The current through western Alaska never looked like this. In aerial photography from the 1980s, it weaved cleanly through the tundra, thin as thread. Today, in satellite images, it appears as a string of black spots: one large dam after another, dozens of meters apart.
This is a transformation that is happening across the Arctic, the result of landscape engineering on an impressive scale. But this is no human effort to reform the world. This is the job of the North American beaver, and there is no sign of it stopping.
If the waddling rodents had made minor intrusions, researchers may never have noticed. But the animals are pouring in and pushing north into new areas. The animals’ total numbers are far from clear, but the dams they create are hard to miss: in the Arctic tundra of Alaska alone, the number of beaver dams on streams has doubled to at least 12,000 in the past 20 years. More lodges are scattered along lakes and river banks.
“What’s happening here is happening on a large scale,” said Ken Tape, an ecologist at the University of Alaska, Fairbanks, who tracks the influx of beavers into the sparse northern landscape. “Our modeling work, which is currently underway, shows that this entire area, the North Slope of Alaska, will be colonized by beavers by 2100.”
The predominance of beavers, which can weigh up to 45 kg, follows a collapse in hunting and the warming of a landscape that was once too dark for occupation. Global warming has driven the vegetation of the arctic tundra; the harsh winter is shorter, and there is more free-flowing water in the coldest months. Instead of cutting down trees for their dams, the beavers build them out of surrounding brush and create deep dams in which to build their lodges.
The new arrivals cause a lot of disruption. For some communities, the rivers and streams are the roads of the landscape, and the dams make effective roadblocks. As the structures increase, more land is flooded and there may be less fresh water downstream to drink. But there are also other, less visible effects. The animals are participants in a feedback loop: climate change opens up the landscape to beavers, whose dams drive further warming, attracting even more paddletail mates.
Physics suggested that this would happen. Beaver dams are new bodies of water covering bare permafrost. Because the water is warm – relatively speaking – it thaws the hard soil, which properly releases methane, one of the most powerful greenhouse gases.
Scientists now have evidence that this is happening. Armed with high-resolution satellite imagery, Tape and his colleagues located beaver dams in the lower Noatak River Basin of northwestern Alaska. They then analyzed infrared images captured by Nasa aircraft flying over the region. Covering the two revealed a clear link between beaver dams and methane hotspots which stretched for tens of meters around the dams.
“The transformation of these currents is a positive feedback that accelerates the effects of climate change, and that is what is worrying,” says Tape. “They speed it up at each of these points.”
Because the Nasa images only give a snapshot in time, the researchers will leave next year to measure methane on the ground. With more measurements, they hope to understand how the emissions vary with the age of beaver dams: do dams release a steady flow of methane, or does the release taper off after a decade or two?
Alaska isn’t the only region scientists are watching. Beavers are on the move in the north Canada also, where creating dams over permafrost will have a similar effect. “The magnitude of the issue in terms of space and numbers is huge,” says Tape.
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Helen Wheeler, an associate professor at Anglia Ruskin University, works with communities in the Gwich’in settlement area of northern Canada. The beaver population appears to be increasing more steadily than in Alaska, but surveys conducted with boats and drones still indicate a doubling since the 1960s. “We do see an increase in beaver, but it’s not the exponential increase seen in some areas of Alaska,” Wheeler says. “There is a lot of volatility from year to year, which probably reflects what a harsh environment it is.”
The beavers do not have an entirely negative impact. The mini oases created by the animals can boost local biodiversity. And for some communities, the animals themselves are a potential source of meat and perhaps even fur.
Still very careful. Although not all beavers build dams, those that do can affect water quality and the movement of fish, and make places inaccessible by flooding the land and blocking the routes through it. Even without methane emissions to worry about, researchers and indigenous communities are wondering what, if anything, needs to be done.
The question will be discussed in February when researchers, indigenous groups, land managers and others in the Arctic Beaver Observation Network hold their annual meeting in Fairbanks, Alaska. The meeting will use experts who manage beavers in other regions to examine the possible options.
“If it’s a problem, what can we do about it? I don’t have any answers,” says Tape. “You can put a bounty out there and start killing them, but the minute you stop, three to five years later, you’re going to be back in the exact same position. Not to mention the fact that it’s logistically impossible to to do.”
“People do eat them, but I’d say less now than they used to,” adds Tape. “I’ve never had it, but I think that’s going to change. I hear it’s good to eat.”
