How Beavers Can Rebuild Our Ecosystems
The role of nature’s hydrological engineers in rebuilding ecosystems, boosting biodiversity, and fighting climate change
All animals play a role in their environment, but one animal stands apart as a prolific habitat creator: the beaver. Native to most of the northern hemisphere, beavers have been a cornerstone of their ecosystems for millions of years. No animal has a greater, wider-ranging, positive effect on their environment. And in the same vein, no animal's absence has been felt more profoundly.
Unfortunately, beavers evolved to have a fur that was phenomenally useful to humans, and it made them the main target of the fur trade for centuries. Across the northern hemisphere, their populations collapsed under this unrelenting pressure, leaving behind forests that are a shadow of their former selves.
So, why are beavers so cool? What makes them so critical to the environment? What drove their populations to collapse? Why is their absence so catastrophic, and most importantly, how do we make it right?
But First, Beavers 101
Beavers are stout, semi-aquatic rodents that grow to be between 2 and 3 feet long and around 1.5 feet tall. They can weigh up to 100 pounds but are usually between 40 and 60. This is pretty comparable to a lab, but certainly chonkier. Despite being so beefy, beavers are herbivores, and their diet mainly consists of the inner bark, or cambium layer, of deciduous trees. These are the trees that change colors and drop their leaves in the fall. To round out their diet, they sprinkle in a mix of different grasses and aquatic plants.
In order to sustain a diet of mostly trees, their long front teeth are covered in iron-rich enamel and grow throughout their life. Gnawing through trees wears down their teeth and continually sharpens them. Beavers call a wide range of ecosystems home— from alpine meadows in the far north, to the swamps of the deep south, to the arid southwest, all the way through to Mexico. But regardless of the habitat, they all share a common passion for finding flowing water and building a dam across it.
You may have heard the saying "busy as a beaver." And well, it's a saying for good reason. Beavers are nature's one true builder, out of sheer necessity. Much to their misfortune, beavers are both delicious and slow, meaning they're an ideal snack for just about everybody. To deal with this, beavers hit the water. They evolved to be great swimmers with powerful tails and the ability to hold their breath for up to fifteen minutes. But to truly be protected, they need calm water that's deep enough to hide in. If they live in a pond or a lake, they might skip the dam building. But if they don't have access to water at the necessary depth, they create it by building a dam.
These dams are truly a masterclass in civil engineering. Beavers will adapt the size and design of their dams depending on the particular river or stream they're working with. And they actively manage the water level of their pond through strategic leaks. Dams can range from just a few meters in length to absolutely massive. The largest one currently in existence is in Wood Buffalo National Park in Canada. It's half a mile long and visible from space.
Once they finish their dam, beavers build a lodge or bank den with underwater access to their new pond. In order to survive the cold winters, beavers store branches and other vegetation underwater near their den in what's known as a feed pile. This is how they access their food in the winter without exposing themselves on land, even if their pond freezes over.
Another curious fact about beavers is that they generally mate for life. Each year, the couple welcomes a new litter, raising them for one to two years before kicking them out. Usually, any given colony consists of the mating couple, the most recent litter, and a few stragglers from the previous one. Eventually, the mating pair will exhaust the food near their pond and abandon their dam in search of a new place to call home.
And while not the most important fact, it's really cool so I'm going to mention it anyway: beavers use their tails for more than just swimming. They're also particularly useful for balance while chewing through trees, and they use them to communicate. When they slap their tails on the water, it can make a noise similar to a gunshot, which is useful to scare off predators and warn their family of danger.
Beavers and Biodiversity
Hopefully by now, you're convinced that beavers are cool. But why are they so important? Well, they're one of the few animals that create habitats. Their dams create wetland habitats of still water where insects and aquatic plants can thrive. This abundance of food leads to an explosion of birds, mammals, amphibians, and fish. Furthermore, as the dams retain nutrient-rich sediment from the stream, and as the area gets cleared of trees, meadows form and remain long after the colony has moved on. These are critical habitats for animals like deer and elk.
Now, if you watched or read my previous piece on salmon, you're probably thinking, "Didn't this guy just say that dams are the worst thing that could happen to salmon?" There was a bit of an unspoken caveat there: manmade dams are the worst thing that could happen to salmon. To make a dam worth the effort, humans tend to build huge ones for water storage or hydroelectric power. These are mostly impossible for salmon to migrate past. Meanwhile, beaver dams are much smaller. If you look at the distribution of beaver dam heights from the American West, you'll see that almost all the dams are less than a meter and a half, or around five feet, tall. Salmon, with their notorious jumping ability, can easily clear five feet. A Native American legend boils it down perfectly: beavers taught salmon to jump. The beaver ponds also provide critical cool water ponds with abundant food, which drastically increase juvenile salmon survival rates.
Despite all of this, humans always seem to think we know better, and salmon migrations are often used as a reason to kill off beavers. These two animals evolved together for millions of years into a perfect symbiosis. When salmon die after spawning, they provide the surrounding trees with critical nutrients. Beavers then eat these trees and create a habitat that's perfect for the next generation of young salmon to grow up in.
Astoundingly, there's even more to this story. These wetlands are more than just habitat— they also create massive distributed water management systems that serve to lessen the severity of forest fires and droughts. But as I dove into this topic, I realized that I want to write a whole standalone piece on beavers and water management, so stay tuned.
How We Got Here: The Fur Trade
Ever since early humans migrated north out of Africa, they've been dependent on beavers for both food and warm clothing. As society progressed, animal fur became one of the first commodities we traded, given its intrinsic and universal value. We have historical references to the fur trade throughout ancient Greece and Rome, and there are even records of Viking fur traders arriving to Constantinople, or modern day Istanbul. As society grew, so did our demand for pelts. But there's one special quality of a beaver pelt that condemned them over all other animals.
There are a few different commodities you can get out of an animal fur depending on how you process it. First is a full pelt, or the skin of the animal with the fur still intact. Second is what we would call leather or suede, which is just the skin of the animal with the fur removed. Lastly is felt, which is the skin of the animal processed with heat and pressure. This product is uniquely pliable, shapable, and waterproof, which made felt one of the most sought after materials for hat making across the world. Unfortunately, the anatomy of beaver fur lends itself perfectly to the felting process. Pretty much every old-timey hat you can think of was made from beaver felt, from the top hat, to the pilgrim hat, to the cowboy hat, and pretty much every military hat from the 1400s to the end of the 1800s.
Early on, the felting process was a trade secret in medieval Russia. This gave them essentially a monopoly over beaver felts until the Eurasian beaver population started collapsing towards the end of the 1500s. This thirst for beaver fur drove the expansion that resulted in what is now modern Russia. As they ran out of beavers and other furbearing animals in their surrounding area, they expanded east into the Eurasian plateau. This expansion and colonization continued all the way into Alaska, which they held until it was purchased by the United States in 1867.
Unfortunately, just as Eurasia ran out of beavers in the beginning of the 1600s, the North American fur trade was exploding as European powers continued their colonial expansion. It's hard to overstate how important this trade was to the region. Almost every single major geopolitical event or conflict was in some way fomented by the jockeying for access to the fur trade. A great example is the Seven Years' War, known regionally in North America as the French and Indian War, fought between 1756 and 1763. Although it was a global war, in North America, the conflict pitted French trappers and their native allies against the British colonies and the Iroquois Confederacy over control of the fur-rich Ohio River Valley. Then, much like in Russia the century before, the fur trade was a major catalyst for the westward expansion of the US, beginning with the Louisiana Purchase in 1803.
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As the decades wore on, waves of fur trappers roamed the American West, combing through every single stream throughout entire watersheds, looking for beavers. Eventually, the fur trade began to decline around 1870, as the populations of fur bearing animals plummeted and fashion trends changed. In the end, the rise of silk was likely what saved the beaver from extinction. The saddest part of this whole story is that since beaver populations were decimated long before American settlers truly began expanding west, we don't even realize that almost every single stream used to be full of beavers. All that's left are names like "Beaver Creek" and "Beaver Road"— that don't even make sense to us anymore.
Generational Memory Loss and Recovery
Thankfully, beaver populations have recovered from the brink of extinction. At the end of the fur trade, the North American beaver population hovered around 100,000 and has since boomed back to around 10 to 15 million. The Eurasian beaver's comeback has been even more inspiring, recovering from a low of just 1,000 to a current population of around a million.
The issue is— both species of beavers are currently listed by the IUCN as animals of "least concern," which is a huge problem. This is the international organization that defines animal species as endangered, extinct, etc. And it's true— beavers are not at any immediate risk of going extinct. But many animals that are at risk of going extinct depend on the habitat beavers create. So in the case of the beaver, not going extinct is just not good enough. Beavers should be thriving.
Historical population estimates of North American beavers range anywhere from 60 to 400 million. And personally, I put more weight on the high end of that estimate. So, modern beaver populations could be as small as 3% of what they used to be. That would mean that only a small sliver of all the habitat they used to create still exists. No wonder we're witnessing a collapse of biodiversity.
And fundamentally, that's the problem with generational memory loss— it makes it impossible to gauge success. Just listen to these two stats: Today, there are 100 times as many beavers in North America as there were in 1900. But even with that explosive recovery, we still have likely only recovered around 3% of the pre-fur-trade population. Both stats are true, but notice they make you feel wildly different. Whether or not we can consider this a success story depends on when you start measuring.
Now, I honestly believe that beavers should be the cornerstone of modern conservation efforts because their existence creates thriving ecosystems and healthy forests. They help tackle our two major ecological goals for the next century: sequester carbon and retain biodiversity. And while we likely will never fully recover beaver populations to what they were before the fur trade, we should make every effort possible with the urgency it deserves.
Unfortunately, beaver restoration isn't necessarily straightforward. I wish it were as easy as dropping a bunch of beavers in streams, but it's not. Because beavers have been absent for so long, many river systems have degraded to the point where they can no longer sustain them. In many places, there's preliminary work to do, like the propagation of deciduous trees and installation of fake beaver dams to begin recovering the landscape in preparation for the beavers' return. But not too dissimilar from the rugged fur trappers two centuries ago, the task of our time is to go creek by creek and put beavers back everywhere they belong.
Imagine if by 2100, we had 100 million or even 200 million beavers and were enjoying ten times the benefits they're currently providing. It sounds daunting, but the current trajectory we're on is wildly positive. Beaver-wise, we've already created a world even better than the one our grandparents saw. And there's no reason to stop there.