Alaskan beavers are carving out a growing web of channels, dams and ponds in the frozen Arctic tundra of northwestern Alaska, helping to turn it into a soggy sponge that intensifies global warming.
On the Baldwin Peninsula, near Kotzebue, for example, the big rodents have been so busy that they're hastening the regional thawing of the permafrost, raising new concerns about how fast those organic frozen soils will melt and release long-trapped greenhouse gases into the atmosphere, said scientists who are studying the beavers' activity.
The number of new beaver dams and lakes continues to grow exponentially, suggesting that "beavers are a greater influence than climate on surface water extent," said University of Alaska, Fairbanks scientist Ken Tape, a co-author of a new beaver and permafrost study published today in the journal Environmental Research Letters.
The research is based on images from commercial satellites that show landscape changes in greater detail than just a few years ago, as well as older images that show larger-scale changes. The precise measurements enabled the researchers to quantify how beavers are reshaping the landscape.
On the Baldwin Peninsula, Tape said the beavers are following a northward spreading belt of shrubs and trees, part of an intensifying cycle of Arctic changes driven by global warming. As they go, they destabilize permafrost and trigger a cascade of effects.
"They build a dam, the pond water gets deeper, it floods a bunch of tundra, which absorbs more heat than the permafrost," Tape said. "It thaws vertically down and to the sides and it collapses the banks."
A Hammer Hitting the Arctic on the Head
The bigger and deeper the pools made by the beavers, the warmer the water. The larger pools hold heat longer, which delays refreezing in autumn. Tape said Arctic vegetation, permafrost, hydrology and wildlife are all linked. Even against the backdrop of other recent Arctic global warming extremes, like raging wildfires, record heat waves and dwindling glaciers and sea ice, the impact of beavers stands out, he said.
"It's not gradual change," he said. "It's like hitting the landscape with a hammer."
"And it's a continual change that the Arctic is just not used to," he added.
The study found that, from 2002 to 2019, the number of dams grew from 2 to 98 in a 38.6-square-mile study area near Kotzebue. In another study area covering all of the northern Baldwin Peninsula, the number of dams increased from 94 to 409 between 2010 and 2019. Overall, beaver-influenced bodies of water accounted for two-thirds of the 8.3 percent increase in surface water area in the Kotzebue study area during the 17-year period.
As a next step, the research team will try to calculate the effects across wider Arctic regions, which would help more accurately forecast greenhouse gas emissions from thawing permafrost.
"We're talking about what's going to happen in the next 20 years to the end of the century," Tape said. "Beavers are a disturbance regime by themselves."
Another way to see them is as "agents of Arctic adaptation," said Ben Goldfarb, author of a recent natural history book that shows how beavers could help many other species, including humans, survive the era of rapid, human-caused climate change.
"Beavers create fantastic habitat for all kinds of species, like songbirds and moose," Goldfarb said. "All of those species are moving northward because of climate change, and beavers are preparing the way." As a habitat-creating keystone species, beavers are also important food for wolves, and recent research shows that beaver ponds are good at keeping carbon locked up, he added.
Beavers may even hold the key to survival for some salmon species that are losing their streams to global warming and other changes farther south.
"We're losing salmon in other places. If they're going to shift their climate envelope, they're probably going to need beavers to help them," Goldfarb said.
A Changing Landscape
Satellite views suggest that there is widespread potential for new beaver habitat across the Arctic, said Ingmar Nitze, a geoscientist studying permafrost and carbon with the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research and a co-author of the study.
"I'm mapping landscape changes in the Arctic, not restricted to Western Alaska, but big areas in northwestern Canada, eastern Canada," Nitze said. "Beavers are pioneers at the frontier where vegetation is expanding. They are checking out new areas."
The expansionist beavers are building their new structures around previously drained lakes in areas where the permafrost is not continuous. Even a small dam at a lake outlet creates a big lake that can increase thawing of a large area of adjacent permafrost, Nitze said.
Lead author Ben Jones, also with the University of Alaska, Fairbanks, said research about increased beaver activity in Canada made him curious to look at an area in Alaska close-up.
"With the images from the high-resolution commercial satellites, we started to dive into the areas that Ingmar was seeing getting wetter or drier over time," he said, referring to Nitze. "We could zoom in and see the dam building activity."
If beavers are the primary drivers of permafrost degradation on the Baldwin Peninsula, that has wider implications for tracking surface area changes across similar parts of the Arctic where beavers may advance, he said.
In lowland Arctic regions, the basins favored by beavers can account for 50 to 80 percent of the landscape. Currently, more than 10,000 beaver dams have been mapped across northwestern Alaska and that data is being used in models to pinpoint the impacts of the new water bodies on permafrost and the carbon cycle.
Permafrost researcher Merrit Turetsky, director of the University of Colorado, Boulder's Institute of Arctic and Alpine Research, said it's not yet clear how beaver impacts may affect regional-scale carbon cycles, but that it's " important to pay attention to all ecosystem-engineers such as the beaver."
One of Many Indicators
People who live in the Arctic noticed the beaver expansion some time ago, and not just in connection with climate change and permafrost, said Vladimir Romanovsky, head of the University of Alaska, Fairbanks Permafrost Laboratory. Residents of indigenous Arctic communities told him they are concerned that the beavers could bring disease to the streams that provide their water. Some beaver populations spread a form of amoebic dysentery, he said.
Measuring the effect beavers have on permafrost is useful and interesting because it's one of the many signs of how fast and dramatically the Arctic is changing right now, he said.
The heating is melting Arctic sea ice, Earth's reflective heat shield, which intensifies warming and likely shifts weather and wind patterns in the Northern Hemisphere in ways that can contribute to extreme storms, heat waves and drought. Melting Arctic glaciers and ice sheets raise sea level, and a massive thaw of permafrost could release a new surge of greenhouse gases.
Romanovsky said it's hard to measure the spatial extent of the melting because so many vast permafrost areas are so remote. But a global monitoring network of about 350 sites shows permafrost is warming about .8 to 1.6 degrees Fahrenheit every 10 years. In one of the coldest parts of the Arctic, in northern Alaska, permafrost 65-feet deep has warmed more than 5 degrees Fahrenheit in the last 30 years.
"That's the coldest permafrost we have. We started measuring it at between minus 6 (21.2 degrees F) and minus 9 degrees Celsius (15.8 degrees F) 35 years ago. Now it's at minus four degrees Celsius (24.8 degrees F), halfway to thawing, so in another thirty years it will be close to zero Celsius (32 degrees F) which means it's thawed," he said.
At the current rate of warming, at least half of all 9 million square miles of Arctic permafrost will be thawing, he said. About 24 percent of land in the Northern Hemisphere has permafrost beneath it, according to the National Snow and Ice Data Center.
Romanovsky said the impacts of beaver ponds shouldn't be discounted because they can compound other impacts like the current heat wave gripping the Siberian Arctic, which followed a record-warm winter in the region, and is tied to the surge of Arctic wildfires in recent years.
That means the seasonal surface thaw of some permafrost areas will go deeper than usual, triggering the formation of small lakes that could, in turn, trigger the start of more widespread beaver colonization, he said.
"In very recent news, there is another serious wildfire in the Yakut area, above the Arctic Circle, the northernmost fire in Siberia," he said. "That's part of this deal, as well. The cycle of impacts from warming and thawing makes the surface drier and more prone to fire."
Nitze said that, overall, it's a good time to be a beaver in the Arctic. Lakes that used to freeze solid now offer beaver-friendlier conditions because of thinner winter ice, and also because they aren't hunted as intensively as in the past.
"But we never would have dreamed they would seize the opportunity so intensively," he said, adding that their expansion will have consequences. "Anyone who wants to predict the future of the permafrost should be sure to keep the beaver in mind."