Landscape Miracle Drugs

6/2/22 – Beavers build climate and ecosystem resilience, one stick at a time

Castor canadensis, the North American Beaver

Hello everyone:

As always, please remember to scroll past the end of the post to read this week’s curated Anthropocene news.

Now on to this week’s writing:

Among the various plagues of the Anthropocene there is one that is both cause and consequence: ecological amnesia. It is a cultural memory ailment, the main result being that we scarcely understand how completely and catastrophically our home landscapes have changed over the last few hundred years, or even within our lifetimes. Animal and plant communities diminish, the climate warms, spring arrives sooner, etc. We notice, or don’t notice, like passengers on a train occasionally glancing out the window. It seems to be in our nature to normalize change, whether incremental or ruinous.

To give just one example, here in eastern North America the forests have lost, and are still losing, tree species (chestnut and elm a century ago, hemlock and ash now) that comprised much of what greeted European colonists as they began to deprive Native Americans of their world. The bulk of forests were old-growth then; now those mature stands, which defined ecological communities, scarcely exist.

The populations of many migratory birds flitting through those trees have dropped precipitously. On the ground, the ancient balance of predator and prey was upended as we eliminated large wolves and mountain lions, fragmented habitats with towns, farms, and roads, and introduced a host of new species. Many of the plants, shrubs, and vines that fill our gardens, yards, and roadsides are as non-native and invasive as we are. Even our gardens’ beloved earthworms are introduced.

The story is repeated everywhere on Earth, from the tundra to the tropics. The oceans, too, from where our toes touch the water to the deepest trenches, are depleting and transforming. The warm hand of climate change now reaches into those corners of the planet we had not yet altered with trawler or chainsaw.

I’m no expert, but I’ve read a little about these transformations. Still, I was amazed to learn from an excellent article by Karl Blankenship in the Chesapeake Bay Journal that North America used to be home to as many as 400 million beavers. Estimates of beaver populations before European invasion actually range widely from 60 to 400 million, spread across a habitat that stretched from Pacific to Atlantic and from Arctic tree line to northern Mexico. These furry landscape engineers had an average population density of 10 to 75 beaver per square mile.

It seems a wonder that any trees were standing on the continent when the colonists arrived…

But even that little joke reveals an aspect of our ecological amnesia, the perception that beavers are somehow or sometimes bad for forests and other habitats. Maybe we think a stream is healthier if it runs narrow, swift, and clear rather than slowed by a series of ponds. Maybe we think that flooding is always bad and that beautiful trees shouldn’t be felled in great numbers by weird rodents. We misunderstand beavers in part because we ourselves cut down too many beautiful trees and create harmful flooding through our landscape mismanagement, and in part because we have been deprived of the opportunity to live alongside an animal which once shaped the continent.

Those tens or hundreds of millions of beavers were reduced to about 100,000 by the mid-1800s, largely due to the fur trade. Even as far back as 1630, hunters and trappers killed 10,000 beaver per year in Massachusetts and Connecticut and took 80,000 per year out of the Hudson Valley and western New York. The rapid development of towns and cities in the centuries since took place without beavers around, and more often than not the few animals left were considered a nuisance as we turned their floodplains into farms and their rivers into canals. Now the population has rebounded somewhat to 10 to 15 million beavers spread thinly across the continent, but there are about 580 million people in that same area. (There is also the Eurasian beaver, from which the North American species derived when it crossed the Bering Strait about 7 million years ago. I’ll talk a bit about the fate of the Eurasian beaver next week.)

An environmental studies professor looking to use beavers to restore the health of the beleaguered Chesapeake Bay watershed has few illusions about the public perception challenge he faces in touting the benefits of increasing the numbers of beavers in neighborhood waterways:

If I mention beavers to any group – my students or faculty – the first two reactions are ‘they cause flooding’ and ‘they chew down trees.’ That is where you are starting at.

So let’s talk about those benefits. I’ve been reading up on beavers and their rightful place in the landscape, and I think those benefits are, in a word, astonishing, and a reason for hope.

beaver pond and lodge, with heron rookery in dead trees - from the Beaver Institute

Like us, beavers transform the landscape for their purposes. Unlike us, they strengthen and diversify ecosystems rather than ravage them. This is not a coincidence, but instead the result of a co-evolution with North American ecosystems for millions of years. Beavers are water creatures, and as a result the beaver-filled North American landscape was a much wetter place. Here’s a nice portrait of the process from Blankenship in his Bay Journal piece:

The downstream flow was further hindered by the huge beaver population. Using twigs, sticks, small trees, mud and stones, their sturdy dams often stood several feet high and could hold back acres of water. The resulting ponds raised water levels enough for the beavers to build underwater entrances to lodges that offered protection from predators.

As water levels rose, beavers made their dams higher and wider, trapping even more water. They eventually abandoned sites when nearby building supplies and food (small trees and shrubs) were used up. The vacated dams broke down, and a succession of wetland plants moved back into the nutrient-rich soils left behind, until the next wave of beavers arrived.

As a result, stream valleys were a mosaic of ponds interspersed with wet meadows through which stream threads would flow.

This landscape-scale hydrologic engineering – building dams, raising water levels, slowing water speed, and redirecting water flow – is an incalculable blessing for wetlands and for life more generally. Beavers increase the number, size, and quality of wetlands, which are an incredibly important source of biodiversity on the continents. Freshwater fish and their young find safer and deeper water in beaver ponds, especially in drought. Migratory fish such as salmon, eels, and alewives must have evolved to bypass beaver dams, since their historically massive numbers coincided with the highest population of beavers. Migratory wading birds traveled a continent that I imagine looked from above like a shattered mirror of ponds, marshes, and meadows. Amphibians and turtles and insects thrive in the millions of ponded habitats. Even the trees killed by flooding become vital habitat for cavity-nesting birds, from wood ducks to tree swallows to chickadees. And beavers, at an adult average of 40 to 45 pounds, were a rich and plentiful source of food for predators.

The landscape itself benefits from the engineering. Beaver dams act as speed bumps on the flow of water, controlling flooding and storing water so that streams, even small ones, can keep running year-round. The dams spread flowing water across floodplains, creating moist environments which resist fires and recharge aquifers rather than sending water downstream. Beaver ponds filter out sediments that would otherwise disappear, and capture water-borne phosphorus and nitrogen in those sediments, which in turn become rich soil when the beavers move on and allow the pond to become a vibrant, species-rich wetland, whether marsh, swamp, or meadow.

beaver meadow in Connecticut - from the Beaver Institute

The capacity of the beaver to increase species richness at the landscape scale is second to none, which is why they are considered a classic example of a keystone species. The simple definition of a keystone species is one which has an outsized influence on its environment. An ecosystem without its keystone species, like an arch without its keystone, falls apart.

As a side note, this capacity to fundamentally influence an environment can take several forms. The beaver is a “keystone modifier,” i.e. a species that modifies the environment in ways that benefit numerous other species. (Pileated woodpeckers, who create habitat for multiple species by creating cavities in trees, are another keystone modifier.) “Keystone predators” like wolves in Yellowstone controlling elk populations, or sea otters in kelp forests controlling sea urchin numbers, allow the species-rich ecosystem to thrive. “Keystone prey” like wildebeests in the Serengeti grasslands maintain their numbers despite being preyed upon by a variety of predators. And the Saguaro cactus is an example of a “keystone host,” a species which provides essential habitat for many other species.

When we consider humans and the ecosystem impacts of our landscape engineering, we seem less keystone than headstone… The decline of species, with a lit path heading toward widespread extinctions, follows us as our population increases and our development and resource extraction intensifies.

We have a long way to go to re-imagine our place in the world with the kind of ecological sophistication that will make us half as useful as beavers. Or, rather, we can imagine it, but the cultural shift – the action – seems formidable, even on a good day. But there are people and nonprofits and agencies working to reintroduce beavers wherever possible, people who understand the beauty of beaver-led restoration, who see the vital work that beavers can do to build landscape resilience in the midst of the climate and biodiversity crises, and who love making that happen.   

One of them is Kent Woodruff, wildlife biologist and former coordinator of the Methow Valley Beaver Project in Washington, who was profiled in a 2015 piece titled “The Beaver Whisperer,” in High Country News.

To hear Methow project coordinator Kent Woodruff tell it, beavers are landscape miracle drugs. Need to enhance salmon runs? There’s a beaver for that. Want to recharge groundwater? Add a beaver. Hoping to adapt to climate change? Take two beavers and check back in a year.

Next week, I’ll discuss the future of beavers in North America (and elsewhere). There is a clash between our necessary environmental values and our business-as-usual values which cannot abide the impacts of beavers on the world we’ve altered for our own purposes. I’ll dig into the magic of beaver restoration/rewilding projects, the specific benefits of beavers in the Anthropocene, our ongoing killing of “nuisance” beavers (25,000 in the U.S. in 2021), and lots of great information sources on beavers, including Eager: The Surprising, Secret Life of Beavers and Why They Matter, by Ben Goldfarb, the author also of the High Country News article I cited above.

For now, if you’d like a much, much deeper dive into the ecological benefits of beavers, you can explore this page full of links at the very enthusiastic and comprehensive “Worth A Dam” website from beaver fans in Martinez, California, where a restoration project has been in place for years. The tagline for the site is “Because the beaver isn't just an animal; it's an ecosystem!”

Here’s a great short segment from BBC Earth on beavers’ extraordinary lives and abilities:

See you next week. Thanks for sticking with me.

In other Anthropocene news:

From Hakai, a funny and thoughtful Icelandic perspective on the dilemma of feral cats ravaging the natural world.

From Nature, a long-term study on old-growth Australian trees finds that they are dying faster in a climate-addled world: “Tropical forests are critical to climate change, but they’re also very vulnerable to it.”

From The Revelator, “We think hydropower is a totally false solution to the climate problem...” Reservoirs are often significant sources of methane and other greenhouse gases.

From CNN, increasing evidence that the "insect apocalypse" is occurring in some areas, particularly where combined impacts from climate change and intensive agriculture are greatest.

From Bloomberg, the U.S. should be sending millions of heat pumps to Europe, not natural gas. In fact, the Netherlands will ban fossil fuel heating by 2026 and make heat pumps mandatory.

From the Guardian, an investigative article on the astonishingly stupid “carbon bombs” that governments and fossil fuel industry are building heedless of the need to stop development of fossil fuel infrastructure and to start shuttering some of what already exists.