Tamarisk's frothy branches of pink and green embellish creeks and river banks — a haze of color that looks fairly benign, and speaks to the plant's original purpose as an ornamental shrub. But since its arrival in America from Eurasia around the turn of the 19th century, tamarisk has managed to play the role of both hero and villain in the American West.
Because of the plant's resistance to heat and drought, the Army Corps of Engineers used it in the mid-19th century to stabilize riverbanks against erosion. Then, during the severe drought of the 1930s on the Great Plains, farmers deployed it and its companion, invasive Russian olive, to provide windbreaks.
In the decades since, the story has shifted. Tamarisk, which can grow to 20 feet tall, has proliferated with a vengeance, colonizing thousands of miles of riparian corridors in the West, including those along the Front Range. It guzzles water, squeezes out any competitors, and sterilizes wetlands by leaving soils parched with salinity — hence its other name, saltcedar.
Besides being hard to destroy, a single plant's blossoms produce thousands of seeds, which easily take root. Tamarisk, by one account, has multiplied 150-fold in just 100 years and now occupies up to 1.5 million acres in the western United States.
Even as water resources are taxed amid drought conditions, this ever-spreading exotic drinks freely via taproots that can reach 50 feet into the ground. One analysis put its consumption of water along the Arkansas River between Pueblo and the Kansas state line as enough to serve 376,000 people annually.
The body of research on the plant is massive and growing. Many have taken up the cause of eradication: government agencies, nonprofits and thousands of volunteers, as well as scientists and researchers, including a Colorado College botany professor and his students. Congress even adopted a law in 2006 ordering the Interior and Agriculture departments to get involved, though significant funding was never allocated.
Some new strategies for controlling tamarisk — including deployment of an insect, which has grown controversial due to its destruction of habitat for an endangered species — show promise. But the war on tamarisk is far from over, and warming temperatures due to climate change could help it spread farther by creating hospitable conditions in new areas.
Its role as villain may be relatively new, but tamarisk has fully embraced the part by being very hard to vanquish.
According to the Global Invasive Species Database, there are three varieties of tamarisk on Earth: tamarix aphylla (shrub), tamarix parviflora (tree) and tamarix ramosissima (tree, shrub). The last type prevails in the American West, in a spread the database refers to as "a massive invasion."
It was the North Dakota Department of Agriculture that put tamarisk acreage throughout the West in 2003 at 1.5 million acres. It also noted that up to 200 gallons of water per day, per plant, is lost through transpiration, or evaporation of water from its leaves. That's half of what the average American family of four uses each day.
In 2005-06, the Tamarisk Coalition, a nationally renowned, Grand Junction-based nonprofit that restores riparian lands and works with hundreds of other agencies, conducted an inventory of tamarisk infestations along the Arkansas River between Pueblo and the Kansas state line. Using aerial photography, satellite imagery and data from various local government agencies and conservation groups, it reported 29,000 acres of tamarisk and estimated those plants consumed about 47,000 acre feet of water a year. (One acre foot is 325,851 gallons.) That equates to 68 percent of the amount delivered annually to the Arkansas River Basin by the Frying Pan-Arkansas trans-mountain water project.
Stands of tamarisk along the river's tributaries and reservoirs — which totaled 15,000 acres in the 2005-06 study period — tap another 12,000 acre feet per year, the coalition found.
More troubling is that the coalition estimates losses in the next several decades will double along the river corridor, and nearly quadruple in the river's tributaries, based on the assumption that tamarisk will "infill" the gaps in current infestations. Such infill is likely, because each tamarisk blossom spews 10,000 seeds.
"They disperse through the wind and down watersheds," the National Institute of Invasive Species Science website explains. "Seeds can germinate while floating and establish themselves on wet banks within 2 weeks."
From there, tamarisk debilitates wetlands by crowding out native species, such as cottonwoods, willows and grasses, and by salinating soils with its salty leaves, which discourages other plants from sprouting and various species of wildlife from living among them. Without grasses, willows and other plants to provide natural filtration for water runoff, streams become filled with silt and salt, says Shane Heschel, who earned a doctoral degree in botany from Brown University and teaches at Colorado College.
Having studied tamarisk since coming here a decade ago, Heschel finds that cottonwoods and willows might consume equal amounts of water as tamarisk but are still preferable, because they provide a healthier environment for animals, fish and birds.
"When the Arkansas gets to Pueblo, it's a mucky mess," he says. "Where you have tamarisk, you have occasional shrubs and a lot of empty dirt. ... What contrasts with that is cottonwood, reeds, wetland plants and grass that fills in space so you get less runoff."
The runoff that does make it into the river in a diverse eco-system, he says, is naturally purified. (That's one of the chief arguments conservationists make on behalf of protecting, and even creating, wetlands.)
"In the longer term, [biodiversity] makes that whole Arkansas River riparian system more stable," he says. "We'll have to worry less about erosion problems and soil loss. Those kinds of plants also act like filters and buffers for all the stuff that runs off from cities, from agricultural fields. That kind of diversity helps to filter that runoff and makes the Arkansas River water a lot healthier, less full of silt, less full of fertilizer."
He notes that while 10 percent of public lands used to be riparian areas dotted with cottonwoods and willows, that's dwindled to about 1 percent, a drop partially due to the spread of tamarisk.
Also, tamarisk, whether dead or alive, poses another substantial downside: It's a fire hazard. In early April, the Fowler Fire Department and other agencies were confronted with the wind-driven Fowler River Fire east of Pueblo that burned for days along the Arkansas riverbed. While that fire charred a lot of cottonwood trees, Fowler Fire Chief Pat Christensen Jr. says tamarisk is the real threat.
"In some areas down in here, you got miles and miles of it," Christensen says. "It doesn't matter if it's green, it's gonna go. There isn't much you can do to stop it. It's a detriment to our area."
Eradication efforts began on the local level sporadically in the 1940s, but didn't get traction on a wider scale until the 1990s, when a project on the Rio Grande River south of Albuquerque was undertaken.
About 15 years ago, the Tamarisk Coalition was formed. Today it works with more than 100 partners to restore riparian lands overrun with tamarisk through education and removal projects.
Some of those were undertaken along the Dolores and Colorado rivers with the help of Troy Schnurr, a ranger with the Bureau of Land Management in Grand Junction. The stretch Schnurr and others worked on isn't accessible by heavy equipment, so crews had to raft down the river, work by hand with chainsaws and apply herbicides to stumps.
The project covered 25 miles and took 15 years.
"It can be overwhelming when you start," Schnurr says. "There's a lot of repair work, reseeding, replacement because the tamarisk has been there so long. That plant's gonna be around for quite a while."
Shelly Simmons, assistant district forester with the Colorado State Forest Service, explains it like this.
"What happens is resprouting," she says. "Tamarisk has an aggressive root system. Once it does get established, you're going to have to watch it for five years and treat it for regrowth. It's rare if you get 100 percent control the first time you try to control it."
Simmons works with volunteers, land owners and various agencies, including conservation districts, attacking tamarisk in the Purgatoire basin, Chico Creek, Fountain Creek, Huerfano Creek and the main stem of the Arkansas River.
"There's been a lot of workshops in the Lower Arkansas Valley over the years," she says. "We focus on riparian restoration, so we've had a lot of land managers and land owners attend those workshops. If a landowner feels they have the equipment and the means, they can undertake projects on their own land." That was the case in an area along the Arkansas east of Pueblo and south of Highway 50, where tamarisk was cut and piled into heaps several years ago.
Simmons estimates that about 2,000 acres along the Purgatoire River, a tributary to the Arkansas, has been treated, along with hundreds of acres along the Timpas tributary, which runs between La Junta and Trinidad and joins the Arkansas at Swink. The heaviest infestations of tamarisk are located around John Martin Reservoir west of Lamar.
Farther east along the Arkansas, in Hamilton County, Kansas, officials have tried a more hands-off approach. A 2004 review showed that tamarisk occupied 75 percent of a surveyed area, while cottonwood had dwindled to 6.5 percent. So, using a helicopter, the herbicide Habitat was sprayed along the channel, according to the Kansas Department of Agriculture.
The project has been deemed a success. But Tamarisk Coalition executive director Stacy Beaugh says herbicide sprays are generally used on monocultures of tamarisk. "The challenge is you can't be super-duper accurate of where that herbicide goes," she says. "If there are willows hidden in the tamarisk, it's going to blanket the affected area."
All told, the Tamarisk Coalition's assessment of the Arkansas corridor a decade ago estimated eradication would cost $44.1 million for the river itself, and $12.2 million for tributaries and reservoirs, figures that Beaugh says are still accurate today.
Even though the plant doesn't do well above 6,000 feet, Heschel has observed tamarisk in Colorado Springs. And it's all along the Fountain Creek corridor, where erosion damage due to localized flooding through the years has rendered the plant useful in some respects. "Tamarisk along Fountain Creek is beneficial to bank stabilization but detrimental to establishing other species that are less water-consumptive and more friendly to wildlife along the creek," Larry Small, director of the Fountain Creek Watershed, Flood Control and Green-way District Board, says in an email.
Small notes the district will remove tamarisk and replace it with willows and other riparian plants as part of its bank stabilization, wetlands and wildlife habitat restoration and flood-control efforts. The district, which covers ground from Palmer Lake and Woodland Park to Pueblo, will receive $50 million from Colorado Springs Utilities after the city's water pipeline project, the Southern Delivery System, goes on-line next year. That money is targeted to improve Fountain Creek, but in what ways hasn't been finalized.
Funding historically has been underwhelming for tamarisk-related projects. For instance, though Congress adopted the Salt Cedar and Russian Olive Control Demonstration Act in 2006, the measure's original $80 million allocation for demonstration projects for long-term management and reestablishment of native vegetation was never funded.
The act did result in a peer-reviewed assessment of tamarisk, though, completed in 2010 by the U.S. Geological Survey. That assessment puts a lot of stock in saltcedar leaf beetles (Diorhabda elongata), citing a study area in Nevada that showed a 65 percent mortality rate in saltcedar five years after the beetle was unleashed there. The beetles "consume saltcedar leaves, depleting root energy reserves until they are exhausted and the plant dies," the assessment says.
These beetles came to Colorado about a decade ago, Beaugh says. Initially imported from Asia where the plant originated, the beetles are collected from areas on the Western Slope, where they're well-established, and housed at the Palisade Insectary, run by the Colorado Department of Agriculture's Biological Pest Control Program. From there, they're shipped around the state, including to the Arkansas River corridor and Fountain Creek.
They arrive in cardboard jugs that resemble ice cream containers. Simmons says workers perch the cartons amid tamarisk bushes, and simply open the lids. The beetles, 1,500 per jug, crawl out and go to work. About 10,000 beetles are released per site, Simmons says, ideally "where tamarisk trees are younger and more succulent."
A Colorado Agriculture Department newsletter says the beetle had settled into the Arkansas Basin by 2012, where some sites have been defoliated multiple times and up to 60 percent of the target tamarisk trees have been killed. The state has taken to calling the beetle "a valuable management tool."
It also lies at the heart of the CC professor's latest research. Heschel wants to know how the beetle affects tamarisk's consumption of water; data to date suggest that in some cases, a tamarisk plant under siege only gets more aggressive.
"When the beetle attacks tamarisk," Heschel says, "tamarisk tends to increase its water use to compensate for getting attacked."
The study, which includes one site just south of the Fountain Creek Regional Park Nature Center, also looks at whether tamarisk that survive the beetle attack somehow become even heartier and more thirsty. "Is that what we're accidentally doing?" Heschel says. "I don't know the answer to that."
The CC study's findings, also based on research conducted at sites near Bent's Old Fort and John Martin Dam, will be submitted to the International Journal of Plant Sciences this summer. In the meantime, the insectary in Palisade reports it's still releasing beetles, and plans to continue doing so this year.
Use of the beetle, however, is being curtailed in some other states due to its potential to destroy habitat for the endangered southwestern willow flycatcher. In September 2013, the Center for Biological Diversity, and the Maricopa Audubon Society, in Arizona, filed a lawsuit against the U.S. Department of Agriculture, alleging the beetles were destroying the songbird's nesting areas. The lawsuit, according to the Los Angeles Times, accused the department's Animal and Plant Inspection Service of failing to protect the flycatcher, which nests in tamarisk thickets. The case is pending before a federal judge.
Robin Silver with the Center for Biological Diversity says while the lawsuit points to problems in Utah, Arizona and Nevada, the beetles also have invaded nesting areas in southwest and south central Colorado. "[Federal agriculture officials] said, 'Don't worry, because the native plants will come back,'" Silver says. But he argues that "unless you change the hydrology, you'll end up with nothing" in the way of vegetation after tamarisk has been removed. "The only chance you have," he says, "is to get out ahead of the beetles and change some of the hydrology for plant recovery. [Officials] don't want to do that because it costs money."
Patrick Shafroth, a research ecologist with the USGS at the Fort Collins Science Center, agrees that restoration is crucial in determining what vegetation comes next in the context of tamarisk control. As stated in a 2011 paper by USGS and other researchers about consequences of using the beetle, "Conditions in many areas now occupied by tamarisk have been so altered anthropogenically that recolonization by native willows and cottonwoods is unlikely without intensive restoration efforts."
Considering the sky-high cost and massive efforts to restore large areas affected by the beetle, the paper says, "widespread tamarisk mortality will likely result in a net loss in riparian habitat for at least a decade or more."
Flooding is an enemy of tamarisk, which will drop in number during scouring by rising waters. But in today's environment there's little flooding on rivers where many dams have been built that didn't exist just 50 years ago.
A 2007 research paper by several experts, including Shafroth, concluded that stream flows are "strong determinants" of vegetation in riparian systems. Deep groundwater, as opposed to more shallow sources, and intermittent river flows favor the deep-rooted tamarisk over the shallower-rooted cottonwood and willow, the study says.
Heschel notes that water management throughout the West has prevented the type of flooding that used to control invasive plants. "I think the best way to regulate tamarisk is to flood our systems more frequently," he says, "but the problem is, you lose your reservoir water. Water is scarce, and we dam it up for agricultural purposes, for hydroelectric. If we could increase flood frequency, by itself it would make for a healthier system."
Because it's not likely that flood conditions will be intentionally created on major rivers, Simmons, in La Junta, says she'd rather focus on doing what is possible. "Dams play a critical role in our water supply," she says. "We have to work within reality and what's possible. I'm not involved with any groups who want to petition the Corps of Engineers about river flows."
No matter how it's done, any tamarisk-fighting measure that gets enacted should be studied closely, says Shafroth.
"If we assume the change is a reduction in tamarisk and an increase in other vegetation, there needs to be associated research and monitoring," he says. "How does the water budget change? Is there more water in the Arkansas River or a rise in the water table? Or does the new vegetation use just as much water? The same thing for wildlife. How are the wildlife species of concern affected by the change in vegetation?"
Beaugh says getting people involved could lead to different approaches to tamarisk, including occasional floods. She notes that tamarisk removal has brought together thousands of people with the common goal of nurturing watersheds, a power that shouldn't be underestimated or confined to just eradicating one plant.
"There's more to protecting riparian areas than just cutting tamarisk," she says. "You have to consider the broader situation you're in. People might say, 'We want to have a say in how a river is regulated.' We're one piece of the puzzle in helping people try to start somewhere and consider the broader ecosystem."
Because there's still a big education piece to be done here.
Asked about the availability of the "ornamental shrub," Beaugh starts to explain that it's been labeled a noxious weed in Colorado and most Western states, meaning it can't be sold. But Ben Bloodworth, the coalition's program coordinator, interrupts her, saying he's just found that tamarisk can be purchased on Amazon and shipped to Colorado.
"That's something we need to look at," Beaugh says.
And then there's the wild card of climate change. Despite all attempts to rid rivers and streams of tamarisk, the hearty plant could get a leg up from rising temperatures. While Shafroth considers the question of climate change's influence "uncertain," the 2010 USGS assessment and other scholarly works say it could foster tamarisk's proliferation, given that it thrives in hot, dry weather, and parts of Colorado remain in moderate to severe drought conditions.
From the assessment: "Further expansion of saltcedar northward (and to higher elevations) is likely to occur due to climate warming."
All of which makes Shafroth wonder if this scoundrel of the West is a cause, or merely a symptom, of the real problem.