Wetland’s Keystone Species: Our Resilient Beaver

by Lon Drake

The beaver has always been a homebody and very territorial, thus easy to trap. By the time the Mountain Men went westward in the decades following Lewis and Clark, the Iowa beaver population had already been greatly reduced by Indians using steel traps. The white settlers finished them off during that century.
But the beaver is a unique creature and their niche remained vacant, so some gradually drifted back into the state from the northwest, probably via the Missouri River. By the middle 1900s, there were some in every Iowa county again.

Everyone knows beavers build dams, which create ponds. But where the water is too big or too fast, like the Cedar and Iowa Rivers, they become bank beavers and live in tunneled homes.
For Iowa beavers, a nearby willow thicket on the floodplain is their best source of food, but unfortunately most of these have been plowed under with corn now growing on them. The beaver has adapted by cutting down cornstalks and eating corn. When you find a muddy trail down the bank lined with cornstalks, it is usually a beaver making the best of the situation.

They can get more creative when necessary. While hiking a trail along a trout stream in northeast Iowa, I once found a small dam decorated with white fence pickets. Backtracking up a steep rocky bluff lead to a house with a dilapidated fence, and the beavers were salvaging everything not firmly nailed down. Good thing they don’t use crowbars.

While their industry and adaptability sometimes gets them into trouble with us, I say let’s use it. When I designed the South Sycamore Outlet Wetlands for stormwater management in 1998, the containment was a set of three nested earthen berms about three feet high, essentially beaver dams without the sticks. Anticipating that Iowa City would do little maintenance, I knew willows would quickly grow on the berms, thus attracting beavers. The beavers did come and they have since made some small modifications to my overflow structures. To this day they maintain the berms against serious leaks. Today these wetland ponds are still performing good stormwater management and providing habitat for a hundred other species, which is why ecologists label beavers a keystone species.