Studying Yellowstone’s Burn Scars to Reveal its Future
This essay is part of Edge Effects Out Loud, a collection of pieces published in both written and audio formats. Stream or download to listen to the audio version of this essay.
It’s lunchtime and we slip a few electrolyte tablets into our water bottles. Though temperatures are in the 70’s and the infrequent breeze is pleasant, the dry air and beating sun leave my fingers cracked and brow caked with dried sweat. I squint west into the piercing blue sky in search of developing thunderstorms and, seeing none, turn back to a lunch of salami, cheese, and trail mix.
Yellowstone National Park is known for many things: bears, geysers, bison, wolves. But we aren’t here to sight-see; well, not like everyone else. Nearly 10 miles from the nearest road, we’re here because of fire.
The forests of Greater Yellowstone are shaped by fire. Occurring every 100 to 300 years throughout the last ten millennia, large, lightning-ignited fires burn during particularly hot, dry summers. Come fall’s first snow, what’s left in the fire scar is a charred landscape with little visible plant life remaining. Such ‘stand-replacing’ fires kill most trees in the fire scar and create a complex mosaic of burned and unburned forest, often across hundreds of square miles.
This mosaic is evident from our lunchtime vantage point. Out on the Madison Plateau, one of Yellowstone’s many forested, high-elevation plateaus, we gaze across a flat, dry expanse riddled with standing dead trees (snags) and fallen logs that were killed by fire over 30 years ago. With few young trees blocking our view, we can clearly make out the surrounding unburned forest behind the snags. This is jarring to me; being able to see hundreds of yards in all directions is not the norm in a 34-year-old fire scar in Yellowstone. Indeed, trying to understand why there are still so few trees coming back decades after fire is exactly the reason we’re here.
To imagine what a typical post-fire forest in Yellowstone looks like, picture a healthy patch of grass in your neighborhood. The individual blades are so tightly packed that the soil beneath isn’t visible. Now imagine each blade of grass is instead a 10-foot-tall pine tree with enough sharp twigs and needles to make long sleeves and safety glasses a necessity. Foresters call these ‘doghair’ forests. We like to call them ‘densetowns’. They’re an incredible part of the natural disturbance-recovery cycle across much of Greater Yellowstone and are emblematic of the extensive areas that burned during the summer of 1988. That year, over a third of Yellowstone National Park burned, 1000 square miles (about half of the burned area) of which was stand-replacing fire.
Special fire-adapted traits in lodgepole pine, the dominant tree species across Yellowstone’s forests, help explain how an area where every tree burned in 1988 transformed into a densetown just three decades later. Though easily killed by fire, some lodgepole pine are serotinous: they form closed cones sealed by resin that are only opened by the heat from a fire. Over time, these cones accumulate on a tree so that, when a fire moves through, many cones open and simultaneously disperse thousands of seeds onto the newly exposed soil. Even if only a few trees possess serotinous cones, forests quickly come back. If nearly all of them do? Well, densetowns.
But fires and climate are changing, and with them the forests of Greater Yellowstone. Average temperatures in Yellowstone National Park have already warmed 2ºC (3.6ºF) since 1980, and more is expected. With warming comes more of those hot, dry summer conditions conducive to big fire years like 1988. Indeed, many researchers expect every year could be a big fire year by the end of this century, an extreme departure from the historical fire-return intervals of 100 to 300 years. With such frequent fire, there’s growing concern that forests won’t be able to recover. By 2100, densetowns may be long gone, with areas like our lunch spot taking their place.
After lunch, we pack up our gear and walk to the next sampling location. As I clamber over the skeletons of trees born at the turn of the 18th century, I can’t help but think that we’re looking at the future of Yellowstone. But understanding what exactly that future looks like takes more than imagination; it takes weeks of intensive fieldwork. Over the next two days, we will visit eight plots in this small section of the fire scar and collect information on how forests are (or in this case, are not) recovering. In each, we identify and count each plant species, quantify how much carbon is stored in recovering vegetation and downed logs, and determine if tree seedlings and young saplings show us that a forest may still come back given enough time. To do this, we divide and conquer. While Zach, Madie, and Eileen lay out transects for counting trees and identifying grasses and wildflowers, I record plot measurements like elevation and distance to unburned forest. Once transects are laid, I focus on identifying every plant species in the plot and estimate its cover, Madie and Zach count and measure trees, and Eileen takes measurements on downed logs for our carbon storage estimates. It takes us anywhere from 45 minutes to 2 hours, depending on the plot. On our best days, we sample five plots. On our worst (and wettest), we sample only one.
Once we are done here, we will pack up camp, hike out to the car, take a few days off in town to recharge and resupply, then head to the next cluster of plots in another corner of the vast Yellowstone wilderness. Throughout the summer, we will be anywhere from 2.5 to 25 miles from the nearest road. We’ll ascend steep mountainsides with no trail to guide us, hitch boat rides down Yellowstone Lake from National Park Service personnel, hike and sample in seemingly unending rain, and fall asleep with nothing but a thin tent separating us from the stars. All told, we’ll hike over 150 miles, gain the equivalent elevation to climbing Mount Everest from sea level, and sample 55 different plots in Yellowstone National Park and the adjacent Teton Wilderness.
What ties these far-flung adventures and sampling locations together is their lack of forest recovery. What motivates us to visit all of them and collect information on plant communities, tree regeneration, and carbon stocks is to understand what failed forest recovery means for the future of these burned landscapes. But our concern isn’t just for Yellowstone’s future; that future is here now. Fires across the mountain west are burning more forest each year, and more of that fire is burning as stand-replacing fire. Recent fires in 2016, Yellowstone’s biggest fire year since 1988, reburned young forests before serotinous cones had a chance to form, so few tree seedlings established after fire. And those hot, dry conditions fanning the flames one year make it awfully difficult for young tree seedlings to survive, let alone thrive, the next. If we are to have any sense of what these currently forested landscapes are to look like in 50 years, we must first understand how these changes are affecting them now.
By late-afternoon we stumble into camp. We’re hungry, mildly dehydrated, and covered in dirt. Fortunately, camp is right next to a lake, and a swim feels better in this moment than any shower could. Dinner is dehydrated chili with instant mashed potatoes and tuna, and tonight we’re sharing camp with someone who’s thru-hiking the Continental Divide Trail. After introductions and dinner, our campfire conversations remain light, sparse as the forests we’re studying. Words aren’t needed when the gentle peace that is evening in the Yellowstone backcountry will do.
Since our return to Madison in mid-August, I’ve begun parsing through all the information we collected during our six-week whirlwind of a field season. So far, we’ve learned that these areas of poor forest recovery following the 1988 fires are primarily at higher elevations and further from unburned forests. Serotinous lodgepole pine don’t grow at higher elevations; instead, Engelmann spruce, subalpine fir, and non-serotinous lodgepole pine, all species with no ability to recolonize quickly following fire, dominate. Recovery can only begin once seeds reach the fire scar from surrounding unburned forest. If that seed source is far, forest recovery could take centuries. But if these areas burn again before forests recover, an increasingly likely outcome in our warming world, forest loss could be indefinite. In some areas we visited this summer, this seems to be the case, with few to no young trees or seedlings in sight.
But this summer and our experiences traversing the wilds of Yellowstone took us beyond data. I learned that organizing and leading a full field season is incredibly challenging. As it turns out, backpacking is hard. Doing so in grizzly bear-country is harder. Doing so while collecting data on post-fire forest recovery is even harder. As time has passed, though, and I’ve settled into my semesterly routine of meetings, research, and coursework, I’ve found myself reflecting more on this summer’s joys than its difficulties. Less and less, I remember the stress of the field season; more and more, I remember the sun, the plants, the mountains, and the stars.
Looking forward 50 years, I’m confident the sun and stars will still hang over Yellowstone Lake and the Absaroka mountains will still define its horizon. But I am also confident that Yellowstone’s forests, where they occur and what plants and animals they contain, will change. Our choice now is to decide what to do about it. Shall we resist it in some locations, maintaining old forests to serve as seed sources for the surrounding burn scar? Should we direct it, encouraging the establishment of fire-adapted tree species and managing for more frequent fire? Or, seeing these as dynamic systems, shall we accept change as a natural outcome of our warming planet? At least now, having studied the areas where forests haven’t recovered after over three decades, we know what one scenario in that future could look like.
Featured Image: Wildfire smoke over a burned area in Yellowstone. Photo by author, 2021.
Nathan Kiel (he/him) is an ecologist and PhD candidate in the Department of Integrative Biology at the University of Wisconsin-Madison. Plants are his passion, particularly why they grow where they do and how they interact with other organisms and their environment throughout their life. Website Twitter Contact
This research was conducted on the past and present homelands of the Shoshone, Bannock, Crow, and other Indigenous nations and tribes forcibly removed during the creation of Yellowstone National Park. All research presented in this article was conducted under the following research permits: YELL-2022-SCI-5238 (Yellowstone National Park, National Park Service) and BUF220205 (Bridger-Teton National Forest, Buffalo Ranger District, U.S. Forest Service). Funding for this research was provided by the University of Wisconsin-Madison’s Hilldale Undergraduate/Faculty Research Fellowship and Vilas Trust and the National Park Service Fuels Reserve Funds (Task Agreement P22AC00588). Special thanks to Monica Turner for suggestions that improved this article; Becky Smith, Diane Abendroth, Alyssa Milo, Annie Carlson, Eric Reinertson, and Art Truman for assistance with field season logistics; and Zach Ausavich, Madie DeMarco, and Eileen Mavencamp for essential help with forest recovery field data collection.