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Nature’s most famous ecosystem engineers are moving north as the climate warms—and thawing permafrost in their new locales.
Expanding beaver ranges mean more beaver ponds, which transfer more heat to surrounding soil and thaw long-frozen ground, according to research that will be presented on 10 December at AGU’s Annual Meeting 2024 in Washington, D.C.
“They’re moving, and they’re bringing with them the ability to remake whole landscapes in a very short period of time,” said Emily Graham, a remote sensing scientist at the University of Alaska Fairbanks and first author on the new study.
Permafrost Be Dammed
The Arctic tundra is a vast, cold, and mostly treeless landscape that was not suitable beaver habitat until recently. Human-caused climate change has warmed the region and allowed for more shrubs and woody plants to grow. In response, North American beavers have been expanding their range into the Arctic.
Beavers are known for reshaping their landscapes via the cascading effects of dam building, and that reshaping is now affecting the Arctic, said Sean Johnson-Bice, an ecologist at the University of Manitoba who was not involved in the new research.
Graham and her colleagues set out to study how beavers may be reshaping Arctic landscapes by studying how beaver ponds may affect permafrost on Alaska’s Seward Peninsula.
“We can learn a lot about melting permafrost by shooting radar signals at it.”
Permafrost—perennially frozen soil—is a key aspect of the Arctic landscape. It stores carbon and methane, which once released via thawing, contribute to climate change. Scientists estimate that Arctic permafrost holds about 1.7 trillion metric tons of carbon: more than 50 times the amount that humans released into the atmosphere as fossil fuel emissions in 2019.
Graham and her colleagues identified more than 850 beaver ponds with high-resolution optical imagery and used data from NASA’s Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), an airborne radar instrument, to map subsidence and uplift around ponds with and without beaver activity. “We can learn a lot about melting permafrost by shooting radar signals at it,” Graham said.
When beavers build dams, the extra water that pools in the ponds behind them transfers more heat to the surrounding soil, accelerating permafrost thaw. Subsidence is a proxy for thawing permafrost because as frozen soil thaws, it softens. The soft, muddy soil cannot support the weight above it and collapses.
The data showed that ground adjacent to beaver-affected ponds had subsided up to 10 centimeters more than ground near ponds unaffected by beavers, though the results are preliminary, Graham noted.
“Let’s not overly blame the beaver.”
“It’s super important research,” said Emily Fairfax, an ecohydrologist at the University of Minnesota who was not involved in the new research. “We clearly have a lot of beavers that are moving northward as the climate is changing. [We should] employ the full suite of science and try to capture everything about how they change that landscape.”
Fairfax said the preliminary results are no surprise: Permafrost is thawing everywhere in the Arctic, and it makes sense that beavers would speed up the process. However, though beavers contribute, other factors, such as rising air temperatures, play a larger role, she added. “Let’s not overly blame the beaver.”
Beaver Behavior
The research suggests that the relationship between beavers and permafrost thaw isn’t straightforward, Graham said. Preliminary results show that the amount of subsidence seems to be dependent on landscape factors, such as slope, and the details of beaver activity, such as how many beavers are in a pond, how long a dam has existed, or whether a beaver has abandoned a pond.
“Beavers are extremely complicated everywhere, not just in the Arctic,” Fairfax said. “How they interact with a given landscape is definitely going to be driven by the topography, the hydrology, and the existing ecology.”
A better understanding of beavers’ population trends in the Arctic is necessary to get the full picture of how beavers’ landscape engineering will alter tundra ecosystems, too, Johnson-Bice said.
Graham said she hopes the research can be used in the future to support predictions of where and how permafrost in the Arctic may change as beavers continue to expand northward.
—Grace van Deelen (@GVD__), Staff Writer
Citation: van Deelen, G. (2024), Arctic beavers advance north and accelerate permafrost thaw, Eos, 105,https://doi.org/10.1029/2024EO240551. Published on 10 December 2024.
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