Tamarisk Tree’s Role as ‘Invasive’ in Southwest Questioned

Washington, DC–(ENEWSPF)–July 22, 2014.  As drought persists across the western U.S., farmers, ranchers, and government authorities looking for solutions to water worries have picked a tough battle, and many are questioning whether it’s worth the fight. The target is the ‘invasive,’ tamarisk tree, also known as salt cedar, a hardy evergreen that can grow nearly 60 feet tall, and has been labeled as a water glutton. In Arizona, many are heralding the arrival of the small tamarisk beetle, itself an ‘invasive’ imported from Kazakhstan by the United States Department of Agriculture (USDA) to control the spread of tamarisk trees. But numerous questions surrounding the campaign highlight a persistent national debate: Are invasives categorically bad or simply convenient scapegoats? Are the solutions worse than the current state of affairs? Can we permanently restore native habitat?

In 2005, USDA approved the release of the tamarisk beetle in Colorado, Utah and a number of other western states. However, five years later, the agency made a quiet about-face on the campaign and stopped any further releases of the beetle into western habitat. The stated reason for the cancellation was “potential effects on the critical habitat of the federally-listed, endangered southwestern willow flycatcher,” notes a press release from Public Employees for Environmental Responsibility (PEER). As PEER explains, USDA released the beetles without a full environmental review, ordering a “finding of no significant impact” (FONSI) under National Environmental Policy Act (NEPA) regulations. The southwestern willow flycatcher, originally adapted to willow trees, established itself in stands of tamarisk and Russian olive as the landscape of southwestern riparian ecosystems changed due to human influence.

The spread of tamarisk trees wasn’t completely an accident. Farmers in the early 1900s needed a hardy, drought-resistant plant to control wind-borne erosion, according to research from Matthew Chew, PhD, at the University of Arizona. The trees were originally brought to Texas and the desert southwest to stabilize soils and provide a windbreak for fields susceptible to erosion. As Dr. Chew explains, perceptions changed in the mid-1900s when studies reported high rates of evapotranspiration (water uptake) by the tamarisk. Rather than merely stabilizing soil, tamarisk was sucking up the scarce waters farmers needed for their crops, so it seemed. As population pressures and water resources became an increasing concern, dams rose up in the southwest, drying out native riparian habitat and fostering the conditions for tamarisks to move in.

But new data has caused many to rethink the trees’ categorical designation as an invasive species to be targeted. In addition to the tamarisk tree’s refuge as a habitat for the flycatcher, data is now revealing that the trees take up much less water than originally thought, and result in negligible differences in river flow whether they are present or not.

Still, many continue to advocate for its eradication. “We view the tamarisk as a pest,” said Joseph Sigg, the government relations director at the Arizona Farm Bureau to The New York Times. “Water is an expensive input, and to the extent that we can lower it, the beetle can help.”

Although the tamarisk beetle is effective at defoliating the trees, complete removal of the tree requires an expensive round of cutting, burning, and herbicide applications to the tree’s stump. Chemicals such as triclopyr, the active ingredient in Garlon, are often employed for this process. Triclopyr is considered mobile and soluble in water, with a high potential to contaminate surface waters. The chemical has been linked to adverse reproductive effects and birth defects. The solution may be more harmful than the current state of affairs.

Even when removal is generally considered successful, it is only a delay tactic. “You’ll never get the last tree,” said Gibney Siemion to, an ecologist with the Grand Canyon Wildlands Council, to The New York Times. “You do your best, but the tamarisk is very adaptable.”

As with most ecological problems that humans confront, whether in farming, gardening, lawn care, or control of invasive species, the underlying conditions that brought about the perceived problem must be addressed, or a shift in viewpoint is needed. Since we may never be able to ever permanently restore a native habitat, we may need to reconsider what is natural and what is invasive.

Beyond Pesticides encourages a lively debate on the role and designation of a species as ‘invasive’, but strongly discourages the use of pesticides to “fix” issues surrounding invasive species. For a take from each side, see Beyond Pesticides’ Invasive Weed Management homepage, or watch Boyce Thorne Miller’s discussion on rethinking invasive species at the 32nd National Pesticide Forum in Portland, OR. You can also read more about misconceptions on invasive and the tamarisk tree from Dr. Chew on his website, or from the talk he gave (min. 25:15) at Beyond Pesticides 31st National Pesticide Forum in Albuquerque, NM.

All unattributed positions and opinions in this piece are those of Beyond Pesticides

Sources: The New York Times, PEER, http://www.beyondpesticides.org