Mapes evokes the wonder and joy of forests, and the poetics and botany of trees, living intimately with her oak through four seasons. She dives deeply into the world of self-described “tree geeks” and becomes one herself, exploring her tree from roots to crown. She also offers a clear-eyed assessment of what the tree tells us about climate change, from the heartwood at its core to the photosynthetic cycle deep in its leaves.
Mixing storytelling, tree lore, and cutting-edge science, Mapes offers a new approach to thinking about how we might live together into the far future on a planet we have changed in ways we never intended—and how trees help show us the way.
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Seasons of Change with a Century-Old Oak
By Lynda V. Mapes
Bloomsbury Publishing PlcCopyright © 2017 Lynda V. Mapes
All rights reserved.
Me and My Tree
We walked in aqueous light, the trees in their first full green leaves of summer, bright against a June-blue sky. Threading our way into the woods, where the ferns were knee-high already, we pushed through the forest understory to the grove where the big oak stood, the biggest tree in its realm. David Orwig, a senior ecologist at the Harvard Forest, rubbed a block of beeswax over the length of his metal tree corer, the better to drive it into the wood after the bite of the bit. An expert at coring trees and reading their inner secrets, he got ready to turn the slender, eighteen-inch-long corer into the tree by hand, ratcheting hard with the corer's T handle. Done correctly, the result of this type of tree sampling is a biscuit-colored, delicate core, cut by the bit in a long, slender wand. Scientists quest deep into the hearts of trees for these cores for a panoramic view into the past. Mounted, sanded, and viewed under a microscope, each band in the core of alternating color, light and dark, tells a story of the tree's life. How much rain fell, relative to other years; whether there was a forest fire or a plague of gypsy moths. The core tells of the doings of a tree's neighbors, too: whether they crowded in close or fell away, leaving a clear shot to the sun. And a core tells age, year by year. Each pair of a light and a dark ring represents a year of growth, through spring and summer.
Coring a tree is harder than its sounds, especially with an oak. It's a noisy business; trees fight back, tightening on the corer as it's pushed deep into the wood. Leave a bit in there for long and it won't come out at all; that is the grip of a tree, closing in on an intruder, and sealing its wound. Every researcher has a story of the bit he or she couldn't get out without breaking it, the metal no match for a tree on the defense.
Orwig is a master corer and a big man. I've seen him core dozens of trees in a day, and I know the sound of his work — krrreck, kreck, kreck, with each turn of the bit, as the tree grips the metal. The sound travels a long way through the woods and can't be confused with anything else. The rhythm of the sound is unique to each person driving the bit; every researcher plays a signature tree-coring song, know it or not. I once made a sound recording of a tree-coring foray in an old-growth stand with a dozen researchers at work. It was a garage band of trees, talking back as the scientists sought their story.
Orwig circled the oak, looking for the best point of attack. He put a hand to the oak's bark, feeling for a good spot, a bit flummoxed by the trunk's shape. Instead of rising straight, the oak leans hard away from the stone wall where it sprouted. It also grows in a twist, rising in a graceful twirl to the first branches of its vast, spreading crown, reaching some eight stories up in the air. Orwig saw a good spot. I was suddenly weirdly anxious. Does this hurt? Of course not, I corrected myself, it's a tree. But I had already spent a lot of time with this oak; I couldn't help feeling attached.
I first met this tree in the fall of 2013, walking these woods to study the seasonal procession of the year in the forest with John O'Keefe. A biologist given to wearing the same two sweaters all winter — that's a long time in Massachusetts — and a slouchy ragg wool hat, O'Keefe had walked the same circuit of fifty trees in this forest for more than twenty-five years. The big oak was part of his tree survey — it wears a badge of science, a shiny metal disk with its ID number in the survey: BT QURU 03. BT for Barn Tower, the location of its research plot. QURU for its species, Quercus rubra, or red oak, and 03, because it was the third oak added to the research plot. O'Keefe liked to say he started his long-term survey of the timing of the seasons, revealed in the budding, leaf-out, leaf color, and drop on the trees, as a way to get outside at least one day every week, then just never stopped. By now he had compiled a valuable and unique record. Seasonal changes in nature are among the most readily observable clues to the biological effects of global climate change, as warming temperatures reset the seasonal clock. In forests, water use, the growth rate of trees — their carbon storage — the length of the growing season, and temperature all are connected. So O'Keefe's work, documenting the seasonal gyre of the woods, was a look, told through the language of leaves, at our changing world.
His foot survey was the ground truth for images also beamed over the Internet of the tree canopy, continually recorded in daylight hours by surveillance cameras, watching these trees' every move, from 120 feet overhead. With O'Keefe's tree-by-tree observations, the forest-level view from the cameras, and other devices on observation towers, and even a drone used to fly regular photographic missions over the forest, these had to be among the most closely monitored trees in the world.
Scientists from around the world are studying changes in the lives of these trees, as levels of carbon dioxide mount in the atmosphere, and temperatures warm. Some trees in the Forest are martyrs, the life sucked out of them by invasive woolly adelgid, tiny bugs multiplying now that winters are too warm to kill them. Yet red oak, the dominant tree in these woods, is growing faster and more efficiently than ever recorded. You could see all this in the very breadth of the trees, in the grain of their wood, in the budding and drop of their leaves. You could, I thought, as I first heard of all this, take a deep long look at even just one tree, and see so much.
Before long, what had started out that first fall as taking a few walks with O'Keefe turned into a regular thing. Pretty soon, I had found myself renting a room in the old farmhouse next to the pasture by the woods, so I could head out into the trees whenever I wanted. But I was still looking for my one tree, to take a deep long look at its life and discover its story and, wound within it, our own. The forest I had come to visit had become a place I didn't want to leave. Why not, I thought, just move into the farmhouse and stay? "John," I wrote O'Keefe one night that fall in an e-mail, "I need a tree."
So we had gone out, on one of O'Keefe's last survey walks of the year. It was the week before Thanksgiving 2013. Frost was already in the ground, and the sun streamed through mostly bare branches. "I'm going to say that is running hard," O'Keefe said, as we crossed the bridge over a brook at the beginning of our walk. The water was flowing faster now than just the week before, O'Keefe explained, because the trees had begun to go dormant for the season. What we were seeing was an indicator that the symphony of the forest was transitioning to the slow movement of winter, the trees taking up less water and leaving more in the stream. This was new to me. What a window the streams, puddles, and vernal pools were into the lives of trees. It had never occurred to me how intimately they are connected.
Surface water, visible in stream flows and vernal pools, is depleted as trees move water from the ground to their crowns and finally breathe it as vapor into the air, through their leaves. As much as 99 percent of the water a tree takes up passes right through it, easing as water vapor through tiny pores by the millions on the undersides of their leaves. Called stomata, these microscopic mouths are the openings through which trees breathe, like us, day and night, taking in the carbon dioxide that provides the substance from which they are built. Trees are interstitial beings, connecting the atmospheric and terrestrial realms. They are rooted in the ground, but made from thin air, conjuring the sky, the atmosphere, and the sun to earthly form. For this alchemy they embody wonder; they are a transubstantiation that has amazed people for centuries. For really, who would think something so solid and long-standing as a tree could be made from the limpid, quicksilver ingredients of sun, water, and air?
We crunched over fallen leaves, releasing their fragrance. The one-note call of a blue jay found us. "That's about sixty percent down," O'Keefe said, lowering his binoculars from a maple in his survey, and making a note of the tree's percentage of leaf fall with a pencil on his clipboard. As we walked on, we were also auditioning trees: I was still on the hunt for the right one, a wizened witness to the story of our changing world. We paused long and hard at a striped maple we both admired. So lovely were its golden tresses of flowers in spring, and nut-brown seeds in the autumn. Its leaves in fall were a soft yellow not seen anywhere else in the Forest. It has snazzy bark, with thin green stripes that photosynthesize. It's an important tree for wildlife: striped maple is beloved by moose, which strip its bark and clip its tender branches for food. And it was a friendly size, with leaves and buds close enough to the ground to study up close. But it was too small; it had no age, no gravitas. And so we reluctantly walked on.
While this forest is a natural wood, reminders that it is also an outdoor laboratory and classroom were never far as we walked. Trees bristled with tags and flagging, and the forest floor was studded with equipment. There were light sensors, and laundry baskets gathering leaf litter. Often, amid the birdsong, came sounds of science, from the buzz of a drone flying a photographic mission overhead, to the hum of computers, motors, and fans. The reality is this forest is under a microscope. It's the full-time, year-round focus of a staff of about forty to forty-five biologists, modelers, GIS (geographic information system) specialists, historians, ecologists, dendrologists, paleoecologists, information and communication specialists, policy experts, atmospheric chemists, research assistants, lab technicians, and administrative staff at the Harvard Forest with an operating budget from $4.5 million to $6 million a year, and a larger cadre of visiting researchers from around the world.
On just one tract of forest, where the big oak stood, more than forty experiments were under way, involving dozens of scientists from Harvard University, and around the country and world. They were interested in everything: root respiration, deer and moose browsing habits, legacies of prior land use, and paleoecology. Forest regeneration, historical archaeology, snow modeling, and lichen population density. Acorn and maple seed production, hydrology, phenology, plants and climate change. Organic nitrogen cycling, forest history, the invasion of the hemlock woolly adelgid, plant hydraulics, and the forest-atmosphere exchange of carbon dioxide and water. Sap flow in trees, and experiments with fungi, vernal pools, and carbon dynamics. And that was just in this plot. Spread over nearly four thousand acres, the Harvard Forest, founded in 1907 and with more than a hundred years of research in the archives, has one of the longest records of some types of data anywhere, compiled in a rich, dimensional, ongoing exploration of the forest.
O'Keefe's survey walk led on into a hemlock wood, and its cool, green shade enveloped us. I could see hemlocks shredding and thinning, as the woolly adelgid destroyed them by degrees. But I didn't want to write a story of nothing but decline and loss. So we passed through their dappled light without stopping. In the black gum swamp, the light changed again, to the open sky where these deciduous trees had already lost all their leaves. I knew the oldest living dated tree in the Forest was here, a more than four-hundred-year-old prize, with bark dark and gnarled as an alligator. But black gum is an obscure species I didn't think most people would know or relate to. So we kept going. I heard a whine as we walked under the Barn Tower, one of five towers in the Forest bristling with instruments: gas analyzers, digital cameras, and more. The sound was an air pump on a device, mounted way up in the metal tower, to measure the breathing of the tree canopy around the clock.
We walked deeper into the woods and I heard something else; I was puzzled at first at the sound. That was it: a fan. Just beyond a stone wall threading through the woods, dating to the 1700s, I could make out a black chain-link fence, and beyond it, plastic-curtained, circular pens. This was Warm Ants: a multimillion-dollar, long-term experiment, with the soil inside the pens artificially warmed with blown air. The object was to see how warming the soil would affect the populations of ants freely traveling between the pens and regularly counted in pitfall traps. A propane tank, big and white as a beluga whale, hulked in the woods nearby, fueling the heating system. "Here," O'Keefe suddenly said, laying his hand on a red oak. "This might be a good one for you." I tipped my head back. We had been on walks together before, but I had never focused on this tree, off in the woods beyond the tower, on the other side of a stone wall. It was my first look at the oak.
It was big. So big, I couldn't see its top without dropping my head all the way back to my shoulders. It had no branches at all for the first forty feet, then flared to a wide crown that dominated its grove. It was a wild tree. If I wanted to climb it, I'd need professional help. Ropes, helmet, harness, the works. But it was old, that much was clear. It was beautiful, that was for sure. It was in O'Keefe's survey — I saw its tag — so I knew we would have records on its seasonal year. It was also in the view of the cameras on the Barn Tower. That put it within the full sweep of the discipline of observing these trees, from O'Keefe's boots on the ground, to using webcams and computer models to observe and analyze leaf-out, color, and drop. And there was also that stone wall.
Sprouted from an acorn there by that wall, the oak was a cultural tree, and a historical artifact. Left, rather than cut, it was a witness to all the changes that had come over this landscape. The pastures and farm fields that used to be here, delineated by that wall. The forest that grew up next, after the farmers left for jobs in the cities — jobs in industries that had both bettered and worsened our world and created the carbon emissions now torquing the seasons. A tree this big, in this spot, has seen it all, from our changing relationship with nature in our urbanized, industrialized, and digitized lives, to the altered clockwork of nature. Like the witness trees surveyors used in the eighteenth century to mark metes and bounds of new landscapes, this tree could be my marker and narrator, a living timeline of cultural and ecological change. And while it wasn't growing in a sylvan, silent setting, but rather right in the middle of science central, that was sort of perfect, too, for a look at the ways — and limits — of knowing the mysteries and wonders of trees. Now we had just needed to core it, to be sure it was old enough. Yet, when the time had come, and Orwig was about to core the big oak, my curiosity was at war with my attachment to its wild heart. The big oak wears a tag, sure, and it's in the view of the cameras. But so far, this tree hadn't been invaded by us.
Orwig pressed in with the borer. The tree did not give up quietly, squeaking as Orwig put his shoulder into it, driving in deeper. Turn by turn, he sank the bit to its hilt. Then quickly, with a light motion, pulling with his right hand and cradling the core with his left, Orwig pulled a continuous cylinder of wood from the depths of the oak, into the sunlight of day. Working with the grace of long practice, Orwig ripped the paper wrapper off a Dunkin' Donuts drinking straw and carefully threaded the core inside. The perfect carrying case — the ongoing debate among scientists as to whether McDonald's, Starbucks, or Dunkin' straws are best is not yet over, but many is the researcher I know who works in the woods and cores trees that snags a fistful of their favorite on coffee runs. Big cores take more than one of these drinking straws, stuck together in the field end to end with masking tape. To save that bit of fuss — and the risk of wrecking a sample — some scientists special-order straws up to twenty-eight inches long from scientific supply companies. They even come in neon colors, the better to not leave them behind in the field. Straws and Ziploc bags — field science in these woods would grind to a halt without them.
Orwig shook his head and circled the tree for a better spot. "Didn't get the heart," he said, and readied for another try. A tree shouldn't be cored more than twice in a year, so this was the make-or-break sample. He took a breath, set the bit, and bore down. The second sample came out long and lovely, its wand of time a deep look into the past. O'Keefe and Orwig studied the core as it lay in Orwig's palm, doing a quick field count they would later check under a microscope. O'Keefe had guessed 100 to 110 years all along; the core showed he had nailed the age nearly to the year. At a solid century or so, it was just about right. So that settled it: the big oak would be my witness tree.
Excerpted from Witness Tree by Lynda V. Mapes. Copyright © 2017 Lynda V. Mapes. Excerpted by permission of Bloomsbury Publishing Plc.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
Chapter One: Me and My Tree, 9,
Chapter Two: A Beneficent Monarch, 23,
Chapter Three: To Know a Tree, 49,
Chapter Four: A Forest, Lost and Found, 67,
Chapter Five: Talkative Trees, 94,
Chapter Six: The Language of Leaves, 119,
Chapter Seven: Witness Tree, 145,
Chapter Eight: Past and Future Forests, 169,
Chapter Nine: Carbon, 186,
Chapter Ten: In This Together, 201,
Selected Bibliography, 216,