Twelve Trees: The Deep Roots of Our Future

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For Pam

My rooting force

My pocketful of joy

My dazzling, gathering light

PREFACE

Between every two pine trees there is a door leading to a new way of life.

—John Muir¹

Afew years ago in Melbourne, Australia, nearly half of the city’s seventy-seven thousand trees were struggling, plagued by drought and other difficulties. City planners mapped all of the trees, gave them individual IDs, and assigned email addresses to each tree so citizens could report problems. This plan was a practical attempt designed to rehabilitate an urban forest. But along with reporting problems, people wrote thousands of love letters—treemail—to their favorites. One fan wrote to an elm, As I was leaving St. Mary’s College today I was struck, not by a branch, but by your radiant beauty. You must get these messages all the time. You’re such an attractive tree. Other responses by the thousands ranged from bad tree jokes to love letters to expressions of concern—not only from Melburnians but from all over the world, often from expats who once lived in the city, or people who’d never visited. A New Yorker wrote to say, You are loved and deserve the world. People asked for advice. I write about a friend of mine… someone who has reached an intersection in life. To the outside world he has control, but within it can feel like a labyrinth with too many possible pathways, all without much clarity or light. How can I help him during this time of decision and indecision?

Every tree has a life, both individually and as part of a collective. I’ve chosen twelve trees that have been on long journeys, have many accomplices as well as enemies, and need our help to survive. They are our instructions, our instruments, and our futures. I’ve picked these trees in the ways that people find friends. In significant ways, they have found me. Some were flashy and omnipresent. A few arrived quietly in unexpected corners of my life, and some were introduced by others—but all started as relative strangers and became comrades. Each has crucial stories to tell.

Trees continue to populate our daily lives. They’ve been part of our sight lines and metaphors, our byways, our contexts. We all know them in one way or another, as consumers and users of their wood and by-products, or through closer associations with individual trees. We all know trees that grew up with us as children. Trees in parking lots, bristling with tiny unseen life, or ones that we witnessed falling, or helped to fell. Trees we hid under for shelter in the rain, or in baking heat. Trees whose smells and sounds and sights trigger deep memories. Trees that sat outside our houses and marked the seasons, losing foliage and growing back, or extending a limb to the windowsill so we could risk climbing down, to a wider, freer world.

Trees are symbionts, working in conjunction with an army of other organisms that build biodiversity and buttress life on the planet. They are ecosystems that sustain life in and among their roots, trunks, branches, and crowns. Forests also regulate our food security, feeding the planet through a profusion of fruits, vegetables, nuts, spices, and other edibles, as well as our medical needs. Trees provide urban identity, splendor, cooling, and coherence. They need to have their own rights, and be accorded their own dignity. They are essential to all of our lives, and they need our help. The salvation of trees can be the salvation of humans.

The Quran has its Tree of Immortality. Besides people and God, trees are the living beings most frequently mentioned in the Bible. Buddhism has dozens of words for trees. They are everywhere in the close and far corners of the world’s languages. We borrow their metaphors (we go out on a limb; we knock on wood; we can’t see the forest for the trees; we branch out; we find root causes; we’re stumped; and we leaf through books). Every language has its tree idioms. The Japanese say, Even monkeys fall from trees; that is, everyone makes mistakes. In Germany, when someone says something embarrassing and no one dares to respond, they say, There is silence in the forest. We have written about, scrutinized, illustrated, photographed, climbed, contemplated, and cared a great deal about trees for a very long time. They serve as sentinels to our lives, deaths, and rebirths. They live in deep literary contexts, their roots everywhere. The poet Wendell Berry described his writing house, built up on wooden posts, as having a peering, aerial look, as though built under the influence of trees.²

The sheer ubiquity of arboreal names also speaks to our cultural desire to signify their importance and to impart some essence of the tranquility and stability inherent in trees. Of the twenty most common street names in the United States, five are trees: Oak, Pine, Maple, Cedar, and Elm. We record them like scribes copying manuscripts, over and over again: holiday cards and directions and job applications and passwords. Larch and birch and oak and arbor. In my adopted state of California, the word wood shows up on the signs of fourteen thousand different streets. They are the nomenclatural currency of our lives, these tree words, and we find our way home through them.

Trees are also our custodians, forecasters, and predictors in an era of changing climates. They protect the ground beneath us through their stabilizing and biodiversifying effects. They lower our pulses and deepen our breath. These twelve species of trees are powerful actors on our environment. In their total biomass they provide nearly bottomless carbon sinks, annually sequestering millions of tons of carbon dioxide—a greenhouse gas that would otherwise remain in the atmosphere or leach into the Earth’s oceans, heating the planet more rapidly. Their work with CO2 is also easy to misunderstand: although it’s often spoken of as a global evil, trees need it to live. Trees don’t just house CO2; they use it as they take it in, appropriate it for photosynthesis, and produce oxygen.

These twelve trees have an army of assistance from other species of trees, too. Some three trillion trees grow on the planet, about four hundred for each of us. Despite their declines, forests still occupy more than 30 percent of Earth’s dry land. Around the world, trees absorb approximately 7.6 billion metric tons of carbon and sequester it in their leaves, stems, roots, and other parts for long stretches. But young trees don’t do this very well, or at all, depending on the species of tree. To sequester a lot of carbon, trees have to live long and healthy lives: at a minimum, ten to twenty years. It takes that long for sufficient foliage to grow into a sizeable reservoir for carbon. And the longer a tree lives, the more carbon it sequesters, as a promise for the future: trees get bigger as they grow, so every year they sequester a bit more carbon than the year before.

The planet’s three trillion trees constitute around seventy-five thousand species.³

The great diversity among trees speaks to the diversity of life on Earth, and not just biological diversity but the cultural and social diversity they foster. Out of some, many and much. Our intersections with these twelve trees’ lives are far more interesting—and more complicated—than people would ever expect. In the course of understanding their role in our futures, I hope you’ll gain a fuller understanding of not just these specific trees, but the classes of trees in which they’re contained: their cousins and aunts and uncles, as it were; the species with which they share a genus or a family or are otherwise allied, through genetics or morphology or destiny.

The ways their characteristics converge or diverge also tell us something significant about the tumbling, messy nature of evolution, including strategies to survive. Evolution has consequences: every tree came from an earlier plant form. To study the science of trees is thus also to study not just the present. It’s a story of the world and its past, a biohistorical novel. Landscapes from deep time can be restored from pollen data; tree rings can tell us about weather and water and climate from both recent and ancient eras; fossil trees can tell us about the long arc of evolution; and all of this information points to the future.

Across all of these lessons, dangers lurk. Without trees, we would be stripped of a key layer of living tissue, on our way to being Mars or Venus. There are only half as many trees as there were at the dawn of agriculture twelve thousand years ago. Forests burn at the rate of twenty-two thousand square feet a minute in the Amazon; in Central Africa, ten million acres a year disappear. We’re the sharpest predators on the planet, and we have done damage. Trees are at risk from many threats: insect and fungal infestations driven by a warming planet have brought down billions of individual trees, airborne poisons drift into forests, and tides are rising while freshwater tables are dropping. The story of decline is voluminous and complex.

The popular press frequently presents climate change as a monolithic threat, but the science is full of entanglements, time frames, geographies, and contradictions. Almost none of these trees overlap in their ranges—and because every species has different talents, and climate change varies greatly across regions, each of these dozen trees has a different relationship with our planet’s warming and changing weather. Climate change is a part of our past, and our present, and, certainly, our human future, and its urgency has been reinforced countless times in recent years from intersecting disciplines. As the climate scientist Richard Alley noted, the more stately and older view was that climate change moved slowly, like a dial; in today’s reckoning, it’s a switch, almost instantaneous in its effects, especially against the background of deeper time.

Time changes everything, and it’s a partner for all of these trees. Their time frames are largely rendered as a vast evolutionary sweep across the face of the planet’s clock. But eons are made up of days and nights—infinitesimal slices of time in the larger march of life, and trees matter on tiny timescales, too. My father—a quiet man, stormy, unhappy, and dogged—spent some of his most satisfying moments on the sprawling grounds of our house, which stood on a cliff overlooking the Pacific Ocean in Hawai‘i, where he planted ironwood saplings he hoped would grow large enough to stanch the constant erosion of our property into the sea eighty feet below. Many are still there, risen huge. One of my strongest childhood memories was of a tree I helped to remove—a large pandanus in our yard, with tall prop roots that emerged out of the ground, so the tree was on stilts. It was hot, sweaty work, but my dad offered to buy me anything I wanted (within reason) if I helped with the job. It took weeks. He had never offered up this kind of prize, so I was committed to the task. I was eleven or twelve, and I had been pining for a crossbow, and true to his word, my dad ordered one for me that soon arrived at our doorstep. I was thrilled, and then proceeded to fire this weapon high into the trunks of gigantic banyan trees on neighboring properties. The arrows are still there, a half century later. Humans are the tip of the arrow. We have paved the way to decline. Now it’s our chance to pioneer a path to rejuvenation.

CHAPTER 1

A Book Older Than God: The Great Basin Bristlecone Pine

The tree is a slow, enduring force straining to win the sky.

—Antoine de Saint-Exupéry, The Wisdom of the Sands

The Great Basin bristlecone pine is not especially imposing in its height, greenery, or bulk. The tallest known individual is just fifty-two feet high, much shorter than many other mature tree species. It produces no oil, no fruits, no usable wood or other products humans covet or monetize. It needs little water. It’s a twisted refugee, growing only at high altitude in cold, windy, and often icy conditions, and in poor soil. But the bristlecone is a beautiful survivor, and its most ancient individuals, the oldest of all trees, are full of instructions and fascinations.

No one knows how old the oldest bristlecone pine might be. One tree clocks in at more than five thousand years—fifty centuries, validated by careful counting of the rings on cores extracted from the living tree. There may well be older individuals. The bristlecone pine’s longevity is baked into its scientific name: Pinus longaeva. Even its leaves can remain green for nearly a half century before dying. It serves as a crucial witness to the extended arc of the past. Many trees are like old books: they mark the passage of our years, including epochs of turbulence and calm. We can find evidence of these changes in numerous ways, but one key technique to understand their lives, and the planet’s lives, year over year, is to study those annual rings. The seasons’ variations in temperatures between winter and spring show up in the tree’s wood: colder weather means slower growth, and warmer means faster development. When a tree begins this rapid growth, it lays down what is known as earlywood, a pale band in its annual rings. As summer slides into fall, wood growth slows and leaves a darker annual ring called latewood. These and other changes in color and cell density mean tree rings are usually highly visible, and thus countable.

The innards of bristlecone pines, in the form of these growth rings, describe a regular turn from the start of the tree’s story to the present. They tell us not just about their lives but about the life around them. These trees record details to be deciphered by those with eyes and tools to see: changes in wind, weather, precipitation, and temperature, studied by attentive scientists who have the background to make sense of minute and subtle distinctions. There is inference, evidence, speculation, speciation—all visible in the rings of the trees, pages in life’s book.

I work with a fellow rare book curator at the Huntington named Steve Tabor, whom I admire. He’s thin, with a white mustache. He likes birds, and bicycles. Tabor is an authority on early printed books who, with no artifice or arrogance, will drop an obscure Latin phrase into a conversation or an email. He is utterly unselfconscious, often with his foot up on his desk through his open door, stretching. A book scientist, Tabor is deeply involved in the minute changes shown by paper, type, ink, and binding: forensic analysis of the fluctuating ways we’ve produced knowledge over the last five hundred years. He pointed out to me that the Latin word liber—the old common term for a book—means the inner bark or rind of a tree. He also explained a number of the deeper etymological ties between books and trees. The Germanic word for book and its cognates derive from the Indo-European word for beech tree. The etymology and physical presence of books is saturated with trees, and with the ghosts of trees and their remains.¹

The book world offers still other cognates. Paper, bindings, sewing, and leather are all part of the stream of testimony. In the same way that dendrochronologists—scientists who study the rings of trees—can tease out evidence you’d not anticipate, the same applies to old books, where papermakers crafted their products from remnants of cotton clothing, and printers and bookbinders created and assembled their products by hand. Old books are simply teeming with evidence if you have the right context and experience, and this applies to tree rings as well as to old books.

Occasionally, in looking at pages in an antiquarian book, you’ll see a small, splattery dot, as if something wet had once landed on the page. Hundreds of years ago, artisans made paper by macerating cotton rags into a watery slurry, and then dipping a mold made of closely spaced wires into the pulpy mix, and draining out the liquid. But what causes that dot? They’re common enough that these splashy marks have a name: vatman’s tears. A vatman was the person responsible for dipping the mold into the heated slurry of water and pulped cotton rags. It was hot work, and the splash mark most likely came from a wet arm or sleeve, or possibly a bead or two of sweat from the vatman’s forehead.

So paper is not just paper. It tells stories. And trees are not just trees, because their lives are marked by events that occur in the strata of formation. Some of this evidence about the past comes from immediate moments, such as a lightning strike. Other marks stem from longer intervals: a beetle boring through a layer of cambium, an ancient piece of barbed wire from a long-gone fence, or an old bullet buried in an even older tree. But more ubiquitously, trees reveal past details about matters of global interest and significance: changes in the climate; in the constitution of the air, water, and soil; and other environmental variations. Climate hovers in and around the tree, literally and metaphorically, because the changing climate and its effects on all lives on the planet is the existential issue of our time.

If a giant standing in the center of what is now California had cupped some seeds of bristlecone pines in his hands and flung them messily eastward, dropping a few and tossing the rest, you’d have the approximate distribution of the bristlecone pine. Its distribution spills across a strap of higher-elevation land that reaches from eastern California across Nevada and into Utah. The tree grows very slowly, sometimes increasing its diameter a mere inch over a century. It doesn’t like shade, and tends to grow fairly widely spaced, and only at high altitudes, typically above fifty-five hundred feet. This distribution reduces competition with other plants. The extreme environment also slackens other predators’ activities. Wood-rotting fungi have a difficult time getting purchase in the cold, dry, and windy climate. The tree lives in challenging soil, too: rocky dolomitic and limestone-based ground, all of which keeps life inching along.

Just as photographs of Charles Darwin invariably show the old, infirm naturalist with his big white beard, though he was once a young man, so too does the bristlecone pine appear in the public imagination as an oldster, which of course it can become. But it starts as a sapling, then fills out, adding many branches and cones. The tree’s height is limited by moisture stresses at its top; it can pump water up only so high. And the taller it gets, the more exposed it is to drying winds. Some old pines on windy summits are shaped into spectacular positions by relentless winds, which sometimes turn a branch so that it’s pointing toward the ground rather than skyward. In a few locales in the tree’s range, such as on Mount Washington in Nevada, you’ll even sometimes see trees so forced into position that they’ve been subdued into a dense mat of growth close to the ground and unrecognizable as a tree. The term for this type of vegetation is krummholz, from the German crooked wood.²

The tree’s capacity to twist into gnarled forms in response to environmental forces has meant that humans can’t use it for lumber, or for much else. Nevertheless, it retains a right to live, and to succeed.

While humans don’t scavenge the tree, other creatures do. Porcupines girdle the bristlecone by eating the bark, which can kill the tree. Bark beetles can cause extensive damage beneath the tree’s outer layers. Lightning strikes on high mountain ridges can burn down a tree, or severely damage it; and the endless freeze-thaw cycles crack limbs and roots. The effects of age and brutal conditions on the bristlecone make it breathtakingly, sculpturally beautiful. At the same time, the oldest individuals look like hell, having taken an intense beating from the elements—the only conditions where they’re adapted to live. But we have convincing evidence that the trees don’t lapse into senescence. Their difficulties stem from the circumstances in which they grow, but not from any inherent biological decline. Old trees form and grow buds with the same vigor as much younger trees, and they make functional cells for thousands of years. Researchers believe that the tree has no upper age limit. Under the right conditions, a bristlecone could survive indefinitely.

But bristlecone pines have been manifesting strange behavior in recent decades. They have started to grow more quickly, especially at higher elevation. Scientists have discovered that the trees’ growth has been greater in the past half century than at any other time in the paleobotanical record. Tree specialists studied, and then rejected, a number of possible reasons: that they had been fertilized by the greater quantity of carbon dioxide in the atmosphere; that we’ve somehow changed the ways we’ve counted tree rings as we’ve worked to refine and standardize our counting techniques; that their freakishly asymmetric, noncircular nature has messed with the count of rings; and so on. Curiously, these fast-growing trees occur within a relatively narrow range, almost all within about 150 meters of the upper tree line. Scientists finally determined that their rapid growth is related to high temperatures at higher elevations.³

It’s now incontrovertible: global warming is a particular danger to the bristlecone pine. Higher temperatures mean that photosynthesis, the chemical process by which green plants convert sunlight into nutritious sugars, occurs more rapidly. The tree then undergoes respiration, using those sugars to produce energy for plant growth. But the bristlecone is a tree that has evolved to conserve resources, not use them up rapidly. If the tree had a motto, it would be Not so fast. But growing quicker and bigger doesn’t begin to cause problems until a frost occurs in late spring or early fall, destroying a tree’s tender tissues at their most vulnerable stages. Warmer temperatures also mess with a tree’s sexual reproduction, lowering its ability to form newer seeds. Higher temperatures also lower the presence of moisture in the ground. Water-stressed trees have fewer defenses, providing an opening for fungal invasions. And snowmelt is less present with higher heat, disrupting the tree’s strategy of absorbing snowmelt over many weeks or months.

The list of recent climate-related woes continues in a cascade. Bark beetles have been a well-known threat to the bristlecone for a long time. Normally, it takes two harsh winters for a new generation to emerge, because the beetles are slowed by the cold. But warming has shortened this gestation period to a single year, so more beetles are produced, and more survive. One attack leads to another, and then another, for the trees cannot evolve fast enough to defend against a rapidly heating planet.

Modern tools and techniques aid our understanding of individual trees’ responses to climate change. Researchers are attaching data loggers to individual trees to track temperatures. These tools can record micrometeorological details not available with older, less precise devices. We can now quantify how cold air can pool in particular divots in the earth; how hyperlocal wind patterns can affect temperature and humidity; and how water from snowmelt can flow in variable routes down the sides of mountains, providing some trees with ample hydration while leaving others high and dry. This fine tree-by-tree analysis wasn’t possible until dendrochronologists started to make use of geospatial data and miniaturized technology. People studying ancient trees are very concerned about present conditions. Their work connects the dots from deep time up to the present, and extrapolates a future for trees.

The precision these tools provide is matched by the complexities of the tree and its workings. Scraping at the simple uncovers the intricate. Take the pine needle. It’s a slender green pin. But it’s not homogenous, for a pine needle is akin to a skyscraper, bustling with movement and life. It has a rigid outer skin, the metaphorical equivalent of the outside cladding of a building. This outer layer is marked by many microscopic holes, called stomata. These holes, analogous to windows in a building, provide access to air. Within the column of the skyscraper are hundreds of flat plates, akin to the floors of a building, which consist of chlorophyll-bearing cells. There is also plumbing in the pine needle: vascular bundles and resin canals that move fluids. The vascular bundles move water into the leaves, and also conduct the sugars formed by photosynthesis back down to the tree’s larger parts.⁴

So it is with all trees: Push the lens in closer, and various forms of biochemical joinery come into view. Lean back for a wider look, and other events swim into focus: the sway and density and variegation of color from cone to cone, from tree to tree, the whole forest standing against an uncertain future.

The most necessary of the tree’s partners is the Clark’s nutcracker (Nucifraga columbiana). The nutcracker is a light-gray, crow-shaped bird renowned for its campground-scrounging ways. It can recall thousands of caches it’s placed in trees, including the bristlecone pine. Individual birds cache more than thirty thousand seeds and can relocate them up to nine months later. And the birds can locate nuts not only within the vertical confines of a tree, but also under the snow.

Biologists and animal behaviorists started studying this phenomenon in the late 1970s. After much speculation, and then experimentation, to resolve just how the birds knew the myriad seed locations, they eliminated various possibilities: it wasn’t done by watching other birds; it wasn’t done by smell. It didn’t involve them visually identifying unique features about the specific locations where seeds were cached. Nor did the task involve random searching. It was all about spatial memory, in the face of enormous, redundant seed production.

As with sea turtle eggs, or tadpoles, or octopi babies, or the offspring of African driver ants (three to four million eggs every month or so), nature often runs on redundant systems. The mortality rate for bristlecone pine seedlings is close to 99 percent because new trees have a tough time in the extraordinarily harsh, windy,