Thread by @ben_a_goldfarb

Last week I made a pilgrimage to Minnesota's @VoyageursNPS, home to America's highest beaver densities.

Any beaver activity is impressive to me. But Voyageurs' dams—well, they're among our most jaw-dropping natural wonders, deserving of international renown.

Time for a thread!

First, let's get oriented. We're on the Kabetogama Peninsula, along MN's border w/ Canada—once the route of the Voyageurs, French-Canadian fur traders who almost completely extirpated beavers by the 19th century.

Yeah, I'd say the beavers are back.

No surprise, then, that @VoyageursNPS is America's best beaver-watching. Normally they're secretive little buggers, but within an hour of arriving in the park I'd already seen a half-dozen — including this very obliging adult at a lodge/dam complex near Ash River Visitor Center.

About that dam: In the Western US, where streams are steep, tight, and flashy, beavers are constrained. A big dam in eastern Washington is 30 feet long and 3 feet high.

In Voyageurs, beavers get ambitious. This run-of-the-mill dam is probably 7 feet tall and *500* feet long!

The biggest difference, I'd guess, is time. The West's flashier streams mean that dams blow out in, say, three to five years. By contrast, dams in the upper Midwest persist for decades or even centuries, permitting dozens of generations to build... and build... and build...

Just look at how well these dams are incorporated into the landscape! These are some of the most durable beaver structures I've ever seen; I suspect the signatures of these dams will be visible in aerial images a century from now. Changing hydrology/geomorphology at a vast scale.

The wide meadows and exposed bedrock at @VoyageursNPS make for prime damming conditions.

Check out this 60+ acre wetland. If you told a BuRec engineer to build a dam that maximized impoundment while minimizing materials & labor, he'd put it in the same spot these beavers did.

For all their durability, Voyageurs' dams *do* fail — often spectacularly. Maybe beavers get eaten by wolves, die of disease, or exhaust food supply. Here's a dam that breached last winter, gradually draining pond. If you see exposed lodge entrances, you know beavs have moved on.

That's bad news for beavs, of course—but good for overall habitat complexity. The draining pond bottom is already turning into a shallow wetland (left); eventually it'll be a lush meadow (right). Even in their absence, beavers transform landscapes; their legacies last millennia.

Here's another site where that beaver-mediated dynamic succession is in full swing. The dam that once created this pond blew several years ago; now it's a 50-acre meadow. Wolves denned in this abandoned lodge this spring — a predator exploiting its prey in a different way!

Voyageurs' landscape is so dominated by beavers that they even structure the forest. Everywhere you go on the Kabetogama Peninsula, you find some variation on this scene: lines of trees that once seeded directly atop long-abandoned dams. 🤯

Not that building dams is the only thing beavers do well. Voyageurs is latticed with beaver-dug canals and trails that they use to access forage. This might not be spectacular on the ground, but check out Google Earth to understand how these features connect wetlands w/ uplands.

Some beavers don't dam at all. @TheBeaverDoctor (who's tagged >1000 beavs in Voyageurs) took me on a lakeside lodge tour. Big life history question: do beavs do better along lakeshores, where they don't need to dam, or in ponds, where they can control water levels? Stay tuned...

Anyway: In #EagerBeaverBook, I lament that we can't truly "imagine the (landscapes) that existed before global capitalism purged a continent of its dam-building, water-storing, wetland-creating engineers."

But now I *can* imagine such a landscape: It looks like Voyageurs.

This park—and the rodents that built it—deserves to be iconic.

Yellowstone has bison.
Glacier has grizzlies.
The Everglades has gators.
Isle Royale has wolves.

And Voyageurs has the world's best beavers.

I hope this thread inspires you to visit this extraordinary place. /end