(Initially published in In the Glen, Fall 2021)

The morning of April 21, 2021 was a rare spring day in Ohio. A brief cold front brought nearly three inches of snow to Yellow Springs, and newly leafed-out trees and wildflowers were buried under this ephemeral blanket. By morning, the sun was out, and it was, objectively, beautiful. It seemed like a great day to take some pictures in the Glen, so before heading into the office, I hiked down the long stone steps toward the Yellow Springs Creek. Nearing the creek, I heard the familiar sound of a gurgling stream. But wait: as wonderful as the Yellow Springs Creek is, it does not normally gurgle. When I reached the bridge over the creek, I immediately saw the reason. Beavers had begun a dam just upstream from the Inman Trail bridge, and water was audibly trickling through the structure.

Over the following months, the beavers made the dam larger, and larger still. As the dam grew, so did the pond behind it, stretching upstream and submerging the riparian wetlands of the Yellow Springs Creek valley. As I write this, the dam is now approximately 50 feet wide by about five feet tall. An impressive structure by any standard.

As visitors to the Glen have noticed the dam, we’ve received a string of social media messages about it, often reflecting strongly held opinions about the animals, coming from the perspective that beavers are a problem that needs to be solved. Here is our take on that, starting with some background.

By a long shot, beavers are North America’s largest rodents, growing to about 70 pounds. Rodents are the most biodiverse order of mammals, and the main attribute which sets them apart from other mammals like people or tigers or whales is that their front teeth grow continuously throughout their lives. They are born to gnaw!

In summer, they eat a broad range of plant material, including leaves, roots, and grasses. Come winter, their diet shifts more to tree bark and the cambium layer beneath. With their strong teeth, they can girdle, and eventually fell, trees multiple feet in diameter. They are territorial animals, and mark their home turf with a waxy secretion that we call castoreum. Remember this point for later in the story: Those who have inhaled the musk of castoreum describe it as pungent, but with floral notes reminiscent of vanilla or perhaps raspberry.

Perhaps more than any animal other than humans, beavers directly manipulate the environment where they live. Their dams and feeding habits change the biodiversity in the areas where they take up residence.

Beavers build dams for shelter, for protection, and to make it possible to float their food to their lodge. In the warm months, they live in a summer lodge, usually on the bank of the pond they impound. These will typically be low slung, a loose pile of sticks atop tunnels and holes. Their winter lodges are more likely the image that comes to your mind if an image comes to your mind when you picture beaver lodges. Often built in the middle of their pond, winter mounds can stand six feet above the water level. They use mud and sticks to form a sealed roof that keeps out the elements. The entrance to the lodges will be underwater. This means that beavers need to be able to tolerate swimming in icy water. Their thick fur, waterproofed with a dollop of castoreum, allows them to thrive in water that would be unsurvivable cold for us.

This thick fur and their castoreum were also nearly their undoing. Castoreum was sought after as a medicine, a food flavoring (thanks to those aromatic notes from their herbaceous diet), and a scent enhancer in perfumes. Beaver pelts were used to make the warmest of the warmest hats. The appetite for beaver pelts was astoundingly insatiable. Beaver trapping is widely credited as a main driver in the westward expansion of the United States! At the peak of the fur trade, in the 1860s, over 150,000 pelts were purchased annually. Unsurprisingly, beavers were nearly driven to extinction by this assault. They were totally wiped out of Ohio by 1830, and didn’t return for 100 years. As beavers returned to Ohio, they entered a landscape taken over by, and changed by, human activity.

Now, in most areas of Ohio, a beaver dam is likely to create conflict because of their – and our – competing interests in the land. Beavers are often labeled as nuisance animals because they flood areas where people live or drive or recreate, they damage crops and trees, and they can be vectors for parasites. This, I suppose, is why people assumed that when beavers took up residence in the Glen, that we would want to forcibly evict them. They damage property, or to restate it with nuance, change property in a way that is different from what their human neighbors had in mind.

The Ohio Department of Natural Resources conducts annual statewide beaver population surveys. Their numbers have swelled from a couple hundred colonies in 1960 (around the time when hunting was reallowed) to about 6500 colonies today. They are found statewide, but are much more populous in northeastern Ohio. In and around the Glen, beaver activity has been on the rise in the last ten years. We have found gnawed trees around Grinnell Mill and Camp Greene, but don’t know of a successful lodge there. Their lodge on the Yellow Springs Creek may be the first one in the Glen in nearly 200 years.

Their presence in the Glen is going to change the preserve, no doubt about it. They are going to girdle native trees that we have watched grow for decades, drown stands of native spicebush and skunk cabbage that thrive in the Yellow Springs Creek valley. They don’t appear too interested in eating invasive species like honeysuckle and privet, which is a shame. We can live with that. They are a native species, creating natural habitat, and making the habitats of the Glen more like they were in the years before European settlement of Ohio. They are also expanding the wetlands along the creek, which will create habitat for species of fish, frogs, turtles, perhaps ducks, and others. The wetlands will perform a crucial ecological service, reducing sedimentation downstream.

We’re fortunate that the beaver dam is located in an area where our trails are raised on boardwalks. So far, it looks like their pond, and our trail system, will be able to happily coexist. Floods may eventually topple the dam, or the beavers may choose to relocate. Until then, join us as we observe and marvel at the changes that they are creating.

Nick Boutis
Executive Director