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Decades of satellite imagery and inventories of the world’s forests have painted portraits of change, the result of human activity in very recent times. Yet the trees and forests captured by any modern technology or on-the-ground efforts are only momentary snapshots of the Earth’s deep history.
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The fossils and petrified pockets of plant matter reveal the stories of life long ago. The past still shapes the present and future too.
If any period has drawn the most widespread intrigue (apart from the Jurassic, that is, as everyone loves dinosaurs), it is the Carboniferous, which began more than 350 million years ago. Its miry forests, primitive, lizard-like reptiles, amphibians with massive skulls, and dragonflies with meter-wide wing spans capture the imaginations of children and adults alike. Oxygen levels were much higher than they are today, maybe also partially explaining the jumbo size of creepy-crawly insects back then.
The curious plant life had a high rate of turnover, meaning vegetative communities changed in waves as new members emerged and others disappeared. Paleobotanists, who study the evolution of plants, continue to debate the details.
But I look back to that period as proof positive that trees can sequester emitted carbon, given that trees were the source of coal. What happened millions of years ago unexpectedly set the stage for the warming world that we face today.
What happened millions of years ago unexpectedly set the stage for the warming world that we face today.
From the Latin carbo (“coal”) and fero (“to bear” or “to carry”) we get carboniferous, or “carbon-bearing.” The trees of these lost forests and a collision of many factors over millions of years gave this age its greatness. What we think of today as the green above became the coal deep below, to be discovered much later, then prized and pursued. Our machines mined the black gold and put smoke in the sky, revolutionizing the world and altering the atmosphere.
When I asked Kevin Boyce, a renowned paleobotanist at Stanford, for the best description he’s come across of the forests from the Carboniferous, he laughed and said, “Dr. Seuss. You know, The Lorax.”
I chuckled too, remembering the lollipop trees from the classic Dr. Seuss book from the 1970s that chronicles the plight of the environment. In the story, the Lorax character “speaks for the trees” and confronts the Once-ler, who clears all the Truffula trees to make Thneeds, these things that no one needs.
“Except, you couldn’t make thneeds out of those,” Kevin added, smiling.
But we did, kind of. We burned those trees—billions of them, maybe more—after they became coal.*
What a forest was then is not what a forest is anywhere now. Green stalks stood like colossal asparagus spears in a swampy landscape; they could reach over 100 feet in height and six feet in diameter at the base. These were the arborescent lycopsids, members of a group of the oldest vascular plants.
Those enormous trees have only minute relatives living today. I mainly know them as members of the Lycopodium genus, but there are others too.
I spent a few summers studying plant communities in Alaska for my PhD about a decade ago; those clubmoss relatives with creeping stems were the tiniest species that we recorded. In the Carboniferous, the lycopsids grew tall, making for the sky and spending much of their lives as verdant poles with thick, scaly bark, like the skin of a flightless dinosaur.
These Dr. Seuss–like forests were replete with intriguing characteristics that have been revealed over time through well-preserved specimens found fossilized underground. The complex root system of a “scale tree” had tubular structures woven underground; they could sprawl over an area nearly eighty feet in diameter, binding sediments below and offering stability to the trunk above.
Unlike many trees today, these individuals didn’t offer much shade. Some lycopsids reproduced just once in their lives. Their stubbly crowns unfurled only as they approached their old and dying days. They grew, grew, grew, reproduced, and then died in their grandeur. They looked different from the living trees that he and I now know, but they were still lungs for the planet, drawing in carbon dioxide and releasing oxygen.
Between about 330 million and 260 million years ago, the highest rates of global organic carbon burial over the past half billion years occurred. That was due, in large part, to the accumulation and burial of peat—the rich, black and dark brown spongy material formed by partially decomposed organic matter in low-lying basins. For about nine million years, the bark of the lycopsids was the single greatest contributor to what became coal.
Even after all the reading I’ve done about the forests of long ago, I still must remind myself that “then” is on a timescale very difficult for most human minds to fathom (mine included). Just as “now-ish” for some paleontologists can mean the last fifty million years, “then” occurred across millions of years.
The trees didn’t all fall down for burial in one dramatic event and then (ta da!) there was coal. Instead ideal conditions came together repeatedly across time. Wet tropics fostered productive forests. There were rain and swamps and cool conditions. Glacial periods came and went, intermittently flooding and drying out the landscape. And the bark of those trees was like concrete, more resistant to decay than anything else.
Bill DiMichele, a paleobotanist at the Smithsonian Institution’s National Museum of Natural History who has spent his career studying the Carboniferous, noted that the lycopsid bark was “the plastic of its day,” accumulating even when everything else was decaying away. During the wettest of times, what got buried below faced a waterlogged world and prime conditions for preservation.
The configuration of the continents was also key. Lands that we know as separate today were contiguous as one massive terrestrial surface—Pangaea, the megacontinent—creating opportunity for burial.
“It was a bunch of continents banging together, which makes mountains,” Kevin told me. We were meeting in his office on the Stanford campus. In the adjacent meeting room was a shelf full of coal balls, black lumps of petrified plant matter found in coal beds—each sample discovered in serendipity, each offering clues to the past.
Whenever mountains uplift, basins form. So, there was this perfect intersection of climate and other factors that enabled tropical organic matter to be buried and preserved. The basins would fill up just as fast as they were subsiding. All of this happened very, very slowly in terms of human time (as opposed to geologic time).
“It’s like you’re accumulating centimeters per century,” Kevin explained.
Basically, it would never look like anything at one point in time; there’s no hole to fill. It’s just the basin bottom dropping out as it’s filling at the top, so that stuff is accumulating rather than being eroded away. There are sedimentary basins in the world with ten kilometers of sediment in them, but that doesn’t mean there was ever a hole ten kilometers deep.
As the basins formed, there was always something to fill them. The carbon-rich trees played that role, becoming buried treasure for people millions of years later. The use of that buried treasure would also become a leading contributor to the unexpected calamity—the warming world.
Coal is the dirtiest of the fossil fuels on many levels; its consumption also has detrimental effects on human health. Between 1850 and 2020, almost half of global CO2 emissions came from coal, more than any other single source.
Now what? People are turning to trees again but, this time, to their thriving verdant form instead of the coal formations that they helped create. They want more trees to absorb carbon dioxide from the atmosphere.
We’ve come full circle in a relationship between people and trees—from where using what was buried became a source of emissions to where the already-standing or freshly planted trees could be our saviors, drawing down carbon through a natural solution. People are chasing after a hope-filled possibility that trees might just help get us out of this mess.
We’ve come full circle in a relationship between people and trees—from where using what was buried became a source of emissions to where the already-standing or freshly planted trees could be our saviors, drawing down carbon through a natural solution.
The Earth has always been in some sort of disequilibrium with volcanic eruptions, rock weathering, changes in sunlight, and other forces driving changes in the climate system. But human activities are pumping about a hundred times more carbon dioxide into the atmosphere than volcanoes do each year; it’s the rate and magnitude of the current disequilibrium that puts the lives of people and many other species in grave danger.
“As long as we’re in disequilibrium, which we are, because humans are a source of disequilibrium, then growing forests matters,” Kevin said.
There is no way for trees to offer the whole solution, but I agreed with him. They have a role to play. Coal and the carbon that it contains accumulated over tens of millions of years.
Forest clearing by humans occurred much later in a relatively teeny sliver of time. The burgeoning interest in planting or replanting forests arises in an even narrower window. Those involved, myself included, sense the clock is ticking.
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Excerpted from Treekeepers: The Race for a Forested Future by Lauren E. Oakes. Copyright © 2024. Available from Basic Books, an imprint of Hachette Book Group, Inc.
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