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Giant dams built to tame the Colorado River have nearly wiped out native cottonwood trees along many riverbanks, disrupting local ecosystems. But new tiny dams, built to mimic ones that beavers make, are helping bring the trees back. David Condos of member station KUER reports.
DAVID CONDOS, BYLINE: Cottonwoods shouldn't be hard to spot in southeast Utah. They're green giants that tower over scrubby red rock landscapes.
MATT MCETTRICK: Yeah, definitely.
CONDOS: But along the Colorado River, the trees have become increasingly elusive.
MCETTRICK: There's one cottonwood tree here. There's maybe another one over there.
CONDOS: Matt McEttrick is an ecologist with the state of Utah.
MCETTRICK: But should be seeing tens - hundreds, probably - at this site rather than just two.
CONDOS: A century ago, he says this riverbank on the south edge of Arches National Park would have been a shady cottonwood forest.
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CONDOS: Now the pale dirt under his feet cracks and curls in the hot sun.
MCETTRICK: The cottonwoods are still here. Every year, you still see thousands of seedlings. They're just not surviving.
CONDOS: Why? Well, those young trees depend on floods that historically pushed water up onto riverside terraces. But since massive concrete dams were built decades ago, those floods rarely happen anymore.
LIZ BALLENGER: Big, old cottonwoods along...
CONDOS: Liz Ballenger is a biologist with the National Park Service. In a region with few tall trees, she says the cottonwoods' vanishing act leaves an unfillable void in desert ecosystems.
BALLENGER: It's potentially a keystone species out here in the plant world.
CONDOS: Cottonwoods offer vital habitat for wildlife and help the soil conserve moisture.
BALLENGER: There's just something so iconic and magical about this large tree that grows in our riparian systems, and our riparian systems are the lifeblood of the desert.
CONDOS: The trees face some big hurdles - cities and farms drawing more Colorado River water, and climate change making droughts more intense. But there are things people can do to give the trees a better chance.
KRISTEN REDD: We call it the Sundial.
CONDOS: That's what Kristen Redd is working on in another part of southeast Utah.
REDD: So right now, we're standing on Indian Creek.
CONDOS: Redd is program manager at The Nature Conservancy's Dugout Ranch.
REDD: Saltgrass. There's...
CONDOS: She's been leading restoration work on this tributary that flows into the Colorado River in nearby Canyonlands National Park. The idea is to counteract those massive concrete dams upstream with a different type of dam - the small ones beavers historically built here.
REDD: What we're trying to do is to just hold the water back on the landscape. So instead of the water, like, rushing through the system and heading for the Colorado River, heading for Lake Powell, the water goes out laterally.
CONDOS: It's a strategy called low-tech process-based restoration. It involves digging trenches in the riverbed and filling them with wooden posts and rocks. And Redd's work is part of a growing trend. In the past few years, federal agencies, universities and conservation groups have increasingly turned to this approach as a way to restore rivers and streams across the West.
REDD: Probably five feet of sediment right here.
CONDOS: Redd leans over a mound of sediment that's built up behind one of the structures. These makeshift beaver dams replicate a river's historical conditions from the time before big concrete dams. They slow the current and spread water out sideways as it flows through. That's just what a growing tree needs.
REDD: Look at all the cottonwoods. Cottonwood. Cottonwood. Cottonwood. All of these - like, all these are new. These are babies.
CONDOS: And you think - because of this work, you think they have a pretty good chance?
REDD: They do have a good chance. They have a great chance of survival.
CONDOS: The next step is to take what researchers are learning here and expand it to more cottonwood habitats. Alix Pfennigwerth manages riparian restoration projects with The Nature Conservancy.
ALIX PFENNIGWERTH: If we can start to scale that work up - not just one stream here and one stream there but, yeah, really scale it up at the watershed scale - then I think we can really start to see an impact.
CONDOS: This year, her team is launching its first effort to do just that. She's collaborating with the Bureau of Land Management to bring this approach to miles of streams in Utah, Colorado, Montana and Wyoming.
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CONDOS: For NPR News, I'm David Condos in San Juan County, Utah. Transcript provided by NPR, Copyright NPR.
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