UAF study links beaver expansion to faster Arctic thaw

UAF study links beaver expansion to faster Arctic thaw

The climate-driven spread of beaver ponds in Alaska's Arctic accelerates the effects of a warming environment by causing pond-adjacent permafrost to thaw and by increasing the amount of liquid water present during winter.

Those are the key findings of the first comprehensive, on-the-ground assessment of the northward migration of beavers. The research was led by postdoctoral researcher Thomas Glass and research professor Ken Tape at the University of Alaska Fairbanks Geophysical Institute.

"The idea was to get on the ground to start to measure some of the effects of beavers on the ecosystem and to get a close-up perspective of what's happening out there," Glass said.

The findings were published Sept. 28 in Ecosphere. The nine co-authors include seven from UAF as well as one each from Colgate University and the University of Toronto.

The research adds to a growing body of work about the beavers' northward movement produced by the UAF science team as part of the Arctic Beaver Observation Networkunder a five-year National Science Foundation grant.

Why it matters

Beaver colonization of the Arctic is likely a result of warming temperatures, which offer the species more shrubs and unfrozen habitat during winter. A rebound from historic trapping may also play a role.

More beavers means more beaver dam complexes and the related expansion of wetlands as Arctic air temperatures continue to rise at a rate four times faster than the global average.

"Climate change is dramatically changing Arctic streams and riparian areas, bringing with it a range of consequences like more shrubs, more wintertime flow and the mobilization of heavy metals from thawing permafrost," Glass said.

Glass and the co-authors write in the research paper that beaver expansion and the related acceleration of environmental change is a useful analog for envisioning rapid climate-induced change.

"We suspect that these beaver-engineered sites offer a window into a warmer and wetter future for Arctic riparian areas," Glass said.

The fieldwork

The research centers on 11 beaver dam complexes on the Seward and Baldwin peninsulas that the science team visited in April and August each year from 2021 to 2024. Previous research into the advance of beavers into the Arctic was conducted through analysis of satellite imagery.

The 11 sites on the Seward and Baldwin peninsulas all were colonized by beavers during recent decades.

Five sites, all on the Seward Peninsula, are in discontinuous permafrost. The remaining six are in areas of continuous permafrost. Continuous permafrost forms an unbroken layer of frozen ground beneath the surface, while discontinuous permafrost occurs in patches separated by areas of unfrozen soil.

The team measured permafrost thaw depth and various aspects of water quality.

They used ground-penetrating radar to locate liquid water below ice in beaver ponds and related water bodies. They measured water depth at 17 ponds across the sites. They used drones to capture high-resolution multispectral images and referred to archival satellite and aerial images back to 1950 to create pond histories.

What they found

The group's work found pond-adjacent thawing at all research sites on the Baldwin Peninsula, an area of continuous permafrost.

"It's striking how rapidly a stream without beavers can transform into a sprawling wetland after they arrive," Glass said.

Sites at the discontinuous permafrost regions of the Seward Peninsula showed little or no thaw during the study period.

"There are several reasons for that," Glass said. "The Seward Peninsula sites have been occupied longer than the Baldwin Peninsula sites, so it's possible those sites have thawed as much as they are going to already."

Glass also determined that beaver activity caused nonwinter surface water acreage to increase a median of 610% per site compared with pre-beaver stream channels.

"The time period varies depending on when beavers colonized a site," Glass said. "Typically this would be around 20 to 25 years, although most of the surface water increase likely happened within the first few years after colonization."

Data from ground-penetrating radar showed a minimum 230% median increase in the extent of wintertime liquid water at the 11 sites as compared with pre-beaver stream channels now connected to modern-day ponds.

"Delays in freezing in some cases are caused by the beavers coming and going from their lodges and from other beaver activity, but mostly it's by creating these massive bodies of water that don't fully freeze because they are deeper," Glass said.

The growing prevalence of wintertime liquid water could benefit aquatic species, the authors write.

Riverine fish generally must swim long distances to reach springs and groundwater upwellings that remain unfrozen and provide stable flow, slightly warmer water and enough dissolved oxygen. The linked ponds and waterways created by beavers could provide closer options.

UAF co-authors include assistant professor Sarah Ellen Johnston and doctoral student Paige Kehoe, both of the Department of Chemistry; research associate professor Benjamin Jones of the Institute of Northern Engineering; professor Chris Maio of the Geophysical Institute and Department of Geosciences; doctoral student V. Sebastian Zavoico of the Department of Biology and Wildlife; and Jason Clark, former Geophysical Institute postdoctoral researcher.

ADDITIONAL CONTACTS: Tom Glass, [email protected]; Ken Tape, [email protected]

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