The beaver may be an unlikely agent of climate change, but the cuddly-looking creatures are transforming the Arctic landscape in a way that could be exacerbating global warming, a new study has suggested.
With their sharp teeth, beavers fell trees and shrubs and build dams, which flood small valleys and form new lakes that can cover several hectares of land.
These new water bodies contribute to the thawing of the frozen permafrost soil, which is a huge natural reservoir of methane — a potent greenhouse gas.
Scientists are concerned that as the permafrost degrades, the climate-changing
In the past few years, scientists have spotted beavers in the Alaskan tundra where they've previously never been seen before — and the animals have been enjoying a dam-building boom in their new neighborhood, according to the study of high-resolution satellite imagery published in the journal Environmental Research Letters Monday.
They also seem to be building their dams and creating new lakes in the very locations that are most likely to intensify the thawing of the permafrost.
"We're seeing exponential growth there. The number of these structures doubles roughly every four years," said Ingmar Nitze, a researcher from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research in Potsdam, Germany, and author of the study.
"Their methods are extremely effective."
The study found that the number of beaver dams in a 100-square-kilometer area surrounding the city of Kotzebue, northwest Alaska, increased from just two in 2002 to 98 in 2019 — a 5,000% increase. Beaver dams in the larger, 430-square-kilometer area on Alaska's Baldwin Peninsula have increased from 94 in 2010 to 174 in 2013 and 409 last year.
"It's possible to see them and spot them (the dams) in the imagery. It's also possible to see the development of lakes. They had a distinctive signal," said Nitze.
BLAME IT ON THE BEAVERS?
Several different factors explain why the beavers have occupied a region they wouldn't normally call home, said Nitze. One is climate change, which is altering the typically treeless tundra.
"We see an increase in vegetation. There are more shrubs coming in there so all the stuff beavers need to build their dams, or as food, is there," he said. Furthermore, the lakes, which used to freeze solid, now offer friendlier conditions for beavers, as a result of their thinner seasonal winter ice cover
The tundra is also not the beavers' usual habitat so they face no predators or competition for resources, plus the animals are better protected now by U.S. federal law and hunted far less by humans than they used to be.
Because the lakes the beavers create contain water that is warmer than the surrounding soil, the new bodies of water accelerate the permafrost thawing.
"The thing about permafrost is that water interacts very strongly with the frozen ground beneath it," Nitze said. "The more surface water you have, the worse it is for the permafrost--because in the winter the cold air cannot penetrate again into the ground, and the water stores a lot of the heat and can even penetrate it into the ground," he said.
Lakes and water bodies influenced by beavers accounted for two-thirds of the 8.3% increase in total surface water area in the Kotzebue study area during a 17-year period, the study found.
The beavers also seemed to intuitively target drained lake basins, turbocharging the impact they had on the landscape and the permafrost.
"It's a special landscape. There's typically a lot of lakes but they are dynamic so they can drain and leave a lot of basins ... and these beavers are smart enough to block the outlet and refill the basin again. They dam up a lot of area with minimum effort."
Nitze said the beaver dam-building boom was also likely taking place in the Canadian tundra, and could also be happening in Siberia.
"We're working to expand the analysis on a bigger scale."
Some climate scientists think that .
"There are a lot of people trying to quantify methane and CO2 emissions from lakes in the Arctic but not specifically yet from beaver lakes," said Nitze.
"It's a very new topic and something we have uncovered over the past few years. Beavers can have a quite significant impact on these landscapes, so there's no real quantification yet for these lakes but it will be done in the future."
