Beavers gnaw at the Arctic permafrost | Polarjournal
Beavers colonize water-rich landscapes and create new habitats with their structures and contribute to flood protection. In the Arctic, however, they could help to strengthen climate change. Photo: Ken Tape, Geophysical Institute, University of Alaska Fairbanks

In Western Europe, the return and re-spread of the beavers is taken with mixed feelings: While nature and animal supporters are happy about the increasing number of those cute rodents, for example, some farmers are not at all pleased about the presence of the builders, whereby interventions in the landscape by beavers are rather on a small-scale. It’s quite different in northern Alaska, where, according to a new study, they seem to be responsible for a faster thawing of the permafrost soil with their landscape conversions, which could significantly further fuel climate change.

With their sharp teeth, beavers cut down trees and shrubs, plant dams and completely redesign the landscape: they flood sinks and create new lakes that can cover several hectares of land. With their way of life, they are the best “ecosystem managers”: wherever beavers live, they create new, diverse habitats with their construction measures, which numerous other animals such as insects, small mammals and rare bird species like to accept – biodiversity is increasing rapidly.

The spread of North American beavers (Castor canadensis) in the Arctic tundra of Alaska, on the other hand, is viewed with great concern by scientists, who fear that the animals’ active construction activity could further exacerbate global warming. For several years, researchers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, the University of Alaska Fairbanks and the University of Minnesota, Minneapolis have been observing the rise of beavers in Alaska heading north. In their study, published in the journal Environmental Research Letters, they describe a veritable boom in dam construction in recent years.

This is not a good development for the permafrost soil, because the water of the resulting new lakes is warmer than the soil and leads to the thawing of the permanent frost areas. Scientists are concerned that the spread of beavers will accelerate the release of methane and carbon dioxide from permafrost into the atmosphere.

Beaver dams, such as here in The Algonquin Provincial Park in Canada, block larger and smaller rivers and create new lakes. Photo: Ingmar Nitze, Alfred Wegener Institute

Using high-resolution satellite imagery, the scientists were able to locate numerous dams and found that the animals build their dams precisely where new lakes could most likely increase the thawing of the permafrost. According to Benjamin Jones, first author of the study and a scientist at the University of Fairbanks, and Ingmar Nitze, a geoscientist at the Alfred Wegener Institute in Potsdam, former lake basins, which have since dried up, are among the beavers’ preferred grounds. “The animals intuitively found that the accumulation of the drain salsials in the places of the former lakes is an efficient way to create habitat. This creates a new lake that breaks down the ice-rich permafrost in the basin, which also increases the depth of the artificial body of water,” Jones adds.

“The thing about permafrost is that the water interacts very strongly with the frozen soil under it. The more surface water you have, the worse it is for the permafrost – because in winter the cold air cannot re-enter the ground and the water stores a lot of the heat and can even penetrate the ground.»

Ingmar Nitze, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam
The study area on the Baldwin Peninsula in northwestern Alaska. (a) Overview map. (b) Land cover map highlighting tundra and wetland vegetation (light brown and light blue). Wooded areas are marked in green. (c) Digital terrain model for the Kotzebue (100 km2) and northern Baldwin Peninsula (430 km2). Illustrations: Jones et al. 2020

In the study area of about 100 square kilometers in northwest Alaska near the town of Kotzebue on the Baldwin Peninsula, the number of dams has increased from two in 2002 to 98 in 2019 — an increase of 5,000 percent. Beaver dams in the larger study area of 430 square kilometers in the north of the Baldwin Peninsula have increased from 94 in 2010 to 174 in 2013 and 409 last year. “We see exponential growth,” explains Nitze. “The number of these structures doubles every four years.” In the 17 years studied, the water area in the Kotzebue region has increased by 8.3 percent, and two-thirds of this increase is attributable to beavers.

Aerial photographs of the tundra in northwest Alaska. The upper images were taken within the study area in 2016 and show the tundra region. The images below are from a similar tundra at Hotham Inlet in 2015 (bottom left) and 2011 (bottom right) and show beaver dams in a drained lake basin outlet or along a pearl stream. Photos: Jones et al. 2020

Several different factors explain why the beavers migrated to a region they wouldn’t normally call their home, Nitze says. One of them is climate change, which changes the typical treeless tundra.

“We see an increase in vegetation. There are more shrubs, so everything the beavers need to build their dams or as food is there,” he said. In addition, the lakes that used to be frozen now offer better conditions for beavers, as they have a thinner seasonal ice sheet in winter.

Since the tundra is not the usual habitat of the beavers, they also do not have to fear predators or competition for resources. Moreover, the animals are now better protected by federal law and are hunted far less by humans than they used to be.

With climate change, the originally treeless tundra has already changed so that beavers find sufficient food and building materials. Photo: Ken Tape, Geophysical Institute, University of Alaska Fairbanks

The authors assume that the beavers are acting in similar ways in Canada and Siberia. “In Canada, for example, the gains are probably even greater,” says Nitze. Each additional lake thaws the permafrost on its shores and at its bottom. The frozen soil can theoretically recover when the beaver dams break. But no one knows if it will be cold enough for it.

According to Nitze, there are many people trying to quantify methane and CO2 emissions from lakes in the Arctic, but not yet specifically from beaver lakes. “This is a very new topic and something that we have uncovered in recent years. Beavers can have a very significant impact on these landscapes, so there is no real quantification for these lakes yet, but that will happen in the future.”

Julia Hager, PolarJournal

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