Arctic beavers are melting the permafrost

The North’s permafrost has a new threat: Arctic beavers building dams.

Humans have achieved amazing feats of engineering, from building sprawling skyscrapers to constructing extensive bridges, but when it comes to eco-engineering, it’s hard to beat North America’s largest rodent, the beaver (Castor canadensis). Though they only clock in at about 60 pounds, these furry masters of manipulation have the ability to reroute rivers, fill lake basins, and flood fields. Beavers are now taking their landscaping prowess to low Arctic tundra regions in Alaska and Canada, shaping their new homes to fit their needs through the construction of dams and lodges.

A team of researchers tracked the rise of beaver dams in northwestern Alaska over a 17-year period and observed that the beaver dams accounted for an 8.3 per cent increase in total surface water over the study period. Pooling groundwater can degrade the frozen ground known as permafrost in tundra regions. As beavers continue to move into Arctic regions, their actions may drive large-scale landscape changes in an environment already threatened by climate change.

Benjamin Jones, a research professor at the Institute of Northern Engineering, University of Alaska Fairbanks, led a team that used high-resolution remote-sensing imagery to document changes in lake surface area in northwestern Alaska. The high-definition images allowed the team to zoom right in and see that there were new construction projects going up on lake perimeters in the state: beaver dams. The team conducted a census of beaver dams in a 100 sq. km study area near Kotzebue and found an increase from two beaver dams in 2002 to 98 in 2019. In a 430 sq. km study area encompassing all of the Baldwin Peninsula (where Kotzebue is located), the number of dams increased from 94 to 409 between 2010 and 2019.

Beavers were found to be constructing dams in thermokarst landforms, configurations that develop when ice-rich permafrost degrades, causing ground-ice to melt and the land surface to subside or sink downwards. Thermokarst landforms can create dynamic lakes that naturally expand and deepen over time, but they also have the tendency to catastrophically drain, says Jones.

The team found that beavers would head to drained thermokarst lake basins and build their dams in outlet channels where the former lake had busted through and drained itself. Beavers were creating their own little wetlands as their dams backed water up into the drained lake basins.

But it appears that by damming the outlet channels, the Arctic beavers set off a series of dominoes that increasingly degraded permafrost in the region. “Water is the enemy of permafrost,” says Jones. Surface water conducts heat and has a really big negative effect on the stability of permafrost, particularly if it’s ice-rich permafrost, he says.

This isn’t the first time that beavers have graced northwestern Alaska with their presence. In the 1960s, researchers uncovered fossil beaver dams and beaver-gnawed wood on the Baldwin Peninsula dating back to a period in time called the Holocene Thermal Maximum, a warm climate phase about 10,000 to 12,000 years ago. Unfortunately, there is a “huge information gap” about what happened to beavers over the last few centuries, says Jones. Widespread hunting of beavers across North America in the latter part of the 18th century and the 19th century almost led to beavers being completely wiped out from the continent, he says. While it’s fairly well documented that beavers have since rebounded, there’s “not a good record of how that repopulation of these sub-Arctic and low Arctic settings progressed over the last 100 years.”

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The jury’s still out on what is now prompting beavers to go construction crazy in the Arctic tundra. But the environmental changes from a warming climate may provide some answers. Warmer temperatures provide a longer growing season for vegetation and an increase in the shrub cover that beavers need for food and building materials. Increasing air temperatures are also leading to thinner seasonal ice growth, which could be helping beavers make it through the winter.

Now that researchers know the substantial impact Arctic beaver dams are having on the surface water in the Alaska tundra, the next steps include expanding field studies to discover the extent that the beavers’ construction efforts are affecting the hydrology, the vegetation, the permafrost, and the ice cover of the region. And because the beavers aren’t the only ones that call the Arctic tundra home, their activities may be affecting local communities and other species. Jones and his team plan to visit communities to ask traditional and local knowledge holders about the effects of beavers moving into the tundra and renovating the landscape.

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