With their sharp teeth, beavers cut down trees and shrubs and built 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 frozen permafrost soil, which is a huge natural reservoir of methane, a powerful greenhouse gas.
In recent years, scientists have identified beavers in the Alaskan tundra where they have never been seen before – and the animals have enjoyed a boom in dam construction in their new neighborhood, according to the study of high-resolution satellite imagery published on the Environmental Research Letters Monday.
It also appears that they are building their dams and creating new lakes in the places that are most likely to intensify the thawing of permafrost.
“We are seeing exponential growth there. The number of these structures doubles roughly every four years,”
“Their methods are extremely effective.”
The study found that the number of beaver dams in an area of 100 square kilometers surrounding the city of Kotzebue in northwestern Alaska increased from just two in 2002 to 98 in 2019, an increase of 5,000. %. Beaver dams in the largest area of 430 square kilometers on the Baldwin Peninsula in Alaska increased from 94 in 2019 to 174 in 2013 and 409 last year.
“You can see them and locate them (the dams) in the pictures. You can also see the development of the lakes. They had a distinctive sign,” said Nitze.
Do you blame beavers?
Several factors explain why beavers have occupied a region 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 shrubs that come in there, so all the things that beavers need to build their dams, or as food, is there,” he said. In addition, lakes, which once freeze solids, now offer more favorable conditions for beavers, thanks to their thinner winter cover
In addition, tundra is not the usual habitat of beavers, therefore they do not have to face predators or competition for resources, moreover animals are now better protected by United States federal law and hunted much less by humans than they were in the past.
Since lakes created by beavers contain warmer water than the surrounding soil, new water bodies accelerate the thawing of permafrost.
“The advantage of permafrost is that the water interacts very strongly with the frozen ground below,” said Nitze. “The more surface water you have, the worse it is 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.
The study found that lakes and water bodies affected by beavers accounted for two-thirds of the 8.3% increase in the total surface water area in the Kotzebue study area over a 17-year period.
Beavers also seemed to intuitively strike empty lake basins, supercharging the impact they had on the landscape and permafrost.
“It is a special landscape. Usually there are many lakes, but they are dynamic, so they can drain and leave many basins … and these beavers are intelligent enough to block the outlet and fill the basin again. They restore a lot of area with the minimum effort. “
Nitze said that the boom in beaver dam construction was probably also occurring in the Canadian tundra and that it could also occur in Siberia.
“We are working to expand the analysis on a larger scale.”
“There are many people trying to quantify methane and CO2 emissions from lakes in the Arctic, but not yet from beaver lakes,” said Nitze.
“It’s a very new topic and something we’ve discovered in recent years. Beavers can have a fairly significant impact on these landscapes, so there is still no real quantification for these lakes, but it will be done in the future.”