Invade, steal water: The plant spreading in Utah’s wetlands

Battling a nonnative reed to protect Great Salt Lake bird habitat.

 

In the summer of 2012, before Christine Rohal applied herbicide to her study plots in the wetlands hugging the edges of Utah’s Great Salt Lake, she trudged through each one of them on foot. She was counting the stems of an invasive reed that formed a nearly impenetrable wall of rigid, splintering stalks stretching above her head. “Just trying to create paths through it was a nightmare, really,” says Rohal, a graduate student in restoration ecology at Utah State University. And the thick vegetation isn’t just a problem for humans — the reeds make the areas they’ve invaded inaccessible to wildlife, including most water birds. “It’s considered one of the biggest threats to these wetlands,” Rohal says.

The wetlands around the Great Salt Lake are a crucial oasis for migratory birds. Millions of avian visitors rest, nest and feed there every year — but the invasive reed, a strain of phragmites, is choking native vegetation out. Phragmites also naturally occurs in the U.S., but the nonnative variety — originally introduced from Europe — spreads much more aggressively. Since its first appearance in the area in the early 1990s, invasive phragmites has infiltrated at least 25,000 acres in and around the Great Salt Lake.

Invasive phragmites in the Great Salt Lake wetlands grow in dense stands up to 15 feet tall.
Christine Rohal

The invasion exacerbates the perennial problem threatening desert wetlands and their avian inhabitants: a shortage of water. Because of invasive phragmites’ extensive growth and productivity, it slurps up much more water than native plants. One study estimated invasive phragmites consumes about 71,000 acre-feet of water in the Great Salt Lake basin in a typical year, while the estimate for native saltgrass is less than half that amount. But scientists, managers and private landowners — armed with relevant research results — are working together to fight phragmites and reestablish native plants, hoping to bolster both the local ecosystem and the birds that depend on it.

The problem of invasive phragmites isn’t limited to the Great Salt Lake. It has existed on the East Coast since the late 1700s or early 1800s, and populations have also popped up in ecologically important wetlands in the West over the last two decades, in the San Francisco Bay delta, Zion National Park and outside Las Vegas.

Invasive phragmites is denser and more robust than native plants like bulrushes, making it difficult for water birds to build nests or feed in. Untreated, it expands more quickly than native vegetation; an established stand can spread 10 feet or more every year. And while it produces a lot of seeds, they’re not as preferred or valuable a food source for birds as native plants, says Josh Vest, science coordinator at the Intermountain West Joint Venture in Missoula, Montana, a bird habitat conservation organization. The group estimates that the Great Salt Lake wetlands may support up to 250,000 fewer migrating ducks because of the phragmites invasion, a 20 percent reduction in the number of ducks the ecosystem can potentially sustain. Other migratory birds are at risk too, including large concentrations of phalaropes and American avocets, as well as more than half of the West’s breeding population of snowy plovers.

To combat the problem, the state of Utah spends hundreds of thousands of dollars per year on aerial herbicide spraying, trampling with track machines, and research, including work done by Rohal’s advisor, ecologist Karin Kettenring. Studies led by Kettenring and her graduate students compared the success of two herbicides. The cheaper of the two herbicides was as efficient as the more expensive one, and applying it in the fall was much more effective than summertime spraying. That may be because phragmites moves carbohydrates into its root system for winter storage, ferrying the lethal chemical to the part of the plant where it can do the most damage, Rohal says.

Scientists evaluate the effects of herbicides by surveying which plants have grown back following the first year of treatment.
Christine Rohal

The scientists’ work also suggests an adequate water supply is crucial to battling the invader, since herbicides don’t work as well against drought-stressed plants — their leaf pores close, and they don’t transport the poison to their roots. “It’s kind of counterintuitive,” Rohal says. “But you actually want your phragmites to be really healthy and happy when you spray it.” That can be a challenge considering the dwindling water supplies of the Great Salt Lake system, already stretched thin by urban and agricultural use and a changing climate.

And herbicides meant for phragmites can also kill beneficial natives. Control via hungry cows is a nontoxic option, says Joel Ferry, who manages five duck hunting clubs on his property on the northeast corner of the Great Salt Lake. To improve the bird habitat on his land, which includes about 3,000 acres of wetlands, he grazes cattle in areas infested with phragmites in the summer, when the plant is growing and full of protein. “If you can graze it to where you really knock it back, you get other plants growing in because you’ve opened up the canopy,” says Ferry, a fifth-generation farmer and rancher.

In dense plots or where cows can’t go, Ferry resorts to herbicides. Kettenring and her graduate students’ projects — like Rohal’s research on towering stands of phragmites — have helped him decide which chemicals to use and when to spray them, reducing the phragmites-impacted portion of his property to less than 5 percent of his wetlands. Continuing that fight everywhere the reed has invaded is vital for the health of the entire Great Salt Lake system, Ferry says. “If we could get a handle on it, I think we’d see a big improvement in the quality of our wetlands.”

Emily Benson is an editorial intern at High Country News.

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