Just How Busy Is the Beaver?

Very, apparently.

When the first Americans arrived in this land many thousands of years ago, the landscapes that they found had already been sculpted. Retreating ice sheets left behind fjords and moraines in the north. Bison grazing under vast skies kept the plains open and free of trees. The roots of oak and hickory, huckleberry and cedar, helped turn rock into soil, which allowed yet more plants to come in and settle. Water carved its way through canyons and valleys that water had itself made.

But one species had transformed the landscape in ways unimaginable to most moderns. The beaver.

Beaver pair in Wyoming. Getty / Chase Dekker Wild-Life Images

Beavers are woefully underestimated. They create the landscapes that they live in, and maintain those landscapes efficiently and fervently. Beavers are indeed busy, and their hard work creates habitat for countless others. Current estimates suggest that beavers have been hard at work in North America for at least twenty million years—and likely far longer.¹ That’s twenty million years of co-evolutionary opportunity between the beavers who actively engineer their ecosystems, and all the other organisms who live here.

Beavers enjoy deep water in which to swim and evade predators. As such, they dam streams and, yes, are perfectly willing to chew through mature trees to generate the materials for their dams and lodges. But one result of the millions of years of co-evolution between beavers and their associates is that, to a large degree, those associates can survive beavers just fine. Beavers like to browse vegetation of many different species, and the large diversity of plants in and around their homes are, in many ways, adapted to beavers. Willow, ash, and maple, for instance, are all adept at coppicing: they put up new growth from what appears to be a wholly dead stump. It takes just the tiniest bit of live cambium—the living heart of a tree trunk that is sandwiched between protective bark and central wood—for these plants to sprout and regrow.

Thinking back to those first Americans again: What would they have seen as they came down from the North and fanned out across the North American continent?

They would have seen a land saturated with beaver gardens. Where today there are flat, fertile valleys, the first Americans would have walked into wetlands from slope to slope. Frogs and fish flourished in the water, butterflies, bees, and birds did so in the air; and all manner of plants thrived on land. Beavers, like nearly all dedicated herbivores, require a diverse diet of many species. Where beavers thrive, so too do the species on which they depend. Beavers had already been dominant for a very long time by the time the first people arrived in America, and had transformed it into a verdant landscape. In the American West, which is now known for its droughts and fires, a beaver engineered landscape was both a wetter and more resilient place, far more immune to the vicissitudes of the weather.²

We have no written record from those first Americans of what they perceived. But we do have some from later explorers. In the late 18th and early 19th centuries, David Thompson mapped one fifth of the entire North American continent, his maps so precise and accurate that both American and Canadian governments were still using them until the mid-20th century. In 1794, Thompson observed that:

this continent from the latitude of forty degrees north to the Arctic Circle, and from the Atlantic to the Pacific Ocean, may be said to have been in possession of two distinct races of beings, man and the beaver….

Except [in] the Great Lakes, the waves of which are too turbulent, [beaver] occupied all the waters of the northern part of the continent. Every river where the current was moderate and sufficiently deep, the banks at the water edge were occupied by their houses.  To every small lake, and all the ponds they builded dams, and enlarged and deepened them to the height of the dams….Thus all the low lands were in the possession of Beaver, and all the hollows of the higher grounds.”³

More than a hundred years later, in the 1930s, esteemed naturalist Joseph Grinnell came through the American West, taking copious, careful notes along the way. He is one of the most trusted observers of the American landscape that we have had, and his system of natural history journaling has become a gold standard.

But in stark contrast to the beaver-rich land that Thompson described, Grinnell saw very few beavers.⁴

Grinnell’s observations have become the benchmark to which we compare modern ecosystems. Any errors that he introduced, therefore, had cascading effects on modern ecology and conservation efforts. Grinnell saw very few beavers, and concluded that they had never even been present in many places where they had likely once been abundant.⁵ Grinnell’s conclusions created the baseline on which modern policy is made. In Oregon now, for instance, beavers are considered a “predator”—the implications for which are that landowners can destroy beavers, and their homes, on sight.⁶

Why did Grinnell see so few beavers? Because he arrived on the heels of the beaver trappers.

Beginning in the early 17th century, and continuing for hundreds of years, beaver trappers ventured into a landscape rich with beavers, and took them out.⁷ That was their job. Demand for fur was high, so beaver pelts were a hot commodity. And their job wasn’t very hard, either, as beavers were docile then, and still are, which makes hunting them relatively easy. So when Grinnell came through, the landscape that he saw had been shaped by beavers, but the animals themselves were gone. Not knowing there was a puzzle to be solved, Grinnell did not solve it.

Now we have an American West wracked by fires, with waterways which have collapsed into deep arroyos and canyons that oscillate between flood and drought. When the landscape was being actively maintained by beavers, it was greener and wetter, and more resistant to both drought and fire.⁸

Humans are the most extreme ecosystem engineers on the planet. As it turns out, there is at least one other species that also transforms landscapes at massive scale.

Far from being simply a pest species, beavers were the water managers of North America. They were builders and gardeners, whose millions of years of work here helped build resilient ecosystems. Some of our most tenacious environmental problems would be alleviated if we welcomed beavers back. The land and water of North America, and the porous and changing borders between them, are healthier with the busy stewardship of the beavers who helped create these landscapes.

Go here, to The Beaver Coalition, if you are interested in learning more, or in partnering with beavers.⁹

1. E.g. Korth and Bailey 2006. Earliest castoroidine beaver (Rodentia, Castoridae) from the late Arikareean (early Miocene) of Nebraska. Annals of Carnegie Museum, 75(4): 237-245. -and- Korth and Samuels 2015. New rodent material from the John Day Formation (Arikareean, middle Oligocene to early Miocene) of Oregon. Annals of Carnegie Museum, 83(1): 19-84.

2. See, for instance, this excellent book: Eager: the surprising, secret life of beavers and why they matter. By Ben Goldfarb, published in 2018 by Chelsea Green Publishing.

3. From pp 197-8 of David Thompson's Narrative of His Explorations in Western America, 1784-1812. Published by the Champlain Society in 1915. (archaic capitalizations and spellings have been modernized)

4. Grinnell et al 1937. Fur-bearing mammals of California. Vol 2. Berkeley.

5. Lanman et al 2013. The historical range of beaver (Castor canadensis) in coastal California: an updated review of the evidence. California Fish and Game, 99(4): 193-221.

6. As per Oregon Revised Statutes 610.002 and 498.012.

7. Naiman et al 1988. Alteration of North American streams by beaver. BioScience, 38(11): 753-762.

8. Fairfax and Whittle 2020. Smokey the Beaver: beaver‐dammed riparian corridors stay green during wildfire throughout the western United States. Ecological Applications, 30(8), p.e02225.

9. Full disclosure: The Executive Director of this fine non-profit is Jakob Shockey, who was my student when I was a professor at Evergreen. I am now grateful and honored to call him my friend.