Beavers are now living as far north as the Arctic, researchers find

North American beavers are colonizing much further north than they used to, according to the U.S. National Oceanic and Atmospheric Administration's annual Arctic Report Card. Using satellite imagery, researchers found ponds with beaver engineering in northern Alaska and Canada.

The study concluded that the number of ponds created from beavers foraging and building dams has doubled in western Alaska in the last 20 years, with over 12,000 mapped. In contrast, researchers looked at decades-old aerial photography of the region and found no beaver ponds in the area prior to 1955.

The area has seen a drastic rise in surface water, and beavers were the dominant factor in almost 66% of such cases, researchers said. In such instances, beavers' dams made rivers more shallow and created inlets. As a result, new ponds are forming and the underlying permafrost is melting, which could affect fish populations and aquatic food webs, but researchers don't have all of the answers yet. 

"The true impact of the spread of beavers into the Arctic on the environment and the Indigenous communities who live there, is not yet fully known," lead author Dr. Helen Wheeler of Anglia Ruskin University said in a press release.

"However, we do know that that people are concerned about the impact beaver dams are having on water quality, the numbers of fish downstream of the dams, and access for their boats." 

Beavers were able to expand their range into the tundra due to an increase in trees and woody shrubs that they use to make lodges — even above the tree line, which was previously inhospitable to the large rodents. 

The team isn't sure if beavers' northward expansion is due to climate change or a reduction in beaver trapping, but they "do know that beavers are having a significant impact on the ecosystems they are colonizing," Wheeler said.

For next year's report, the team hopes to focus more on the Canadian expansion and continue to document the changes beavers bring to the tundra.