DULUTH — While they might be a nuisance when they flood roads or dam trout streams, beavers are a critically important component of the Northland’s forest ecosystem.
That’s the finding of a study by the University of Minnesota Duluth’s Natural Resources Research Institute published recently in the journal Ecography.
The study, which focused on five streams along Minnesota’s North Shore of Lake Superior, found that beavers are “essential for freshwater conservation and ecosystem stability” because of the impact of their beaver ponds storing water, even years after the beavers are gone.
“Although there are many studies on how beavers change ecosystems, the scale of this study, spanning 70 years across five different watersheds, is really unprecedented,” said Tom Gable, head of the Voyageurs Wolf Project and a researcher on the beaver project. “We think this work will be of value to many conservationists, scientists and citizens who want to understand how reintroduced or recovering beaver populations can positively affect their ecosystems.”
The study looked at the Kadunce, Cascade, Manitou, Split Rock and Knife rivers along the North Shore and suggests beavers, as ecosystem engineers, can be a biological tool that helps buffer ecosystems against disturbances and alterations such as climate change.
The project, headed by Sean Johnson-Brice, who studied at UMD, found beavers’ impacts, and their population, varied widely depending on their locations. But their overall regional populations varied very little.
Researchers looked at how beavers influence water storage using 800 aerial photographs of five watersheds taken from 1948 to 2017. Over that time, beaver numbers recovered from being trapped heavily and regained their place in the North Shore ecosystem.
Like most beaver populations in North America, North Shore beaver populations were decimated during the fur trade era and the decades following. Trapping was prohibited in Minnesota starting in 1909 and remained closed on the North Shore into the 1960s. Since then more modest trapping has resumed, but regional beaver numbers have held fairly steady.
“We suggest restoring beavers to landscapes is a viable method for increasing surface water storage and will ultimately help advance numerous conservation and rewilding objectives,” the study concludes.
The study found that:
Beavers are major drivers of water retention in ecosystems, suggesting that restoring beaver populations to ecosystems where they no longer exist may be a valuable method that land managers could use for freshwater conservation.
The longer beavers are present in an ecosystem, the more old and abandoned ponds help contribute toward storing water. While the abandoned ponds may no longer have beavers living in them, their dams can still store water.
Across a wide region, beaver populations are resilient to moderate environmental and human disturbances.
Even though beaver populations within each of the five watersheds studied showed considerable variation in population size, overall water storage remained stable across the entire region. Essentially, changes in beaver population size in one watershed would be balanced by changes in the other watersheds, which helped stabilize water storage amounts across the entire North Shore.
“The resulting dataset provided significant insights into the critical role beavers play in regulating water storage along the North Shore,’’ said George Host, now retired director of NRRI’s Forest and Land Initiative and Geographic Information System laboratory and a member of the beaver project research team.
Funding for the research came from the National Oceanic and Atmospheric Administration and Minnesota’s Environment and Natural Resources Trust Fund. The full study is available free to the public at onlinelibrary.wiley.com/doi/10.1111/ecog.05814.