By Lambert Strether of Corrente
“The augmentation of the complexity and intensity of the field of intelligent life.” –Ursula Leguin, The Left Hand of Darkness
I’m not sure what I encountered in my perambulations through the biosphere that drove me to write about the world’s second largest rodent, the beaver[1]. (The largest is the preternaturally placid capybara, a far less interesting and impactful creature, albeit also semiaquatic.) Beavers are nocturnal, and I would see one come out at dusk on the Stillwater, swimming with amazing speed upstream away from the falls, leaving a silver wake, carrying material to stock or build its lodge (which it was quite noisy about; the Stillwater is quite still).
That is what is intrigues about the beaver: Like humans, the beaver is a builder. From the U.S. Fish and Wildlife Service:
Beavers need two to three feet of ice-free water year round. To maintain the necessary water level, beavers construct dams. Piled logs and trees are secured with mud, plants, rocks and sticks. They also build canals to float and transport branches and logs for food and construction. Food for the winter is stored in underwater food caches; beavers eat bark, leaves, aquatic plants, roots and grasses.There are two types of dens beavers use as food caches depending on water fluctuations: bank dens and lodges. Lodges are constructed where water levels are more stable, as in ponds or lakes. The same lodge is used by a family year after year and may house up to ten beavers at a time. The main room of the lodge is often more than 3 feet tall and 4 to 5 feet wide.
The lodges seem like quite comfortable little homes:
Within each lodge beavers will hollow out a chamber where they sleep, eat, groom each other, and the baby kits are born and nursed each spring. Beddings of grasses, reeds and wood chips are changed regularly. In order to breathe fresh air beavers do not apply mud to the peak of the lodge, creating a ventilation shaft. Note: If you have an opportunity to visit a beaver lodge on a very cold winter day, look very closely and you may see the beaver’s breath escaping from this chimney-like peak, or even hear the murmurs of the beaver family inside!
Each lodge contains at least two water-filled tunnels leading from the chamber to the pond so the beavers can enter and exit the lodge underwater without being spotted by predators. The walls of the conical lodge are very strong due to layers of mud and sticks, and are extremely insulated. Even with subzero outside temperatures it will not drop below freezing inside the lodge due to retained body heat from the family of beavers.
But what beavers build that’s really interesting is dams, that create the ponds[1] that surround their lodges:
The simple answer is that beavers build dams to deepen watercourses, so that they can create “lodges” that can be better defended from modern predators including bears, wildcats, otters and other mammalian forebears with whom the beavers shared prehistory. It seems that deep water is particularly important to beavers. Lakes and ponds allow for a kind of floating structure of sticks and branches that can be accessed from a secret hole beneath, a key real-estate feature that reduces the need for terrestrial entrances through which land-based predators can climb. Upon finding shallow watercourses, colonising beavers immediately begin damming, creating canals along which trunks and branches can be dragged along to add to this, their anti-predator superstructure. In these lodges, beavers rear their young and see out winter, safe and sound.
Here is a magnificent diagram (credit illustrator Bill Donohoe) of the entire lodge and dam complex, showing details of the construction:
And here is a beaver dam encountered in nature:
Woudn’t it be nice to encounter something so beautiful on a walk through the forest! Readers can just look at the photograph to see the ecological niches such a wetland creates: The pools and streams, the shady nooks, the sticks and vegetable matter; beaver dams have been said to encourage songbirds, salmon, ducks, frogs, and who knows what else. Moose? Yes, moose. That’s why beavers are considered a keystone species[2]:
The North American beaver is a keystone species, a unique organism that supports the entire biological community.
“To acknowledge that beaver create environments that store water and help sustain other creatures is insufficient. Beaver are nothing less than continent-scale forces of nature and in part responsible for sculpting the land upon which Americans built their communities.”
— Ben Goldfarb in Eager: The Surprising Secret Life of Beaver, 2018
But that dam was only a small one:
A Canadian ecologist has discovered the world’s largest beaver dam in a remote area of northern Alberta, an animal-made structure so large it is visible from space.
Another such “animal structures” being, oh, Manhattan. More:
Researcher Jean Thie said Wednesday he used satellite imagery and Google Earth software to locate the dam, which is about 850 metres (2,800 feet) long on the southern edge of Wood Buffalo National Park….
Construction of the dam likely started in the mid-1970s, said Thie, who made his discovery quite by accident while tracking melting permafrost in Canada’s far north.
“Several generations of beavers worked on it and it’s still growing,” he told AFP in Ottawa.
Thie said he recently identified two smaller dams sprouting at either side of the main dam. In 10 years, all three structures could merge into a mega-dam measuring just short of a kilometer in length, he said.
The region is flat, so the beavers would have had to build a massive structure to stem wetland water flows, Thie said, noting that the dam was visible in NASA satellite imagery from the 1990s.
“It’s a unique phenomenon,” he said. “Beaver dams are among the few animal-made structures visible from space.”
Here is that dam (the resolution is what it is):
Beavers, then, are not merely keystone species; they can and do re-engineer the landscape on a very large scale. Turning less rhapsodic and more science-adjacent, beaver re-engineered landscapes have effects on carbon capture (good) and methane generation (potentially bad).
Turning first to carbon, we find the following in Geophysical Research Letters, “Landscape‐scale carbon storage associated with beaver dams“:
Beaver meadows form when beaver dams promote prolonged overbank flooding and floodplain retention of sediment and organic matter. Extensive beaver meadows form in broad, low-gradient valley segments upstream from glacial terminal moraines. Surveyed sediment volume and total organic carbon content in beaver meadows on the eastern side of Rocky Mountain National Park are extrapolated to create a first-order approximation of landscape-scale carbon storage in these meadows relative to adjacent uplands…
I present landscape-scale estimates of cumulative sediment and organic carbon storage associated with beaver dams in mountainous headwater catchments within Rocky Mountain National Park (RMNP) in Colorado, USA, as an example of the regional assessments necessary to understand the cumulative effects of reduced beaver populations.
And, presumably, carbon capture with increased beaver populations[3]. More:
Although values of carbon storage can be refined, the trends indicated in this analysis are robust: beaver meadows store the great majority of carbon along rivers in these mountainous headwater catchments; this source of carbon storage cumulatively represents ~8% (relict) to 23% (active) of estimated total landscape carbon storage; and riverine carbon storage has declined substantially with the replacement of beaver meadows with drier “elk grasslands” [Wolf et al., 2007]. The estimated 23% of total landscape carbon storage within active beaver meadows also agrees well with an earlier estimate of 25% of total carbon storage in unconfined valley bottoms that included beaver meadows and old-growth forest with substantial downed wood.
That seems like a lot of carbon.[4]
On a more granular level, we have from Geoderma, “Beaver pond effects on carbon storage in soils“:
The density and stratigraphy of carbon storage was studied in soils of boreal beaver meadows, graminoid wetlands that develop after a beaver pond is abandoned and drained, at Voyageurs National Park on the U.S.–Canada border, where beaver re-colonized the landscape during the latter half of the 20th century. Carbon density was measured to a depth of 60 cm by collecting volumetric samples in mineral soils from the side walls of hand-dug trenches….. [C]arbon density to a depth of 60 cm was still significantly greater in beaver meadow pedons …. than in adjacent forest soils that had not been impounded…. The difference was attributed to the accumulation of graminoid [here, in contrast to forbs (!)] plant debris in thick surface O horizons [topsoil[5]. Volumetric carbon concentrations were greatest in O horizons, and a linear regression between O horizon thickness and carbon density was significant.
And we learn from “Beaver Ponds and the Carbon Cycle” that beaver-pond peat is better than bog peat:
Carbon takes a variety of forms in beaver ponds and beaver meadows, including live plant biomass, standing dead biomass, soil organic matter, soil carbonates, dissolved organic carbon, and trace gases….The slow decomposition rate of beaver meadow plant litter under anaerobic conditions promotes the accumulation of organic (O) soil horizons, which have a calculated mean residence time of 69 years. The carbon per unit area in soils that were formerly impounded by beavers (15.1 ± 6.8 km C m−2) was nearly twice that of adjacent never-impounded forest soils (8.2 ± 2.9 km C m−2). Beaver meadow sedge peat mineralization was compared with that of bog peat in long-term (80-week) laboratory incubations. Beaver meadow sedge peat had significantly higher carbon mineralization rates under all incubation conditions except aerobic incubation at 15 °C (other treatments were anaerobic incubation at 15 and 30 °C and aerobic incubation at 30 °C).
In other words, all those sticks and all that rotting plant matter adds up to — switching to scientific terminology here — a boatload of carbon captured, because beavers work to the landscape scale. And carbon capture is a Good Thing, especially if we leave the carbon in the ground.
However, beaver ponds and meadows, besides being carbon sinks, are also methane sources[6]. In Phys.org, “Effects of growing beaver population on habitat and methane gas emissions“, we find the process explained:
Beavers are skilled at building dams in rivers to create standing open-water ponds and neighboring wetlands. Such ponds are generally shallow, with dams seldom being more than 1.5 metres high. Carbon builds up in the oxygen-poor pond bottoms and methane is generated. This climate warming gas cannot adequately dissolve in the shallow water and is released into the atmosphere.
According to Whitfield, it has long been known that release of methane from beaver ponds to the atmosphere is more intense than for other types of wetlands. To quantify methane release, his team estimated the size of the current global beaver population. They also determined the area covered by beaver ponds.
Whitfield’s team found that global beaver numbers have grown dramatically, to a population of over 10 million. The Eurasian population could grow by an additional four million. In the process of population recovery, beavers have dammed up in excess of 42,000 square kilometres of aquatic pond areas, which are bordered with over 200,000 kilometres of shoreline habitat.
Parallel to the increase in beaver populations is also a notable increase in methane emissions because of their pond-building efforts. At the end of the 20th century, beaver activities contributed up to 0.80 teragrams (or 800 million kilograms) of methane to the atmosphere each year. This is about 15 percent of what wild cud-chewing animals, such as deer or antelope, contributed.
(This contribution is expected to grow.) By comparison, the US oil and gas industry emits 13,000 million kilograms of methane a year. But (expanding on this post on ponds at NC) there is also the issue that beaver ponds in the warming Arctic also release methane. From WBUR, “The Unusual Connection Between Beavers, Permafrost And Climate Change“:
As temperatures warm and boreal beavers migrate north, they’re creating ponds — more than 10,000 of them — that are flooding millennia-old permafrost. When thawed, permafrost can release dangerous greenhouse gasses such as carbon and methane.
University of Alaska Fairbanks researcher Ken Tape says the beavers are, in effect, creating dangerous oases around the Arctic. He’s one of the authors of a recent study on beavers and permafrost….
The influx of beavers building ponds is starting to thaw the permafrost — land that’s been frozen for at least two years but often hundreds or thousands of years — under the ground.
Permafrost makes the beavers moving up into the tundra a global concern. When beavers flood the tundra to make ponds, the water transfers heat to the ground and starts thawing the permafrost, releasing the greenhouse gases stored inside, he says.
Leaving us, I suppose, with a public policy issue. Since beavers work to landscape scale, do they also work to planetary scale? What if they — with a little help from us — do manage to convert the Arctic permafrost into an enormous wetland? What do we do? Exterminate them again?
I am inclined to believe not, because I don’t think “the science” at this point can do more than serve as a heuristic, probably because I don’t trust models as anything more than heuristics. (Suppose Google did in fact engineer a working quantum computer and managed to model the climate with it. Would we trust the data or the algorithms of their model? Why?) I feel — underline feel — that the way forward is through more (natural[7]) complexity, not less. A world with Arctic wetlands engineered by beavers could end up being preferable to a world where the Arctic as it has been is basically a tear-down anyhow. It’s likely preferable to a world where the Arctic becomes an enormous tree plantation to feed BECCS plants. I understand this is an aesthetic judgment. And perhaps that’s what an animist would think. Readers?
NOTES
[1] Here is a good presentation on beaver biology from the National Park Service. Among other adaptions, beavers have pelts to keep them warm while swimming, flat tails that they use like rudders while swimming, big front teeth, and webbed back feet. Their front feet are like hands, but without thumbs, perhaps fortunately for us. Beavers eat the bark, buds, stems, and twigs of trees. “Because a beaver’s front teeth grow all the time, a beaver must constantly chew on wood to trim the teeth down.” There are only two species of beaver: The American beaver (Castor canadensis), and the Eurasian beaver (Castor fiber).
[2] We discuss keystone species (and food webs) further here. What appeals to me about the beaver-as-builder is that they are keystone species without being predators, unlike wolves or sea otters.
[3] I am going to skip over both the ugly story of how we homo sapiens (yeah, right) nearly exterminated the beaver in order to make hats from their fur, and the happier story of how we brought the beaver back through a combination of regulation and rewilding, globally. I might make this the topic of future post. There is, for example, the question of whether wetlands are more important than real estate development.
[4] And when you see the neat “hockey stick” curves, you wonder if the stories they tell include the carbon storage services lost when we nearly exterminated the beaver, besides the carbon we dumped in the atmosphere by burning fossil fuels.
[5] See Naked Capitalism here for a diagram of soil horizons, including horizon O.
[6] Nobody seems to know how it all nets out. “Beaver ponds can indeed be large sources of potent planet-warming greenhouse gases such as methane and nitrous oxide, says Jennifer Edmonds, an aquatic ecologist at the University of Alabama, Tuscaloosa. (Over the course of a century, methane traps heat in Earth’s atmosphere about 25 times as effectively as carbon dioxide; nitrous oxide does so almost 300 times as effectively over the same interval.) But considering the whole landscape, she adds, ‘if I had to bet, I’d bet that [the beaver meadows] are storing more carbon than they’re producing.'” Perhaps it’s not knowable?
[7] Whatever that means. Ecological?
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Thanks, I enjoyed this very much
the preternaturally placid capybara, a far less interesting and impactful creature, albeit also semiaquatic.
Shots fired! I was going to suggest you were just prejudiced towards North American mammals over South American mammals, because nationalism, but then I read more about capybaras. They’re important food for jaguars, so there’s that. But given we keep killing all the jaguar, they’re growing out of control. They tend to reproduce much like their smaller, prolific guinea pig cousins.
Not to mention the capybaras that escaped from a small zoo in Toronto and eluded capture for weeks a couple of years ago. They were finally found Healy and happy living in a big city park.
I never heard of the potential beaver influence on the loss of permafrost before. Especially as the eurasian beaver doesn’t build the type of big dams that north American beavers construct.
In Europe, they are a major conservation success – from near extinction, they’ve been reintroduced in many areas, with a lot of success. They are re-establishing in Scotland and England and hopefully they will soon start to reintroduce them to Ireland. They have have a very positive impact on river ecology, although unfortunately they also wreck havoc in commercial forests.
I dunno. Do they wreak more havoc in commercial forests than flooding? Because beaver dams are really good flood control measures. The English beaver introductions are at least in part supported by the Forestry Commission in their commercial forestry plantations (otherwise known as “national parks”) because reducing flooding is *valuable*.
I was lucky enough to have a close encounter with one fishing here in Southeastern PA, in a public park no less, no too far from a hiking trail. I was unsuccessfully fishing when I saw something sitting in the water.
“What’s that groundhog doing in the water? What’s that BIG groundhog doing in the water?” I asked myself.
I’ve always been fascinated by them because they just will not cooperate with human taming of the environment. They are a nightmare for agriculture and a nightmare for agroforestry. Our two viewpoints on the use of a waterway just will never meet.
However it was nice to see one operating in a suburban environment! And just to give you an idea of their expanding numbers in my section of the world, I saw one as roadkill. That means there’s enough that they’re venturing around looking for new places to dam up.
Re: operating in a suburban environment.
I’ve seen at least two of them in this area. I found a damn they’d built in this park right here: https://www.google.com/maps/@42.2868071,-71.405429,269m/data=!3m1!1e3
Just past the two baseball fields and the tennis courts, under the cluster of trees is a small stream. They’ve dammed it with a leaky dam.
They also showed some real adaptability in their willingness to use plastic trash as construction material. They also swim comfortably through storm drain tunnels under the road that are there to let the stream flow.
I never saw a Beaver in the Sierra’s until I was in my 40’s, now the dams are everywhere.
And I’ll take wetlands over development any day in the week.
Mountain man Jedediah Smith thought that the rivers emanating out of the western slopes of southern Sierra were perhaps the most plentiful for beavers that he’d seen anywhere in his travels.
But that was in 1828, they’ve been extirpated since the 19th century, and i’ve never seen one around these parts, but you’d have better luck around Tahoe where they were reintroduced.
I and some buddies would occasionally pack in to a little lake just a few miles west of Carson Pass (this was in the late ’80s to mid ’90s). The lake had a grove of quaking aspens growing along its northshore, with many trees attaining a foot to maybe up to two ft. in diameter. Arriving year or so later,we found the entire grove was, um .. ‘beaverized’, resulting in the damming the lake’s outlow, raising the water level by several feet. I can’t remember noticing a lodge: all I remember was that all those trees were simply GONE! .. everyone of em. For such a small lake, it changed the esthetic character considerably.
If at all possible, you should eat them, not just strip them from their pelts.”
Eating Beaver.
Anthony Bourdain!
A fascinating post this. I had not realized that those beaver lodgers were so sophisticated but there they are. They look so thick that it does not look like a bear could get in but having only underwater access is just ingenious for these animals. I wonder if beaver lodgers were the original inspiration for Inuit igloos millennia ago.
Not directly related to the role of beavers in the carbon cycle, but still noteworthy: one of the most famous CBC interviews on our national animal was made a quarter century ago in northern BC. A woodsman described in colourful terms how he suffered an unexpected attack from a beaver which had become stranded on a highway bridge: https://www.cbc.ca/archives/entry/beaver-attack
We can only imagine what the outcome would have been if this incident had occurred back in the Pleistocene when the Giant Beaver, which weighed up to 100 kg and measured 2 m in length, roamed North America: https://www.beringia.com/exhibit/ice-age-animals/giant-beaver
One of my favourite show-and-tell specimens is a stick with an obviously beaver-chewed end which I collected from thawing permafrost when doing field work with geologists a dozen years ago in the west-central Yukon. Based on the stratigraphy of the site, I was told that this sample would have been buried during the last interglacial, so it could be well over 100,000 years old.
One can see a lot of beavers’ handiwork in the Boundary Waters of Minnesota and the adjacent Quetico Provincial Park in Ontario. My appreciation of their work was reinforced on a long weekend outing I’d taken with my daughter back in the naughts. Because of her limited time we had chosen to enter at the Sawbill Trail Head, one of the closest to the “civilization” of the Twin Cities area where I live. Before leaving home base I had made the mistake of not dealing with a plantar wart on my heel, and on the first portage out of Sawbill Lake it strenuously objected to the additional weight of the canoe and my pack. As we paddled through a wetland I was looking forward to the fact that before we would get to the long portage over the hump of the Laurentian Divide that separates the Atlantic and Arctic Ocean watersheds to Cherokee Creek, the next portage around a beaver dam would be just a haul-over followed by an easy paddle.
We stroked our way up the short stretch of creek downstream from the dam and . . . the dam which had been there ever since I’d first come this route 15 or more years before and was still in tact the previous year wasn’t there! Whether by the hand of man, the paw of beast or the rage of weather I didn’t know, but the creek left in the late reservoir ’s wake was not navigable. Instead there was not well beaten rocky path beside the creek for what seemed like miles to someone carrying a canoe and pack and wincing every other step.
Let’s hear it for beavers!
Better pictures of the large dam in northern Alberta: https://www.theweathernetwork.com/ca/news/article/largest-beaver-dam-on-earth-wood-buffalo-national-park-alberta-lac-st-clair
One of the most shameful examples of Canadian imperialism is the introduction of C. canadensis to Patagonia, which has caused no end of mayhem:
https://www.nationalgeographic.com/animals/article/beaver-overpopulation-tierra-del-fuego
https://phys.org/news/2021-04-brought-humans-beavers-threaten-patagonia.html
https://www.washingtonpost.com/news/animalia/wp/2018/08/09/why-two-countries-want-to-kill-100000-beavers/
My daughter’s home here in Mobile backs up to about 25-30 acres of woods, most of which is protected wetlands. The local beavers have built a large dam across the little creek running through the swamp. One effect has been that their pond is beginning to encroach on her back yard, making it very swampy. Her ducks love it, but she’s not so excited. If the water gets much higher it’s going to get into the lower level of a storage shed which would be problematic.
The beaver pond is now so deep that the sanitary sewer access that used to stand five feet high on the bank of the creek is now almost covered. Apparently, the city knew what to expect when they built that access.
Lambert – I’m going to see if my daughter can get me some pictures of the beaver dam. I’ve seen a couple and it’s an impressive structure. If she can get some photos, I’ll send you a couple.
> Lambert – I’m going to see if my daughter can get me some pictures of the beaver dam. I’ve seen a couple and it’s an impressive structure. If she can get some photos, I’ll send you a couple.
That would be great. In a sane world, we’d have some way of adjudicating property rights between humans, beavers, and, I suppose, the wetlands, and your sister would be compensated in some way. Ultimately, I think we have to get on with not cooking the planet…
Beaver activists are so sane they’ve designed escapement tools that stabilize pondwater height, which beavers learn to live with. They can’t stand flowing water, so they famously attack culverts. But if you fence off culvert openings 5 feet all around the mouth and make water sift through, the beavers don’t notice it, and the pond stops growing. Same treatments work on dams. The beaver-human interface tide is turning, I learn from this good book:
Eager: The Surprising, Secret Life of Beavers and Why They Matter by Ben Goldfarb
https://www.chelseagreen.com/product/eager-paperback/
Here in Southern Arizona, we say, “Release the Beavers!”
Link: https://watershedmg.org/article/video-san-pedro-beaver-release
And another link to place things in a larger context:
https://watershedmg.org/river-run-network/beavers
Perhaps one should mention the beaver holocaust brought about by European settlement and the cruel way they were killed by steel traps that held them under water until they drowned. Then they went to London to become waterproof hats made of beaver felt.
I’ve only seen one once. Muskrats are easier to spot and look similar except for the tails.
See Note [3].
Great read: “Three against The Wilderness” Eric Collier Homesteading , ecology, beavers in BC
https://www.goodreads.com/book/show/3084797-three-against-the-wilderness
Keystone Species. In my midddle of night worryings, I pondered that I have yet to read an ecological assay of a given biome with keystone species that includes man-unkind. Big oversight. I guess we are harder to behaviorally follow, predict, and account.
Middle of the night worry changes everything!
If global warming is inviting beavers into the permafrost-zone to start building dams and ponds, which will speed-thaw more permafrost, then the problem is global warming and the spread of beaverdams into the permafrost zone is only a symptom of global warming. The solution, if it is not too late now, is enough global de-warming/ global re-cooling that the beavers are disinvited from the permafrost zone and then evicted from it outright. Failing that, beavers in the permafrost zone is just part of our grand new adventure.
Meanwhile, beavers all over their traditional range would begin sinking more carbon in and around every beaver pond and associated higher water table zone. Enough to offset the carbon that the permafrost beavers are releasing just lately? I don’t know.