With their sharp teeth, beavers fell trees and bushes and built dams, which flood small valleys and form new lakes that can cover several hectares of land.
These new bodies of water contribute to the thawing of frozen permafrost soil, which is a huge natural reservoir of methane, a powerful greenhouse gas.
In recent years, scientists have seen beavers in the Alaskan tundra, where they have never been seen before, and the animals have been enjoying a dam-building boom in their new neighborhood, according to the study of satellite imagery from Alta resolution. published in Environmental Research Letters Monday.
They also appear to be building their dams and creating new lakes in the same places that are most likely to intensify permafrost thaw.
“We are seeing exponential growth there. The number of these structures doubles approximately every four years,” said Ingmar Nitze, a researcher at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research in Potsdam, Germany, and author of the study. .
“His methods are extremely effective.”
The study found that the number of beaver dams in a 100-square-kilometer area surrounding the northwestern Alaska city of Kotzebue increased from just two in 2002 to 98 in 2019, an increase of 5,000%. Beaver dams in the largest 430-square-kilometer area on Alaska’s Baldwin Peninsula have increased from 94 in 2019 to 174 in 2013 and 409 last year.
“It is possible to see and detect them (the dams) in the images. It is also possible to see the development of the lakes. They had a distinctive signal,” Nitze said.
Blame the beavers?
Several different factors explain why beavers have occupied a region that they would not normally call home, Nitze said. One is climate change, which is altering the typically treeless tundra.
“We see an increase in vegetation. There are more bushes coming in there, so everything beavers need to build their prey, or for food, is there,” he said. Also, the lakes, which used to freeze solids, now offer beaver-friendly conditions as a result of their thinner seasonal winter ice cover
The tundra is also not the usual habitat for beavers, so they face no predators or competition for resources, plus animals are now better protected by United States federal law and humans hunt them much less than they do. used to be.
Because the lakes that beavers create contain water that is warmer than the surrounding soil, the new bodies of water accelerate the thawing of permafrost.
“The thing about permafrost is that the water interacts very strongly with the frozen soil below it,” said Nitze. “The more surface water it has, the worse it will be for permafrost, because in winter cold air cannot penetrate the soil again, and the water stores a lot of heat and can even penetrate it into the soil.” he said.
Beaver-influenced lakes and bodies of water accounted for two-thirds of the 8.3% increase in total surface water area in the Kotzebue study area over a 17-year period, the study found.
Beavers also seemed to intuitively target the drained lake basins, increasing the impact they had on the landscape and permafrost.
“It is a special landscape. There are usually many lakes, but they are dynamic so they can drain and leave many basins … and these beavers are smart enough to block the exit and refill the basin. Area with minimal effort “
Nitze said the beaver dam construction boom was likely also occurring in the Canadian tundra, and that it could also be happening in Siberia.
“We are working to expand the analysis to a larger scale.”
“There are many people trying to quantify methane and CO2 emissions from Arctic lakes, but not specifically from beaver lakes yet,” Nitze said.
“It is a very new topic and something we have discovered in recent years. Beavers can have a fairly significant impact on these landscapes, so there is no real quantification for these lakes yet, but it will be done in the future.”
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