Animals and Environments 3: Beaver of the Breaks

Apologies for the repeat. Day Job is in a bit of a crunch mode because the End of the Quarter is Nigh. Plus we’re all having to cover for those out ill.

Ah, beaver, the cute rodent property owners love to hate. Beaver are, as one author described them, “nature’s wetland engineers,” re-working the local hydrology to suit their own needs. In the process they can have some very long-term effects on the environment around and down stream of their chosen location. The Canadian River valley, although at the margins of beavers’ usual domain, showed the effects of their activities in several different ways.

Industrious Beavers at Niagara Falls, as shown on a 1731 edition Moll's map of the British Colonies in North America. Library of Congress, Geography and Map Division. From

Industrious Beavers at Niagara Falls, as shown on a 1731 edition Moll’s map of the British Colonies in North America. Library of Congress, Geography and Map Division. From

OK, so early European authors had a slightly inaccurate view of how beavers did their thing. They had a good reason for the confusion: European beavers live in the banks of streams instead of making ponds and lodges. But the basic idea’s pretty close.

Beaver build lodges and dams on fresh-water streams, usually in areas with ready access to the types of small trees and plants beaver prefer to eat (willow, birch, aspen). Beaver do not eat older wood per se, but do eat the inner bark and small, tender twigs and branches. Their digestive systems include bacteria to digest some of the cellulose, but they prefer bark and the cambium layer. Beavers gnaw down saplings and small trees, then drag them into the water and use them, along with sediment from the stream, to build water-resistant and water-tight structures. The pond behind the dam serves as the location for the lodge, where the beaver raise their kits. The beaver also stash food in the pond for winter, preserving and protecting it. Their dams can be very impressive and sturdy, at times requiring a considerable amount of effort and explosives to remove them from the waterway.

The beaver dam and pond has several effects on the hydrology of the stream. The largest known dam to date is one in Woods Buffalo National Park in Canada, and measures roughly 2790 feet from bank to bank. Most dams are not quit that large, but they all have the same hydrologic effects. The dam stops stream flow for a while, until the pond outgrows the dam and water overtops it, or finds a new, slower way through the mass of material. The pond raises the local water table, allowing water to seep into the surrounding soil and creating a larger wetland than was there before, and potentially favoring some kinds of plants while drowning others. The pond acts as a flood buffer, slowing the rush of water and making the rise and fall of the stream less dramatic. The stream becomes less “flashy,” less prone to rise and fall abruptly when storms come through or snow melt hits the watershed. In like manner the pond and dam keep more water in the stream during dry periods, up to a certain point. After ten months without rain, even beaver ponds won’t help a stream. The wetland and pond can act as water purification systems, allowing the slow filtration and decomposition of sediment and biological materials in the water.

Along with water, the pond and dam catch sediment. Over time, the pond fills in, becoming first a smaller pond, then a marsh, then a beaver meadow lush with grasses and forbs. When the Hispano settlers first moved into the Canadian River valley in Texas in the early 1870s, they used those old beaver meadows for hay meadows as well as setting up their acequias, their irrigation systems, there in the rich and relatively level soil. By that point, the beaver have already moved on, usually after having eaten out all their preferred trees and bushes.

As mentioned above, the Canadian River valley, especially the western section in what became Texas and in far eastern New Mexico, provided beaver with at best marginal habitat. The semi-arid climate did not favor the kinds of trees beaver prefer, and what did grow (cottonwood, hackberry, scrub oak, juniper, slippery elm) tended to be a bit sparse. Still, the valley formed a connection between the Rocky Mountains to the west and the lusher Great Plains and Low Rolling Plains to the east, and early Anglo explorers commented on the enormous beaver dam they found on one of the tributaries of the North Canadian, probably not far from modern Perryton, Texas in the northeastern corner of the Panhandle.

The Hispano residents made a few attempts to trap the beaver, but without much success. Muskrat too lived along the streams feeding the Canadian, but their structures tend to be less dramatic than those of the beaver.  The Canadian Valley, off the main fur-trade routes, didn’t see the heavy trapping so well-known to the north. I also suspect that the pelts of southern beaver would have brought lower prices on the market, but that’s just a guess. The lush under-coat of the beaver, beneath the guard hairs, brought enormous amounts of money in the hat trade, as the history of Canada and of the US fur trade attests.

The brown gold of Canada: beaver on the Parliament Building in Ottawa.

The brown gold of Canada: beaver on the Parliament Building in Ottawa.

The droughts of the 1850s-60s likely stressed the beaver population even farther. The arrival of the Hispanos and Anglo ranchers brought and end to the beaver as people cut down the few remaining trees to build with. The first Anglo residents’ accounts do not mention beaver, a telling omission. Without beaver, their dams decayed and washed out. Without the dams, the streams ran free, surging and declining, eroding their beds more heavily. This in turn contributed to changes in the Canadian River as additional sediment washed into the main stream, and the water supply from tributaries peaked and fell at greater speed. How much this contributed to the physical changes one of the Hispano residents, Jose Ynocencio Romero, recounted to a later historian remains uncertain because of other events going in the river’s “life” at the time, but it likely played at least a small role.

Like the bison on the uplands, beaver were a keystone species in the Canadian River valley. They shaped their environment, which in turn affected the larger valley’s hydrology and biology.


13 thoughts on “Animals and Environments 3: Beaver of the Breaks

  1. Beaver were the basis of John Jacob Astor’s fortune, and so ceramic Beaver decorations were set in the tiled walls of the Astor Place subway station on the IRT Lexington Avenue line. Since Lexington Avenue doesn’t exist that far south, the station lies at the place where Lafayette Place joins the nascent and short-lived Fourth Avenue, which once upon a time was the home of used book dealers. At least one of them, Biblio and Tanner, was also a small publisher. There were still a handful of them, run to seed, around 1980 Biblio and Tanner among them.

  2. It’s fun to listen to the whining in MD and NoVA, now that beaver are reintroduced and are making drainage basins, streams, and yards into dammed ponds. All those thoughtfully planted trees and shrubs are a perfect appetizer. They’re re-creating wetlands one pond at a time. Animal Control’s reply is essentially nope, we relocate ’em upstream, but they come back; anyway, endangered species, so learn to like it. It’s more fun if the whining can be traced to a EPA or state Environmental Protection employee.

  3. I trapped beaver quite a bit growing up, and found a lot more bank beaver than lodge beaver. Beaver in fast moving rivers seldom build dams, but beaver in small streams or wetlands usually always do, they will build lodges in wetlands or large ponds, but in steeper sided rivers or small streams they commonly dig bank dens. Many of the small streams I trapped had ponds the size of your living room, and a lodge would have taken up a large percentage of the pond, probably why they preferred bank dens.
    I have seen several dams over a quarter mile long in swamps, but don’t know that I have seen one over a half mile like you describe.

    • I suspect being in the national park has a lot to do with the size and age of the big dam.

      European beaver are (or were) bank dwellers, and I’ve heard that some of the introduced North American beaver also prefer the banks to a lodge. Not sure if that is because of the speed/size of the rivers or for another reason. I’ve not been to any of the parks in Europe that have the imported rodents.

      • This is totally unscientific, just my personal observations; but they tend to build lodges in swamps, shallow lakes, and large shallow ponds. I suspect both a lack of steep banks where they can dig a hole from underwater a reasonable distance and have the dwelling both above water and with an acceptable overhead thickness of soil. And in the inverse of deep lakes and/or ponds, deep, swift flowing rivers or small ponds there isn’t a large availability of acceptable lodging sites.

        From my personal observations beaver tend to be both opportunistic and very practical, they use whatever type of lodging is most appropriate for the terrain.

  4. I think Heinlein said the following (roughly).

    “The man who admires the beaver’s work but damns human works, shows his hatred for humans”. 😉

    (Pun not intended).

  5. Our river used to have a lot of willow (apparently very common before white settlers came in), but there’s a lot of aspen and a bit of birch around. A previous neighbor started some fruit trees just above the bank, and was rather unhappy when the beavers found them tasty. Knowing the neighbor, I’m sure most people sided with the beavers. 🙂

    I haven’t seen any lodges or dams, but have seen one beaver by us. The river right by us isn’t great habitat for dams, but there could be some up and downstream.

  6. I have seen a small beaver marsh fill in. It only took a couple of years.

    Unfortunately, they built a housing development on it. I guess nobody wanted to remember it was “wetlands” before.

  7. I’ve never spotted a beaver in the wild, but I have seen their handiwork often enough near the banks of many a body of water.

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