U.P. study shows long-term impact of beaver “engineering”

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Capital News Service
LANSING — The North American beaver has been called “the quintessential ecosystem engineer,” and any doubters can look at the animal’s long-term environmental impact in the Upper Peninsula.
Many of its engineering feats are still evident on the landscape after more than 150 years — longer than such other engineering marvels as the Eiffel Tower, the Mackinac Bridge, the Trans-Siberian Railroad and Toronto’s CN Tower have stood.


Beaver. Credit: Smithsonian Institution.

The proof is visible in the continued existence of dozens of Ishpeming-area beaver ponds first mapped in 1868, according to newly published research.

“This study shows remarkable consistency in beaver pond placement over the last 150 years, despite some land use changes that altered beaver habitats,” ecologist Carol Johnston wrote in the study. “This constancy is evidence of the beaver’s resilience and a reminder that beaver works have been altering the North American landscape for centuries.”
And in an interview, Johnston said a major lesson from the study is that beavers come back to the same spots on the landscape and reuse them time and time again. That means wildlife managers and public lands managers can expect beavers to return.
The U.S. beaver population has gone through periods of boom and bust, being wiped out in many regions of the country in the 1700s and 1800s, but surging back since the 1940s.
There are no precise figures on the number of beaver in the state. The Department of Natural Resources (DNR) reported from survey data that trappers captured 12,179 beaver in 2013.
That was 18 percent fewer than in 2012, a change that the DNR said should be “viewed cautiously because Michigan experienced unseasonably cold temperatures and above-normal snowfall during December 2013 through February 2014.”
“Populations have done big swings,” said Adam Bump, a furbearer specialist in the DNR Wildlife Division. “We have beaver throughout the state, even in southern Michigan.”
Beavers can be trapped with a furharvester’s license during open season, and there’s no bag limit. Year-round trapping is allowed only for damage control  with a DNR permit or by a nuisance control business with a permit, he said.
Bump said, “On the landscape as a whole, beaver provide huge benefits,” including creation of wetlands and reducing stream sedimentation.
Professor John Bruggink, a wildlife ecology expert at Northern Michigan University, said, “From the human side, they’re regarded often as a nuisance” because the result of dam construction can include flooded roads and other problems.
“From a wildlife viewpoint, they can influence the landscape on a pretty broad scale, probably second only to us. Beaver dams can have long-term effects,” said Bruggink, who isn’t involved with Johnston’s new study.
Johnston, a professor at South Dakota State University, compared an 1868 map prepared by amateur anthropologist and naturalist Lewis Morgan with a series of aerial photos from the 1940s through 2014. Morgan wrote a classic book still valued by experts, “The American Beaver and His Works.”
The map shows 64 beaver ponds along streams where he fished between 1855 and 1867, including Carp Creek and Ely Creek. During that time, Morgan was a lawyer for the Marquette and Ontonagon Railroad, she said.
Morgan’s map includes rivers, railroads, settlements and mines in an area straddling the drainage divide between lakes Superior and Michigan. And he made the map without the benefits of modern technology such as geographic information systems and digital aerial imagery.
“Beavers were still abundant in the region” at that time, “although the beaver fur trade in Michigan had begun to decline by the late 1830s,” Johnston wrote.
The study found physical evidence — called “artifacts” — of 46 of the 64 ponds still visible in 2014. Sixteen remain largely intact, another 16 are beaver meadows and 14 still have shrub wetlands or other surviving bodies of water.
“Beaver dams, ponds and meadows are durable landscape features,” the study said.
The 18 ponds that have disappeared since Morgan mapped them were victims of iron mining, stream channelization, forestation and the development of Ishpeming, the study said.
The largest remaining one is a 30-acre pond created by a beaver dam downstream of Grass Lake in Marquette County.
Beavers probably didn’t continuously occupy all the sites because they abandon ponds when there’s not enough food to forage. However, beavers may repopulate the same places later, it said.
Bruggink, of Northern Michigan University, said one factor in how colonies disappear and reappear is how beavers may leave a pond when a favored type of food, such as aspens, is gone. Sometimes the abandoned pond fills in, transforming the landscape into a beaver meadow that eventually becomes reforested.
As the forest regenerates, trees grow closer to the shore, attracting beavers back.
“They don’t like to get super-far from water” for fear of predators, Bruggink said.
Johnston, who’s now writing a book about beavers in Northern Minnesota’s Voyageurs National Park, acknowledged that the beaver’s engineering skills aren’t always appreciated.
“There is some anti-beaver sentiment. Beavers do economic damage,” she said.
She described a situation at a Lake Ontario-area wetlands where the transportation agency opened up a culvert that beavers had plugged. The beavers then built a semicircular dam around the culvert.
“It’s amazing how intuitive they are,” she said.
Johnston’s article appeared in the journal Wetlands.
“Fate of 150 Year Old Beaver Ponds in the Laurentian Great Lakes Region”: https://www.researchgate.net/publication/281675761_Fate_of_150_Year_Old_Beaver_Ponds_in_the_Laurentian_Great_Lakes_Region#full-text.
EDITOR’S NOTE: This story was updated on Oct. 23, 2015, to reflect that out-of-season trapping is allowed only with a permit for damage control.

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