Beavers Are Reshaping the Arctic Tundra. Here’s Why Scientists Are Concerned

Ponds made by the large rodents are causing permafrost to thaw, releasing methane and carbon dioxide once stored in the frozen Earth

A beaver sits in the water in front of a wall of mud. It's gnawing on a stick, and mud, roots and vegetation surround the water.
Beavers can create shallow pools of water when they build dams, changing the landscape.  Eric Heupel

Beavers have the ability to completely transform landscapes. They gnaw through trees, build dams and flood new areas to create ponds, earning them the title of "ecosystem engineers." But a northward migration of these bucktoothed builders has scientists concerned, Hannah Osborne reports for Newsweek.

A new report about beavers is part of the National Oceanic and Atmospheric Administration's (NOAA) annual Arctic Report Card. By comparing decades-old aerial images of a region in western Alaska with newer ones, researchers found the number of ponds created by beavers has doubled in the last 20 years. They found more than 12,000 ponds; in that same area in 1955, there wasn't a single one, Alexandra Larkin reports for CBS.

"We didn’t know what we would find and ended up being very surprised," Ken Tape, an ecologist at the University of Alaska, Fairbanks tells Oliver Milman for the Guardian.  

"There are areas of Alaska that had no evidence of beavers 50 years ago that are now apparently saturated with them," he says. "It’s just a matter of time before they head even further north. When you consider this is likely happening across the rest of the Arctic in Canada and Russia, that gives you an idea of the scope of this change."

Beavers can create shallow pools of water when they build dams. That has increased the total surface water in the region, raising concerns since these ponds are warmer than the surrounding ice, causing permafrost—the permanently frozen ground—to thaw out. Permafrost is a critical carbon sink, and its thawing releases carbon dioxide and methane that have been stored for years, Newsweek reports.

Researchers saw a dramatic increase in surface water across the region, and they attributed around 66 percent of this increase to the beavers' presence, CBS reports.

"Those ponds absorb heat better, they change the hydrology of the area and the permafrost responds to that," Tape tells the Guardian. "It’s accelerating the effects of climate change. When you realize what’s happened in western Alaska is likely to happen to northern Alaska, it does give you pause."

There's also an added concern about how the reshaped landscape and waterways will affect Indigenous communities in Alaska. Beaver dams could affect aquatic food webs and fish populations, as well as make boat access more difficult. More research is currently underway to parse through how the beavers will affect the ecosystem and Indigenous livelihoods, says Helen Wheeler, an ecologist at Anglia Ruskin University in England, in a statement.

It's still unclear why the beavers are expanding northwards in the first place. It could be that the effects of a warming climate—such as more abundant vegetation—has made the region more habitable to beavers, the Guardian reports. 

It could also be a booming population of beavers expanding northwards to predator-free zones, or a combination of the two.

"[It] is not entirely clear, but we do know that beavers are having a significant impact on the ecosystems they are colonizing," Wheeler says.