Beavers gnawing arctic permafrost

Alaska beavers are benefiting from climate change and are spreading rapidly. In just a few years, they have not only expanded into many tundra regions where they have never been seen before; They are also building more and more dams in their new homes, creating a host of new bodies of water. This could accelerate the thawing of permafrost soils and thus intensify climate change, as a US-German international research team reports in the journal. Environmental Research Letters.

When it comes to completely transforming a landscape, beavers are hard to beat. Very few animals are able to change their habitat as precisely as these brown-haired rodents, which can weigh up to 30 kilograms. Armed with sharp teeth, they fell trees and bushes and built dams, causing small valleys to fill with water and forming new lakes, which can easily measure a few hectares. “Their methods are extremely effective,” says Dr. Ingmar Nitze of the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) in Potsdam / Germany. They often build their dams at precisely those points where they can achieve major effects with minimal effort.

This is something Ingmar Nitze has repeatedly seen in the arctic regions of Alaska, where the American beaver is active. The researcher is an expert in remote sensing and is especially interested in those parts of the Earth where the ground is permanently frozen. Climate researchers fear that as temperatures rise, this permafrost could thaw more and more and become unstable. If that happens, it could release massive amounts of greenhouse gases, intensifying climate change.

Consequently, Nitze and his colleagues are monitoring the development of these landscapes with the help of satellite imagery. An interesting aspect in this regard: how lakes and other bodies of water are distributed. Because the water they contain is somewhat warmer than the surrounding soil, these lakes and ponds can further accelerate the thawing of permafrost. And beavers seem to be actively contributing to the process.

In 2018, Ingmar Nitze and Guido Grosse of the AWI, along with colleagues from the U.S., determined that beavers living in an 18,000-square-kilometer section of northwest Alaska had created 56 new lakes in just five years. For their new study, the AWI team, the University of Alaska at Fairbanks and the University of Minnesota at Minneapolis have taken a closer look at this trend. Using detailed satellite data and extended time series, the experts tracked beaver activities in two other regions of Alaska, and were surprised by what they found.

“Of course, we knew that beavers there had spread substantially in recent decades,” says Nitze. This is due in part to climate change; Thanks to rising temperatures, more and more habitats now offer the bushes animals need for food and construction material. Also, the lakes, which used to freeze solid, now offer more favorable conditions for beavers, thanks to their thinner seasonal winter ice cover. Finally, rodents are not hunted as intensively as in the past. As a result, it is a good time to be a beaver in the Arctic.

“But we never would have dreamed that they would seize the opportunity with such intensity,” says Nitze. High-resolution satellite images of the study area of ​​approximately 100 square kilometers near the city of Kotzebue reveal the scale of the animals’ activities there. From just two dams in 2002, the number had increased to 98 in 2019, an increase of 5,000 percent, with the construction of more than 5 dams per year. And the largest area studied, covering the entire north of the Baldwin Peninsula, also experienced a beaver dam boom. According to Nitze, “We are seeing exponential growth there. The number of these structures doubles approximately every four years.”

This has already affected the balance of the water. Apparently, rodents intentionally do their job in those parts of the landscape that can flood more easily. To do so, they sometimes block small streams, and sometimes the exits of existing lakes, which expand as a result. “But they especially prefer drained lake basins,” said Benjamin Jones, lead author of the study, and Nitze report. In many cases, the bottoms of these ancient lakes are privileged places for beaver activity. “Animals have intuitively discovered that damming outflow drainage channels at ancient lake sites is an efficient way to create habitat. Thus, a new lake forms that degrades the ice-rich permafrost in the basin, which increases the effect of increasing the depth of the designed body of water, “Jones added. These actions have their consequences: over the course of the 17 years studied, the total area of ​​water in the Kotzebue region grew by 8.3 percent. And about two-thirds of that growth was due to beavers.

The researchers suspect that there have been similar construction booms in other regions of the Arctic; consequently, they now want to expand their ‘beaver hunt’ across the Arctic. “Growth in Canada, for example, is probably even more extreme,” says Nitze. And each additional lake thaws the permafrost below it and on its banks. Of course, the frozen soil could theoretically recover after a few years, when beaver dams break; But no one knows if the conditions will be cold enough for that to happen. To Ingmar Nitze, all of these aspects mean that there are many reasons to keep an eye on these four-legged landscape engineers: “Anyone who wants to predict the future of permafrost must make sure to keep the beaver in mind.”