“Restoring Our Forests by Trusting in Nature”

“The world’s forests will be restored not by trying to recreate the past, but by providing the space for such forests to find their own new future.” –Fred Pearce

Fred Pearce is the author of The New Wild, which challenged the conventional wisdom that native species are inherently superior to non-native species and the closely related assumption that all non-native species are competitors of native species.  The New Wild is the most effective of the many critiques of invasion biology, which made his latest book required reading (for me).    

A Trillion Trees:  Restoring Our Forests by Trusting in Nature (1) examines the popular notion that planting one trillion trees around the world can deliver us from the death grip of climate change.  Once again, Fred Pearce challenges the conventional wisdom.  The claim that planting a trillion trees can compensate for our continuing burning of fossil fuels is an oversimplification, but with much truth at its core.

Forest Accounting:  Debits and Credits

Pearce begins by reminding us of the ecological value of forests and the role they play in reducing greenhouse gas emissions causing climate change.  In addition to absorbing carbon dioxide from the atmosphere during photosynthesis, forests also release water into the atmosphere in the form of water vapor.  Trees pump moisture from the ground into their leaves where excess moisture is transpired from pores (stomata) in leaves, moistening the atmosphere and returning moisture to the Earth as rain.  In a time and place where extreme drought is a major issue, this is a strong argument for retaining our forests.

On a global scale, forests are responsible for carrying moisture from coastal forests irrigated by moist sea breezes into drier regions on streams of moisture transpired by forests, Pearce calls flying rivers.  Where coastal forests are destroyed, this moisture delivery system is interrupted, resulting in drought in interior regions.  Observational data confirms this cycle:  “Air coming from forested areas delivered more than twice as much rain as deforested areas.  Forests make rain; taking them away creates if not deserts, then certainly aridity.”

The aerial river of moisture transpired by forests is carried by the wind and forests contribute to the wind.  Transpiration emits buoyant water vapor that condenses to water as it rises and cools.  Liquid water takes up much less space than water vapor, causing a pressure drop where water vapor becomes liquid water, resulting in wind. Some scientists believe that this “biotic pump” creates stronger wind than the winds that are created by cool ocean breezes meeting hot continental air.  These theories are controversial, but Pearce finds them credible. 

All trees emit volatile organic compounds, commonly abbreviated VOCs. VOCs neutralize a chemical known to neutralize methane, resulting in increased methane emissions from forests. Methane is the most potent greenhouse gas, although it does not persist in the atmosphere as long as carbon dioxide. 

Source: Wikipedia

Although forests create their own cooling environment with shade and moisture, they also absorb heat from the sun.  Albedo is the technical term used to measure light reflection and absorption. Because dark colors absorb heat and light colors reflect heat, this balance of cooling and heating factors varies. In Northern and Southern latitudes where winter snows reflect sunlight, dark forest canopies absorb more sunlight than treeless snow-covered ground.  Likewise, desert sand reflects more light than dark forest canopy.  Measuring the net effect of the many intervening factors such as albedo on climate change is controversial, even speculative at this time.

Evaluating Planting Projects

Pearce visited tree planting projects around the world and concluded that many are counterproductive in the short term and others are not sustainable in the long term. 

  • Some projects are planting plantations of fast growing trees such as eucalyptus and pine with the intention of logging them within about 10 years to produce timber, pulp, or biofuels.  The short term objectives of these projects do not address the long term problem of climate change. 
  • Some projects are planting single tree species that aren’t necessarily well adapted to local conditions.  The resulting monoculture is more vulnerable to disease, insects, and changed climate conditions.
  • Many huge projects exist only on paper.  Elaborate plans don’t necessarily produce new forests. 

Israel’s strong commitment to planting trees on its desert land illustrates the pros and cons of tree-planting projects.  Trees are important in Jewish culture.  Jews around the world celebrate an annual holiday of trees, Tu BiShvat.  A national nonprofit group created in 1901 bought land to support the Zionist cause and has planted 250 million trees on a quarter-million acres in the desert in what is now Israel. 

Yatir Forest in Israel. Source: Wikimedia Commons

One such project has planted 4 million Aleppo pines on the slopes of Mount Hebron near Tel Aviv since 1964.  Aleppo pines grow naturally in wetter Mediterranean regions.  They cope with drought by growing only briefly during spring rains in Israel and are dormant during most of the dry, hot year.  There are limits to this adaptation.  A year-long drought in 2010 killed 10% of the forest.  Because of the slow growth of the forest, the carbon storing capacity of the forest has yet to match the heat the forest absorbs that would otherwise be reflected by light-yellow desert sands.  Scientists who study this forest do not expect the forest to attain net cooling advantage for another 80 years.  There is some doubt that the forest will live that long, given rapidly rising temperatures and associated drought. 

Deforestation and Rewilding

Pearce also visited places where forests are being destroyed in Indonesia, South America, and Africa.  In Indonesia, the economic value of the trees themselves is the primary motivation for destroying forests.  In Brazil, the primary goal of deforestation is to convert forests to pastures for livestock and agricultural fields for commodity crops that feed animals. 

Developed nations have exported much of their agricultural and animal production to undeveloped nations.  As agricultural land in developed nations is abandoned, forests have regenerated.  In New England, for example forest cover was only 30% by the mid-19th century after 200 years of timber exploitation and clearance of agricultural land.  Industrialization brought farmers into cities and marginal agricultural land was abandoned.  Today most of New England is forested again.  As that transition from an agricultural to an industrial economy was made in developed nations, forests in undeveloped nations were destroyed to produce agricultural products exported to developed nations. 

Deforestation in Para State, Brazil. Source: Wikimedia Commons

In Brazil, the rewilding of agricultural land is already occurring.  Forests were cleared and seeded with grass for cattle pastures, but the poor soil is quickly exhausted and grass won’t grow after a couple of years.  These abandoned pastures recover their forests even on exhausted soil, but they won’t be mature rainforests again for many years. When forests cleared for agricultural crops lose most of their rainfall, agricultural crops fail.

Pearce visited agricultural communities in Africa that have figured out that it isn’t necessary to destroy forests in order to grow crops.  Farmers had to ignore the dictates of their government to clear their land before planting crops to learn that planting crops within groves of trees is just as productive.  The trees provide shade and moisture that shelter crops as well as create a more comfortable home for the community. 

Forests that are embedded in indigenous communities are more safeguarded than forests in so-called protected areas, where indigenous people have been evicted.  If forests are sustainably used by the community, the community has a direct economic interest in its preservation.  When indigenous people are evicted from forests, a handful of salaried rangers can’t provide the same level of surveillance, making forests more vulnerable to poaching and corrupt encroachment.  People have tended their forests for eons and community forestry is an extension of that relationship.  They understand the forest as no outsider could. 

 Pearce’s Message

Pearce believes that protecting the forests we have and allowing forests to regenerate naturally where agricultural land can be abandoned is preferable to planting trees because:

  • Planting trees where trees have never grown in the past is not likely to create a sustainable forest. If soil and climate conditions have not supported trees in the past, it is probably an unsuitable location for trees.
  • Huge projects that plant millions of trees are often creating monocultures of a single species of fast-growing trees.  Such monocultures are vulnerable to pathogens, insect infestations, and changes in climate.  Forests that regenerate naturally are more diverse, although they aren’t necessarily the same species as in the past because of epidemics of pests and pathogens.  “However clever the foresters were, the planted trees were less well suited to the space they were occupying than those chosen by nature” and “Natural regeneration helps species to shift and adapt to climate change.”
  • Newly planted trees require more support than a forest that is regenerating from roots and seedbanks.  They must be irrigated while they are establishing the fungal networks that give them access to moisture in the soil.  They don’t benefit from moisture and carbon resources shared by their mature neighbors.  They aren’t members of an existing, sharing community of trees.

Much of what is done in the name of “conservation” is destructive.  Pearce makes a strong case for natural recovery rather than active intervention in natural processes:  “Most of the fifteen-percent increase in forest cover across the eastern United States in the past four decades has come from natural regeneration rather than planting.” However, urban areas in America have lost 175,000 acres of trees cover each year for the past decade, according to the US Forest Service.  We have experienced such loss of our urban forests here in the San Francisco Bay Area. 

Bringing it home

Pearce’s message is consistent with my personal experience based on observations of tree-planting projects in the San Francisco Bay Area.  Our urban forests are being destroyed for many reasons:  to make way for development, to reduce fire hazards, and to eradicate non-native trees.  Little planting is done when trees are destroyed.  The tree species that are planted are often not suitable for the location.  When new trees aren’t irrigated regularly, they don’t survive.

Point Isabel is one of many parks in the East Bay Regional Park District where redwoods have been planted that died because they are not well adapted to places where they are directly exposed to salty, ocean winds.

More effort should be devoted to preserving forests because replacing them is largely a fiction. 

When East Bay Regional Park District acquired Oyster Bay in San Leandro, they destroyed the wind breaks of non-native trees.
Over 10 years later, the attempt to create a wind break of native trees at Oyster Bay has made little progress. This is another coastal location with salty ocean winds that are not hospitable to native tree species. Most of coastal California was treeless grassland prior to European settlement.

  1. Fred Pearce, A Trillion Trees:  Restoring Our Forests by Trusting in Nature, Greystone Books, 2021.  All quotes in this article are from this book. 

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.

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. 

Lab Girl: A tribute to the challenges of science

lab-girlLab Girl is a memoir of a scientist, Hope Jahren.  Jahren is a geobiologist, which is the scientific discipline that “explores the interactions between the physical Earth and the biosphere [global ecosystems].” (1) She describes the arduous journey from curious student to full-fledged scientist.  That transition involved physically demanding collection expeditions, digging deep into the soil for the samples that informed her research into the complex relationships between the soil and the plants that live in it.  Then long, tedious hours in the laboratory are required to analyze the soil and plant samples to develop the hypotheses needed to explain those relationships.  Finally, complicated laboratory tests are needed to test the hypotheses.

If you don’t already have a deep respect for the demands of science, Lab Girl will help you to appreciate the dedication of the scientists engaged in the process of refining our scientific knowledge.  At a time in our social history when science is being questioned by those with political agendas, Lab Girl is an antidote to skepticism about science and scientific expertise.

Familiar Themes

Jahren alternates chapters about her career with chapters about the plants she studies.  As we might expect, Jahren has a profound respect for trees and so her book is relevant to the mission of Million Trees.  She eloquently makes many of the same observations we make on Million Trees.  Here are a few:

On the value of observation and the complexity and changeability of nature:

“Time has changed me, my perception of my tree, and my perception of my tree’s perception of itself.  Science has taught me that everything is more complicated than we first assume, and that being able to derive happiness from discovery is a recipe for a beautiful life.  It has convinced me that carefully writing everything down is the only real defense we have against forgetting something important that once was and is no more, including the spruce tree that should have outlived me but did not.” (2)

On the importance of fungi to forest health:

“Underneath every mushroom is a web of stringy hyphae that may extend for kilometers, wrapping around countless clumps of soil and holding the landscape together.  The ephemeral mushroom appears briefly above the surface while the webbing that anchors it lives for years within a darker and richer world.  A very small minority of these fungi—just five thousand species—have strategically entered into a deep and enduring truce with plants.  They cast their stringy webbing around and through the roots of trees, sharing the burden of drawing water into the trunk.  They also mine the soil for rare metals, such as manganese, copper, and phosphorous, and then present them to the tree as precious gifts of the magi.” (2)

Placing blame for “invasive” weeds where it belongs:  ON US!

“A plant that lives where it should not live is a weed.  We don’t resent the audacity of the weeds, as every seed is audacious; we resent its fantastic success. Humans are actively creating a world where only weeds can live and feigning shock and outrage upon finding so many.  This mixed message is irrelevant:  there is already a revolution taking place in the plant world as invasives effortlessly supplant natives within every human-modified space.  Our impotent condemnation of weeds will not stop this revolution.  We aren’t getting the revolution we want; we are getting the one that we triggered. (2)

On the future of our forests:

“Every year since 1990 we have created more than eight billion new stumps.  If we continue to fell healthy trees at this rate, less than six hundred years from now, every tree on the planet will have been reduced to a stump.  My job is about making sure there will be some evidence that someone cared about the great tragedy that unfolded during our age.” (2)

And that is the job of Million Trees as well…to make this record of fighting to preserve our urban forests.  We echo Hope Jahren’s final message in Lab Girl:  “Here is my personal request to you:  If you own any private land at all, plant one tree on it this year.  If you are renting a place with a yard, plant a tree in it and see if your landlord notices.  If he does, insist to him that it was always there.  Throw in a bit about how exceptional he is for caring enough about the environment to have put it there.” (2)

Hope for 2017

We have had some big disappointments in 2016, and it isn’t easy to find something useful to do to improve the political climate in our country.  Planting a tree is something positive that many people are in a position to do.  When you feel discouraged about the future of our country, go visit your tree and pat yourself on the back for making an investment in the future of our country.

Happy New Year


  1. https://en.wikipedia.org/wiki/Geobiology
  2. Hope Jahren, Lab Girl, Alfred Knopf, 2016

Despicable behavior: The Sierra Club sinks to a new low

If you’re a member of the San Francisco Bay Chapter of the Sierra Club, you will soon receive a letter from a fellow Club member exposing the Club’s advocacy for deforestation and pesticide use on public lands in the Bay Area. It will also contain a postcard which you can return to express your opinion of the Club’s policy.

The Sierra Club is worried. They’ve already issued a “pre-buttal” in the form of a note tucked into their newspaper, the Yodeler (available here: SierraClub – Yodeler Insert) that directed members to read their on-line “pre-buttal.”  Their “pre-buttal” is factually inaccurate, for which the national Sierra Club takes no responsibility.

Herbicide spraying in one of the project areas
Herbicide spraying in one of the project areas

Why would they allow an opposing letter through to their membership?

The Sierra Club didn’t allow the member’s letter to go to their mailing list out of any interest in members hearing both sides of the story. It’s the law.

California State law requires that non-profit organizations with elected boards, such as the Sierra Club, enable their members to communicate with fellow members. This doesn’t mean they release their members’ contact information. The letter must be given to the non-profit organization, which uses a third-party direct mailing company. In this case, the mailing was arranged with the national headquarters of the Sierra Club, which manages the mailing list of the entire membership.

The Bay Area Chapter of the Sierra Club has 6,300 members, so it is expensive to take advantage of this privilege. All the more reason to be outraged by the fact that the Chapter pre-emptively sabotaged this effort to communicate with its membership.

Here’s the story

We will let the author of the letter to the Chapter members tell you what happened by publishing her report to the many people who are collaborating in the effort to prevent the destruction of our urban forest (emphasis added):

January 27, 2016

Friends, I am writing to tell you the fate of my letter to the members of the San Francisco Bay Chapter of the Sierra Club. My letter has not been sent yet, but it probably will be soon. The local chapter inserted a printed letter into the published version of the Yodeler informing members that they would be receiving my letter. That letter told them to go to the Chapter website to see a point-by-point “pre-buttal” to my letter. That is available on-line HERE.

I sent the staff in the national headquarters the email below and copied the Chapter staff who signed the letter in the Yodeler. You can read that email to see what I asked for. Now I have had a conversation with Bruce Hamilton who is in the legal office of national headquarters and I am writing to tell you the final outcome:

Mr. Hamilton freely admits that he gave my letter to the Chapter before my letter was sent. He did not see anything wrong with having done that. He says that the national headquarters assumes no responsibility for what the Chapter has done nor anything they say in their “pre-buttal.” I pointed out that I have provided evidence that the Club has refused to meet with us. He says the national headquarters takes no responsibility for ascertaining the facts. He has refused to request that the Chapter remove their “pre-buttal” from the website or revise it in any way. I told him that I would consult a lawyer about what “remedies are available to me.” [Redacted personal information]

So that is the fate of my letter to the members of the local Chapter of the Sierra Club. One hopes that members will now be so curious about my letter that they may actually read it! [Redacted personal comments]

In solidarity,

Mary McAllister

From: Mary McAllister
Sent: Wednesday, January 27, 2016 6:50 AM
To: michelle.epstein@sierraclub.org ; bruce.hamilton@sierraclub.org
Cc: Michelle Myers

Subject: Letter to members of the San Francisco Bay Chapter

Dear Mr. Hamilton and Ms. Epstein,

As you know, I have been trying to arrange a mailing to the members of the San Francisco Bay Chapter for some months. My letter has not yet been sent, yet the Bay Chapter has preemptively sabotaged my letter with an insert in the printed Yodeler alerting people to read the Chapter’s on-line prospective rebuttal to a letter that has not yet been sent.

The on-line “pre-buttal” starts by claiming that the Sierra Club has never refused to meet with me. I have attached [available here:  sierra-club-petition-to-national-leadership] my letters to the Sierra Club requesting a meeting that were sent in November. Those letters were sent certified and I have the return receipts, proving that the Club received my request for a meeting. The Club did not reply to those letters.

Also, below is my email correspondence with a member of the Chapter Conservation Committee attempting to get this issue on the agenda of the Conservation Committee in September 2015. This request was also ignored or denied. Since no one responded to me, I do not know which. [These emails are available here: Sierra Club – Conservation Committee]

These are just two of the most recent attempts to discuss this issue with the Chapter. I have a much longer paper trail of attempts that go back several years, including an email from someone representing Mr. Brune.

If the Chapter and/or the national Club are now willing to meet with us, I am still ready and willing to do so.

Meanwhile, I ask that the on-line “pre-buttal” be removed until my letter is actually sent and received by Chapter members. The well has already been poisoned, but this is the only remedy available to me at this time.

When my letter has been sent and received by members, I hope that the Chapter rebuttal will be more accurate than what is presently on-line. The Chapter leadership has been sent a multitude of studies, reports from environmental consultants and government professionals such as the US Forest Service. They therefore know—or should know—that nothing they are saying in their “pre-buttal” is accurate. I would be happy to present all these materials to you and others in a meeting.

I am one of hundreds of people who have been fighting for the preservation of our urban forest in the San Francisco Bay Area for nearly 15 years. Please understand that although I am required by law to make this request as an individual member, I do so on behalf of thousands of people who share my commitment.

Mary McAllister

The bottom line

We are still trying to get the facts out to all Sierra Club members, and to all those who recognize that its views are out of step with the environmental realities of the 21st century.

We hope that those who are still members of the Bay Area Chapter of the Sierra Club will read the letter from a fellow member and send the postcard expressing their opinion of Chapter policy regarding deforestation and pesticide use. Thank you for reading this post.

As a reminder: The map below shows all the areas that are affected by this massive deforestation scheme that will fell nearly half a million trees. It’s a travesty that the Sierra Club is not only supporting these projects, but has also filed a lawsuit demanding that they be even more destructive than planned.

FEMA Project Areas
FEMA Project Areas

Adventures in the Anthropocene

Adventures in the AnthropoceneAdventures in the Anthropocene:  A Journey to the Heart of the Planet We Made is, indeed, a journey. (1) Its author, Gaia Vince, traveled the globe for two years to witness first-hand the impact of human civilization on the planet.  It is an even-handed account, in which grim realities are described but are balanced with optimistic predictions of the innovations that will ultimately enable us to cope with them.

Ms. Vincent takes us to remote corners of the Earth where undeveloped communities are further impoverished by climate change and related changes in the environment.  Rising temperatures and reduced rainfall have forced many agricultural communities off their ancestral lands and into a more marginal existence.  In Bolivia, for example, former farmers have been displaced into brutal mines where life span is typically shortened by health and safety hazards.  Some Pacific and Indian Ocean islands have been drowned by rising sea levels, forcing mass evacuations onto those that remain.  Their protective reefs are dissolving in the increasingly acidic ocean.

Meanwhile, enterprising people are responding to threats their communities are facing.  In the Indian Himalayas, for example, artificial glaciers are being created to replace those that are melting.  Glaciers were the irrigation system that enabled agriculture in marginal conditions.  Torrential downpours caused by climate change are frozen on dammed, flat plains to create artificial glaciers that perform the same function.  In a remote village in Nepal, a villager returns from his Western education to bring his impoverished community into the 21st century by creating a wi-fi network that provides internet access.  The internet brings education to a village that could not afford teachers.  It is powered by a small hydroelectric generator in a glacial stream.  The stream is expected to disappear when the glacier melts in a decade or two, a problem yet to be solved.

These stories and a multitude of others are both sobering and inspiring, but we will focus on the issues relevant to Million Trees.

Harvesting fog with trees

The coast of Peru is one of the driest places on the earth.  There are places in Peru where no rain has been recorded.  The city of Lima is near the coast and its climate is similar to San Francisco.  There is little rain, but there is a great deal of fog.  Lima, like many cities in undeveloped countries, is surrounded by shanty towns in which poor people build make-shift shacks and live without modern services such as water, power, and sewage systems.

Demonstrating once again, that poverty is sometimes the mother of invention, the people of one of these shanty towns are attempting to grow a forest on their sand dune.  The trees are being irrigated with water harvested by huge fog nets, which are also supplying the community with drinking and washing water.  Within four years, the community expects the trees to be large enough to harvest the fog without the help of the fog nets, “producing a self-sustaining run-off that will replenish ancient wells and provide water for the community for the first time in 500 years.” (1)

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

This is a familiar scenario to the readers of Million Trees.  Fog drip in the eucalyptus forests in San Francisco has been measured at over 16 inches per year.  In the driest months of the year, soil moisture in San Francisco’s eucalyptus forest has been measured at over 10%, while soil moisture in grassland was only 2% and 4% in shrubs.  (2)

The value of forests and the dangers of deforestation

Each chapter of Adventures in the Anthropocene is devoted to a different ecosystem.  Each ecosystem is introduced with a description of the importance of that ecosystem and the way in which is it being compromised by the activities of humans in the Anthropocene.  Here are a few excerpts from the chapter about forests, which will be familiar to the readers of Million Trees.

  • “Forests play an important role in local and global climate. The world’s forests absorb 8.8 billion tonnes of carbon dioxide each year through photosynthesis—about one-third of humanity’s greenhouse gas emissions.”
  • “…their canopies provide shelter from the sun and wind, making forests much wetter, cooler environments than surrounding treeless areas. This nurtures streams and rivers, provides habitat for a range of amphibians and other life, helps cool the regional and global atmosphere, and recycles water.”
  • “Although forests help create the climate, they are also exquisitely sensitive to it—and the smaller a forest gets, the less resilient it is. When trees are chopped down, sunlight enters in the gap and dries the soils. Drought upsets the forests’ delicate water cycle—trees start to die and the entire ecosystem can tip from rainforest to grass-dominated savannah.”
  • “Deforestation emits carbon dioxide from soils and decaying plant matter, and is responsible for around 20% of all carbon dioxide emissions.”

One point bears repeating because it is relevant to our local version of deforestation.  In some cases, native plant advocates have succeeded in their demand to destroy 100% of our urban forest because it is predominantly non-native.  In other cases, they have only been able to convince land managers to “thin” the forests, although “thinning” does not seem an accurate description of destruction of 90% of the trees.  In any case, we should all understand that the ultimate likely outcome of the “thinning” strategy is an eventual clear-cut because “when trees are chopped down, sunlight enters in the gap and dries the soils….trees start to die and entire ecosystem can tip” from forest to grassland.  The drying of the soil is only one factor in this prediction.  The remaining trees also will be vulnerable to wind throw.  And the herbicides used to prevent the destroyed trees from resprouting are mobile in the soil and are likely to damage the trees that remain.  Plans to “thin” the forest are either based on ignorance or are a strategy designed to achieve the same goals as a clear-cut with less public opposition.

Are invasive species a problem?

We were gratified that there was barely a mention of “invasive” species in the detailed accounts of the impact of human civilization on the planet.  The conventional wisdom that “invasive” species are one of the primary causes of species extinction is waning and this book reflects that fact. 

Galapagos Islands
Galapagos Islands

The pros and cons of introduced plant species are debated in the context of the Galapagos Islands, where biodiversity is worshipped because it was instrumental in Darwin’s theory of evolution.  Ms. Vince interviewed the conservationist who has been battling invasive plant species on the Galapagos for 20 years.  He recently decided that attempts to eradicate introduced plants are futile and he now calls them native plants.  His surrender to this reality is controversial, but he is resolute.  He is supported in this decision by scientists who have studied novel ecosystems and find ecological value in them.  The rebuttal to such defense of novel ecosystems is that the globalization of ecosystems is homogenizing the world’s biota.

Ms. Vince concludes that proponents of eradicating non-native plants are losing the battle against the “McDonaldization” of nature:  “From the Galapagos to Hawaii, conservationists are switching tack and starting to embrace the introduced species of Anthropocene ecosystems…” because “In some places, invasives have enhanced the landscapes, reducing erosion, providing handy cash crops or food and habitat for other wildlife.”

We can only hope that our local version of “conservation” in the San Francisco Bay Area will catch up with this new realistic perspective in time to save our urban forests from being needlessly destroyed.


The final chapter of Adventures in the Anthropocene is an epilogue, which takes place in 2100 in London.  The author’s son muses at the age of 87 about which of his mother’s many predictions occurred in the 21st Century.  As we would expect, it was a tumultuous century, one in which drastic changes were made to accommodate the changing climate.

We notice that 22nd Century vegetation of London is tropical:  “Now, carpets of sedges and mosses fill the spaces, interspersed by grasses grazed by capybara, and the planted fig and mango trees, noisy with wild birds.”     We marvel that people claiming to be environmentalists are blissfully unaware of the fact that the native plants they are demanding we restore are not adapted to current climate conditions, let alone the climate foreseen in the near future.

We conclude with the final paragraph of Adventures in the Anthropocene, because it is the most optimistic prediction in this excellent book:

…the world has become a kinder place.  The terrible wars, the famines, the terrorism, extremism and hate, the drownings and deaths of hundreds of thousands of migrants the humanitarian crises…they seem to be over now…The great global mix-up of people that has occurred as a result of climate migration, urbanization, and online networks has produced a new, socially mobile, egalitarian society.  The world’s giant cities force people to live together in close but diverse communities, and it has generated a spirit of cooperation.”

We look forward to a time of greater equality for humanity as well as for the natural world, when the meaningless and unnecessary distinction between native and non-native will be retired from our vocabulary.


(1) Gaia Vince, Adventures in the Anthropocene:  A Journey to the Heart of the Planet We Made, Milkweed Editions, 2014

(2) Kevin M. Clarke, et. al., “The influence of urban park characteristics on ant communities,” Urban Ecosyst, 11:317-334, 2008

Deforestation update is good news

We don’t have many opportunities to tell our readers positive stories, so we are grateful for a recent article in The Economist magazine about deforestation. (1) In many places around the world the rate of deforestation has slowed and some places are being reforested. Greenhouse gas emissions from deforestation were contributing 25% of all emissions just 15 years ago.  Now deforestation accounts for only 12% of total emissions.  The Intergovernmental Panel on Climate Change which represents international scientific consensus said in its most recent report, “deforestation has slowed over the last decade.”

Amazon rainforest.  Creative Commons - Share Alike
Amazon rainforest. Creative Commons – Share Alike

The reasons for this improvement are important because they give us clues about how we can make further progress.  The Economist sees a pattern in the success stories:  “Typically, countries start in poverty with their land covered in trees.  As they clear it for farms or fuel, they get richer—until alarm bells ring and they attempt to recover their losses.  This happens at different stages in different places, but the trajectory is similar in most:  a reverse J. steeply down, then bottoming out, then up—but only part of the way.”  Here are a few examples that illustrate this principle:

  • Fifteen years ago, Brazil was losing 20,000 sq kilometers (7,700 sq miles) of forest per year. Since then a national policy has created national parks and protected patches of forest which has reduced deforestation to a rate of less than 6,000 sq kilometers per year.*
  • Mexico has cut its deforestation rate even more than Brazil.
  • India and Costa Rica are replanting their forests. India had 640,000 sq km of forest left in 1980.  It now has 680,000 sq km of forest.  Only 20% of Costa Rica was forested in the 1980s.  Now 50% of Costa Rica is forested.

These countries have in common some of the factors that predict success in reducing deforestation.  They are all more prosperous than they were in the past.  Their fertility rates are declining.  They are all democracies, in which public policy is largely a reflection of what the voters demand of their elected officials.  These are also countries in which the government is sufficiently functional to enforce their forest policies.  Developments in satellite imagery have helped these governments to monitor and enforce their policies.

(*Since this report was published by The Economist, the Yale Environmental Review 360e has published data on deforestation in Brazil for 2013.  After reducing the rate of deforestation since 2004, the rate of deforestation increased from 2012 to 2013 due to new roads and dams, and illegal logging.)

None of these factors would predict the relatively low deforestation rate in the Congo because its population is growing rapidly, it is still very poor, and its government is dysfunctional.  The Economist attributes the relatively low deforestation rate of the Congo to the movement of its rural population to distant urban areas.  The distance of forests in the east of the country from the cities in the west makes them less vulnerable to deforestation.

Deforestation continues to be a serious problem in Indonesia, despite the fact that the fertility rate has declined and farm output increased.  The rate of deforestation in Indonesia has exceeded that of Brazil since 2011.  The government of Indonesia is hostile to anti-deforestation policy, seeing it as foreign intervention.  Indonesia has only recently achieved democratic elections, which may enable reconsideration of forest policies.

China is also an interesting case because it has invested huge effort in reforestation without making any perceptible progress toward democratization.  However, the population is stable and increasingly urbanized and the country is significantly more prosperous than it was in the 1980s.  The effects of China’s deforestation were so dire as to motivate its autocratic rulers to take immediate action.  (2)

Only 2% of China’s original forest is still intact, according to Greenpeace.  Rampant logging and overgrazing have degraded its soil to the point that 25% of its territory is now covered in sand.  The desert is so close to Beijing that its roads are often clogged with sand, its railways inundated, and its pastures desiccated.

In 1978, China began one of the biggest reforestation projects in the world.  Since then 66 billion trees have been planted to create a shelterbelt along the edges of its northern desert that is projected to be 2,800 miles long by 2050.  Unfortunately, the Chinese selected few species of trees, which would grow quickly.  Some species were short-lived and some weren’t suited to soil conditions, so only 15% of trees planted since 1949 are still alive.  This is probably another example of a country that could make greater progress against deforestation with a more open democracy, which improves decision-making.



Deforestation in the United States

Deforestation in the United States is largely a thing of the past.  About half of the United States was forested in 1600 compared to about one-third today.  Most of this deforestation occurred by 1910, when demand for lumber decreased significantly due to changes in building materials.  In the northeast of the country, much of the land has been naturally reforested as land that had been cleared for agriculture was abandoned.  It was always marginal land for agriculture, so as the population became more mobile, it moved west to find better land for farming.  This graph reflects these changes in land use and informs us that the south and the west are still supplying lumber for the world.  The US is supplying about one-fourth of the world’s timber.   Wildfires and insect infestations caused by climate change are also factors in declining forest cover in the west (although probably not reflected in this graph which ends in 1997).  (3)

Forest cover, USA. US Forest Service

Meanwhile, our local experience with deforestation is an outlier in these national trends.  Much of California was naturally treeless grassland and chaparral and it is being returned to that landscape by the native plant movement.  Most of our urban forest in the San Francisco Bay Area is not native to California.  It is being destroyed by most managers of public land because it is not native.  The public often objects to these destructive projects, but we are being ignored.

As we have seen in the examples above, deforestation and reforestation are largely political decisions.  American democracy is increasingly more responsive to economic interests than to the public.  Declining voter participation rates are undoubtedly a factor in this disturbing trend.  If you are not registered to vote, please give some thought to how our democracy has been damaged by lack of participation.  Midterm elections will take place this November.  Much is at stake.


(1) “A clearing in the trees,” The Economist, August 23-29, 2014

(2) “Great Green Wall,” The Economist, August 23-29, 2014

(3) http://en.wikipedia.org/wiki/Deforestation_in_the_United_States

Our urban forest is under siege

The urban forest on Mt. Davidson is slated for destruction.

According to California Trees (1) the US Forest Service has determined that tree cover in the country’s urban areas is decreasing by 4 million trees a year.  Although no research has been done on tree loss throughout California, the US Forest Service reported a one-percent decline in trees and shrubs in Los Angeles despite a big campaign to plant one million trees there.

You might think that the loss of trees in urban areas is the result of increasing development and you would probably be at least partially correct.  But many trees are lost for more trivial reasons that we think could be easily prevented.  Here are some local examples of trees in the Bay Area that were needlessly destroyed or soon will be.

  • The City of Oakland has a “view ordinance” which guarantees homeowners the preservation of their view at the time they purchased their home.  This view ordinance was invoked by a resident in the Oakland hills who demanded that her neighbor and the City of Oakland destroy trees obstructing her view.  Her neighbor purchased her house because of its forested view.  Yet, the desire for a forested view was trumped by her neighbor’s desire for a treeless view.  The law required that 25 trees be destroyed on private property and 21 trees on city property in order to restore the view of a 95-year old property owner who no longer lives in her home.  When trees are destroyed for such trivial reasons, we should not be surprised by the following compendium of absurd excuses to destroy trees.  (The story is here.)
  • The people of San Francisco are trying to prevent the destruction of their urban forest which is almost entirely non-native.  The City of San Francisco is systematically destroying non-native trees in order to return the landscape to its historical origins as grassland and dune scrub.  The latest battle in this long war is a particular park, Glen Canyon, in which the City proposes to destroy about 160 trees in the short -run and 300 trees in the long-run.  A handful of the trees are hazardous and aren’t disputed, but most have been evaluated as “poor suitability” which is the latest euphemism used by native plant advocates to describe non-native trees.  They propose to replace most of the trees with native shrubs and a few tall trees that are native to California, but not to San Francisco, such as Douglas Fir and Cottonwoods.  It remains to be seen if either of these species will survive in San Francisco.  Douglas Fir requires more rainfall than San Francisco receives and Cottonwoods are hot-climate trees which don’t tolerate mild temperatures without seasonal fluctuations.  We suspect that is the strategy, i.e., to plant trees for the sole purpose of placating the public without any intention that the trees will survive.  (The story is here.)
  • The space shuttle Endeavor was recently retired from service.  Its permanent home is now a museum in Los Angeles, where 400 street trees were destroyed to accommodate the delivery of the space shuttle from the airport to the museum.  The neighbors were not pleased, as you might imagine.  They unfortunately live in a blighted part of Los Angeles, so they didn’t have the clout needed to save their trees.  Do you think these trees would have been destroyed in Beverly Hills?  We doubt it.  (The story is here.)
  • The neighbors of Dimond Park in Oakland are trying to save the trees in their park from being destroyed by a “restoration.”  We often marvel at the use of the word “restoration” to describe projects which are more accurately described as “destruction.”  This is yet another native plant project, which is hell bent to remake nature to its liking.  In this case 42 trees would be destroyed, of which 27 are native, including 17 redwood trees.  Please help the neighbors save their trees by signing their petition which is available here.
  • Finally, we share the story of a property owner on 65th St in Oakland who with a great deal of courage and tenacity was able to save most of the street trees on her block from being destroyed by the City of Oakland.  The trees weren’t posted as required by Oakland’s ordinance.  The crew who came to cut them down couldn’t tell her why they were being cut down, nor could they tell her who owned the trees.  We encourage you to read her story because it will give you a brief lesson on the difficulty of advocating against the needless destruction of trees.

Deforestation causes climate change

We have been accumulating these stories in the past few months, but are finally inspired to share them with our readers because of the recent storm on the East Coast, Sandy, which caused over $50 billion in damage and the lives of over 100 people.  What’s the connection?  The connection is that Sandy has finally forced people to take the threats of climate change more seriously. 

When will this new interest in climate change translate to an interest in saving our trees?   Probably not soon, because few people understand that globally, deforestation contributes 20% of greenhouse gases that cause climate change.  The public and its elected representatives are focused primarily on transportation as the source of climate change.  Transportation contributes only 10% of greenhouse gases globally. 

Here in California, we are gearing up to put our climate change law (AB 32) into action by creating a cap and trade auction which will enable emitters of greenhouse gases to purchase carbon offsets.  Ironically, one of the things that carbon emitters can do to offset their contribution to greenhouse gases is to plant trees.  Yet, those who destroy trees are not being required to purchase carbon offsets.  Until the people who destroy trees are required to pay for the damage they do to the environment, we are unlikely to see a change in the cavalier attitude that governments seem to have about destroying trees.   


(1)    California Trees, Winter 2012, Vol 20, no 2

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)

Jared Diamond’s History Lesson for Us

In Collapse:  How Societies Choose to Fail or Succeed, Jared Diamond reviews the histories of societies that have failed in climates as diverse as Polynesia and the Arctic North.  He identifies a handful of factors that were instrumental in those failures, but only one of those factors is shared by all the examples he describes:  deforestation.

In every case deforestation reduced agricultural productivity by causing soil erosion and reducing rainfall.  The roots of trees hold soil in place and absorb rainfall which would otherwise wash over the surface of the soil, flushing it into watersheds where it increases turbidity and destroys fisheries.  The rainfall that is absorbed by the roots of trees is transpired by the leaves into the air where it rejoins the water cycle to be returned to the land as rainfall.  When the trees are destroyed, the water cycle is interrupted in that location and rainfall is reduced. 

In some cases, the loss of trees had a more immediate, observable effect on the society.  On Easter Island, for example, the loss of trees quickly meant the loss of their main source of food:  fish.  Easter Island was the most easterly of the islands inhabited by Polynesians.  It was far from any other island.  Therefore, when their trees were gone and their boats eventually fell apart and could not be replaced, they had no means of fishing from their rocky shores.  (see video)

Likewise, the Norse population in Greenland eventually starved to death when they could no longer grow the hay needed to keep their cows alive.  In this frigid climate, they had used all of their trees as fire wood for warmth and to pasteurize the milk that was their principle food source.  As their fuel source diminished, they burned the peat that fed their cows. 

In both cases, as well as in others, these societies made choices that eventually contributed to their demise.  The failure of their societies was not inevitable.  On Easter Island, for example, the Polynesians chose to cremate their dead, unlike other Polynesians who bury their dead.  And they devoted much of their time, effort, and resources to building the gigantic stone tributes to their ancestors.  These stone sculptures were carved in quarries and then transported many miles by rolling them on logs.  These cultural uses of wood were not essential to the islanders’ physical survival.

Easter Island, Wikimedia Commons

In Greenland, the Norse brought the cows from their homeland that were central to their culture.  Their lives were devoted to keeping their cows alive by spending the brief summer growing the hay to feed the cows during the long winter in the huge stone barns in which the cows were protected from the extreme cold.  The milk had to be boiled to prevent it from spoiling.  As they depleted the wood needed to boil the milk, they simultaneously destroyed the land needed to grow the hay to feed the cows by burning the peat and causing erosion. 

Meanwhile, the Inuit neighbors of the Norse made other choices that enabled them to survive in the harsh climate.  They hunted whales and seals that were their principle food as well as the source of oil that heated their homes.  The Norse considered the Inuit enemies with whom they did not interact or trade.  Therefore, they were unable to learn these survival skills from them. 

Diamond contrasts these histories with those of cultures that have made other choices.  One of the most dramatic examples is the island of Hispaniola, shared by the nations of Haiti and the Dominican Republic.  Haiti is almost entirely deforested and its ability to feed itself is destroyed by erosion.  In contrast, the Dominican Republic is heavily forested because of a strong commitment to its forests made by its leadership.  There are intervening factors, to be sure, but the deforestation of Haiti is a major factor in its impoverishment. 

Diamond’s book intends to challenge us to look at the choices we are making for our own society.  He asks and answers the rhetorical question, “Why did these societies make choices that contributed to their failure?”  The short answer to that question is that long-term goals were sacrificed to short-term goals and that entrenched cultural practices were incapable of responding to changed conditions.  When you are freezing cold today, you might choose to burn your last tree even if it means you don’t have any wood tomorrow.  And when your entire diet is based on milk you can’t conceive that eating whale blubber may be a better choice for your long-term survival.

Million Trees sees these poor choices made by failed societies as similar to the poor choice that is now being made here in the Bay Area to destroy our non-native trees because we prefer native plants and trees. 

We live in a place in which there were few trees prior to the arrival of Europeans.  The landscape goal of native plant restorations is therefore grassland, scrub, and chaparral.  Native trees are unlikely to survive in most of the places which are now forested by non-native trees.  Native trees are being killed by Sudden Oak Death and bark beetle. Their historic ranges are changing in response to climate change.    Releasing carbon sequestered in the trees and eliminating that source of carbon storage in the future will contribute to the greenhouse gases that result in climate change.  Erosion is a likely consequence.  Rainfall could be reduced by the absence of trees.  Denuding our landscape of non-native trees is likely to result in a barren, weedy mess.

Grizzly Peak Blvd is being undermined by erosion resulting from clear-cutting of non-native trees

We urge native plant advocates to re-examine their demands for the destruction of non-native trees and plants in light of the changing climate which is exacerbated by deforestation.  As Jared Diamond says as he concludes his book, “The other crucial choice illuminated by the past involves the courage to make painful decisions about values.  Which of the values that formerly served a society well can continue to be maintained under new changed circumstances.”  

We do not ask that native plant advocates abandon their preference for native plants.  We encourage them to plant more native plants.  We ask only that they quit destroying those that are not native.