“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. 

Retreat from invasion biology becomes a stampede

The New Wild by Fred Pearce (1) is the third book to be published in three years which challenges the conventional wisdom that native species are inherently superior to non-native species and the closely related corollary assumption that all non-native species are competitors of native species.  These are the assumptions that underlie invasion biology.  Each book has been progressively more pointed in its criticism of this ideology, masquerading as a scientific discipline.

Rambunctious Garden

Rambunctious GardenThe first book to be published in 2011—Rambunctious Garden by Emma Marris (2)—was timid in its approach in comparison to The New Wild.  Ms. Marris visited “restoration” projects all over the world.  She described unsuccessful efforts to eradicate non-native plants and animals as well as extreme attempts to “rewild” that are often a mishmash of plant and animal species from different native ranges and time periods.  She implied that these projects were futile as well as artificial, but she was not explicitly critical.  Despite her cautious approach, she has been subjected to intense criticism from both academics and practitioners of invasion biology.   The following excerpt of a reader’s review of Marris’s book found on Amazon.com is typical of the criticism:

“Earth as cookie jar”

“Emma Marris, the author of Rambunctious Garden (RG), loves the nature hiding in back street alleys and along the highway median strip. Marris believes it’s time to abandon (or de-emphasize) what she sees as outdated and naïve conservation strategies such as creation of national parks and wilderness reserves. She feels the biggest obstacles to a bold new world of “designer” and “novel” ecosystems is the “wilderness cult” that naively wants to preserve “natural” landscapes–which she says do not exist anymore.

Marris espouses the anthropocentric perspective that the Earth is more or less a resource cookie jar for humans–to be used carefully to be sure–but she doesn’t really question whether ethically or ecologically this is ultimately a good idea…

However, by moving the goalposts to vacant city lots as an acceptable desired future condition of the landscape, she implicitly, if not explicitly, provides cover for all manner of environmental degradation.”

Most of the 35 readers’ reviews about Rambunctious Garden on Amazon.com are equally critical.  This particular review was rated as “helpful” by 141 other readers and 21 comments were also posted in support of the critical review.  Marris and her book have been thrashed in many other venues, including conferences where she is called out by name as an enemy of nature by invasion biologists.

Where do camels belong?

Where do camels belongThe second book, which challenges the assumptions of invasion biology, was published in September 2014.  Where do camels belong? by Ken Thompson, a British academic, (3) is much more explicit in its criticism of invasion biology.  One of its strong suits is the examples of the ambiguity and absurdity of the often muddy distinction between native and non-native.  As we might expect, this distinction is less clear in Britain because it has a much longer history of “invasion” than North America (only because invasion biologists have chosen to define “native” in North America as any species that precedes the arrival of Europeans).  Professor Thompson offers some comic examples of how status as a native has been conferred in Britain and the contortions that are required to provide preferential treatment to these “natives.”

Despite kicking up the level of criticism of invasion biology a notch, reviews of Professor Thompson’s book are far more positive than those of Ms. Marris’s book.

The New Wild

The New Wild was published in the US in April 2015.  Fred Pearce does not pull his punches in The New Wild.  He methodically lays out all the reasons why invasion biology no longer deserves the status of a scientific discipline.  The readers of Million Trees are familiar with all of these arguments, so we will summarize them here and provide links to articles on Million Trees that illustrate each issue:

Although The New Wild is a full frontal assault on invasion biology, it has been very favorably received by reviewers on Amazon.com.  Here is a review by a reader for whom the book was an epiphany:

“An important—even essential—look at our global challenges”

“Let me cut to the chase: read this book. I want to follow that statement with several exclamation points, but I’m trying to control my enthusiasm. Perhaps the book seems so important to me because I was so ignorant when I first started reading it. Perhaps my level of ignorance is extraordinary, but I just checked the websites of several environmental organizations I respect and it looks to me like they too need to read the book. Certainly it is provocative, controversial, and challenging. It will anger some, but it is not an ad hominem attack against anyone. Whatever you think of Fred Pearce, Daniel Simberloff, and others on either side of this debate, it is clear that the debate is important, even urgent. It made clear to me that I have put too much faith in environmental organizations to ferret out the facts and explicate the issues for me. Clearly, I have allowed myself to be misled. Even more important, scientific standards are not being rigorously followed. Have you noticed the headlines about all the “invasive” species that “need” to be eradicated? About the billions of dollars that are required to do this purportedly important work? I have been asking why so much killing is necessary. Pearce states that it isn’t. In fact, he goes further and suggests that the species targeted for eradication may be our salvation precisely because they have the adaptability and resilience to survive in environments disturbed and dramatically changed by mankind. His arguments are articulate and persuasive.

Environmental writers and organizations sometimes make conclusory and inflammatory claims about the damage done by those species they choose to characterize as invasive. And supporters such as myself accept those claims unquestioningly. As Pearce points out in his eye-opening treatment of the subject, too often one environmentalist repeats or even amplifies the unsubstantiated claims of another, and when this happens again and again with no one questioning the science along the way, dangerous, counterfactual conclusions are spread and soon become gospel. Pearce’s probing, incisive exploration into several of those claims in his seventh chapter, “Myths of the Aliens” is alone worth the price of the book.

Pearce woke me up. I respect the scientific method and believe it must be adhered to without fail in environmental writings. I have naively accepted that other environmentalists feel the same. We cannot make intelligent decisions if we are uninformed about true facts. False allegations have no value for any of us. “Invasive” species need new, clear-eyed, unbiased consideration by environmentalists. We need to look again at our underlying assumptions. What does “native” really mean? Which species are natural to an area? Which can survive in the “wild”? Pearce asserts that there is a “New Wild” and that we will do better to respect it sooner rather than later, to work with it rather than against it. I learned so much from Pearce not only about the facts of our situation, but also about new ways of looking at our extremely challenged world. I highly recommend this book and hope you get the opportunity to read Pearce’s insightful and creative ideas.”

This reader understands for the first time that the environmental organizations he/she had previously trusted had misled him/her into believing that non-native species are the cause of environmental damage rather than symptoms of that damage.  He/She was always uncomfortable about all the killing that was motivated by that viewpoint, which is perhaps what opened his/her mind to Pearce’s message.  This sequence of realizations describes my own journey to the other side of invasion biology.  I was initially appalled by the killing, but I did not realize that the justification for the killing was entirely bogus until I began to do my own research.  I initially assumed that they knew what they were doing.  After reading innumerable books and studies, I began to understand that there is little evidence supporting their claims that non-native species are damaging the environment.  Quite the opposite is true.  We hope that Pearce’s book will start many other readers on the same journey of discovery.

(To be fair, the first critique of invasion biology was Invasion Biology:  Critique of a Pseudoscience by David Theodoropoulos, published in 2003.  Although it was ahead of its time, virtually every criticism of invasion biology in that book remains true to this day.  However, at that point in time there were few empirical studies testing the hypotheses of invasion biology and few “restorations” based on those hypotheses.  It was therefore more difficult to make the case against invasion biology.  Theodoropoulos foretold the fate of invasion biology as a discredited ideology based primarily on his personal observations in nature.)


In just three years, three hard-hitting books have been published which confront the unfounded assumptions of invasion biology.  Although each book is progressively more aggressive and explicit in its criticism, the reaction of the public has been progressively more positive.

We admired all three of these books, so we are reluctant to conclude that the more favorable reaction to the more recent books is because of improved quality.  Perhaps the more explicit criticism of the more recent books makes it easier for readers to appreciate the strength of the argument.  Although we are deeply grateful to Emma Marris for leading the way, Rambunctious Garden requires the reader to reach the conclusion she only implies. The New Wild makes no such demands on the reader’s judgment.

However, we have our own optimistic theory about why readers are welcoming The New Wild.  The more experience the public has with the destructive projects which attempt to eradicate non-native species, the more likely they are to understand the futility and the damage being done to the environment.  We choose to interpret the positive reception for The New Wild as an indication that the public is ready to abandon the fantasy of returning our public lands to some mythical ideal landscape.

  1. Fred Pearce, The New Wild, Beacon Press, April 2015
  2. Emma Marris, Rambunctious Garden, Bloomsbury, 2011
  3. Ken Thompson, Where do camels belong?, Greystone Books, 2014