Missing the Ecosystems for the Trees

"Will planting trees get us out of our climate pickle? Not entirely. But it could increase the world's natural drawdown of atmospheric carbon by 25%."

Most mornings when I get up I check the weather. I’d like to know what it will be doing so I can plan my day around that.

Even after all these years of observing patterns, I am often surprised. I will walk out on my deck and look at the mercury and it reads ten or fifteen degrees below what my Apple Watch tells me the temperature should be. The watch gets its data from a local weather sensor, likely somewhere near the Post Office in town. The thermometer on my deck is reading its temperature 20 feet above ground in an oak forest.

Inside, during the heat of the day, the air will be ten degrees below even the forest because I have a living roof and the green mossy cover works exactly the same way a refrigerator does, dropping coolth into the enclosure as overnight dew is wicked and evaporated.

Transpiration is one of the cooling effects of a forest. So is photosynthesis. A single oak tree may have one million leaves and a solar collecting area of two acres. Using sunlight for energy, it draws carbon dioxide from the sky, reserves the carbon and sends the oxygen back. We are all told as children that this is a reciprocity arrangement we have with plants because we are air breathers and need that oxygen. We mammals draw in oxygen, add carbon from our bodily wastes, and then exhale the CO2. Trees gratefully accept that carbon and add girth.

The tree has carbon waste too. Some of the CO2 it inhales, as it were, goes into leaves, bark, branches and roots, but nearly half—more than 90 percent in the case of a bamboo forest—is excreted into the soil. In a bamboo forest that carbon pool is very shallow because bamboo’s roots do not run very deep. In an oak forest like mine, the roots extend down until they hit bedrock or perhaps as deep as the tree is tall if there is no rock encountered. That carbon pool—the sugar “exudates” the tree exchanges with root nematodes and soil microbes for calcites, nitrates, sulfates, and trace minerals the tree needs—is in a labile form of carbon and so will move through the soil food web, some returning to the surface and possibly being released by bacteria and fungi to the sky, and some going even deeper into the soil profile, not to return to the atmosphere again for millennia, if ever.

Trees die. They will fall over and be decomposed by worms, fungi, and myriad soil creatures. They will become food for countless generations of primary decomposers and soil builders. Sometimes they will be blown over by a windstorm, toppled by ice, or consumed by fire. The result is the same—they return most of their aboveground carbon to the sky from whence it came. Below ground, the carbon lingers. Decades pass. Centuries. Although it may cycle amongst many different life forms, it is still there. Trees are a carbon pump and much of that goes down, not up.

Often it is argued by anti-tree people (yes, they exist) that not only are trees only carbon neutral at best, not carbon-negative (which I just rebutted), but that forests can only scale a little—far less than what is required to restore Earth’s carbon balance—because they will compete with farms, cities, parks and grasslands.

There are several reasons why this reasoning is wrong.

Reforestation opportunities abound on nonagricultural lands such as post-disturbance forest areas, abandoned mine lands, abandoned farmland, roadsides, parks, and urban areas. There is more than enough of that kind of land to accommodate a few trillion more trees.

Forest carbon management practices such as restocking understocked stands, reducing the risk of catastrophic wildfire, low-impact logging, active replanting, and biochar or silvicultural practices that improve growth expand the potential of even smallholdings.

Agroforestry integrations boost benefits for rural economies and build soil carbon without shifting land uses away from family farms. They improve small farms’ bottom lines.

 

Carbon stock in aboveground woody biomass (in green), litter (in grey), and soil (in orange) in the different successional stages. The relative contribution (in %) of each carbon pool is reported for each successional stage.

Counting the Trees

Trees currently sequester 16 billion metric tons of CO2 annually, according to a study in Nature Climate Change. Sadly, that is relying on the fragmented 1-2 trillion trees that remain from the 6 trillion or more that we had after the last ice age. If human emissions were reduced to less than 16 billion tons, trees would zero them out (although they are already tasked with emissions from volcanoes and other natural sources, so let's not Bogart the sink). Thanks to land clearing, wildfires, and the burning of wood products, forests emit an estimated 8.1 billion tons of greenhouse gases back into the atmosphere, roughly half their potential capacity to store. We can definitely improve on that. Even as we reduce emissions by building solar and wind substitutes for fossil fuels, we can reduce land degradation by learning how to benefit from and protect living forests.

In 2019, a team at ETH Zurich estimated in Science that around the globe, there are 900 million hectares of land — an area about the size of the United States — available for planting new forests and reviving old ones without impinging on farmland, parks or urban areas. Every trillion trees planted there would trap about 206 billion tons of carbon (755 GtCO2). Another study reported that the carbon uptake potential of letting forests regrow naturally has been underestimated by at least a third—as much as 53% in the tropics.

Trillionization

 

In January 2020, the World Economic Forum launched the One Trillion Trees Initiative, a global movement to grow, restore and conserve trees around the planet. One trillion is also the target for other organizations that coordinate global reforestation projects, such as Plant-for-the-Planet’s Trillion Tree Campaign and Trillion Trees, a partnership of the World Wildlife Fund and Wildlife Conservation Society. Given we are 3 to 5 trillion trees shy of what grew a few thousand years ago, I consider one trillion a good start, not the end goal.

It is sometimes argued that as soils warm, forests may go from net sequesters to net emitters. Forests in Southeast Asia now emit more carbon than they absorb due to clearing for plantations and uncontrolled fires. The Amazon’s forests may flip from carbon sponge to carbon source for the same reason. Preventing new deforestation in the Amazon would reduce the area burned by 30%, and shrink emissions of carbon dioxide and other gases by 56%. This is not about climate change warming the soil and causing outgassing. It is about wildfires from recent and ongoing human-caused deforestation. Forests actually cool soils, as I can attest just by standing on my deck on a hot day.

Shade from a tree can cool surfaces underneath by 20-45°F compared to unshaded areas. The Tree Equity Score online tool shows that the lowest-income neighborhoods have 29% less tree cover, making them 7°F hotter. Neighborhoods with the highest percentage of people of color, regardless of income, have on average 40% less tree cover and are 10 degrees hotter.  When Phoenix discovered this in 2021, the City Council began a program of “tree equity,” placing trees within 100 carefully selected “cool corridors” to provide shade for walking, biking, and public transit stops. 

In a 2019 study in Nature, it was estimated that if all 350 million hectares pledged under the Bonn Challenge were allowed to regrow natural forest, 42 GtC (154 GtGO2) would be withdrawn from the sky and sequestered. Conversely, if the land were to be filled with single-tree commercial crop plantations, carbon storage would drop to about 1 GtC. Right now, plantations make up a majority of carbon-credited restoration plans. Plantations are not forests.

Climate Ecoforestry

 

In a paper I wrote with Frank Michael a decade ago, we estimated planting forests over 200 MHa/y (an area equivalent to 4 Spains) could sequester 11 GtCO2e/y in the emergent phase and ~50 GtCO2e/y at equilibrium. The later ETH Zurich study scaled our ambitions back from 4.8 GHa to 0.9 GHa, so 10 gigatons of annual drawdown, not 50.

Our mental exercise assumed 10,000 saplings and ~5 tons of biochar per hectare with a rotational, selective patch harvest of mixed-aged, mixed species, 90 percent of which eventually went to biochar. Once you reach the maximum land extent, the system is cyclical and continuously productive, as I will illustrate more from the example I’ll write about next week. Also, as I will describe in later installments, land is not the only part of Earth you can reforest.

Our model found that continuing rotational cycles at 200 Mha/yr on the same land would sequester a cumulative 667 GtC, the amount of carbon required to bring atmospheric CO2 back to 300 ppm by year 56. With reductions in fossil fuel emissions, 300 ppm could be achieved in years 45 to 48. If the rate of implementation were raised to 300 Mha/yr, the goal of 300 ppm would be reached in years 35 to 37 from startup.

Unfortunately, if the newer ETH Zurich’s numbers are accurate, we have to lower our sights by four-fifths, to 125 GtC removal (460 GtCO2e), and we won’t get back to 300 ppm for some centuries.

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Here is Carl Sagan, in 1985, explaining the greenhouse effect in a way you may never have heard before: 

Even as the enthusiasm for tree planting takes root in the policy world, there’s a growing awareness among researchers and conservationists that local community engagement must be built into any plans. It’s indispensable to their success.

On November 11, 2019, National Forestation Day, volunteers across Turkey planted 11 million trees at more than 2,000 sites. In the Çorum province, 303,150 saplings were planted in a single hour, setting a new world record. Within three months, however, 90% of the new saplings were dead from to a combination of insufficient water, lack of expertise, and because they were planted at the wrong time of year. Similar horror stories abound.

The plan has some prominent backers. President Donald Trump announced in 2020 that the United States would join a global initiative to plant a trillion trees, despite his antagonism toward climate science.

— Washington Post

These massive tree-planting efforts didn’t have to fail. They just missed the ecosystems for the trees. A study published in Bioscience found:

People-centered climate solutions will be the most effective natural climate solutions because they will align conservation goals and the interests of the rural people responsible for managing ecosystems. Natural climate solutions that count saplings rather than address both the ecological and social drivers of ecosystem destruction are unlikely to succeed.

In Braiding Sweetgrass, Robin Wall Kimmerer wrote:

Just as old-growth forests were richly complex, so too were the old-growth cultures that arose at their feet. Some people equate sustainability with a diminished standard of living, but the aboriginal people of the coastal old-growth forests were among the wealthiest in the world. Wise use and care for a huge variety of marine and forest resources allowed them to avoid overexploiting any one of them, while extraordinary art, science, and architecture flowered in their midst. Rather than to greed, prosperity here gave rise to the great potlatch tradition in which material goods were traditionally given away—a direct reflection of the generosity of the land to the people. Wealth meant having enough to give away—social status elevated by generosity.

Will planting trees get us out of our climate pickle? Not entirely. But it could increase the world's natural drawdown of atmospheric carbon by 25%. I’ll take that.

That’s like dropping a 426 hemi into your 1969 GTO.

In the weeks to come we will look at ways to get at that other third; natural solutions such as marine forestry, biochar, remineralization, and whales. This is not to say we won’t need every tool in the kit. Let’s not count any of them out.

Next week we’ll tell the story of a man who planted a million trees in Missouri at the start of the 20th century, and what we’ve learned from his small, personal experiment.

References

 

Fleischman, Forrest, et al. "Pitfalls of tree planting show why we need people-centered natural climate solutions." BioScience 70.11 (2020): 947-950.

Badalamenti, Emilio, et al. "Carbon stock increases up to old growth forest along a secondary succession in Mediterranean island ecosystems." PLoS One 14.7 (2019): e0220194. https://doi.org/10.1371/journal.pone.0220194.g002

Bastin, Jean-Francois, et al. "The global tree restoration potential." Science 365.6448 (2019): 76-79.

Bastin, J. F., et al. "Erratum for the Report:" The global tree restoration potential" by J.-F. Bastin, Y. Finegold, C. Garcia, D. Mollicone, M. Rezende, D. Routh, CM Zohner, TW Crowther and for the Technical Response" Response to Comments on 'The global tree restoration potential'" by J.-F. Bastin, Y. Finegold, C. Garcia, N. Gellie, A. Lowe, D. Mollicone, M. Rezende, D. Routh, M. Sacande, B. Sparrow, CM Zohner, TW Crowther (vol 368, eabc8905, 2020)." Science 368.6494 (2020).

Bates, A., Climate Ecoforestry, Resilience (March 7, 2017).

Cochrane, J. 10 Trends Carbon Market Experts are Talking About Right Now (2023)

Lindsey, Rebecca. "Climate and earth’s energy budget." NASA Earth Observatory 680 (2009).

Lewis, Simon L., et al. "Restoring natural forests is the best way to remove atmospheric carbon." Nature 568.7750 (2019): 25-28.

 

 

Meanwhile, let’s end this war. Towns, villages, and cities in Ukraine are being bombed every day. Ecovillages and permaculture farms have organized something like an underground railroad to shelter families fleeing the cities, either on a long-term basis or temporarily, as people wait for the best moments to cross the border to a safer place or to return to their homes if that becomes possible. There are 70 sites in Ukraine and 500 around the region. As you read this, 24 Ukrainian ecovillages have given shelter to more than 2500 people (up to 500 children) and now host up to 1400 persons (around 200 children). We call our project “The Green Road.”

For most of the children refugees, this will be their first experience in ecovillage living. They will directly experience its wonders, skills, and safety. They may never want to go back. Those that do will carry the seeds within them of the better world they glimpsed through the eyes of a child.

Those wishing to make a tax-deductible gift can do so through Global Village Institute by going to http://PayPal.me/greenroad2022 or by directing donations to greenroad@thefarm.org.

There is more info on the Global Village Institute website at https://www.gvix.org/greenroad or you can listen to this NPR Podcast and read this recent article in Mother Jones. Thank you for your help.

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The COVID-19 pandemic destroyed lives, livelihoods, and economies. But it has not slowed climate change, a juggernaut threat to all life, humans included. We had a trial run at emergency problem-solving on a global scale with COVID — and we failed. 6.95 million people, and counting, have died. We ignored well-laid plans to isolate and contact trace early cases; overloaded our ICUs; parked morgue trucks on the streets; incinerated bodies until the smoke obscured our cities as much as the raging wildfires. The modern world took a masterclass in how abysmally, unbelievably, shockingly bad we could fail, despite our amazing science, vast wealth, and singular talents as a species.

Having failed so dramatically, so convincingly, with such breathtaking ineptitude, do we imagine we will now do better with climate? Having demonstrated such extreme disorientation in the face of a few simple strands of RNA, do we imagine we can call upon some magic power that will arrest all our planetary-ecosystem-destroying activities?

As the world emerges into pandemic recovery (maybe), there is growing recognition that we must learn to do better. We must chart a pathway to a new carbon economy that goes beyond zero emissions and runs the industrial carbon cycle backward — taking CO2 from the atmosphere and ocean, turning it into coal and oil, and burying it in the ground. The triple bottom line of this new economy is antifragility, regeneration, and resilience. We must lead by good examples; carrots, not sticks; ecovillages, not carbon indulgences. We must attract a broad swath of people to this work by honoring it, rewarding it, and making it fun. That is our challenge now.

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