Tamarisk may be not such a bad guy after all


Tamarisk crowds out most other plants along the Arkansas River near the Kansas state line, but the plant isn't the demon that some researchers have made it out to be, an Arizona biodiversity expert says. - PAM ZUBECK
  • Pam Zubeck
  • Tamarisk crowds out most other plants along the Arkansas River near the Kansas state line, but the plant isn't the demon that some researchers have made it out to be, an Arizona biodiversity expert says.

A couple of weeks ago, we ran a cover story ("Bushwhacked," May 6, 2015) about the invasion of tamarisk in the West and how it's threatened water supplies and diversity in riparian areas.

The other day, we opened an email from Matthew Chew, an assistant research professor at Arizona State University, Tempe, with expertise in biodiversity, conservation, ecology and science policy.

He had somehow come across our story, and took us to the woodshed about a report that ignored a growing body of research that opposes the demonization of tamarisk as a water guzzler and wetlands destroyer.

Like he related to us via email, "The majority of academics working on tamarisk study it in order to (a) complain about it or (b) try to find ways to get rid of it. That actually about sums up invasion biology. There are more and more heretics who start with the plant rather than the problem, but shift will be gradual at best. Especially since having a villain with no constituency is politically and bureaucratically convenient."

Here's his initial letter:
Dear Pam-

I too have spent my life in tamarisk country. But I don't get angry at plants.

I encourage you to dig a little deeper into the tamarisk story. So far you seem to have swallowed the Tamarisk Coalition view hook, line and sinker. As a result your articles are semi-informed at best, and include statements of fact that are not quite facts.

For example, all riparian plants (native or otherwise) use water pretty freely, so specifically indicting tamarisks for non-beneficial water use is disingenuous. Unit-for-unit (plant, stem, volume of vegetation) they don't use any more water than anything else. They're just better than most at waiting for it to arrive.

Tamarisks are thriving in the west because they are very well adapted to the artificially altered hydrologies of our heavily exploited rivers. And tamarisk is not one species; at least nine species have been introduced and are hybridizing to evolve (and I'm using that term in its strictest biological sense) populations of new types that exist nowhere else - some of which are more tolerant of high elevations or high temperatures than others.

I'm attaching three papers you really need to understand if you want to tell the tamarisk story well, rather than simply joining the chorus railing against the plants as if they were "the problem" and killing them was "the solution". Tamarisks are likely here to stay, no matter how many beetles the Colorado's insectary cranks out and how much Walton money the Tamarisk Coalition soaks up. Because the water use entailed by western economic development over the past century has incidentally amounted to a gigantic tamarisk housing project.


Matthew K Chew Ph.D.
Arizona State University
School of Life Sciences
The studies he referenced are below. We found this passage in one of them that contradicts what many other studies have suggested:
It seems logical to suppose that removal of Tamarix (or any plant that uses groundwater) should result in lower riparian water use and therefore higher flows in a river system, but empirical studies suggest otherwise. For example, a large-scale, chemical eradication program initiated on the Pecos River in Texas in 1999 resulted in extensive mortality of Tamarix, but no documented increase in river flow as of 2003 (Hart et al. 2005). Various processes preclude the potential water salvages. Vegetation removal may raise the water table, but consequently produce more bare-soil evaporation (Hu et al. 2006). Furthermore, it is impractical to maintain bare floodplains and rivers banks. Cleverly et al. (2006) reported a one-time annual savings of water when Tamarix and Russian olive (Elaeagnus angustifolia) were removed from beneath Plains cottonwood (Populus deltoides) but projected the ET reduction to be short-lived because of rapid understory regrowth.

Hopes that significant quantities of water can be salvaged for human use remain a prime motivation for Tamarix eradication schemes (Zavaleta 2000; Shafroth & Briggs 2008), despite recent reviews and reports indicating that such actions offer no panacea for western water shortages and despite studies concluding that ET [evapotranspiration] rates show relatively small variability between Tamarix and other woody phreatophytes (Graf 1992; Shafroth et al. 2005; Owens & Moore 2007; Nagler et al. 2008b). The studies suggesting that such a possibility were methodologically unreliable and are now out of date.
See related PDF Chew_2009_Monstering_Tamarisk_JHISTBIO_.pdf See related PDF Chew-Hamilton_2011_Rise_Fall_Bio_Nativeness.pdf See related PDF Stromberg-Chew-Nagler-Glenn_2009_Changing_Perceptions_Tamarisk_RESTECOL.pdf

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