Beavers in the News: 150-year-old map reveals that beaver dams can last centuries

THIS JUST IN: Railroad director and entrepreneur Lewis Henry Morgan goes exploring the upper peninsula of Michigan in the mid 1800’s. While looking for places to lay railroad, he comes across huge “beaver district” composed of 64 glorious beaver dams. Although he admittedly isn’t much of a nature guy, the sheer ingenuity of the beaver’s engineering compelled him to document the beaver district in a hand drawn map. Curious modern scientist stumbles across 1860’s map while serving as a post-doc, compares it to Google Earth style aerial images and discovers that 74% of original dams are still around. Beavers are stubborn and very resilient.

There’s not a whole lot of controversy to this news story, but I thought it was too cool to not include on my blog. Basically, a scientist at South Dakota State University found concrete proof that beavers dams can last an incredibly long time even in the face of land use changes like mining, logging, and development.

This news is awesome and worth sharing for two main reasons: 1) if beaver dams can last that long, then the effects of their damming can easily last several human lifespans. How much of the landscape we see today was shaped at some point in history by beaver occupation? 2) The guy who drew the map back in the 1860’s is a great example of how even people who don’t really like nature can get really excited about beavers.

dam map
Here is the old map! All those little bitty filled in circles are beaver ponds. 
modern map
Here is a modern satellite image of the same area, with Teal Lake marked by a pin in the upper right corner. While many of the ponds have drained, a few ponds do remain. More importantly, most of the original dams are still in place, even if they no longer are holding back any water.

Super old dams = dams fundamentally changed the landscape throughout history.

To the first point of beaver dam effects lasting a really long time. The dams that Lewis Henry Morgan drew maps of were already in existence when he found them, thus the MINIMUM time they have been around is like 150 years. For all we know, they could have been there for 150 years before he found them, making their total time in the landscape 300 years. Or maybe they were already there for 300 years! It’s so hard to know because we rely on aerial photographs (which date back ~75 years) and historic maps like this (which date back 300 years at most) when we talk about how long beaver dams can stick around for. But, as the article points out, some scientists believe that some beaver dams might actually last 1000 years!

Damming up a stream for 1000 years is going to have a profound impact on the landscape and ecosystem. What was originally a narrow mountain stream might be transformed into a broad alpine meadow. Then when those dams that brought about the change finally fail or are buried beneath continually accumulating sediments, all that remains is the meadow. Someone could walk up to the meadow today and see it and have no idea that beavers were responsible for creating it! Some people credit much the extremely fertile croplands in the central US to tens of thousands of years of beaver damming helping to enrich the soil with organic matter and nutrients. It makes me stop and think, how different would the country look if there were never any beavers? They are second only to humans in terms of impact on the environment, so I imagine things would look really different.

Did a beaver make this meadow? Spoiler: yes, it did. This is Upper Beaver Meadows in Rocky Mountain National Park. An alpine meadow that resulted from thousands of years of beaver occupation changing a rugged mountainous landscape into a flat, gentle meadow.

Lewis Henry Morgan as a poster child for how even people who don’t like nature much can get obsessed with beavers.

I love reading about Lewis Henry Morgan, the original mapper of the beaver dams discussed in the news article. This man is not your typical granola-crunching, yoga-participating, chaco-wearing nature fanatic (I definitely fall more into this category). Lewis Henry Morgan was a railroad director. Lewis Henry Morgan was an entrepreneur. Lewis Henry Morgan was a politician. Lewis Henry Morgan pioneered anthropological studies of Native Americans. He was a man who was firmly rooted in the world of human civilization. But when he took his railroad engineers and planners up to the upper peninsula of Michigan and saw all those beaver dams, he was hooked.

Another great beaver dam drawing from Lewis Henry Morgan’s work. This guy was incredibly detailed in his drawings – they actually provide more useful information than just about any of the modern images available.


For much of the 1850’s and 1860’s, he meticulously studied the beavers. Where did they live? What did they eat? Why do they build dams? What do the dams look like? How big are the beavers? How big are the dams? How many live in one place? Do they live like families or as loners? The result of this multi-decade obsession was his 396 page book called The American Beaver and His Works, which included many maps of dams drawn in great detail by his team of railroad engineers.

dams in gorge
Seriously, this guy is my hero. These drawings are incredible.

I see a little of myself in Lewis Henry Morgan. I, too, have a somewhat unusual obsession with beaver dams. I, too, plan to publish a long (although not 400 pages…) dissertation summarizing many years of research and studies. Unfortunately, I am not a railroad tycoon with a team of engineers at my disposal, but what I lack in resources I make up for in creativity and enthusiasm (or at least that’s what I like to tell myself).

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