Arctic Beavers

Beavers are poised to invade and radically remake the Arctic.

In the summer of 2023, University of Alaska Fairbanks ecologist Ken Tape walked across the tundra on the outskirts of Nome, Alaska, to a site where a shallow stream just a few meters wide had flowed 2 years before. In its place he found an enormous pond, created by a dam made of branches bearing the distinctive marks of beaver incisors.

It was a vivid illustration of how beavers are transforming the Arctic. In Tape’s past work studying Arctic landscapes, such places changed little over decades. “It gives you a sense of timelessness,” he says. “With beavers, that couldn’t be further from the truth,” as the chunky rodents quickly replumb vast areas by building dams that can stretch hundreds of meters.

Soon, the land-altering power of beavers could be felt in a region currently beyond their reach: the farthest northern parts of the Alaskan Arctic. In a 30 July paper in Environmental Research Letters, Tape and James Speed of the Norwegian University of Science and Technology forecast that as a warming climate eases Arctic temperatures, beaver populations will march northward, sweeping across Alaska’s North Slope this century. Their arrival could bring dramatic change, the researchers say, upending ecosystems in places such as the Arctic National Wildlife Refuge and accelerating the loss of permafrost that stores vast amounts of carbon. (...)

Tape has spent the past decade documenting this upheaval in parts of the Alaskan Arctic farther south and west, including the Seward Peninsula, where Nome is located. When he and colleagues scrutinized aerial photos of the region from the middle of the 20th century, they found no sign of the distinctive ponds beavers create to protect their mound-shaped lodges, accessible only underwater, and to cache branches for food in winter.

Today, satellite images show more than 11,000 beaver ponds dotting the Arctic tundra south of the Brooks Range, a wall of mountains running east to west that isolates the North Slope. The number there doubled from 2003 to 2017. (...)

Tape suspects warmer weather is critical because it means more unfrozen water in winter. A completely frozen pond can trap beavers in their lodges and make food caches inaccessible. Milder winters could preserve pockets of liquid water around springs or ponds. Melting permafrost also creates more groundwater-fed springs. And earlier spring thaws enable beavers to forage just as their food supplies dwindle.

“The ecological bottleneck for beavers is the end of winter,” Tape says. “Now imagine that comes 2 weeks earlier.”

Using computer models that forecast how a warming climate could expand the amount of Alaskan tundra suitable for beavers, the researchers found that the area dotted with ponds could nearly double by 2050, and more than triple by the end of the century, from 30,000 square kilometers to 99,000 square kilometers. In these scenarios, beavers would breach the Brooks Range and spread across the North Slope to the shores of the Beaufort Sea. (...)

This isn’t the first time beavers have occupied the Arctic, notes Emily Fairfax, an ecohydrologist at the University of Minnesota Twin Cities. There is fossil evidence of beavers in the Alaskan Arctic—though none has been found in the North Slope—dating to between 6000 and 10,000 years ago, when temperatures there were warmer and the landscape more forested. In fact, it’s thought that beavers might have evolved to build dams and cache food to adapt to one of the Arctic’s cooling phases millions of years ago. Still, Fairfax says the forecast that sensitive North Slope ecosystems “will probably be full of beavers is probably going to cause a lot of strong reactions.”

Residents of the Arctic have mixed feelings about their new neighbors. Ezra Adams, a member of the Native Village of Noatak, just south of the Brooks Range, says his father first saw a beaver there in the late 1990s, when Adams was 6 years old. Now, the animals have altered his family’s way of life. Their dams have reduced creeks where Adams once caught whitefish and salmon to a trickle. When out trapping or gathering firewood in the winter, he must beware of breaking through the ice on beaver ponds. Whereas his father once drank straight from lakes in the backcountry, Adams now brings treated water to avoid giardia in beaver feces. There are some upsides. Adams uses beaver meat to bait traps and beaver pelts for garments. “They provide a lot for our trapping,” Adams says. “But then for the general population it would be beneficial if there weren’t as many.”

Researchers, too, see both risks and benefits in beaver expansion. New ponds could become hot spots for songbirds and other wildlife. But they also hasten the thaw of permafrost, promoting the release of planetwarming carbon dioxide. A soon-to-be-published survey of 11 beaver pond systems in Arctic Alaska, for example, found that the water-covered area increased more than 600% once beavers arrived. Nearby ground thawed so much that researchers could plunge 1.2-meter-long rods used to test permafrost all the way to the tip.

Ponds could also create ample new habitat for microorganisms that convert carbon to methane, an even more potent warming gas, Griffin notes. “If we are going to start having expansion of wetlands because of beaver dams, how is that going to tip the balance between carbon and methane?” he wonders.

He might soon find out. Tape has already stumbled on one beaver pond on the northern slope of the Brooks Range. Although it disappeared a few years later, the pond showed beavers can cross the mountains. To spread even farther north, Tape notes, “they just have to swim downstream.”

by Warren Cornwall, Science |  Read more:

Image: Ken Tape