Tackling tamarisk

In the exotic shrub an ecological menace or merely the best our degraded rivers can muster?

  • Keith Duncan of NMU oversees the spraying of tamarisk

    Photo courtesy Keith Duncan
  • Tamarisk crew on the Virgin River in Zion Nat'l Park

    photo courtesy Deuser
  • Chain sawing "old-growth" tamarisk

    photo courtesy Tom Egan
  • Tamarisk in bloom

    Steve Dewey photo
 

Note: two sidebar articles titled "Killing tamarisk frees water" and "Fighting exotics with exotics" accompany this feature story.

For seven years entomologist Jack DeLoach had searched, like a driven cancer doctor, for a cure to one of the American West's most widespread plagues. It was no ordinary ailment that sent the Texas-based Department of Agriculture scientist to places like Kazakhstan, China, Italy and Israel. It was a subtle affliction, a green rash moving quietly - and unnoticed by most Westerners - up the rivers and streams of California, Arizona, Texas, New Mexico, and later into Colorado, Utah and Wyoming.

With its billowy pink flowers and bright green foliage, the woody tamarisk, or saltcedar, seemed a beautiful addition to the flora that survives along the waterways of the West. But DeLoach, along with a growing number of ecologists, understood there was more to the plant than met the eye.

The Eurasian native was naively introduced into Southern California and Arizona as a streambank stabilizer and ornamental shrub back in the early 1800s. It had no predators or diseases and it spread rapidly - more than 12 miles a year by one estimate - into virtually every river system in the West. Wherever it colonized, it choked out native plants, provided scant habitat for wildlife, sucked up inordinate amounts of precious water, concentrated salt on the soils beneath it, and spread damaging fires through riparian areas.

Federal and state land managers tried cutting down tamarisk and burning it, but that only strengthened its hold. Chemical poisoning worked better, but the plant was so ubiquitous that managers needed a vast and well-supplied army - one that lawmakers would never fund - to tackle the thousands of miles of infested rivers.

After traveling the temperate world, DeLoach thought he had finally found a better weapon. But today the weapon - two species of insects - sits, quarantined, in a lab in Temple, Texas.

These are not just any bugs. They evolved in Eurasia with the same species of tamarisk that was loosed upon North America. The Israeli mealybug and Chinese leafbeetle were the best prospects out of several dozen insect predators. The larvae of the beetle attack the tamarisk's foliage, while the mealybug larvae eat the stems.

"We believe we can get 80-85 percent control of tamarisk," DeLoach says. "We might get more in some areas and less in others."

With that kind of miracle cure on hand, land managers in the West should have lined up at his door with open bug jars. But none have. As DeLoach has discovered, not everyone likes the idea of releasing exotic bugs to fight an exotic plant. One critic said, "There's no telling what the insects will do once they eat through the tamarisk."

DeLoach says that fear is unfounded because rigorous tests ensure that the insects will eat only target plants. But behind the fear stands another and larger obstacle: a contentious debate over the ecological demise of Western rivers - and the role played by tamarisk. Some scientists think the whole notion of wiping out tamarisk is wrongheaded. The plant, they say, is a symptom of a sick system. Focusing on it distracts from the real causes of the West's damaged rivers - human-constructed dams, desert agriculture and livestock grazing.

"There are two opinions out there about tamarisk," says Mike Scott, a biologist with the United States Geological Survey based in Fort Collins, Colorado. "One camp says it is an aggressive invader that is vigorously displacing natives and must be eradicated. The other says it is more passive, that it is an opportunist that has taken advantage of man-made changes to the rivers."

This intellectual squabble rolled along quietly for years, surfacing from time to time in scientific journals. But in 1995, something brought it to a loud and roiling flood.

A bird in the bush

At the time, DeLoach was eagerly moving toward a real-world test of his insects. He had received permission from the U.S. Department of Agriculture to release the insects in nine locations, including sites in Wyoming, Colorado, Utah, Nevada, Arizona and New Mexico.

In the spring of '95, he returned to Israel to do the final insect collecting. It was there that he got the bad news.

"I had just finished packing the insects for shipment," DeLoach recalls, "when a fax came in from the states. It said that I might have a problem with the Endangered Species Act."

The southwestern willow flycatcher, a small native songbird, had just been declared an endangered species by the U.S. Fish and Wildlife Service. The bird was hanging on by a thread along Southwestern rivers and reservoirs. By law, DeLoach now needed to prepare a biological assessment to demonstrate that eliminating the tamarisk would not harm the flycatcher.

It took him two years to complete. Today, three years later, and ready to retire at age 65, DeLoach still awaits a final decision on his five-inch-thick, 600-page proposal.

"It's frustrating," he says. "When I got started on this, there wasn't any endangered species listing. If I had gotten done earlier, we could have already released the bugs and been on our way."

The contrarians

On the surface, the conflict between the insects and the bird is simple. A significant number of the remaining 400 pairs or so of willow flycatchers have taken to nesting in tamarisk. The attraction is proximity to water, shade and a branching structure that apparently reminds the birds of the native willow trees they historically nested in. If DeLoach's insects ate up all of the tamarisk, the reasoning went, an important chunk of nesting habitat would disappear, pushing the bird closer to extinction.

This line has been pushed hardest by Bob Ohmart, an ecologist with an activist bent who teaches at Arizona State University.

"I don't have any great love for tamarisk," says Ohmart. "It provides poor habitat for wildlife compared to our native plants. But we're stuck with it."

For Ohmart to resist tamarisk control seems almost odd. He did pioneering studies in the 1970s showing that tamarisk supports less animal life - from insects to birds and mammals - than native vegetation. But Ohmart argues that tamarisk has merely taken advantage of our sick, static river systems, and that removal of it will leave next to no habitat for the willow flycatcher and other riparian-dependent species. Dams and water diversions have permanently altered river corridors in the West, he says, rendering many inhospitable to native cottonwoods and willows.

"If you wipe out saltcedar, what will replace it? Not much," says Ohmart. "I'd rather see a monoculture of saltcedar than bare dirt. At least it holds in soil and provides a little habitat. We're damn lucky tamarisk came along when it did."

Backing up Ohmart is Bertin Anderson, an ornithologist turned soil scientist based in Blythe, Calif.. "Removing tamarisk and replacing it with native vegetation isn't going to happen on any major river in the Southwest," says Anderson, who has spent the last 25 years restoring native vegetation to sites along the lower Colorado River for the Bureau of Reclamation, various Indian tribes and other clients.

Rivers and their banks have become saltier and drier since irrigated agriculture and dams came in more than 50 years ago, he says, and these conditions favor the hardier saltcedar over the cottonwoods and willows. Anderson says that dams have prevented the nurturing floods that wash salts out of the soil and moisten it to sustain native plants.

Anderson says he analyzed a large portion of the Southwest's rivers, looking at soil conditions, and found that 75 percent of the area is no longer suitable for natives. "But a large percentage of the area is still suitable for tamarisk," he says. "In some places, the conditions are so bad that even tamarisk can't survive."

Ohmart's and Anderson's viewpoints have elicited visceral reactions from those involved with tamarisk control:

"I had one scientist in their camp come up to me and say that we should start considering tamarisk a naturalized plant in North America," says Jeff Lovich, an ecologist with the U.S. Geological Survey in Riverside, Calif. "I thought, what are we going to do, give it a green card?"

Lovich says he understands the river degradation wrought by dams and irrigation, but he still can't stomach the idea of sitting idly by while tamarisk takes over the West. "Tamarisk has caused severe ecological problems and it needs to be controlled."

"I think Ohmart has forgotten one of his basic principles from Ecology 101: Nature abhors a vacuum," says Keith Duncan, a weed specialist from New Mexico State University. "Something is going to come in when we take out the tamarisk, especially if we give it a little help."

Duncan and a coalition of water conservation districts and irrigation companies are trying to do just that on 5,000 acres along the Pecos River in southern New Mexico. The members of the Pecos River Native Riparian Restoration Organization have raised nearly $1 million to manually and aerially spray a mixture of herbicides Arsenal and Rodeo or Roundup on the tamarisk. "It's the biggest project I know of," says Duncan (see story on facing page).

After three years of spraying, the tamarisk is mostly dead now, says Duncan. The next step is getting something else to grow.

"We're going to get something back in there this summer, especially with the help of some El Niûo moisture," says Duncan. "The skeletons of the tamarisk will remain for a long time, providing some soil retention and a nursery bed for other plants. It won't be like a parking lot tomorrow."

As for DeLoach, he can't help but note the irony of being held up by a bird that could ultimately benefit from his insects.

"I don't want to damage the willow flycatcher, but it's clear that the willow flycatcher has been hurt by saltcedar," says DeLoach. "There are 50 other endangered riparian species that could benefit from biocontrol of saltcedar. The Fish and Wildlife Service needs to look at the benefits to the whole ecosystem, not just the willow flycatcher."

A losing battle

Curt Deuser could really use DeLoach's insects. He heads an elite, 10-person tamarisk control team for the National Park Service out of Nevada's Lake Mead National Recreation Area.

Deuser's team uses a two-step approach: One person chainsaws a tamarisk tree at the base and another quickly sprays on a chemical called Garlon before - within 30 seconds - the tree's cells close.

This method is pretty effective for the side canyons and streams where tamarisk is just getting established, says Deuser, whose team has cut and sprayed in Arches National Park and Colorado National Monument, as well as at Lake Mead. But it is no threat to tamarisk in the larger scheme of things.

"I was driving along the lower Colorado the other day, and I just couldn't believe how much tamarisk is out there," Deuser says. "We need biological control (insects) to knock back the immense tamarisk seed source along the mainstem rivers. Otherwise, whatever areas we clear will be reinvaded, and we might as well just resign ourselves to living with tamarisk monocultures along every river in the West."

That's no overstatement. Tamarisk is notoriously fecund; it can reproduce vegetatively, growing shoots from its extensive root system, or sexually, sending pinhead-sized seeds into the air or water by the hundreds of thousands. The seeds sprout wherever they encounter moist soil. Once established, tamarisk resists drought better than native cottonwoods.

In Arizona, The Nature Conservancy has battled tamarisk for more than a decade on its 333-acre Hassayampa River Preserve. Every summer weekend, a crew of volunteers - self-dubbed Tamiwhackers - breaks out the chainsaws and the backpack sprayers and goes at it, says preserve manager Greg Gamble.

"They've knocked out the biggest stuff on two-thirds of the preserve," says Gamble, "but it's a treadmill. New tamarisk seeds are always coming in and re-establishing themselves. We feel we have a leg up on the problem, but it's never going to go away."

Despite the difficulties in attacking tamarisk, practitioners such as Deuser maintain that their efforts can still pay big ecological dividends, especially in areas where humans have not disrupted the natural hydrology. He points to a place called Sacatone Springs in southern Nevada, where his team began cutting and spraying in 1991, when tamarisk started taking over a riparian area once dominated by willows, cottonwoods, mesquite and other natives.

"The invasion there had nothing to do with dams or anything else," he says. "Tamarisk was just plain outcompeting the natives."

Today, the tamarisk has all but disappeared and the natives have vigorously reclaimed their turf. "We've seen the whole drainage - maybe four miles long - come back with natives," says Deuser.

Even Ohmart believes that getting rid of tamarisk makes sense in places where the conditions are right - in his book, where there is a natural flooding cycle and the absence of bank-trampling, cottonwood-eating cows.

Ohmart likes to cite Grand Gulch, Utah, where cows and tamarisk once ruled an undammed river corridor below ancient Anasazi ruins. Twelve years ago, the Bureau of Land Management removed the cows, and now the tamarisk is dying back and the cottonwoods and willows are returning, he says. "Last time I was there, I pulled out a four-foot-tall tamarisk - by hand. You can't do that unless its roots are weak," he says.

Ohmart speculates that, absent the cows, the stream has begun to flood over the banks more regularly, giving native vegetation a competitive advantage.

Still, he is skeptical about restoring habitat along rivers such as the Colorado, the Rio Grande and the Gila. "We'll never get rid of tamarisk along the mainstems, because they are just too heavily managed."

The timing is all

If anyone knows about fighting tamarisk along a large Western river, it is Phil Norton, manager of the Bosque del Apache National Wildlife Refuge in southern New Mexico. Norton manages 13 miles of habitat along the Rio Grande near the town of Socorro.

The refuge's primary mission is to accommodate thousands of snow geese and sandhill cranes during the winter, but for the past decade Norton has also tried to return native vegetation to the tamarisk-choked banks of the river. His work gained urgency two years ago, when a dense tamarisk patch beneath a gallery of ancient cottonwoods caught fire and burned eight miles of riverfront.

"We lost a couple of thousand acres of cottonwoods and what has come back is tamarisk, not cottonwoods," he says.

Over the years, Norton has used every control method, including bulldozers and chemicals. Each has its downside and none of them is cheap. "Bulldozing runs about $500 an acre, and chemicals $100 an acre or more," he says.

Though Norton says introducing insects could help reduce the cost of control, he is pinning his hopes on another tool that most managers lack: a senior water right. With plenty of water available, Norton tried to mimic the floods of a natural river last year to see if that would give cottonwoods and willows an advantage over tamarisk. He inundated a section of cleared bottomland so that he would have a mudflat at the exact time that cottonwood seed flies in May. Then he dropped the water back in the weeks that followed.

"I thought we'd just grow tamarisk, but we got stands of baby cottonwoods without any tamarisk," Norton says.

Why did it work? Timing. The cottonwood trees let their seeds fly a week before the tamarisk. By wetting the mudflat and slowly drying it out right after cottonwood germination, the managers didn't give tamarisk a chance to get established, he says. "You've got to remember that the cottonwoods evolved to release their seeds right at the peak of spring runoff from the mountains," says Norton.

Norton hopes his experiments will eventually prod water management agencies around the West to try their own experiments.

"My argument is that the river was never static," says Norton. "You don't want to manage for a particular tree or simply because a flycatcher has been seen in a particular tree. You want to manage for flux."

A tale of two agencies

For most of its 96-year history, the federal Bureau of Reclamation has built dams to subdue those wild swings of water. Today, the agency no longer builds big dams, and its leaders proclaim a new mission: water management for both ecological and economic health. Releasing water from Glen Canyon Dam to flood Grand Canyon two years ago (HCN, 7/22/96) symbolized the agency's transformation. But the persistence of tamarisk is a stark reminder that it will take much more than an occasional flood to undo the ecological havoc wrought by dams.

That stark truth is not lost on Debra Eberts, a botanist and biocontrol expert for the Bureau based in Denver, Colo. Eberts has secured money for much of Jack DeLoach's work, even as the willow flycatcher issue has heated up. She says people who believe the Bureau is merely looking at the tamarisk-eating insects as a silver bullet to destroy the ecological sins of its past are mistaken.

"We understand that revegetation is the big issue," she says. The insects shouldn't be released until everyone has agreed on a set of stipulations regarding how revegetation will be accomplished, Eberts says. Hand-planting cottonwood plugs beneath the surface layer of salty soil along rivers may be one way, she suggests.

But some biologists say they don't see the Bureau making any real commitment to revegetation. "If the Bureau said it was going to throw in $100 million over the next 20 years to change flow regimes from its dams and protect new vegetation, then I'd feel a lot better about this (DeLoach's insect) proposal," says Mark Sogge, a Flagstaff biologist who studies the willow flycatcher for the United States Geological Survey.

Meanwhile, another agency in the Department of Interior, the U.S. Fish and Wildlife Service, seems hesitant to attack DeLoach's proposal. "It sounds like a valid proposal," says Ron McClendon, an Endangered Species Act specialist for the Service, based in Phoenix. "It might be that we could allow the insects to be released outside flycatcher habitat in Wyoming or Nevada. I just can't say." Because DeLoach has requested an informal Endangered Species Act consultation, the agency has no time limit on making a decision. Agency officials plan to meet in early June to further discuss the proposal.

"This is going to be a tough call for the Service," says former agency biologist Rob Marshall, who now works for The Nature Conservancy in Tucson, Ariz. "You can't really do controlled experiments in the wild, because there may be limited ability to control the insects after they are released."

DeLoach says he could live with a limited release. But even loosing the insects in prime willow flycatcher habitat would not be a problem, he maintains, because they would not immediately kill all of the tamarisk in the area.

"Biocontrol itself is not total," says DeLoach. "There's never been a case of biocontrol eradicating anything. We just see reductions."

A silver lining?

It seems that almost everyone involved in the tamarisk debate understands that getting rid of tamarisk cannot be separated from the task of restoring rivers and streams.

"We need to resist taking a classic USDA approach to the tamarisk: "It's an alien bolshevik invader that we need to crush before it crushes us," "''''says biologist Michael Scott with the USGS. "This plant causes problems, but it hasn't created them. We've dammed and diverted flows, irrigated saline soils and cleared the land. Just talking about getting rid of tamarisk is playing around the edges."

Scott says getting serious about addressing riparian restoration will require fundamental changes. "Are we willing to do the things it takes to bring back riparian areas - buy easements, move people out of the floodplains and retire irrigation from saline soils?" he asks.

Ohmart, for one, doubts it. "When all is said and done, more will be said than done," he says. "Maybe 50 years from now, when our water is so salty and filled with selenium that it is unusable, the public will finally say, "let's take out the dams." But it won't happen in my lifetime."

But the tamarisk debate has started a long overdue public dialogue that could lead to substantial changes.

Says Mark Sogge, "This proposal to introduce insects has forced us to ask whether there is something we, as a society, want to do about our riparian areas."


Paul Larmer is the editor at High Country News' syndicate, Writers on the Range. Reach him by e-mail at plarmer@hcn.org.

You can contact ...

* Bob Ohmart at the Center for Environmental Studies, Arizona State University, 602/965-4632;

* Jack DeLoach, U.S.D.A. Agricultural Research Service, 817/770-6531 or email: a021ctemple@atmail.com;

* Scott Stenquist, Regional Integrated Pest and Weed Management Coordinator, U.S. Fish and Wildlife Service, Portland, Ore., 503/231-6172;

* Or, for a detailed scientific discussion of the tamarisk management controversy, check out the proceedings of the 1996 Saltcedar Management and Riparian Restoration Workshop held in Las Vegas, Nev., placed on the Web by the U.S. Fish and Wildlife Service: http://refuges.fws.gov/NWRSFiles/HabitatMgmt/PestMgmt/SaltcedarWorkshopSep96/wkshpTC.html