts…biological control introductions are considered to be responsible for extinctions of at least 15 native moth species [in Hawaii].”  (1)

There are also several cases of biological controls escaping from the laboratory setting before they had been adequately tested and approved for release.   A virus escaped the laboratory in Australia and killed 90% of the rabbits in its initial spread through the wild population.  Very quickly, the virus evolved to a less fatal strain that killed less than 50% of the rabbits it infected.  A second virus was then tested and also escaped its laboratory trial and has spread through the rabbit population throughout Australia.

A fly being considered for introduction to control yellow starthistle apparently escaped and damaged a major cash crop of safflower in California according to a study published in 2001, illustrating the risks of biocontrols to agriculture.

This is but a brief description of the diverse ways in which nature has foiled the best efforts of the scientists designing biological controls for non-native species of plants and animals.  The source of this information (1) therefore concludes, “…many releases of species have inadequate justification…The first goal of research must be to show that the introduced biological control agent will not itself cause damage.”  Given this wise advice, we will return to the question, “What damage is being done by cheatgrass and does that damage justify the introduction of The Black Fingers of Death?”

Why is cheatgrass considered a problem?

Cheatgrass is one of the many non-native annual grasses which have replaced the native grasses which were not adapted to the grazing of domesticated animals.  Cheatgrass is a valuable nutritional source for grazing animals when it is green and loses much of its nutritional value when it dries.

Grazing is only one of the types of disturbance which create opportunities for non-native grasses to expand their range into unoccupied ground.  Fire is another disturbance which gives cheatgrass a competitive advantage over native grasses because it uses available moisture and germinates before native grasses can gain a foothold on the bare ground cleared by fire.

Cheatgrass is said to increase fire frequency by increasing fuel load and continuity.  Unfortunately, increasing levels of CO₂ (carbon dioxide) in the atmosphere is increasing the fuel load of cheatgrass:  “…the indigestible portion of aboveground plant material [of cheatgrass] …increased with increasing CO₂.” (2)

Carbon dioxide is the predominant greenhouse gas which is contributing to climate change.  And increasing frequency of wildfires is one of the consequences of the higher temperatures associated with climate change.  Therefore, one of the causes of the expanding range of cheatgrass is increasing levels of the greenhouse gases contributing to climate change.  Rather than address the underlying cause, we are apparently planning to poison the cheatgrass with a deadly fungus.

If we are successful in killing the cheatgrass, what will occupy the bare ground?  Will native grasses and shrubs return?  Will whatever occupies the bare ground be an improvement over the cheatgrass which has some nutritional value to grazing animals?  The US Forest Service plant database gives us this warning, “Care must be taken with methods employed to control cheatgrass so that any void left by cheatgrass removal is not filled with another nonnative invasive species that may be even less desirable.” 

Recapitulating familiar themes

The project to develop a deadly fungus to kill cheatgrass is another example of the issues that we often discuss on Million Trees:

  • Are the risks of the methods used to eradicate non-native species being adequately assessed and evaluated before projects are undertaken?
  • Are the underlying conditions—such as climate change–that have contributed to an “invasion” being addressed by the methods used to eradicate them?  If not, will the effort be successful?
  • Is the damage done by the “invasion” greater than the damage done by the methods used to eradicate the invader?  Is the cure worse than the disease?

We do not believe that these questions are being addressed by the many “restoration” projects we see in the San Francisco Bay Area.  Consequently, we believe that these projects often do more harm than good.


(1)    Cox, George W., Alien Species and Evolution, Island Press, 2004

(2)    Ziska, L.H.; Reeves III, J.B.; Blank, R.R. (2005), “The impact of recent increases in atmospheric CO2 on biomass production and vegetative retention of cheatgrass (B. tectorum): Implications for fire disturbance.”, Global Change Biology. 11 (8): 1325–1332,

Professor Arthur Shapiro’s comment on the Environmental Impact Report for the Natural Areas Program

Mission blue butterfly Wikimedia Commons

With permission and in its entirety we are publishing the comment of Arthur M. Shapiro.  He is Distinguished Professor of Evolution and Ecology at UC Davis and a renowned expert on the butterflies of California.  We hope that you will take his credentials into consideration as you read his opinion of native plant restorations in general and the Natural Areas Program in San Francisco in particular.  We hope that Professor Shapiro’s comment will inspire you to write your own comment by the deadline,  which has been extended to October 31, 2011.  Details about how to submit your comment are available here.


October 6, 2011

Mr. Bill Wycko

San Francisco Planning Department

                              Re: DRAFT EIR, NATURAL AREAS PROGRAM

Dear Mr. Wycko:

Consistent with the policy of the University of California, I wish to state at the outset that the opinions stated in this letter are my own and should not be construed as being those of the Regents, the University of California, or any administrative entity thereof. My affiliation is presented for purposes of identification only. However, my academic qualifications are relevant to what I am about to say. I am a professional ecologist (B.A. University of Pennsylvania, Ph.D. Cornell University) and have been on the faculty of U.C. Davis since 1971, where I have taught General Ecology, Evolutionary Ecology, Community Ecology, Philosophy of Biology, Biogeography, Tropical Ecology, Paleoecology, Global Change, Chemical Ecology, and Principles of Systematics. I have trained some 15 Ph.D.s, many of whom are now tenured faculty at institutions including the University of Massachusetts, University of Tennessee, University of Nevada-Reno, Texas State University, and Long Beach State University, and some of whom are now in government agencies or in private consulting or industry. I am an or the author of some 350 scientific publications and reviews. The point is that I do have the bona fides to say what I am about to say.

 At a time when public funds are exceedingly scarce and strict prioritization is mandatory, I am frankly appalled that San Francisco is considering major expenditures directed toward so-called “restoration ecology.” “Restoration ecology” is a euphemism for a kind of gardening informed by an almost cultish veneration of the “native” and abhorrence of the naturalized, which is commonly characterized as “invasive.” Let me make this clear: neither “restoration” nor conservation can be mandated by science—only informed by it. The decision of what actions to take may be motivated by many things, including politics, esthetics, economics and even religion, but it cannot be science-driven.

In the case of “restoration ecology,” the goal is the creation of a simulacrum of what is believed to have been present at some (essentially arbitrary) point in the past. I say a simulacrum, because almost always there are no studies of what was actually there from a functional standpoint; usually there are no studies at all beyond the merely (and superficially) descriptive. Whatever the reason for desiring to create such a simulacrum, it must be recognized that it is just as much a garden as any home rock garden and will almost never be capable of being self-sustaining without constant maintenance; it is not going to be a “natural,” self-regulating ecosystem. The reason for that is that the ground rules today are not those that obtained when the prototype is thought to have existed. The context has changed; the climate has changed; the pool of potential colonizing species has changed, often drastically. Attempts to “restore” prairie in the upper Midwest in the face of European Blackthorn invasion have proven Sisyphean. And they are the norm, not the exception.

The creation of small, easily managed, and educational simulacra of presumed pre-European vegetation on San Francisco public lands is a thoroughly worthwhile and, to me, desirable project. Wholesale habitat conversion is not.

A significant reaction against the excesses of the “native plant movement” is setting up within the profession of ecology, and there has been a recent spate of articles arguing that hostility to “invasives” has gone too far—that many exotic species are providing valuable ecological services and that, as in cases I have studied and published on, in the altered context of our so-called “Anthropocene Epoch” such services are not merely valuable but essential. This is a letter, not a monograph, but I would be glad to expand on this point if asked to do so.

I am an evolutionary ecologist, housed in a Department of Evolution and Ecology. The two should be joined at the proverbial hip. Existing ecological communities are freeze-frames from a very long movie. They have not existed for eternity, and many have existed only a few thousand years. There is nothing intrinsically sacred about interspecific associations. Ecological change is the norm, not the exception. Species and communities come and go. The ideology (or is it faith?) that informs “restoration ecology” basically seeks to deny evolution and prohibit change. But change will happen in any case, and it is foolish to squander scarce resources in pursuit of what are ideological, not scientific, goals with no practical benefit to anyone and only psychological “benefits” to their adherents.

If that were the only argument, perhaps it could be rebutted effectively. But the proposed wholesale habitat conversion advocated here does serious harm, both locally (in terms of community enjoyment of public resources) and globally (in terms of carbon balance-urban forests sequester lots of carbon; artificial grasslands do not). At both levels, wholesale tree removal, except for reasons of public safety, is sheer folly. Aging, decrepit, unstable Monterey Pines and Monterey Cypresses are unquestionably a potential hazard. Removing them for that reason is a very different matter from removing them to actualize someone’s dream of a pristine San Francisco (that probably never existed).

Sociologists and social psychologists talk about the “idealization of the underclass,” the “noble savage” concept, and other terms referring to the guilt-driven self-hatred that infects many members of society. Feeling the moral onus of consumption and luxury, people idolize that which they conceive as pure and untainted. That may be a helpful personal catharsis. It is not a basis for public policy.

Many years ago I co-hosted John Harper, a distinguished British plant ecologist, on his visit to Davis. We took him on a field trip up I-80. On the way up several students began apologizing for the extent to which the Valley and foothill landscapes were dominated by naturalized exotic weeds, mainly Mediterranean annual grasses. Finally Harper couldn’t take it any more. “Why do you insist on treating this as a calamity, rather than a vast evolutionary opportunity?” he asked. Those of us who know the detailed history of vegetation for the past few million years—particularly since the end of Pleistocene glaciation—understand this. “Restoration ecology” is plowing the sea.

Get real.


                                     Arthur M. Shapiro

                                     Distinguished Professor of Evolution and Ecology

Professor Arthur M. Shapiro, at work, UC Davis

Facts about carbon storage in grasses do not support assumptions of native plant advocates

We have received many comments from native plant advocates regarding carbon storage.  These comments defend projects in the Bay Area to destroy non-native forests and “restore” native plants by claiming that native plants will actually sequester more carbon than the forest that they propose to destroy.  As always, we are grateful for comments that give us the opportunity to research the issues and report what we have learned about this complex and important subject.

Carbon cycling in a terrestrial plant-soil system

The storage of carbon in plants and soil occurs as plants and soil exchange carbon dioxide (CO₂) with the atmosphere as a part of natural processes, as shown in the following diagram (1):

Green Arrow:  CO₂ uptake by plants through photosynthesis

Orange Arrows:  Incorporation of Carbon into biomass and Carbon inputs into soil from death of plant parts

Yellow Arrows:  Carbon returns to the atmosphere through plant respiration and decomposition of litter and soil Carbon.  Carbon in plant tissues ultimately returns to atmosphere during combustion or eventual decomposition.

Rates of carbon uptake and emissions are influenced by many factors, but most factors are related to temperature and precipitation:

  • Higher temperatures are associated with faster plant growth, which accelerates photosynthesis and carbon uptake.
  • Higher temperatures also accelerate decomposition of plant materials, thereby accelerating the return of stored carbon into the atmosphere.
  • The effect of moisture in the soil on decomposition can be graphed as a “hump.”  In extremely dry soils, decomposition is slow because the organisms that decompose vegetation are under desiccation stress.  Conditions for decomposition improve as moisture in the soil increases until the soil is very wet when lack of oxygen in the soil impedes decomposition.

Although temperature and precipitation are important factors in carbon storage, they don’t change appreciably when one type of vegetation is replaced with another.  Therefore, these factors aren’t helpful in addressing the fundamental question we are considering in this post, which is “Does native vegetation store more carbon than the forests that presently occupy the land in question?”

Where is carbon stored?

Source: U.S. EPA, 2018

Much of the carbon stored in the forest is in the soil.  It is therefore important to our analysis to determine if carbon stored in the soil in native vegetation is greater than that stored in non-native forests.  The answer to that question is definitely NO!  The carbon stored in the soil of native vegetation in Oakland, California is a fraction (5.7 kilograms of carbon per square meter of soil) of the carbon stored in residential soil (14.4 kilograms in per square meter of soil). (9)  Residential soil is defined by this study as “residential grass, park use and grass, and clean fill.”  This study (9) reports that the amount of carbon stored in the soil in Oakland is greater after urbanization than prior to urbanization because Oakland’s “wildland cover” is associated with “low SOC [soil organic carbon] densities characteristic of native soils in the region.”

Native plant advocates have also argued that the carbon stored in the soil of perennial native grasslands is greater than non-native trees because their roots are deeper.  In fact, studies consistently inform us that most carbon is found in the top 10 centimeters of soil and almost none is found beyond a meter (100 centimeters) deep. (1, 4) In any case, we do not assume that the roots of perennial grasses are longer than the roots of a large tree.

Another argument that native plant advocates use to support their claim that native perennial grasslands store more carbon in the soil than non-native trees is that native grasses are long-lived and continue to add carbon to the soil throughout their lives.  In fact, carbon stored in the soil reaches a steady state, i.e., it is not capable of storing additional carbon once it has reached its maximum capacity. (1)

It is pointless to theorize about why grassland soils should store more carbon than forest soils.  The fact is they don’t.  In all regions of the United States forest soils store more carbon than either grassland or shrubland soils.  (9, Table 5)

We should also describe Oakland’s native vegetation before moving on:  “Vegetation before urbanization in Oakland was dominated by grass, shrub, and marshlands that occupied approximately 98% of the area.  Trees in riparian woodlands covered approximately 1.1% of Oakland’s preurbanized lands…”  (5)  In other words, native vegetation in Oakland is composed of shrub and grassland.  When non-native forests are destroyed, they will not be replaced by native trees, especially in view of the fact that replanting is not planned for any of the “restoration” projects in the East Bay.

The total amount of carbon stored within the plant or tree is proportional to its biomass, both above ground (trunk, foliage, leaf litter, etc.) and below ground (roots).  Since the grass and shrubs that are native to the Bay Area are a small fraction of the size of any tree, the carbon stored within native plants will not be as great as that stored in the trees that are being destroyed.

Whether we consider the carbon stored in soil or within the plant, the non-native forest contains more carbon than the shrub and grassland that is native to the Bay Area.

Converting forests to grassland

If we were starting with bare ground, it might be relevant to compare carbon sequestration in various types of vegetation, but we’re not.  We’re talking about specific projects which will require the destruction of millions of non-native trees.  Therefore, we must consider the loss of carbon associated with destroying those trees.  It doesn’t matter what is planted after the destruction of those trees, nothing will compensate for that loss because of how the trees will be disposed of.

The fate of the wood in trees that are destroyed determines how much carbon is released into the atmosphere.  For example, if the wood is used to build houses the loss of carbon is less than if the wood is allowed to decompose on the forest floor.  And that is exactly what all the projects we are discussing propose to do:  chip the wood from the trees and distribute it on the forest floor, also known as “mulching.”  As the wood decomposes, the carbon stored in the wood is released into the atmosphere:  “Two common tree disposal/utilization scenarios were modeled:  1) mulching and 2) landfill.  Although no mulch decomposition studies could be found, studies on decomposition of tree roots and twigs reveal that 50% of the carbon is lost within the first 3 years.  The remaining carbon is estimated to be lost within 20 years of mulching.  Belowground biomass was modeled to decompose at the same rate as mulch regardless of how the aboveground biomass was disposed” (8)

Furthermore, the process of removing trees releases stored carbon into the atmosphere, regardless of the fate of the destroyed trees:  “Even in forests harvested for long-term storage wood, more than 50% of the harvested biomass is released to the atmosphere in a short period after harvest.”  (1)

Will thinning trees result in greater carbon storage?

Native plant advocates claim that thinning the non-native forest will result in improved forest health and therefore greater carbon storage.  In fact, the more open canopy of an urban forest with less tree density results in greater growth rates.  (3)  Although more rapid growth is associated with greater rates of carbon sequestration, rates of storage have little effect on the net carbon storage over the life of the tree.  (6)  Net carbon storage over the life of the tree is determined by how long the species lives and how big the tree is at maturity.  These characteristics are inherent in the species of tree and are little influenced by forest management practices such as thinning. (6)

More importantly, even if there were some small increase in carbon storage of individual trees associated with thinning, this increase would be swamped by the fact that over 90% of the urban forest will be destroyed by the proposed projects we are evaluating in the East Bay.  The projects of UC Berkeley and the City of Oakland propose to destroy all non-native trees in the project areas.  The project of the East Bay Regional Park District proposes to destroy all non-native trees in some areas and thin in other areas from 25 to 35 feet between each tree, reducing tree density per acre by at least 90%.  No amount of “forest health” will compensate for the loss of carbon of that magnitude.   

Responding to native plant advocates

  • The vegetation that is native to the Bay Area does not store more carbon above or below the ground than the non-native forest.
  • Chipping the trees that are destroyed and distributing the chips on the ground will not prevent the release of carbon from the trees that are destroyed.
  • Thinning the trees in our public lands will not increase the capacity of the trees that remain to store carbon.



  1.  Anderson, J., et. al., “The Potential for Terrestrial Carbon Sequestration in Minnesota, A Report to the Department of Natural Resources from the Minnesota Terrestrial Carbon Sequestration Initiative, February 2008.
  2. Birdsey, Richard, “Carbon storage and accumulation in United States Forest Ecosystems,” USDA Forest Service, General Technical Report WO-59, 1992
  3. Environmental Protection Agency, “Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008,” April 15, 2010., EPA 430-R-10-006
  4. Fissore, C.,  et.al., “Limited potential for terrestrial carbon sequestration to offset fossil-fuel emissions in the upper Midwestern US,” Frontiers in Ecology and the Environment, 2009, 10.1890/090059
  5. Nowak, David, “Historical vegetation change in Oakland and its implication for urban forest management,” Journal of Arboriculture, 19(5): September 1993
  6. Nowak, David, “Atmospheric Carbon Reduction by Urban Trees,” Journal of Environmental Management, (1993) 37, 207-217
  7. Nowak, David. Crane, Daniel, “Carbon storage and sequestration by urban trees in the U.S.A.,” Environmental Pollution, 116 (2002) 381-389
  8. Nowak, David, et.al., “Effects of urban tree management and species selection on atmospheric carbon dioxide,” Journal of Arboriculture 28(3) May 2002
  9. Pouyat, R.V. (US Forest Service)., et.al., “Carbon Storage by Urban Soils in the United States,” Journal of Environmental Quality, 35:1566-1575 (2006)

Climate Change: Not just global warming anymore

When climate change first became a hot topic (pardon the pun) about 10 years ago, it was consistently described as “global warming.”  When scientists observed the effect that global warming was having on plants and animals in California, they reported that the ranges of native plants and animals were moving to higher elevations and northern latitudes in search of cooler temperatures. 

A study published in Nature magazine in December 2009 found that plants and animals must move as much as 6 miles every year from now to the end of the century to find the conditions they occupy now. When the plants move, the animals that depend on them must adapt or move with them to survive.  Professor Art Shapiro (UC Davis) has been studying California butterflies for over 35 years.  He reported (1) that native butterflies are moving to higher elevations, where temperatures are lower, but that ultimately, “There is nowhere else to go, except heaven.”

More recently we have experienced extreme weather that cannot be adequately described as “global warming.”  We have seen epic storms that have resulted in unprecedented flooding, while other places have experienced prolonged drought.  We are as likely to have an extremely cold winter as we are to have an extremely hot summer.  So the phrase “global warming” has evolved into the more accurate description:  “climate change.”  Aside from our anecdotal observations of these extreme weather events, science is beginning to catch up to provide an analytical understanding of our observations.  The story of climate change is now much more complex and the challenges it presents have become correspondingly more difficult and unpredictable.

Changes in Precipitation

Although places like Pakistan, Australia and some states in the US have recently experienced more rain and flooding than history has recorded, scientists have been reluctant to attribute this to climate change until very recently.  Computer modeling of nearly 50 years of weather data has finally enabled scientists to confirm that these increases in precipitation are the result of “…the effects of greenhouse gases released by human activities like the burning of fossil fuels.” (2)

And, like increases in temperature, changes in precipitation also result in the movement of plants and animals to “find” the conditions to which they are adapted.  Scientists have recently challenged previous assumptions about the movement of plants and animals to higher elevations.  They now report (3) that in some places in California in which precipitation has increased, plants have responded by “moving” to lower elevations.  Scientists acknowledge that the affect on the animal populations in their historic ranges is unpredictable because insects, for example, are more sensitive to changes in temperature and may not be able to move downhill with the plants they presently depend upon. 

Changes in Fog Patterns

Fog is another weather event that is important in California, particularly along the coast, where the warm air from the interior meets the cold air from the ocean.  The result of this confluence of cold and warm air is fog, particularly during the summer when the difference in temperatures is greatest. 

The redwood is our native tree that is closely associated with the foggy coastal conditions in California.  The redwood requires the fog drip to irrigate it during the dry California summer and its range is limited to sheltered areas because it does not tolerate wind.  The range of the redwood in California is therefore limited to a few hundred miles along the coast.  Its narrow range makes it particularly vulnerable to climate change. 



Redwood National Park, NPS photo



In Muir Woods, for example, higher temperatures have reduced coastal fog by 30% in the past century.  Scientists expect this loss of summer fog drip to result in a significant loss of water to the trees and they predict that it will affect the survival of the redwoods in the long-run.(4)

Implications of climate change for native plants?

Clearly, we still have much to learn about climate change:

  • Which weather events are indicators of long-range trends?
  • Climate change is apparently not just one trend, such as increased temperatures.  It is probably many different types of weather events, such as increases or decreases in snow and rainfall, hurricanes and typhoons, fog and wind.  Obviously, we don’t yet have the complete picture of what or where long-range changes have occurred or which are likely in the future. 
  • We know little about the affect that climate change will have on the natural world.  How will plants and animals respond to climate change?  Which plants and animals will survive and, if so, where will they survive?

We marvel at the confidence that the local native plant advocates have in their agenda.  How did they select the pre-European landscape of the late 18th century to replicate?  What makes them think that plants and animals that lived here 250 years ago are still sustainable here, let alone that they will be sustainable in the future? 

These are rhetorical questions, which we will presume to answer for our readers:  Native plant advocates may compensate for radically changed environmental conditions by using intensive gardening methods.  The use of herbicides, irrigation systems, prescribed burns, constant weeding, soil amendments, fences and boardwalks, etc., may artificially mimic the conditions of 250 years ago.  However, the result is a native plant garden that is neither natural nor more biodiverse than what can be achieved with less effort, with less toxicity and fewer scarce resources.  While we can see the value of a native plant garden to preserve our horticultural heritage, we find it more difficult to justify the large-scale efforts that we currently find in all of our public lands.  Is it realistic to garden all of our public lands in perpetuity? 

(1) Arthur Shapiro (UC Davis), Contra Costa Times, 1/19/10

(3) “Mountain plant communities moving down despite climate change, study finds,” Los Angeles Times, 1/24/11


(4) “Fog burned off by climate change threatens to stunt Muir Wood’s majestic redwood,” Marin Independent Journal, 2/5/11   http://www.marinij.com/marinnews/ci_17297751?IADID=Search-www.marinij.com-www.marinij.com