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Leave It to Beavers—How These Legendary Dam Builders Bolster Ecosystems

Beavers are nature's ecosystem engineers

For thousands of years, a giant species of beaver, Castor californicus, was a feature of the North American landscape. These 200-pound beavers feasted on aquatic vegetation and wallowed in streams and ponds. But early beavers relied exclusively on wetlands for habitat, and, during the last ice age, a drying climate likely led to their extinction. Now North America knows only one species of beaver, the relatively diminutive Castor canadensis.

Beavers are a keystone species that holds together an ecosystem.   ©DoucetPh, Montréal, Canada
Beavers are a keystone species that holds together an ecosystem. ©DoucetPh, Montréal, Canada

Beavers’ remarkable ability to transform their environments makes them a keystone species or an organism that holds together an ecosystem. They change habitats not just for themselves but for other wildlife, and those new habitats become essential for the survival of other species, especially bird life, including great blue herons.

Beaver populations benefit human beings, too, as their famous dam-building activities can help mitigate many of the negative effects of climate change.

Beaver dam structures filter water, and beaver ponds create surface water that can counter drought, flooding, and wildfires.

To build a dam, beavers begin by building a foundation with a layer of stones and then intricately weave in fallen trees, branches, and limbs that they have harvested themselves. They use their extremely sharp teeth to eat the green sugary layer of tree limbs that lies just below the bark. This behavior not only provides nourishment but also building materials. The dams are reinforced with pond plants and mud—and are astonishingly sturdy: In 2005, a group of scientists found what they believed to be the fossilized remains of a beaver dam that could be 125,000 years old.

When beavers build dams, they can transform an ecosystem.   ©iStock
When beavers build dams, they can transform an ecosystem. ©iStock

When beavers move into an area, they can swiftly transform an ecosystem—their newly dammed areas generate open water, wetlands, and meadows. Beavers can even convert a desert creek into a lush oasis. For example, beaver activity in the Nevada desert helped revive the Susie Creek watershed after other restoration efforts attracted the furry rodents to the site. Their return also rejuvenated the creek’s riparian habitat—the new healthy vegetation on the banks provides shelter for wildlife and water for agriculture in the area.

Human Opposition

Despite such dramatic results, beavers still run up against opposition from their chief competitor for habitat, human beings. Humans, who also like to live in valleys near water sources, can react poorly if a beaver family moves in and turns a little stream into a big pond.

The Beaver Institute, based in Southampton, Massachusetts, provides education about how landowners can coexist with beavers.

“Beavers have been around for millions of years, and they’re second only to us in changing their environment to suit their own needs,” said Michael Callahan president and founder of the Beaver Institute.

“Beavers get a bad rap because the only times they get in the news are when they’re causing problems for people … but if we want a healthy landscape with streams, rivers, and clean water, we need beavers,” he said.

Callahan became interested in helping beavers in 1996 when Massachusetts legislators passed a law banning specific kinds of traps for hunting and property management. This prompted some residents to warn that the state will soon be overrun with beavers. This is a common concern, but because beavers have a territorial nature and because each beaver pair only has a few kits a year, there’s little chance of being overwhelmed.

The green marker indicates a flow device that lowers water levels if the beaver pond (right) should interfere with the adjacent road.   ©The Beaver Institute
The green marker indicates a flow device that lowers water levels if the beaver pond (right) should interfere with the adjacent road. ©The Beaver Institute

Conversely, if beaver activity is flooding roads or interfering with agriculture, it can become necessary to curtail them. There are often simple solutions for handling animals who have become a nuisance: Trees can be fenced so that beavers won’t cut them down, or a drainage device can lower water levels if a beaver pond has caused flooding.

“Trapping is only a short-term answer,” said Callahan, “because if you remove the beavers, the habitat is still there, and young beavers will move in.”

Ultimately, learning to live alongside beavers will have benefits far beyond the welfare of the animals themselves, he explained. “By coexisting with beavers, we’re helping not just beavers, but the planet. With climate change, it seems like there’s so little that individuals can do. But it’s very empowering to know that if we keep beavers in the landscape, it will have a lot of benefits.”

Beavers Helping Conservationists

Some conservationists who see those benefits are trying to use these industrious mammals to reinvigorate landscapes and other natural resources.

One way to attract beavers is to place sturdy posts and other building materials that can be used as a base for a dam in key waterways.

Another way to attract beaver families is to make a false dam with similar materials. These structures, called beaver dam analogs (BDAs), are part of the current efforts to restore habitat in Oregon, also known as “The Beaver State.”

BDAS and beaver families are being used in the Upper Klamath Basin, where toxic algae have caused fish that were once a plentiful food source for the Klamath Tribes to become a rarity.

The positive effects on climate change that beavers provide inspired filmmaker Sarah Koenigsberg to create an award-winning 2018 documentary, “The Beaver Believers,” which follows several activists as they work to multiply beaver populations in the American West.

“I was looking for a story that could frame climate change as something tangible we could relate to, and I wanted to stay away from a doom-and-gloom apocalyptic narrative,” said Koenigsberg.

“Beavers can ameliorate nearly every negative climate impact that we feel here in the inland West from too much water to not enough, from habitat loss to crazy out-of-control wildfires,” she said.

Beavers build extensive dams.   ©Christian Kutschenreiter
Beavers build extensive dams. ©Christian Kutschenreiter

Koenigsberg also believes that humans play an essential role in partnership with beavers, that “there are ways human cultures have participated productively and in peace with the natural world since time immemorial, and there are ways that we can try to do better.” She has furthered this goal of bringing people and beavers together as a founding member of a new nonprofit called The Beaver Coalition. The organization’s mission is “to empower humans to partner with beavers through education, science, advocacy and process-based restoration.”

For instance, when a landowner becomes alarmed by the appearance of a new beaver pond, education can help resolve the issue, Koenigsberg said. “You can just share with folks that this is actually a really good thing for biodiversity, for fish habitat, and all the things good thing beavers do. Sometimes it’s a very quick turnaround,” she said.

But sadly, in most states, there are few, if any, restrictions on trapping and killing beavers. Although they are not considered a threatened species, North American beaver populations have not recovered from the fur trade that reduced their numbers from as many as 200 million to less than 100,000. Today’s beaver population has recovered to only 15 million, and ecosystems are still suffering from their absence.

Koenigsberg and Callahan are working to spread information about the broad environmental value of beavers.

“Like a keystone in an arch, if you pull it out, the whole arch collapses. If you take beavers out of the landscape, then their whole ecosystem collapses, and all these other species suffer,” he said.

Koenigsberg put it this way: “The fact is that beavers are a key missing piece, they have to be allowed to come back because they engineered these [eco]systems, and these [eco]systems will forever be impoverished without them.”


*Mal Cole is a freelance science and nature writer based in Massachusetts.

Editorial Note:

Mal Cole interviewed Michael Callahan of Beaver Institute; and Sarah Koenigsberg of The Beaver Coalition.

Further Reading:

Ancient Beavers Leave Traces of Dam in Yukon | CBC News.” CBCnews. CBC/Radio Canada, November 19, 2005.

Beavers, Water, and Fire-a New Formula for Success • The National Wildlife Federation Blog.” The National Wildlife Federation Blog, October 30, 2018.

Feinstein, Kelly. “A Brief History of the Beaver Trade.” History Department UC Santa Cruz. Accessed September 29, 2022. l.

Osborne, Jari, and Paul Freer. “Nature/Leave It to Beavers.” Episode. Nature 32, no. 17. PBS, May 13, 2014.


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