Storygram: Cally Carswell’s “The Tree Coroners”

tree coroners
Tree physiologist Nate McDowell, center, climatologist Park Williams, left, and ecologist Craig Allen, right, are studying how trees die to help predict how forests will fare in a hotter future. (Originally published in High Country News.) © Michael Clark


The following story diagram—or Storygram—annotates an award-winning story to shed light on what makes some of the best science writing so outstanding. The Storygram series is a joint project of The Open Notebook and the Council for the Advancement of Science Writing. It is supported in part by a grant from the Gordon and Betty Moore Foundation.

As a hiker and trail runner, I’m sorry to say that I had become somewhat inured to the depressing sight of dead and dying conifers, victims of an epidemic of pine beetles that has been killing untold numbers of trees from Alaska to Mexico. After all, as a westerner I’ve been living with the reality of decimated forests for about a decade.

But then I read “The Tree Coroners,” Cally Carswell’s award-winning story in High Country News.

The very next day, I went for a walk in the woods along a trail that took me through mixed stands of lodgepole and limber pines high in Colorado’s Indian Peaks Wilderness. Carswell’s story changed the way I experienced the forest. I slowed down and noticed details that I had previously missed. Some trees, particularly my favorite species—the limber pines—had died. Others were like the walking dead, clearly weakened and on their way to the grave. Yet many others seemed to be doing okay.

A few years ago, voracious pine beetles had come swarming over the Continental Divide from the west like a wave breaking over a seawall. Yet on my hike, one thing was obvious: The forests here on the eastern side of the divide have not been totally decimated like forests on the other side. Why is that?

That thought kept coming back to me on my hike. And that, in turn, brought me back to the central question Carswell posed in her story. As she put it:

Why do trees die? It’s a deceptively simple question in urgent need of answers: Trees are dying at alarming rates not only in the Southwest but in Colorado, the Northern Rockies, Alaska and elsewhere. This summer in northern New Mexico, even junipers began to expire in droves.

Alarming rates indeed. Carswell’s story is important because of that context.

On my walk in the woods the day after I read her piece, I wondered whether the epidemic has simply slowed down here, and if so, why? Could it be that drought, a factor that can help weaken trees and make them more susceptible to beetles, has eased for now? Is some other factor at work?

Indeed, why do trees die? With an answer to that question, perhaps we can get some insight into why other trees don’t die. Even more important, we might be able to anticipate what will happen to trees in a warming world.

In her exploration of why trees die, Carswell explains complex science in terms that ordinary folks can understand. But even more important, she writes about the technical details in a way that makes them fascinating. She also provides insights into how science really works (as opposed to the cartoon version so prevalent elsewhere in the media). And by humanizing the story expertly, she helps us appreciate what motivates scientists to dedicate decades of their lives to studying trees. All of these elements come together in a way that make this a compelling narrative, one that I could not put down.

What follows is an annotated version of her story, with comments about individual elements that add up to a tour de force of science journalism. After having read it, I will never view these forests—and their individual trees—in quite the same way again.


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Story Annotation

The Tree Coroners
To save the West’s forests, scientists must first learn how trees die.
By Cally Carswell, High Country News
Published December 16, 2013
(Reprinted with permission)

There are few better places than Frijoles Mesa to study the mortality of trees. This tongue of land lies partly within the grounds of Los Alamos National Laboratory in northern New Mexico’s Jemez Mountains. To the west rises Cerro Grande, a mountain riddled with the charred skeletons of fir and pine trees.Right from the outset, Carswell uses vivid language and metaphor to grab our attention. To “riddle” means to “fill or permeate (someone or something), especially with something unpleasant or undesirable.” And that vision of “skeletons” of trees riddling the landscape certainly is unpleasant—while also conjuring a clear mental image.

To the southwest are the lingering scars of another fire, one so intense that its heat alone killed trees that weren’t consumed by the flames themselves.A telling detail that helps us feel in a visceral way what happened here. This is evidence of good reporting. Carswell had to ask or otherwise learn what killed trees that were not actually burnt.

The mesa itself is an exceptionally tough place to be a tree, even where the land has escaped conflagration. This summer, many ponderosas were so short of water that their weakened limbs snapped like pretzel sticks.Some readers might not realize just how dry and brittle a living tree can become when it is starved of water. So using the “pretzel sticks” simile here really works to help us understand that. I think we all know just how dry and brittle pretzel sticks are. The trees that sit behind a padlocked gate off State Road 4 were also struggling. This is tree physiologist Nate McDowell’s outdoor laboratory. Here, he’s enclosed piñon and juniper trees in transparent silos, cranked up the heat and deprived many of water – in order to watch them die.Being able to “crank up the heat” on trees is intriguing. I find myself wanting to know more: How does he do that? What are the results? By giving us this intriguing detail, Carswell compels us to keep reading—so we can get answers. Also, “in order to watch them die” is dramatic, and so it too compels us forward. And by putting it at the end of the sentence, Carswell calls attention to it. We’re left with that powerful idea as we move on.

McDowell spent his early career studying the towering conifers of his native Pacific Northwest and came to Los Alamos in 2003, eager to begin a U.S. Department of Energy job that would allow him to set his own research agenda.Thanks to vivid writing, and intriguing details, we’re curious about the science. But all except the most dedicated science geeks could get bogged down in the details this high up in a story. So with a deft transition, Carswell humanizes the narrative here by introducing McDowell’s personal story. But looking out his office window at New Mexico’s characteristic piñon-juniper woodlands, he had second thoughts. “This is not a forest,” he scoffed. The stout, pear-shaped junipers – one of the most common species here – resembled ill-kept hedges more than trees,An apt simile. Carswell comes back to it in the next paragraph to make an important point about the durability of junipers. all arms and twisted torsos,Metaphor that helps us picture what these trees look like. barely showing any leg. “They were like a weed to me,” he remembers.

Like weeds, junipers are durable. Those outside McDowell’s window were still green, but the piñon around them were dead. During the deep drought of 2002 and 2003, piñon died throughout the Southwest in historic numbers. Had the Old Testament told stories of forest die-off, as it did of floods, the carnage around Los Alamos would have been called “biblical”: More than 90 percent of the area’s piñon succumbed.An amazing fact that gives us further reason to stick with the story. “What a bummer,” McDowell sulked. “I’m a tree physiologist, and the trees are all dead. What am I gonna do?”An effective use of a quote—to drive a point home that the writer has just made using cold, hard statistics. The quote lends meaning and significance to the numbers. It also continues to humanize the story. We are starting to get a sense of McDowell as a person.

At first, the cause of the trees’ demise seemed obvious. The punishing drought badly weakened them, and when beetles bored through their bark, the trees couldn’t muster enough sap to pitch them out.A clear way to describe a natural process without a lot a fuss. With deft use of the verb “pitch,” Carswell summarizes something technical: how pine trees secrete sap to push beetles back out of their trunks, right through the holes the insects have bored. (Perhaps this was unintended, but that word has two relevant meanings. “Pitch” as a verb that means to “throw” or “fling,” and as a noun that refers to “a sticky resinous black or dark brown substance”—much like sap. And in this case, the pitch-like stuff is indeed pitching the bugs out!) Once inside, the beetles mated, multiplied, dug tiny tunnels and spread a fungus that cut off the flow of water and nutrients, killing the tree.Once again, a clear and compelling explanation of something rather technical without a lot of fuss and extra verbiage. Here, Carswell boils things down to their basics while helping us picture in the mind’s eye what’s going on.

But Dave Breshears, a University of Arizona professor and arid lands ecologist who had studied the woodlands for years, suspected that the truth was more complicated. During the 1950s drought, tree death seemed less extensive, even though that drought was longer and drier than the more recent one. What was different about this drought was temperature: It was a degree or two hotter.Writers who don’t have a lot of experience reporting on the natural world sometimes want to force nature to fit a simple narrative. For example, it’s tempting with every extreme weather event to jump to the conclusion that climate change is to blame. But nature is often more complex than we want it to be—and a talented science journalist can see this as an opportunity, not a hindrance. That’s because complexity often contributes to mystery. And who doesn’t like a good whodunit? So when a spate of vicious storms hits a particular part of the country, many complex factors typically are at play. Good old-fashioned variability of weather certainly plays a role. Longer term, natural climatic variations, such as El Niño, can also be important. And so too can climate change. Some editors and writers might view this complexity as an impediment to crafting a story with impact. After all, a headline tying a spate of storms and floods to climate change is probably easier to write and more compelling than one for a more nuanced story characterized by shades of gray—a story with no single “front page thought,” as New York Times blogger Andrew Revkin has put it. But the teasing out of the relative contributions of different factors can also be written as a compelling scientific detective story. Such a story would focus just as much on the detectives, how they go about their sleuthing, and what it was that attracted them to sleuthing in the first place, as it would on the mystery itself. Here, very high up in the article, Carswell is telegraphing to us that this is the kind of story she is going to tell. With this single, short paragraph, she has challenged a simpler, earlier scientific narrative and introduced a mystery and a new character as well.

Breshears’ observations inspired McDowell to take a second look at the struggling forest. It’s common knowledge that trees die during and after a drought, McDowell says, but “nobody can predict where it will happen, when it will happen, what trees it will happen to. That means we don’t understand it. That was exciting to me – there’s a science question there.”

Why do trees die?The introduction to her story all leads to this: A short and deceptively simple statement about what the article is going to be about. She has led us to this point with writing that employs effective use of metaphor and vivid action verbs. She has also introduced intriguing characters, along with the whodunit that those characters have dedicated themselves to unraveling. Even if you didn’t think you would be interested in the answer to this question, I think you will be compelled to keep going. It’s a deceptively simple question in urgent need of answers: Trees are dying at alarming rates not only in the Southwest but in Colorado, the Northern Rockies, Alaska and elsewhere. This summer in northern New Mexico, even junipers began to expire in droves.


tree coroners
Forests in New Mexico have experienced significant die-off in recent years due to wildfire, drought and beetle kill. USGS research ecologist Craig Allen says the damage is a preview of the impacts climate change could have on forests globally. (Originally published in High Country News.) © Michael Clark


It might seem surprising that, in 2013, we don’t know how trees die. We understand tree growth so well that we can decipher its code – tree rings – and reconstruct droughts thousands of years in the past. So why is tree mortality such a mystery?

“There has been a long tradition in plant science where, if your plant died during your experiment, you were bummed out,” McDowell explains. “It was like, ‘Ugh, we’ve gotta start over.’ The question was never, ‘Why did it die?’” Besides, he adds, tree death didn’t seem particularly pressing. “I think people inherently look at trees as these stable things in our lives, like mountains. We didn’t know there was a problem.”It can be tempting to use longish quotes like this higher up in the story, and throughout as well. After all, who better to introduce and then tell the story than the expert? But writing the story is not the expert’s job. It’s the writer’s. And by definition, the writer usually knows how to write it better. So quotations should mostly be used to drive the writer’s points home, to elaborate on things, to enliven, to humanize, and to break up long stretches of exposition. Here, we have a longer quotation than we’ve seen previously in the story. But it still works very well. Carswell built tension in the first part of the article. Now that this tension has helped to hook us, she is letting the story—and us—breathe a bit by having one of her characters speak at greater length than before. And we understand what he’s talking about because Carswell has prepared us well. It’s all about rhythm—the building of tension to keep us reading, but also small releases so that we, the readers, don’t become exhausted. We do need to breathe as we’re taken through the mystery.

Western forests are confronting new versions of familiar foes. In the 1990s, a series of warm winters and summers in south-central Alaska allowed bark beetle populations to explode and kill millions of old spruce trees. Beetles gained similar strength in the Rockies during mild winters in the late ’90s and early 2000s, killing not only their usual victims but also entire hillsides of ancient whitebark pines, which live at altitudes once too frigid to support the insects.A beautifully concise explanation of what has happened in a large portion of the West, thanks in part to climate change. Carswell gives us just enough to understand what happened, and no more. She’s keeping us on track.

Farther south, piñons were also attacked, but by a beetle that, unlike its fellows in the Rockies, typically preys only on the weak. Here, scientists believed the industrious insects were less the cause of death than the final straw: a strong shove to trees with one foot already dangling over the cliff.What a wonderful metaphor. We can picture trees about to fall over a cliff, and that helps us understand the technical scientific point without bogging us down.

The piñons died during what Breshears dubbed a “global-change-type-drought.” It’s impossible to blame any particular weather event on climate change. Still, the drought was a glimpse of the future, when droughts are predicted to be hotter and drier. Breshears and his colleagues found that it took 15 months in extremely dry soils to kill the piñons around McDowell’s office. The heat, they believed, had increased the overall death toll by siphoning more water from soil and plants, though they couldn’t yet prove it.

Dramatic changes in Southwestern forests had been expected – eventually. Desert edges are already marginal tree habitat, and were predicted to become especially vulnerable to the future’s hotter, more intense droughts. Still, the amount of dead wood around Los Alamos was startling. Piñons didn’t die only at the ecological boundary between woodland and grassland, the dry end of their range where Breshears and others believed climate change impacts would first become visible. Instead, piñons died almost everywhere they grew.With all of the deft preparatory work that Carswell has done in the story, this scientific medicine goes down easy. We’re willing to take it!

No community can comfortably afford to lose its forests. Besides being nice places to hike and ski, forests provide food and shelter for birds and wildlife. Leaves scrub the air of pollutants humans saturate it with. And forests shelter winter snow, the source of most Westerners’ water supply, filtering it to rivers and streams in spring.

More important from a global perspective is the fact that forests ingest an estimated quarter to a third of the carbon dioxide released by fossil fuels, effectively keeping the earth’s burner turned down. When trees die, they not only stop absorbing CO2, but they also decompose, gradually releasing the carbon stockpiled in their wood. If enough forests collapse, the flame on the planetary heating element could turn from “low” to “high.” Instead of slowing global warming, forests could start to make it worse.Here, Carswell provides the answer to a critical question: Why should we care? If a writer can’t provide a convincing answer to that, many readers will simply stop reading.

Computer models either don’t account for future tree death caused by climate change, or they do so simplistically. These shortcomings worry scientists, and with good reason: The most troubling thing it could mean is that the dramatic forecasts the models currently produce – the ones predicting not only a warmer climate, but also the fundamental transformation of life on earth – are understated.Just as Carswell helped us take a step back and breathe with the longish quote from McDowell, here she is having us take an even bigger step back—so that we can see the big picture, and thereby appreciate even more deeply why the answer to the deceptively simple, direct question at the center of her story is actually really important.

Before scientists can more accurately predict our future climate, they have to complete a simpler task – at least, one that sounds simpler. They need to understand, in mechanistic detail, how trees meet their end.A journalist reporting a multifaceted and nuanced story about a complex scientific question can be confronted with an avalanche of information. A novice writer can be overwhelmed by this and not know how to bring order to such a massive, chaotic pile. An experienced writer will use the central question or issue of the piece as a filter. (Of course, that requires identifying and clearly articulating a central question or issue!)  Everything in the avalanche that’s directly related to answering that question is caught by the filter. The rest flows through into a file, for potential use in another story at some point. Doing that filtering can be daunting enough. Organizing what you’ve retained in your filter into a compelling narrative can be even more confounding. In this paragraph, Carswell shows that she has thought through this challenge carefully. The paragraph provides an effective transition to a new section of the article. We may not know yet exactly where we are heading. But through the use of an effective transition like this, as well as her expert guidance earlier in the piece, Carswell shows us that we can trust her to be our guide. I think we intuit that we’re heading down a path that will ultimately lead to a satisfying resolution of the central question.


tree coroners
Nate McDowell at his research facility at Los Alamos National Laboratory. Los Alamos National Laboratory


After Nate McDowell spent a few years studying the inner lives of junipers, his attitude toward the trees softened. What junipers lack in majestic height and open, shady understories, they make up for in pluck and perseverance. McDowell, a spry, 41-year-old former endurance runner, began to appreciate these qualities. “They’re just so tough,” he says. “You have to respect someone who’s tough.”This humanizes the story in two ways: We get to know McDowell, and we see how his experiences as an endurance runner may have produced an affinity for his scientific subjects—and a drive to understand what has harmed them so.

Juniper doesn’t cower in the face of drought.We’ve been set up by McDowell’s story not just to accept this anthropomorphizing but also to have it seep into us and give us an appreciation for these tough trees. Also, it helps provide a bit of sweetness that will help the scientific details about stomata go down easier. Even when extremely short on water, it doesn’t close its stomata – the tiny pores on its needles that regulate the tree’s basic bodily functions. Stomata allow trees to consume carbon dioxide and photosynthesize. They also let water escape, creating the tension that pulls water upward through the tree’s circulatory system. If there’s too little water in the soil, a tree’s pipes can fill with air and break.

If you’re enjoying this Storygram, also check out two resources that partly inspired this project: the Nieman Storyboard‘s Annotation Tuesday! series and Holly Stocking’s The New York Times Reader: Science & Technology.

To prevent this, many trees close their stomata during droughts. Juniper, with its deep roots and sturdy build, doesn’t. When extremely stressed, it begins severing the water supply to entire limbs – reducing the amount of water the whole tree needs to survive. This is why smooth, naked branches – the desert’s version of driftwood – often protrude from living junipers otherwise covered in stringy bark and sharp needles.Again, the setup at the top with McDowell comparing junipers to himself really helps make this work. When I read this, I found myself reacting as I would to a human who has to lose a limb. I also really appreciate an explanation for something I see in nature quite frequently: those gnarled, bare branches on junipers. I’ve often wondered ‘why’?  Now I know!

Piñon is more cautious, slamming its stomata shut during drought. Perusing data Breshears and another colleague collected during the drought, McDowell had an epiphany: For a year, the piñons that died endured a level of water stress that should have kept their stomata shut. Photosynthesis is to trees what cooking is to people. It’s how they eat.A very effective analogy. In trying to protect themselves from dying of thirst, he thought, maybe piñons had starved to death instead.And a beautiful conclusion to a technical explanation. We get it because we feel for these trees. We feel an affinity for them. At least I did when reading this.

McDowell hypothesized that drought could kill trees either through thirst or starvation, and that owing to their different coping strategies, juniper would die of thirst while piñon would starve. Since the hypothesis is based on fundamental plant biology, and because juniper and piñon manage risk so differently, studying them could reveal basic mechanisms of death that can be tested and tweaked to model mortality elsewhere.This is pretty technical language, but Carswell has prepped us for it, so I think it works. Readers will know what it means.

McDowell first tested his hypothesis in a drought experiment in central New Mexico. One set of trees was irrigated, another deprived of water, a third received whatever the sky provided, and all were poked and probed. The piñons in the “droughted” plots, nudged by beetles, perished first, but within a few years junipers, which beetles ignored, died too. Apparently, neither strategy was enough to protect the trees from long-term drought. Rather than perishing of thirst or hunger alone, both species died from some combination of both.Toward the top, Carswell put forth the central issue of the piece: “Why do trees die?” And specifically, what roles do drought and beetles play in different species of trees? Here, we are starting to get an answer. But we’re also getting something else: a compelling lesson in how science works. That may be as important for readers as the answers themselves, especially at a time when climate science in particular is so badly misunderstood, with significant implications for policy.

The Frijoles Mesa experiment adds another variable: heat. On the mesa in mid- August, McDowell pried open an acrylic cylinder enclosing a diminutive, maybe 6-foot-tall juniper, and invited me to wedge myself inside. The tree was alive, but had the scrappy look of Charlie Brown’s Christmas tree. A fan roared on and off. The air was warm, the experience claustrophobic. After a minute or two, I showed myself out.Had I been Carswell’s editor, I would have encouraged her to start using first person sooner, closer to the top. That said, it works, because her personal exploration of the issue of tree mortality really is part of the overall story. This calls for one comment about the use of first person in feature writing: It once was almost unheard of in conventional journalism. As writers, we weren’t supposed to be part of the story. We were supposed to be objective observers who reported what we learned from our sources, and from using our senses. Of course, the idea that we could be purely objective was always a myth. True, we could employ an objective method, much as scientists do, to get at the truth. But we don’t approach each story with a clean slate, just as a scientist doesn’t do the same with each study. We have ideas about what we will find with our reporting, and what the story really is. We typically have something of a hypothesis going into each one. Once we get into the reporting, what we learn may require us to shift. That’s okay. That’s the point of reporting. But to deny that we have hypotheses at the outset is to deny our humanity. Once journalists came to accept that reality, journalistic practice began to change, at least in feature writing. So first person is now much more common. But it shouldn’t be automatic. It should be done for good reason—when, in fact, staying out of the story would be misleading. If Carswell had kept herself out, she would have been misleading us into thinking that her ideas, her perspectives, and her experiences speaking with these sources, and hiking these forests, were mostly not significant. Clearly they are, so first person seems right in this piece.

The chambers are kept at a consistent 9 degrees Fahrenheit above ambient temperatures, the sort of weather all these trees may have to cope with in the latter half of this century, especially during a drought. The study is young, but McDowell has found evidence of heat’s disruptive effects. Elevated temperatures seem to cause both piñon and juniper to devour their carbohydrate reserves more quickly, for instance. “But it’s not that clean,” he says. During winter, extra warmth can boost photosynthesis.An important caveat that some writers might be tempted to omit, favoring to keep the story less muddied than the science. But as journalists, our job is to tell the truth. By omitting that caveat, a writer would be less than truthful. There’s also a flip side here: By including it, not only is Carswell hewing to the scientific truth, she is once again furthering our understanding of how science really works. Science often does not provide completely “clean” answers. And that’s important for readers to know.

Tree mortality is a complex and dynamic process. But despite all the remaining questions, a flurry of research over the last five years has helped crystallize an important message, says Breshears. “We have gained a huge amount of confidence that, under warmer conditions, we’re going to get a lot more mortality.”


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A tree at Nate McDowell’s Los Alamos research facility grows inside a chamber whose temperature is carefully controlled. Los Alamos National Laboratory


In mid-August, I hiked into the Sangre de Cristo Mountains outside Santa Fe with Park Williams, a 32-year-old climatologist who, until recently, worked out of the Los Alamos National Laboratory with McDowell. When we strolled past Hyde Park Lodge, his eyes began to dance. In two weeks, the California native would marry his girlfriend at the lodge. He had proposed to her underneath a coast redwood, his favorite tree.Okay, we’ve had a lot of science in the past few paragraphs, and we’ve gained some insights into how science works. Time now for a little breather, and Carswell provides it here by introducing a new character and engendering interest in him by providing some details we can all appreciate. A feature writer is like a Sherpa guiding us through complex and potentially tiring terrain. She needs to anticipate when we need a break from the heavy going. Here, Carswell shows that she’s an expert at it.

A half-mile or so up a steep trail, we gained a sweeping view of the fortresses of pine and fir on facing hills. Williams wore a navy trucker hat and aviator sunglasses with blue-blocking lenses.There are details and then there are telling details. Details of the appearance of a character in a story, including clothing he’s wearing, what he looks like, etc., are often examples of the former. And it can be difficult to decide how much of that to provide. With just enough, it helps us as readers picture a character. That, in turn, encourages interest. But too much might not tell us much about the character. So it can be gratuitous and thus bog things down. Here, though, Carswell gives us just enough—and pairs the quick details about his hat with a telling detail about the sunglasses. Here is a man whose science helps determine what he puts on in the morning, namely those sunglasses. “When I first look at this mountainside, it looks totally green,” he remarked, handing me his sunglasses. The lenses made it easier to see red-orange flecks in the blanket of green, like the first autumn leaves snagged in a lawn. “I think we’re seeing the beginning of something that in another one or two years will be much more widespread.”

Williams hasn’t studied this forest, but his offhand prediction has some basis. Last fall, he authored a high-profile study concluding that if climate models’ temperature projections are correct, and if carbon emissions remain at current levels, most mature conifers in the Southwest could die by 2050 or soon after. The tall ponderosa haunted by Mexican owls? Mostly gone. The old piñon that produce sweet nuts prized by New Mexicans? For the most part, toast. Douglas fir, the largest conifers native to Arizona and New Mexico? Them, too.These specifics, told concisely and conversationally, help make real that statement, “most mature conifers in the Southwest could die by 2050 or soon after.” That’s an abstract idea. By tying it to concrete examples that readers of High Country News can appreciate, Carswell drives the point home, helping to show us why we should care.

Williams made a convincing – and frightening – case that warmer temperatures alone could kill the trees, even without changes in rain and snowfall. Using tree rings from piñon, ponderosa and Doug fir – the species that occupy the Southwest’s warm and dry, and cool and wet niches – Williams created something called a “forest drought stress index.” It showed, surprisingly, that drought stress is driven as much by growing season temperatures as winter snowpack.Carswell is deftly layering in the science and building a case about the impact of future warming.

Drought is not always a problem of scarce rain or snow, though that’s how we usually think of it. Hot weather can also impose drought conditions on plants. Minor temperature increases have an outsized effect on the amount of water the atmosphere can hold: When the temperature goes up, the atmosphere gets a lot spongier.Carswell could have said, “When the temperature goes up, the atmosphere can hold a lot more water in the form of vapor.” Too many dry statements like that can cause a story to drag. So instead of being purely literal, Carswell uses the metaphor of a “sponge,” and we get it right away.

The relationship is exponential. Stubbornly set on fulfilling its potential, warm air sucks water more greedily from both plants and soil. If the water supply it’s drawing on becomes depleted, the tension begins to strain a tree’s water columns. Picture an eager child sucking the last drops of a milkshake from a straw: The water columns, like the straw, collapse. That’s bad news for trees, no matter their coping strategy.The analogy of a child drinking from a straw helps us get the concept quickly—without a potentially off-putting technical explanation of the kind that you might read in a scientific paper.  We can picture this, and thereby understand what’s going on inside a tree.

Williams also found a strong correlation between water stress and the forested acreage killed by beetles and wildfire in the past 30 years. “Even if we think of a couple degrees of warming as relatively minor,” Williams says, “forests notice a couple of degrees, and they express it by dying.”Once again, we see the wisdom of choosing quotes carefully to drive points home, rather than letting sources go on and on. In its brevity, this comment is very powerful. And again, we see how effective it can be to end a sentence with a powerful idea.

Because the atmosphere’s sponginess is so strongly dictated by temperature, climate models can help predict how fast it will climb. “I considered a scenario where we begin curbing emissions significantly yesterday,” Williams says. “Even in that most optimistic scenario, we’re looking at megadrought conditions by the 2070s.” In other words, even if we began to aggressively control carbon pollution tomorrow, the heat guaranteed by past and ongoing emissions could still devastate Southwestern conifers.

“By 2050, it doesn’t matter if it’s wet or dry, it’s just too damn hot out,” McDowell explains.About half way into the story, we arrive at one of its key points right here. But we know that there is more to come. How will Carswell handle the fact that she has just made a very depressing point?: It actually doesn’t matter what we do now; forests are going to die. How will she keep us going despite this grim news?… The sense of inevitability that accompanied Williams’ conclusions changed how McDowell views his work. At first, he was intrigued by the novel scientific questions involved in tree mortality. “Now I feel like I have a moral obligation to speak up,” he says. “We’re not just going to lose a bunch of trees, we’re going to lose most of them in the Southwest. By 2050, we could be looking at Albuquerque vegetation in Los Alamos,” a landscape now surrounded by forests. “Albuquerque has grass and creosote bush.”Anyone who has been to both Albuquerque and Los Alamos will immediately know the significance of this. But those who have not been to those places need a little help. And Carswell provides it with the concrete examples.

Such radical changes are unlikely to be confined to the Southwest. A newer modeling effort that Williams and McDowell participated in estimates that the Pacific Northwest could lose 60 percent of its conifers to heat-induced water stress by 2100 – an especially sobering finding for McDowell, whose love of forests was lit at an early age by the old Doug firs on Puget Sound and the Olympic Peninsula. “Can you imagine the Olympic Peninsula without trees?” he asks.Another quotation that functions like an exclamation point.


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Cards attached to trees in the Los Alamos facility resemble toe tags. (Originally published in High Country News.) © Michael Clark


Such a future is hard to imagine. Many Western forests still look healthy, with plump, verdant canopies. But even some of the healthiest-looking stands may already be stressed.

In mid-July, U.S. Geological Survey forest ecologist Nate Stephenson drove me to a long-term forest-monitoring plot in Sequoia National Park, a few hours north of Los Angeles. As we left the shrubby foothills, where one could break a sweat standing still at 9 a.m., the temperature dropped 20 degrees, shadows painted the pavement, and giant sequoia appeared – the titans of the Sierra Nevada.Telling details that help us appreciate the environment changes as you go up in elevation. The plot itself was blanketed with ferns, and full of soaring sequoias and lichen-covered sugar pines.

Stephenson helped establish the network in 1982, measuring off the first plots with string. He is wildly passionate about the Sierra Nevada: In graduate school, he designed a thesis project that allowed him to hike 500 “glorious” miles a summer in Sequoia’s backcountry. After he earned his Ph.D., he returned to Sequoia with no promise of permanent employment.Another quick breather. And we can see the pattern: We get to take a breather with the introduction of each new character. It’s a rhythm that helps move us through a science story smoothly and without fatigue. He wasn’t interested in going where the jobs were. Stephenson has now studied this place for 34 years. But it can still surprise him. When he expanded the plot network across different elevations in the early ’90s to study how climate affects forests, he says, “It didn’t occur to me that by the mid-2000s, we would already be able to detect an increase in tree mortality.”

Around that time, Phil van Mantgem, a scientist who worked in Stephenson’s shop, began analyzing growth and mortality in the plots. He expected dull results – birth and death rates usually reach equilibrium in old growth – but something peculiar appeared in his data: Background mortality rates – the rate at which trees die in a healthy forest – had doubled. “We thought we did something wrong,” Stephenson says. “We tried to make it go away. We couldn’t.” The only possible cause they couldn’t eliminate was the average temperature, which had risen almost 2 degrees F since the 1980s.

Stephenson and van Mantgem ran the same analysis for old-growth forests West- wide. They found the same pattern: At many high-, mid- and low-elevation plots, from California to Idaho, Arizona and Colorado – even in Washington’s Hoh Rainforest – conifers were dying at double the rate they used to.

“Every year, you expect some people to die in your hometown,” Stephenson analogizes. “If that death rate started to creep up slowly, it doesn’t create a dead landscape all at once, but you would sit up and go, ‘Oh my gosh, what’s happening?’”Once again, the use of analogy—this time an effective one from a source—helps us appreciate the significance of the scientific findings.

As in so many ecological stories, what’s happening is complicated.What follows is another lesson about science—and nature. Both do not necessarily conform to our desire for simplicity. When handled well, as Carswell has done it, the complexity winds up being an advantage. We get to the end of the story realizing that we’ve really learned something valuable. “There is something tied to temperature that is probably responsible for what we’re seeing,” says van Mantgem. But exactly what that something is may vary from forest to forest. At mid-elevations in the Southern Sierra, where the sugar pines and sequoias live, the increase in mortality seems to be tied primarily to a temperature-induced increase in the atmosphere’s demand for water – the same thing Park Williams expects to happen more in the Southwest. But at higher elevations and in wetter forests, like the Hoh, warmer temperatures may instead be favoring the fungi and insects that attack trees.

What the uptick in background mortality ultimately portends is also uncertain. But the forests’ response to mild temperature increases, van Mantgem says, indicates their vulnerability. “(The results) might be telling us that they have chronic stress as things get warmer. Then if you get an acute stress, like a severe drought, it might be something that hits you over the head.” That is, it might be something that takes out a centuries-old forest in a year, or two – or, in the case of a forest fire, overnight.Here we have a reverse one-two punch. First an explanatory quote from the source, then a short, pithy statement from the writer that drives the point home—and helps us see why we should care about these complex, nuanced scientific findings. Also, by finishing this section with her own statement, Carswell gets to lead us by the hand to the next one…

The Southwest has already experienced such sudden shocks. One of the most dramatic occurred just a few miles from McDowell’s outdoor There, in 2011, an aspen tree fell onto a power line, sparking a fire stoked by hot, dry weather and drought-seasoned fuelsA concept clearly explained in three words. A less “seasoned” writer might take an entire sentence or more to explain it! that burned 43,000 acres in its first 14 hours. The Las Conchas blaze raged through pine and fir canopies on the Jemez Mountains’ eastern flank, killing entire stands. Some are unlikely to regenerate, ever, and are already being replaced by oak and locust shrubs. The worst-hit and driest areas have yet to sprout much of anything at all.

“That is the land manager’s worst nightmare,” Stephenson says of the Las Conchas Fire. “The biological potential has been lost, there’s going to be soil loss, erosion, the trees’ seed source has been killed off. That was not an easy transition.”

If the warming trend continues – as it surely will without heroic intervention – Stephenson hopes land managers can slow the pace of change and influence its outcome for key forests in the Sierra.Carswell is telegraphing here that as we get toward the end of the piece, she’ll tackle what can be done with such a depressing situation. This comes not a moment too soon. The Giant Forest in Sequoia National Park, for instance, contains the most massive tree on the planet – known the world over as the General Sherman. “It’s a place of high social value,” Stephenson says. To help protect the Giant Forest from sudden death in an insect outbreak or a big wildfire, managers can thin trees and set small, controlled fires to reduce competition and increase the resilience of individual trees. If research begins to show that certain species can’t survive the future climate, Stephenson says, managers may decide to let those trees go, assisting their migration to more hospitable terrain and perhaps planting new species in their place.

So far, though mortality among many of the area’s tree species is increasing, the giant sequoias seem unchanged. There’s too little information to draw strong conclusions about the whole population, but preliminary studies suggest that, in their prime habitat, the trees are actually thriving, benefiting perhaps from an extended growing season. Coast redwoods also appear to be growing vigorously, perhaps basking in extra sunlight as coastal fog declines.Once again, nature can be confounding. An unsophisticated reader could come away from this paragraph exasperated. But I think the readers of High Country News are, for the most part, sophisticated in their understanding of the nature of the West. So I think they will appreciate this paragraph for what it shows: a science writer dedicated to getting as close to the messy and nuanced truth as possible, whatever that may be. As a Sherpa, Carswell has taken us on quite a journey. The path has not been straight, but we’ve taken no major detours that have diverted us from progress toward the ultimate destination: understanding what a changing climate may do to the forests we cherish. We haven’t finished the journey yet, but the end of the trail is in sight.

Of course, this trend could change. These two iconic giants slurp more water than any other trees on earth, and future changes in water supply could hurt. Desperate measures to save them – like installing sprinkler systems – are already being discussed. “Mortality of big trees is a one-way street,” says Stephenson. “You can’t replace them once they’re gone.”


USGS research ecologist Craig Allen inspects a dead pine to gain information about how it died. Photo courtesy of Michael Clark.
USGS research ecologist Craig Allen inspects a dead pine to gain information about how it died. (Originally published in High Country News.) © Michael Clark


Models are useful in planning for the future, but we needn’t wait for them to be perfected in order to start grappling with the effects of climate change on forests.With this, Carswell gives us a transition that is a clear break from the narrative. She’s telegraphing that we’re getting close to the end, and that she’ll now pull all the loose ends together into something coherent. The mechanisms and trends scientists like Nate McDowell, Park Williams and Nate Stephenson are uncovering are already in motion – and gaining momentum. The future is all around us, plain to see.

That’s especially true in the Jemez Mountains. USGS research ecologist Craig Allen has spent his career in this landscape, never growing bored. Allen is a whip- smart man with boyish, straight-cut bangs whom McDowell calls “one of the godfathers of tree mortality.” Like Stephenson, a colleague and friend, he’s studied the same place for 30-plus years.Another telling detail. This one gives us confidence that Allen knows of what he speaks. We can trust him as a source. It’s also something of an amazing fact. Imagine someone who has dedicated so much of his life to studying the same place. That really is amazing. (And any time as a writer that you can make your reader go, “WOW,” that’s a very good thing indeed.)

Change itself does not surprise him. But some of the changes he’s seeing now are painful. “Because trees live longer than we do, we tend to view them as timeless,” Allen says. “It’s unsettling when these landscapes flip overnight.” Asked about his favorite tree species, Allen deflects the “unfair question,” but acknowledges that he loves old trees the most. The longer a tree lives, the more visible its history becomes – in gnarled bark, fire scars, and in the case of conifers, flattened tops. “You can feel this sense of endurance,” Allen remarks. “In human terms, we would call it wisdom.”The scientists themselves come back time and again to an anthropomorphizing impulse. After having read this story, and experiencing that, it has influenced how I experience my own walks through western forests. I am not viewing them in quite the same way as before. What a marvelous impact for one story to have.

Allen has spent a lot of time thinking – and publishing papers – about the global significance of the rapid changes in the Jemez. “I don’t want to overstate the lessons of the Southwest for the rest of the world,” he says. “But it’s a preview of what could happen.” Drought won’t kill all of the world’s trees; some forests may get wetter and grow better.An important point! The nuance and messiness of nature once again. Still, the expected increase in global temperature is so extreme that it could easily convince most trees that they’ve moved to a new planet, and outweigh the potential upsides of climate change for plants, such as more carbon dioxide to consume.Are we now coming to think of these trees as sentient? They’re not (at least not in the way that we are). So by anthropomorphizing like this even more, Carswell does take a risk of engendering a misperception about trees. They are not like us. They do not think, and they couldn’t possibly be aware that there are other planets out there. Yet it’s a risk worth taking. I think we get it. Of course the anthropomorphizing isn’t meant to be taken literally. It is a technique that helps us understand trees better—and appreciate just how much of an impact we humans are having on them. Moreover, Carswell is given license to do this by her sources, who have anthropomorphized with abandon.  By showing us that, she has helped us understand them better, not just as scientists who collect and analyze data, but as people who could be our neighbors or even our relatives. We’re now at the end of the story, and we have gotten more than just an answer to the central question Carswell posed toward the top. I think we now have an even deeper appreciation for trees and the people who study them. And that too is a marvelous accomplishment.

Forests’ widespread vulnerability is already evident. A hot, dry spell in Europe in the mid-2000s wiped out oak, fir, spruce, beech and pine. Drought has picked off aspen, jack pine, and black and white spruce in Western Canada’s boreal forest – at both high and low elevations. A once-in-a-century drought in 2005, followed by another five years later, killed vast numbers of trees in the Amazon rainforest.

“One thing we are going to lose, and it might be in most places later this century, is old trees,” Allen says. “Even if the system can still grow abundant vegetation, the historically dominant old trees are dominant because they’re tuned to that historic climate window – which is already not the climate that we’re in.”

As grim a prospect as that is, it is also an opportunity to make the forests we still have more resilient – and to start doing so now. It is possible, even in the Southwest. The region goes through natural wet and dry cycles, and within the next 10 years, says Allen, the current dry spell is likely to let up. That will ease the pressure on trees from wildfires, beetles and the weather itself, and allow land managers to more safely thin forests with low-intensity fires. Combined with landscape-scale mechanical thinning, these measures could soften the blow of the next drought, and reduce the risk of future catastrophic fires or insect outbreaks. If managers want to plant trees – perhaps more drought-hardy species from other places – the wetter cycle will give seedlings an opportunity to establish themselves.

Most of the old trees we love may still perish, but there are better and worse ways for that to happen. When landscapes change incrementally, they are more likely to maintain species diversity, soil health, and basic functions like erosion control. Past droughts that killed trees in what seemed like apocalyptic fashion, Allen says, in fact caused a gradual reshuffling of the landscape. The 1950s drought, for instance, killed most ponderosa at the dry end of the tree’s range, but not all. It didn’t leave a treeless landscape, prone to the kind of erosion and soil loss that follows severe wildfire. “It didn’t leave a desert,” Allen says. Piñon and juniper replaced the dead ponderosa. Going forward, change of this sort may represent a best-case scenario. The question is: How fast can new trees colonize landscapes as the old trees die?Carswell has pivoted from the deeply depressing conclusion a little earlier in the story to something that can give us a little hope—and even a mission. True, even if we were to act now, we probably cannot forestall significant changes to forests in the West. It’s too late for that. The greenhouse gases we’ve already added to the atmosphere, and the climate changes already evident, have locked in quite a lot of future change. That’s the depressing part. But if we take to heart the full lesson of Carswell’s story, perhaps we can manage the big changes and avoid the worst-case outcomes.

If his daughter or his twin boys have children, Allen wonders, what will they want to know about the forests he knew? He is brainstorming a new project: documenting the size, age, diversity and three-dimensional structure of trees in old forests, archiving tree-ring samples and the histories they hold, and recording the sounds of birds and wind blowing through the canopy. He also hopes to document what ancient forests mean to people by involving artists, poets, ethnographers and the elders of cultures for whom forests are important. Such a project, he is starting to think, might be just as important as scientific research. Someday, even if only through a virtual experience, his grandchildren could still walk through the Jemez Mountains’ ponderosa or the Olympic Peninsula’s rainforest, and hear the whisper of the breeze through the treetops.Oh my, what a “kicker.” Environmental feature writing doesn’t get any better than this. The allusion to grandchildren brings us a grander scope of time — in a personal and emotional way. We all care about children, whether they are own or not. And we like to think that the world they inherit will not be bereft of some of the wonders we now appreciate. But here, we are faced with the prospect that children will only be able to experience these forests through art, poetry, and stories. I’m sure those works would be beautiful and evocative. But still, what a loss.


A Conversation with Cally Carswell

Tom Yulsman: How did you first get on to this story? 

Cally Carswell: A few of us at High Country News knew we were due for a significant story on the West’s troubled forests, and so I was looking for ways to wrangle that big topic into a focused and grounded story. At some point, I did a web Q&A with Park Williams, a forest and climate scientist then based in New Mexico who had just published a significant study in Nature Climate Change that reached some stark conclusions about the future of Southwestern forests. The conversation with Park really set me on the path toward this story. I gleaned two important things from it: A simple, focus question: Why do trees die? And insights into how higher temperatures could impose severe drought stress on trees—enough to kill them—no matter what happened with precipitation. That struck me as really important because in the Southwest, while there’s still quite a lot of uncertainty about how precipitation will trend in the future, scientists are very confident that temperatures are going up, up, up. That made the conclusions about the effects of warmer temperatures on trees pretty meaningful.

TY: What first drew you to it? And what convinced you that it was worth pursuing?

CC: I personally thought the science was fascinating and accessible, and I knew it was really relevant to our readers, who’d been watching the forests around them change a lot in recent years, thanks to beetles, fire and drought. After I had that initial conversation with Park, I talked to a couple more scientists who were looking at this question of how trees die from different angles, in New Mexico and California. That gave me confidence that it was an important question and relevant to a regional audience—broad enough to be worth an in-depth exploration, but focused and simple enough to be manageable for me and my readers.

TY: You grappled successfully with a multifaceted and nuanced story involving a lot of complicated science and multiple human sources. Considering the huge amount of raw information you no doubt had to deal with, tell us about your process for making sense of all of it, and for weaving the various strands together into such a compelling narrative. 

CC: I did a lot of reading and phone interviews, and then made trips to both New Mexico and California to meet scientists in person. I settled on my frame pretty early on—both the focus question and the title of the piece—so in a basic sense, I knew before I did my field reporting how I would approach the story, and that helped guide how I collected human elements in the field. I also knew that I’d ground the story primarily in New Mexico because that was where the most dramatic forest die-offs had happened, and it was also a hub of important research. Still, it was definitely a challenge to figure out how to structure a story with no real central character, and with multiple settings. My editor, the one and only Michelle Nijhuis, suggested using scale as a structural device, starting with a local story, then going regional, then going global, then back to local, and that ended up working quite well. I also wrote a list of what I called “fascination points” that I tried to write around each draft. Those were the things that most captured my imagination from my reporting. I wanted to be sure to emphasize them for readers, to keep them engaged despite the complexity.

TY: As you point out, no matter what we do, forests are going to suffer badly (and already are), in large measure because all the greenhouse gases we’ve already pumped into the atmosphere will be influencing the climate for decades to come. You introduce this dispiriting idea about half way into the story. With that in mind, what was your strategy for keeping readers going?

CC: That’s such a great question, and to be honest, I’m not sure I consciously made super strategic moves right after introducing that idea. Those “fascination points” I mentioned were one of my main strategies throughout the piece, though. I thought a lot about how to not just make people depressed with this story. A lot of climate science is reaching pretty downer conclusions, but it’s also revealing really cool stuff about how the world works. A lot of my fascination points had to do with explaining things I knew a lot of our readers would see around them all the time, but probably didn’t understand, like how juniper trees kill off limbs to cope with drought stress—the kind of stuff you might tell your buddy next time you were hiking or biking in a pinon-juniper woodland, that would animate the landscape in a new way. I also tried to get my sources to talk about what trees they loved and why, and made sure to use that material to remind readers of their own emotional connections to the landscapes I was writing about. That, I thought, would make the science engaging and compelling even if it wasn’t exactly uplifting. You would care, and hopefully want to know more.

TY: Your scientific sources, and you as well, anthropomorphize trees quite a bit. Some scientists, and editors as well, frown on anthropomorphizing. It can also be overdone. (But for the record, I thought it worked beautifully in your story.) What are your thoughts about this?

CC: I thought it worked really well as an explanatory device, to help people get the science, and it brought some playfulness to a serious and sober story. And let’s be honest, anthropomorphizing is partly how we relate to the natural world, how it comes alive in our imaginations. We’re also talking about plants here, long-lived ones that grow slowly, don’t move, etc. Taking some creative license to use what we know about them scientifically to give them some personality, some life on the page, and help people relate to them felt A-OK to me. That way, people might actually read the story! Also, this is how my sources actually talked about the trees. I admit that I at no point considered asking them, “Excuse me, but could you please put that in drier, more technically accurate terms?”

TY: Your story works well on many levels. You explain complex science in terms that ordinary folks can understand—and you also make it darn interesting. You provide insights into how science really works, as well as the motivations of scientists. And you humanize the story expertly too. All of these elements come together in a way that made this an award-winning story. I found myself thinking that it might have been a culmination of years of effort focused on perfecting your journalistic craft. Is that true? And whether it is or not, tell us just a little about the journey you took to get to the point where you could report and write such an impressive piece. 

CC: I’m still fairly early in my career, so I don’t know that I’d say it was the culmination of many years perfecting my craft, but certainly some! (And plenty of writerly anxiety and self-flagellation.) Let me take this opportunity to praise High Country News, where I’d been working as a writer and editor for about 3 or 4 years when I wrote this piece. I learned so much of what I know about environmental reporting and good writing at HCN, where depth and nuance are prized and demanded, and young writers are nurtured and encouraged to be ambitious. Working as an editor at HCN gave me the breadth and depth I needed to recognize that this was a good and important story, and also made me a much better writer—as did being edited by my colleagues there. Before coming to HCN, I worked a bit in public radio. In a lot of ways, radio is great prep for magazine writing, because you learn how to write really conversationally.


Cally Carswell
Cally Carswell Courtesy of Cally Carswell

Cally Carswell is a freelance journalist covering science and the environment, and a contributing editor at High Country News. She likes to write about living things as well as dying things. She lives on a dusty lot in Santa Fe, New Mexico, and is populating it with flowering plants that require shockingly little water. Her HCN story “The Tree Coroners” won the National Association of Science Writers’ Science in Society Award and the Society of Environmental Journalists’ Kevin Carmody Award for In-Depth Reporting, Small Market. Follow her on Twitter @callycarswell.




Tom Yulsman
Tom Yulsman Courtesy of Tom Yulsman

Tom Yulsman directs the Center for Environmental Journalism at the University of Colorado Boulder and is a professor in the College of Media, Communication and Information’s Department of Journalism. He keeps an active career as a journalist going by covering the Earth and environmental sciences for major magazines and online publications. He writes regularly for Discover magazine, where he runs ImaGeo, a visual blog he created that focuses on the intersection of imagery, imagination and planet Earth. His book, Origins: The Quest for Our Cosmic Roots, was published in 2003. Before joining CU in 1996, Yulsman was editor-in-chief of Earth magazine. In addition to Discover, his work has appeared in a wide variety of publications, including TimeThe New York TimesThe Washington PostThe Denver PostAudubon, and Astronomy. Yulsman received his MS degree in 1980 from the Graduate School of Journalism at Columbia University. Follow him on Twitter @yulsman.



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