Beaver: the Ultimate Keystone Species

A Bit of History:

During the nineteenth century, man’s extermination of any living creature that had fur or feathers was so extreme that some have dubbed the period the “Age of Extermination”. It is estimated that between 60-400 million beaver populated North America prior to the 1500’s. By the 1900’s, there were about 100,000 beavers left. We currently have about 15 million beaver — it is not an endangered species, but it’s numbers are certainly reduced from it’s historical representation. Let’s explore what makes beaver such an important keystone species with respect to wetland habitats.

DEFINITIONS:

  • Wetland: An area of land saturated with water. There are five types of wetlands: ocean, estuary, river, lake, and marsh. In this post, we are referring to river wetlands.
  • Hyporheic zone: Describes the area in a stream bed where the water moves in and out carrying dissolved gas and solutes, contaminants, particles, and microorganisms. Depending on the geology and topography, the hyporheic zone may be only a few centimeters deep or extend up to tens of meters deep. Both water mixing and storage happen here.
  • Hyporheic exchange: Refers to the speed at which water enters or leaves the hyporheic zone. The rate of exchange can be quite variable depending on a number of structural and geomorphic factors.
  • Incised stream / Degraded channel: A stream channel in which the bed has dropped and as a result, the stream is disconnected from its floodplain.
  • Floodplain: The flat area adjoining a river channel constructed by the river in its present climate and overflows during moderate flow events.
  • Algal blooms: A rapid increase in the population of algae in a freshwater or marine system. Algal blooms refer to microscopic unicellular algae, not macroscopic algae. The bloom is a result of excess nutrient (like nitrogen or phosphorous from fertilizers) entering an aquatic system and causing excess growth.

Wetland Habitats — Why are they Important?

We now recognize wetlands to be critical habitat for a healthy ecosystem and focal points of biodiversity, however they were historically viewed as places of darkness, disease and death. In short, they were considered wastelands that needed to be converted to usable land. It would be impossible now to restore our landscape such that it could support the historical number of beaver seen in the early 1800’s as the landscape is too altered by humans — homes, roads, pastures, and orchards with many streams that have degraded to the point that beaver are unable to restore them to wetland areas. Ben Goldfarb, in his book Eager quotes Kent Woodruff of Washington’s Methow Beaver Project as saying “We’re not smart enough to know what a fully functional ecosystem looks like, but beaver are.”

In the western U.S., wetland habitats cover about 2% of land area yet support about 80% of species biodiversity. These habitats provide numerous critical functions, such as: water filtration, flood and erosion control, food and shelter for fish and wildlife, absorbing and slowing floodwaters, absorbing excess nutrients (e.g. nitrogen from fertilizers), heavy metals, and sediments before they reach rivers, lakes, and other water bodies. They also serve to provide wildfire breaks in the landscape.

The Amazing Beaver

The North American Beaver (Castor canadensis) are best known for their unrelenting desire to build dams, often to the distress of land owners that don’t particularly want their land flooded. Beaver are rodents that weigh about 60 pounds and can live up to 24 years. Interesting physical characteristics include:

  • Extremely dense fur — this feature is what the early pioneers sought to make hats and use for trading.
  • Duck-like hind feet that make them agile swimmers.
  • Ability stay underwater for up to 15 minutes.
  • A second set of eyelids that function as goggles underwater.
  • A second set of lips that can close behind their front teeth so they can chew and drag branches underwater without drowning.
  • A multi-functional tail serving as a rudder, fat storage and thermoregulatory device, and alarm system by slapping it against the water to warn other beavers about the presence of predators.
  • Amazing incisors that grow continuously and self-sharpen as they gnaw down trees.

Beaver are totally herbaceous, eating the cambium (inner sugary layer of trees) mostly from willow, aspen, cottonwood, as well as other green vegetation. They create two types of structures with trees; the lodge which serves as living space with underwater tunnels and an elevated nesting chamber, and dams. Generally 2 – 8 beavers inhabit one lodge — the adult mating pair and three years of offspring. Beaver build both of these structures in order to extend their habitat. They are quite vulnerable to predators (bear, cougars, coyotes, and wolves) on land but much safer underwater, so by extending the surface area of water they are providing their own protection. Dams hold water in low-gradient areas creating ponds which submerge their lodge entrances and give them a place to stash their food caches. The ponds created by the dams also irrigate water-loving trees allowing beavers to operate as rotational farmers — they’ll cut down vegetation in one area while cultivating their next crop in another.

A beaver lodge I came upon while enjoying a picnic in southern France

Beaver dams range in size from quite small (1 x 3 feet) to quite large (15 feet high by a half-mile long). There are three basic requirements needed in order for beaver to set up shop in a given riparian area; water (wadable creek-type), a low valley landscape that allows a gentle stream flow to avoid blowing out their dams, and deciduous vegetation in sufficient quantity for food and construction material. If a stream is allowed or forced to become incised, it becomes challenging for beavers to establish themselves since incised streams tend to blow out the dam(s) during times of heavy stream flow. The pond created by the dam provide a number of benefits to the beaver: underwater escape from predators, increased foraging areas, allowing logs and branches to float in the water, and ensuring the entrances to their lodges remain underwater. Sometimes several dams are built by the same colony. If beaver inhabit an area that already has existing and adequate pond coverage, they will not build dams.

The Benefits of Beaver Dams

American farmers collectively add about twenty million tons per year of fertilizers to agricultural fields. Rain sweeps much of the excess nitrogen and phosphorous from these fertilizers into rivers and eventually into lakes and seas. Suburban lawns, septic tanks, and even cars contribute to this nitrogen dump into watersheds. This nutrient stew fertilizes algal blooms that decompose when they die off, devouring dissolved oxygen in the water and giving rise to “dead zones” — lifeless expanses of anoxic water that drive away all fish and kill stationary bottom dwellers. Global oceans are afflicted by nearly a hundred thousand square miles of dead zones. One solution to this crisis is healthy wetlands which, like kidneys, filter out suspended nutrients and other pollutants long before they reach the sea. In addition to beaver ponds capturing and storing excess nutrient run-off, one study has shown that bacteria living in the sediment of beaver ponds broke down added nitrate, effectively purging the pollutant from the water by converting it to nitrogen gas.

Beaver are amazing architects of wetland ecosystems. Here’s a short list of other species that benefit from sharing beaver habitat:

  • Primary producers such as algae and diatoms increase as more sunlight becomes available (not to be confused with an algal bloom), this leads to more secondary producers such as micro-and macroinvertebrates. The secondary producers form the base of the food web that young salmon and steelhead rely on.
  • Aquatic insects live in the spaces created by dams and lodges.
  • Waterfowl and other bird species increase due to the abundance of aquatic insects for food as well as increased vegetation for protection from predators.
  • Amphibians, turtles, and lizards are more abundant near beaver ponds.
  • Wetland plant species increase in areas where beaver are present. Initial loss of trees and shrubs due to flooding opens up the landscape to allow more sunlight into the expanded riparian area.
  • Fish communities are more diverse. Fish expend less energy foraging in the slow productive waters of beaver ponds.
  • Mink and raccoon hunt crawdads and snakes in beaver complexes.
  • Nutrients from beaver feces breed zooplankton.
  • Sawflies lay eggs on beaver-browsed cottonwood shoots.
  • Moose follow beaver ponds to feed on the wetland plants.
  • And on and on….

The potential ecological benefits of restoring beaver to appropriate landscapes include: higher water tables; reconnected and expanded floodplains; more hyporheic exchange; higher summer base flows; expanded wetlands; improved water quality; greater habitat complexity; more diversity and richness in the populations of plants, birds, fish, amphibians, reptiles, and mammals; and overall increased complexity of the riverine ecosystems.

In light of all the ecological benefits attributed to beaver, it becomes clear why many scientists consider beavers to be the “ultimate keystone species”.

Making the Connection

Conservation biologists point out that people often fall victim to shifting baselines syndrome. This is a type of long-term amnesia that causes successive generations to accept its own degraded ecology as normal. Salmon fisherman that boast of catching ten-pound chinook forget that their fathers once hauled out fifty-pound chinook. Current biologists who marvel at mayfly hatches never experienced the insects emerging in clouds so thick their bodies piled up in three-foot windrows. Every year our standards slip a little further; every year we lose more and remember less. Currently, there are more than 142,500 species on The IUCN Red List, with more than 40,000 species threatened with extinction, including 41% of amphibians, 37% of sharks and rays, 34% of conifers, 33% of reef building corals, 26% of mammals and 13% of birds. This data is stunning and should be causing everyone to act as if their hair were on fire. Those of us that have been around for many decades can usually relate to the concept of shifting baselines syndrome; I recall from my younger days how the insect splats on a car windshield used to require regular windshield cleaning whereas now you hardly notice any splats.

The intersection of human and wildlife habitats tends to be fraught with conflict. When beavers choose urban settings to set up their household, this conflict plays out with flooded roads or fields and unwanted vegetative chewing. The tendency is often for humans to either physically remove (relocate) or kill the offending wildlife. When there is an understanding of the benefits that the beavers can provide even in an urban setting, a wiser alternative is to consider each situation and look at the full range of alternatives available for mitigating the problems while allowing the beaver to stay. These alternatives include placing fencing around culverts, notching inactive dams, and placing deterrents on active dams that may inhibit rebuilding, placing protective wire meshing on trees. It is also important to provide education where needed to engage farmers, city managers, etc. in understanding the benefits that beaver will provide to a local ecosystem. This has been done successfully in many areas around the country. Several states now have beaver management protocols in place.

Our world will always be improved when we work with nature instead of against it. For far too long man has viewed the natural world as a resource to be exploited without regard for the harm caused in the process. More and more people are coming to realize, now that our one and only planet is in crisis, that we need to better understand, protect, and preserve everything that exists in the natural world because it is all interconnected and necessary for the health of the whole. I hope this blog is helping you to understand that when we sever the links between vital species in an ecosystem there are always negative repercussions if not total collapse. There are many incredible individuals and organizations working to provide sustainable solutions to problems that crop up in the interface between human activities and various species that are trying to go about their lives.

For more information about beaver, I recommend this site: https://www.beaversww.org/. I’m including a video from this site.

WORKS CITED:

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