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Time in the Alaskan Arctic moves slowly. Layers of permafrost inter the chilled remains of mammoths and early humans; dwarf birches and lichens grow at almost imperceptible clips; glaciers creep down mountains at annual rates measured in millimeters. Abrupt disturbance is rare: There are no hurricanes or tornadoes, and few floods and wildfires. Landscapes are static. Change, when it comes, is subtle and incremental. Besides the beavers. 

Climate change has given the industrious mammals a foothold in Arctic Alaska, the vast tundra ecosystem in the northern reaches of the state. As the region has , new willows have sprouted and invited beavers, who both eat the inner bark and harvest stems for dam-building material. Beavers have also benefited from more open water, as their ponds are less likely to freeze solid in balmier winters. Near the city of Kotzebue in western Alaska, beaver dam construction spiked 50-fold between 2002 and 2019. “Just about everywhere you go, you’re going to run into a beaver dam,” says Cyrus Harris, an Iñupiaq hunter and natural-resource advocate in Kotzebue.

Plenty of animals, including moose and red foxes, are moving into the fast-warming Arctic. But beavers aren’t just taking advantage of environmental change; they’re accelerating it. The indefatigable architects’ dams transform streams into chains of ponds and wetlands so immense they’re visible from space. In its 2021 Arctic Report Card, the National Oceanic and Atmospheric Administration called beavers a “” transmogrifying the tundra “stream by stream and floodplain by floodplain.”

The Arctic isn’t the only place beavers are booming. Once nearly exterminated for their pelts, 10 to 15 million beavers North America; they thrive in ecosystems as diverse as boreal forests and southwestern deserts. Conservationists and scientists hail them as ecological champions whose ponds filter out heavy metals and other pollutants, slow wildfires, store water, and furnish habitat for birds including Hooded Mergansers and Trumpeter Swans. Today states like California, Colorado, and Washington are aggressively pursuing their restoration. “There’s been this great positive feedback loop of encouragement for working with beavers,” says Emily Fairfax, a University of Minnesota beaver researcher. “They’re a super-valuable ecosystem ­engineer.”

In the High North, however, beavers have been cast as something more akin to antiheroes. Their ponds underlying permafrost and release heat-trapping methane, and Indigenous people have observed beaver dams blocking fish migrations. In 2017, deemed them “agents of Arctic destruction.” Harris considers them an “invasive species.”

This was a different beaver story than I was accustomed to telling. In 2018 I published a book on the movement to re-beaver North America, and I’ve seen beavers work wonders: They’ve turned seasonal trickles into perennial streams, revived trout populations, and captured contaminants better than many wastewater treatment plants. They’re the ultimate keystone species, stout miracle workers that can address an array of environmental ills. Ken Tape, a University of Alaska Fairbanks biologist who studies the species, likewise seems more fascinated than perturbed by their Arctic takeover. “It’s becoming a more dynamic place,” he says, “and it’s hard not to be excited about that.” 

Could a rodent the size of an Airedale terrier really be terraforming a region as vast and timeless as the tundra? I wanted to see some Arctic Alaska beaver ponds for myself. So I went north.

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he city of Nome perches on the Seward Peninsula, the arm of western Alaska that juts into the Bering Sea. For millennia the Iñupiat have inhabited the peninsula, called Sitnasuak. Nome was founded at the turn of the 20th century after miners struck gold, and today it’s mostly known as the terminus of the Iditarod dogsled race. It also sits near the front lines of beavers’ northward march. Over the past several decades, they’ve dispersed into the region by swimming up- and downstream from their natal lodges, waddling overland between watersheds, and, though freshwater animals, cruising the Bering Sea between river mouths. “There are some very, very healthy beavers here,” one trapper told me. 

One morning I drove with Tape and his research team north from Nome along a potholed dirt highway. Although the town lies just below the Arctic Circle, the treeless, green-gray tundra gave off strong Arctic vibes. Low clouds clung to the mountains and musk ox browsed the roadside, lending the scene a Pleistocene cast. Telephone poles unmoored by thawing permafrost tilted at funhouse angles.

Few researchers have observed the region’s changes more closely than Tape, who cut his teeth studying shrub expansion in the Arctic and wildlife like moose, snowshoe hares, and Willow Ptarmigan that followed. Around 2016 his thoughts turned to beavers, the most influential of the new browsers, which prompted him to connect with Benjamin Jones, a University of Alaska Fairbanks specialist in applied remote sensing. In a 2018 study, “Tundra Be Dammed,” Tape, Jones, and their colleagues compared mid-century aerial photographs with modern satellite images to show that Northwest Alaska, beaverless in the 1950s, was rapidly becoming dotted with rodent-built wetlands. They’ve since calculated that more than stipple the Alaska Arctic. “Even after that first paper, people shrugged off beavers, like they were just a novelty,” Tape said as we jounced past derelict mining cabins. “We could say, ‘No, whole streams are being transitioned.’ ”

After an hour, we arrived at one of Tape’s research sites. Like so many beaver ponds, this one inspired awe: a two-acre sweep of water held back by a curving 600-foot-long rampart. A dome-shaped lodge rose from the pond like a volcanic island. Short-billed Gulls swooped and screamed, defending a nest they’d laid atop the lodge’s crown, as the crew, mostly graduate students, fell to work. Some checked groundwater wells to determine whether beavers had saturated the floodplain, while others measured water temperature and oxygen content and scooped up samples.

Tape and a colleague set to measuring the depth of the permafrost, the underground layers of soil, sand, and gravel bound together by long-frozen water. They walked roughly 200 feet from the pond and jabbed a long metal pole into the tundra. It sank about a foot, then thunked audibly against a rock-hard lens of permafrost. They moved closer and closer to the pond, shoving the probe into the ground as they went. The nearer they got to the water’s edge, the deeper the probe went. At the pond’s marshy fringe, the 10-foot probe disappeared into the earth without hitting ice at all. To the extent the researchers could measure, the permafrost had vanished.

This wasn’t surprising: As an Arctic adage goes, water is the death of permafrost, just as it’s death to the ice cubes in your glass. And beavers, by spreading water across the landscape and pooling it underground, are permafrost killers. As permafrost thaws, it releases carbon that has been stored for centuries within frozen plants, animals, and other organic matter. That, in turn, is devoured by methane-emitting microbes. In a , Tape and others found that beaver ponds on the Arctic tundra cough out around 50 percent more methane, a greenhouse gas roughly 30 times more potent than carbon dioxide, than other waterbodies.

In other words, Arctic beavers sit within a climatological feedback loop, both exploiting warming and exacerbating it—a that can turn at astonishing speeds. A few days later, we visited an abandoned beaver pond that resembled an enormous crater within a collapsing permafrost plateau. Truck-size wedges of sod tumbled across the pond’s muddy, exposed floor. Evidence of beaver handiwork was everywhere, mostly in the form of burrows they’d excavated in the banks, which had funneled water laterally into the frozen earth and undermined the permafrost. During a 2019 rainstorm, one of their dams had breached, triggering a flood that gouged out the unstable permafrost terraces. Although the beavers moved on, their pond continued to thaw the surrounding ice, peeling off the massive earthen blocks that now littered the valley. “When you think about permafrost degradation, it can take decades or centuries,” Jones said as we surveyed the rubble. “But a beaver can almost do it in a year.”

To Tape’s mind, the pace and scale of these changes force us to reconsider what, in ecological terms, a beaver is. It’s fundamentally unlike migrants such as moose or snowshoe hares, whose own browsing does little to change the Arctic. Instead, beavers are more akin to wildfire, another transformative force that’s recently become more prevalent upon the tundra. “All of a sudden a beaver shows up,” Tape marveled, “and everything just looks completely different.” 

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efore we indict a humble rodent for the despoliation of the Arctic, some perspective is in order. While beavers are releasing methane in Alaska, elsewhere they sequester carbon by storing organic material in pond-bottom sediment. And compared to ongoing and proposed development—the Willow oil-drilling project in the National Petroleum Reserve, for example—beavers hardly register as a source of atmospheric carbon or a force of landscape-scale change. If anyone was responsible for damaging Alaska, it seemed to me, it was fossil fuel companies and drill-happy politicians. “It’s almost like they’ve become a scapegoat,” says Seth Kantner, a writer in Kotzebue.

Whatever beavers mean for the carbon cycle, there’s no ambiguity about their biodiversity benefits. In the Lower 48, they furnish breeding pools for frogs, rearing ponds for trout, and fishing grounds for otters. Few animals profit more from beavers than birds. Waders like Great Blue Herons stalk fish in their ponds; cavity nesters like Wood Ducks dwell in drowned trees; and warblers of all stripes perch and feed in coppiced willows. In Poland, researchers have found that overwintering birds are more diverse and abundant not only at beaver ponds themselves, but well into the surrounding forest—making beavers an aquatic rodent with massive terrestrial impact.

The Arctic seems no different: Everywhere we went, oases constructed by beavers hummed with life. Wilson’s Warblers flitted through willows at spongy wetland margins; Green-winged Teals and Harlequin Ducks bobbed atop glassy ponds. At one site 30 miles north of Nome, we witnessed a striking demonstration of an ecosystem made bountiful by beavers. We arrived at a mirror-like pond tucked against a mist-shrouded mountain to find that the resident beavers had gone bonkers since Tape’s team visited a year earlier. Beaver-built bulwarks weaved across the floodplain, cleaving a once-sedate stream into countless labyrinthine channels. “Oh yeah, dude, it’s happening,” Tape enthused, his scientific stoicism no match for this impressive rodent architecture. One dam, its crest caked with fresh mud, extended 100 feet onto the tundra, submerging still-green lichens, mosses, and grasses—indicating they’d just recently been inundated. This ancient ecosystem was transforming in real time.

New life, too, was pouring into the valley. As Tape’s team worked, a pair of Red-necked Phalaropes alighted on the pond and, to my astonishment, promptly performed their signature behavior: paddling in circles and pecking avidly at invertebrates trapped in the vortices their feet kicked up. Beavers had flooded this patch of tundra just days earlier, but birds were already taking advantage.

The scene suggested an idea that had been gnawing at me for days: Rather than agents of Arctic destruction, beavers may be agents of Arctic adaptation. Researchers estimate that climate change already has nearly half of the world’s species on the move. The Arctic is becoming a refuge for some of these immigrants: Salmon follow receding glaciers into northern rivers; moose browse on emergent willow; migratory birds arrive on their breeding grounds earlier and depart later. Elsewhere on the continent these creatures find succor in beaver ponds; they may in the Arctic, too. 

To date, Tape’s team has primarily studied the geophysical impacts of beavers, not the ecological ones. That’s changing. The group is collecting water samples to analyze for genetic traces of fish, insects, and duck and songbird species that seasonally inhabit the Arctic—a monitoring technique that should provide the team with new insights into evolving wildlife communities. Sebastian Zavoico, a Ph.D. student in Tape’s lab, also recently installed acoustic monitors at several ponds to record birdsong continuously during migration season. The audio will help him determine whether beavers are truly enhancing avian abundance and shifting community composition.

“Because beavers remove ice, maybe these ponds become refugia in the spring and the fall,” Zavoico said as we watched the phalaropes forage. “Maybe it’s really good for waterfowl, or maybe invertebrates come out earlier and songbirds are able to nest earlier and have a more successful brood.” Through this lens, Arctic beavers are both opportunists and altruists, terraforming homesteads for longtime residents and new arrivals alike.

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or all of beavers’ virtues, however, few animals are more polarizing. In the Lower 48, they’re blamed for flooding roads, felling fruit trees, and damming irrigation ditches, offenses for which workers for Wildlife Services, the USDA’s branch tasked with managing problematic animals, kill more than every year. We embrace beavers one day, execute them the next.

Nome residents, too, seemed conflicted about the beavers in their midst. When I visited, some complained about flooded roads; others lauded improved fishing. One woman told me beavers created terrific salmon habitat. Another said they’d been trying to drown her dog. At a coffee shop, a gold miner named Bob, clad in hard hat and waders, gave me an earful about how beavers formed wetlands, which in turn allowed the government to impose regulations. At the visitor center, a crusty old birder told me a horrifying, impossible-to-verify story, the gist of which was that a beaver had recently hauled itself onto a beach, whereupon townsfolk flung logs at the poor creature in an attempt to bludgeon it to death. “I was pretty pissed off,” he growled.

The few beaver aficionados I met took a utilitarian perspective. One day I visited Drew McCann, a bank manager and recreational trapper who, locals told me, was among Nome’s foremost beaver experts. On his phone, McCann scrolled through photos of dead, bedraggled beavers captured via snare and trap. Beaver stew was pretty good, McCann said, and the meat and scent glands, called castor sacs, can be used in lynx traps. (The average lynx pelt runs around $100 at auction these days; a beaver pelt, just $20 or $30.) The meat, McCann says, “is the number-one bait.” As for the castor sacs: “The smell goes a long ways.”

While most people considered it a given that beavers had recently arrived, I couldn’t help but wonder whether they were truly colonizing the Arctic or recolonizing it after being wiped out by fur trappers decades earlier. It wouldn’t be the first time humans had purged beavers from a landscape and then claimed they’d never been there: The rodents were considered nonnative to much of until the 2010s, when researchers assembled archaeological and linguistic evidence proving they’d lived in the state before being nearly extirpated in the 1800s. Arctic paleontologists have likewise found scattered beaver bones and teeth dating back 8,000 years, and place names like Beaver Creek, near Nome, hint at their possible presence. On the other hand, the paucity of beaver stories among Indigenous communities argues for their absence. “One of the questions we haven’t really been able to answer is where beavers were before the fur trade,” Tape says.

Whatever the answer, beavers certainly feel like an incursion to many Arctic residents. Harris, the Iñupiaq hunter, didn’t see his first beaver until the early 1990s. Although he shoots a beaver once in a while for its pelt and meat—he says it tastes like seal—he’s no great fan of the animals. “We’re not a beaver people,” he says.

Harris is most concerned about what beavers mean for fish. In the Lower 48, beavers create prime salmon habitat, but near Kotzebue, Harris says that their dams have prevented whitefish—a species that lacks salmon’s leaping prowess—from entering streams where Alaska Natives historically harvested them. “Some of the hotspots for our traditional fishing grounds, beaver dams are completely blocking them,” Harris says. Beavers have also flooded some routes traveled by foot and boat. “Beavers and the Arctic don’t go together,” says Alex Whiting, environmental program director at the Native Village of Kotzebue.

What, if anything, to do about it? Harris and Whiting are more or less resigned to beavers, since low pelt prices have discouraged villagers from trapping. Some Alaskans have proposed a bounty program, an approach that seems unlikely to work. “Even if you went to town on the Baldwin Peninsula and wiped out every beaver in one year,” Whiting says, “it would only take a year or two and this place would be full of beaver again.” They reproduce quickly, disperse widely, and engineer habitats to their own advantage. Beavers, in the end, are likely inevitable.

They’re also conspicuous harbingers of a far more powerful force: climate change. The Arctic has nearly four times faster than the global average since 1979, and for subsistence hunters like Harris, who describes the natural world as his “supermarket,” hotter temperatures have spelled chaos. Sea ice freezes later in fall and thaws earlier in spring, impairing the pursuit of marine mammals; storms batter the coast; novel species replace familiar ones. “We’re seeing lots of changes,” Harris says. “Everything is all together, all at once.” Arctic beavers confer their own distinct impacts, yes, but it occurred to me that they may be resented, in part, because they’re ­symbols—flesh-and-fur portents of a warming world.

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curious aspect of Arctic beaver discourse is this: We know much about how they’re altering the tundra, yet little about how they’ve adapted to their new circumstances. How have beavers, which don’t hibernate, managed to thrive in such an inhospitable environment? To me there seemed something profoundly relatable in their ability to modify their environs, to scrape out a home in a harsh and unfamiliar land. How could a rodent seem so human?

During my week in the Arctic, signs of beaver ingenuity were everywhere. Although all beavers are skilled diggers, the submerged networks of tunnels and cavities they’d excavated with their paws here were much deeper than those I’d seen in more temperate climes—likely to prevent ponds from freezing solid during the unforgiving winter. The lodges, too, were gargantuan, up to 10 feet tall and 30 feet wide—swollen with insulating mud. The beavers themselves were unusually active, often emerging to slap their tails in irritation or grab a willow snack. Elsewhere beavers favor a nocturnal lifestyle; here they’d adjusted to a land without night.

On my last day in Alaska, Zavoico and I clambered into an A-Star helicopter and flew north of Nome, over the mountains. The tundra, from above, was patterned by ice: A checkerboard of irregular polygons, cleaved by expanding permafrost veins, carpeted the earth, and frost boils erupted from the hills. We banked low, following a thread of river toward the Chukchi Sea, where polar bears stalk seals on dwindling sea ice. “This is pretty close to the edge of beaver range on the Seward Peninsula,” Zavoico said into his headset, and I wondered how they could possibly make a living here.

Yet they had. Along a skinny tributary called Teller Creek, a kidney-shaped pond sat within a willow copse. When the helicopter landed and we squelched over for a closer look, we found that the pond had formed behind a colossal dam, eight feet tall and solid enough to stroll across. Blocks of destabilized earth slumped into the creek, staining it the color of milky tea. Moose tracks pressed into the mud, and American Tree Sparrows perched on the massive lodge. Here were both sides of the Arctic beaver coin: permafrost degradation and ecological flourishing, collapse and oasis.

What’s next for the Arctic’s beavers? Today Alaska’s North Slope, the coastal plain that plunges away from the Brooks Range and toward the Beaufort Sea, remains free of beavers. To reach the slope, the rodents would have to waddle over a mountain pass patrolled by wolves or disperse west along the coast from the Kongakut River—daunting but not impossible tasks. “It kind of looks like it’s a matter of time,” says Tape. Like humans, beavers will soon have few lands left to conquer.

Like us, too, they will continue to transform the places they already live. Flying back to Nome, we soared over myriad sun-flecked lakes and streams, a rolling expanse ribboned with open water and fringed with halos of new willow. Although we passed a few lakeshore lodges, I was struck not by how many beaver ponds we saw, but by how few—and how much prime habitat beckoned to future waves of colonists. The future, it seemed, would be beavery. 

This story originally ran in the Spring 2024 issue as “Appetite for Construction.” To receive our print magazine, become a member by .