Beavers Emerge as Agents of Arctic Destruction

A North American beaver in Denali National Park and Preserve in Alaska.

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Even as climate change shrinks some populations of arctic animals like polar bears and caribou, beavers may be taking advantage of warming temperatures to expand their range. But as the beavers head north, their very presence may worsen the effects of climate change.

The issue isn’t just that the beavers are moving into a new environment — it’s that they’re gentrifying it.

Take the dams they build on rivers and streams to slow the flow of water and create the pools in which they construct their dens. In other habitats, where the dams help filter pollutants from water and mitigate the effects of droughts and floods, they are generally seen as a net benefit. But in the tundra, the vast treeless region in the Far North, beaver behavior creates new water channels that can thaw the permanently frozen ground, or permafrost.

“When you start flooding areas with permafrost you immediately trigger permafrost degradation,” said Ken Tape, an assistant professor at the University of Alaska in Fairbanks who has researched the beavers. “You start thawing the frozen ground that’s holding the soil together, and that water and soil and other things are washed away.”

What remains is a pitted landscape, with boggy depressions, that directs warmer water onto the permafrost, leading to further thawing. As permafrost thaws it releases carbon dioxide and methane, which in turn contributes to global warming and helps increase the speed that the Arctic, which is already warming faster than the rest of the planet, defrosts. Worldwide, permafrost is estimated to contain twice as much carbon as is currently in the atmosphere.

The beavers are far from primary drivers of global warming — that distinction belongs to humans, after all. And arctic permafrost is already thawing because of warmer temperatures. But the beavers’ handiwork accelerates the thawing and exacerbates climate change, Dr. Tape said.

“Whether you want to call them ecosystem engineers or keystone species, beavers have a huge impact on the landscape,” he said.

Dr. Tape presented his team’s work last week at the annual meeting of the American Geophysical Union.

Because the beavers modified their environment so strikingly, the researchers were able to use satellite imagery to spot areas where the rodents had taken up residence. They used the images to track changes around lakes and streams in a 7,000-square-mile region of Alaska’s North Slope, in the northwest corner of the state.

Ordinarily beavers can’t live north of the tree line, the region where it becomes too cold and dry to sustain the trees and woody vegetation that beavers depend on for food and dam materials. But as climate change warms the Arctic and thaws the permafrost, the growing season extends. What was once tundra gives way to brush.

Images taken over several decades show that beavers are magnifying this climate-driven effect. Pictures from 1950 to 1985 illustrate how much disturbance researchers typically see in the Arctic: not much. But when beavers enter the scene, the changes are hard to miss. The beaver dams create pools of water in the normally icy landscape. The relatively warmer water flows into the surrounding permafrost, creating the dark areas seen from above.

To verify that beavers were responsible for the changes they had seen over time, Dr. Tape and his colleagues turned to aerial photography and newer, higher-resolution satellite images. Dams could be seen at 90 percent of the possible beaver locations they had identified in the initial satellite data. They estimated that scores of beavers had entered the region since 1999.

“The story with beavers sounds completely plausible to me,” said Matthew P. Ayres, associate director of the Institute of Arctic Studies at Dartmouth College, who was not affiliated with the research. “There are a lot of indications that the woody growth that they depend upon, especially willows and poplars in that part of the world, are growing more and extending into areas that they didn’t use to be, or were not big enough to support beavers.”

Researchers cannot yet say definitively that beavers are moving north because of climate change. It is possible the beavers are reclaiming territory they lost when widespread trapping nearly wiped out their numbers in the 18th and 19th centuries. But Dr. Ayres said their movement was in keeping with patterns that ecologists are seeing globally, as plants and animals migrate toward the warming polar regions.

And people are increasingly spotting beavers across the Arctic. The Anchorage Daily News quoted a biologist, Tom Jung, who said he discovered a beaver dam just south of the Arctic Ocean in the northern Yukon Territory of Canada.

“Beavers are these agents of disturbance that come from outside of the ecosystem and impose their construction, their activities on this landscape,” said Dr. Tape. “Probably the best analog for beavers in the Arctic are mankind.”

In Other News

Beavers Emerge as Agents of Arctic Destruction

A North American beaver in Denali National Park and Preserve in Alaska.

Want the latest climate news in your inbox? You can sign up here to receive Climate Fwd:, our new email newsletter.

Even as climate change shrinks some populations of arctic animals like polar bears and caribou, beavers may be taking advantage of warming temperatures to expand their range. But as the beavers head north, their very presence may worsen the effects of climate change.

The issue isn’t just that the beavers are moving into a new environment — it’s that they’re gentrifying it.

Take the dams they build on rivers and streams to slow the flow of water and create the pools in which they construct their dens. In other habitats, where the dams help filter pollutants from water and mitigate the effects of droughts and floods, they are generally seen as a net benefit. But in the tundra, the vast treeless region in the Far North, beaver behavior creates new water channels that can thaw the permanently frozen ground, or permafrost.

“When you start flooding areas with permafrost you immediately trigger permafrost degradation,” said Ken Tape, an assistant professor at the University of Alaska in Fairbanks who has researched the beavers. “You start thawing the frozen ground that’s holding the soil together, and that water and soil and other things are washed away.”

What remains is a pitted landscape, with boggy depressions, that directs warmer water onto the permafrost, leading to further thawing. As permafrost thaws it releases carbon dioxide and methane, which in turn contributes to global warming and helps increase the speed that the Arctic, which is already warming faster than the rest of the planet, defrosts. Worldwide, permafrost is estimated to contain twice as much carbon as is currently in the atmosphere.

The beavers are far from primary drivers of global warming — that distinction belongs to humans, after all. And arctic permafrost is already thawing because of warmer temperatures. But the beavers’ handiwork accelerates the thawing and exacerbates climate change, Dr. Tape said.

“Whether you want to call them ecosystem engineers or keystone species, beavers have a huge impact on the landscape,” he said.

Dr. Tape presented his team’s work last week at the annual meeting of the American Geophysical Union.

Because the beavers modified their environment so strikingly, the researchers were able to use satellite imagery to spot areas where the rodents had taken up residence. They used the images to track changes around lakes and streams in a 7,000-square-mile region of Alaska’s North Slope, in the northwest corner of the state.

Ordinarily beavers can’t live north of the tree line, the region where it becomes too cold and dry to sustain the trees and woody vegetation that beavers depend on for food and dam materials. But as climate change warms the Arctic and thaws the permafrost, the growing season extends. What was once tundra gives way to brush.

Images taken over several decades show that beavers are magnifying this climate-driven effect. Pictures from 1950 to 1985 illustrate how much disturbance researchers typically see in the Arctic: not much. But when beavers enter the scene, the changes are hard to miss. The beaver dams create pools of water in the normally icy landscape. The relatively warmer water flows into the surrounding permafrost, creating the dark areas seen from above.

To verify that beavers were responsible for the changes they had seen over time, Dr. Tape and his colleagues turned to aerial photography and newer, higher-resolution satellite images. Dams could be seen at 90 percent of the possible beaver locations they had identified in the initial satellite data. They estimated that scores of beavers had entered the region since 1999.

“The story with beavers sounds completely plausible to me,” said Matthew P. Ayres, associate director of the Institute of Arctic Studies at Dartmouth College, who was not affiliated with the research. “There are a lot of indications that the woody growth that they depend upon, especially willows and poplars in that part of the world, are growing more and extending into areas that they didn’t use to be, or were not big enough to support beavers.”

Researchers cannot yet say definitively that beavers are moving north because of climate change. It is possible the beavers are reclaiming territory they lost when widespread trapping nearly wiped out their numbers in the 18th and 19th centuries. But Dr. Ayres said their movement was in keeping with patterns that ecologists are seeing globally, as plants and animals migrate toward the warming polar regions.

And people are increasingly spotting beavers across the Arctic. The Anchorage Daily News quoted a biologist, Tom Jung, who said he discovered a beaver dam just south of the Arctic Ocean in the northern Yukon Territory of Canada.

“Beavers are these agents of disturbance that come from outside of the ecosystem and impose their construction, their activities on this landscape,” said Dr. Tape. “Probably the best analog for beavers in the Arctic are mankind.”

In Other News

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