Maybe you’ve seen it billowing gently in the wind? Possibly, you’ve been enraptured by its colors of brilliant green with beautiful pink blossoms. You may think it would look wonderful along that stream bank near your home. But, before you take a cutting of Tamarix ramosissima, or any one of its kin, you might want to review some history.
Tamarisk, or Salt Cedar was introduced into the western United States as a decorative shrub in the early 1800s. As a result of that introduction, Tamarisk is considered an invasive species. An invasive species is something that is non native, meaning it didn’t originate where it now lives, and can cause economic, environmental or health problems to other species in its new habitat, including humans.
Since its introduction by east coast nurseries the early 1800s, the plant is now found in half of the country. It grows ferociously along rivers, can tolerate soils high in both salt and alkaline, and produces thickets of trees and shrubs nearly twenty feet high. It out-competes native plants with deep tap roots that intercept water tables and disrupt the surrounding aquatic system.
“I’ve heard of roots going down over 100 feet,” says Fred Nibling. He’s a Research Botanist for the Bureau of Reclamation’s Denver Technical Center . As Team Leader of Invasive Species Research, Nibling says their thirst isn’t the only thing they’re known for. “Water consumed by the plants isn’t there to turn turbines or irrigate fields. We’ve also looked at damage to recreational benefits,” he says.
An invasive species can enter the environment in one of three ways: (i) deliberate introductions, (ii) species imported for a limited purpose which then escape and, (iii) accidental introduction.
The Zebra Mussel is an example of accidental introduction. The finger-sized crustacean, native to the Caspian Sea , came to the Great Lakes via ballast water from transoceanic vessels around 1988. Since then, it has escaped and spread to all of the Great Lakes and many of the lakes and river systems of the Northeast. They can attach to anything, including each other, to clog pipes and engines.
Henry Messing is the lead biologist for the Environmental Resources Division for the Bureau of Reclamation’s Lower Colorado Region, based in Boulder City , Nevada . He is one of the point-men in the agency’s campaign against invasives of all kinds. “We’ve got a really large program in the state where we’re trying to stem the invasion of exotic species.” Some of them include the mosquito fish, the red shiner, the large mouth bass and the channel catfish. “A lot of fish were brought in and stocked by the state, into the Gila River Basin . And these fish either eat the natives while they’re still in the minnow stage, or just out-compete them for food.” Messing is also working on Tamarisk.
But the plant is hardy. Drought causes the seeds to go dormant and they can remain viable for years. Fire, on the other hand, helps Salt Cedar. It’s flammable, and has compounds in its foliage that’ll let it burn green. After the other vegetation has been destroyed, Salt Cedar re-establishes itself.
Erika Zavelta is with the Department of Biological Sciences at Stanford University . Her research on Tamarisk focuses on impacts of human changes on the ecosystem. She says eradication is possible, and points to successful projects in central Texas . Through a program of cutting, root plowing, application of environmentally safe herbicide, rearing and replanting of native species and monitoring over a 20-year period, she says benefits would keep pace with control costs and afterwards, would accrue indefinitely.
Some attempts to control species X through the introduction of species Y has been very successful, says Nibling. “Most bio-control that’s been done in the plant area with insects has been very well managed and successful.” But, in some cases, species X provides habitat for species Z, so maybe you don’t want to, or can’t eradicate it. “Salt Cedar has a branching pattern which is very alluring to the southwestern willow flycatcher, an endangered species. It has this perfect forked pattern that this bird loves to build its nest in. It also likes to nest close to the water, and likes wet soil.” But Zavaleta’s research indicates that native riparian vegetation provides superior habitat to the songbird. “Protecting flycatcher populations during restoration from tamarisk to native stands will,” she says, “require careful planning.”
Tamarisk costs the U.S. economy millions of dollars annually, and is laced with complicated environmental questions. But, that it interferes with water delivery is enough to focus the attention of many of the bureaus within the Department of Interior, including the Bureau of Reclamation, to find ways to control it.