New Mexico: The Water-Sucking Soldiers

Salt Cedar tree. Credit: Morton County, ND

Although I've only been in New Mexico for a little over two months, I already know about the war against the foreign invader of the Southwest: the salt cedar tree, known more formally as tamarix or tamarisk.

The folks at the Bosque del Apache Wildlife Refuge are proud to have vanquished this malevolent pest.

The salt cedar is the November weed of the month in the 2013 New Mexico Noxious Weeds Calendar. Described thusly:

Tamrix invades riparian (stream side) areas throughout New Mexico. It accumulates salt in its tissues which is later released into the soil, making it unsuitable for many species. ... Introduced from Asia as an ornamental and for erosion control. 

Salt Cedar. Credit: BLM

In a 2002 article in the U.S. Water News Online, titled In the West, Battle Rages Against the Invasive Salt Cedar, the first sentence proclaims: 

An army of water-sucking soldiers is marching along the banks of nearly every waterway in the West.

Another 2002 article, in the Southwest Farm Press, in New Mexico Works to Remove Salt Cedar: 

One salt cedar is a giant straw, sucking as much as 200 gallons of water per day out of rivers, springs and wetlands. “When we remove the salt cedar, water begins to come back."

It is commonly "known" that a mature salt cedar tree will guzzle 200 gallons of water per day, as attested to by these experts:

• Department of Ecology, State of Washington
• US Department of Interior, Bureau of Land Management, Wyoming
• Total gallons not specified, but referred to as "huge water hogs" by Texas A&M

I swallowed whole the old-timey religion that salt cedar was the agent of the devil.


... until I checked this book out of the library: A Guide to Plants of the Northern Chihuahuan Desert, by Carolyn Dodson, in which pp. 42-44 are devoted to the salt cedar. I was surprised to read this: 

It is now becoming clear that tamarisk invasions are the result of human-made changes to vegetation and wildlife. Tamarisk shrubs don't cause saline soil - dams and irrigation projects do. Removal of saltcedar does not increase water levels or reduce salinity. .... 

Why this sudden change in attitude toward tamarisk? ... a careful reading of previous saltcedar reports reveals .... overlooking the role in human activities in the spread of this shrub ... 

I think the reference to a "sudden change in attitude" is a little premature, based on most discussions I see regarding salt cedar, and considering it's still on many states' kill list.

Salt cedar in fall. Credit: The Thirsty Tree

Melissa Lamberton, in her article, The Thirsty Tree: Confronting Invasive Salt Cedar in the American Southwest, provides a reader-friendly analysis and history of how salt cedar got (and continues to get) blamed for problems actually created by .... us, and not by the salt cedar. Ms. Lamberton's discussion is based on research conducted by Matthew Chew, which he shared in his article The Monstering of Tamarisk, published in the Journal of the History of Biology.

If I can summarize two points that struck home for me: 

• When humans denied riparian areas their natural spring floods via dams and other water-control systems, native trees such as cottonwoods and willows could not compete with salt cedars, which were drought and salt resistant, and did not rely on seasonal floods to propagate. When researchers (and in one case, a private farmer) created a spring flood situation along a riparian galley, they discovered that long-waiting cottonwood seeds shot up among the salt cedars readily. As long as the old spring flood patterns were allowed to occur, salt cedars had no competitive edge over the cottonwoods.  Also, the spring floods washed away salt that accumulated - not from salt cedar generation of same - but from the lack of floods' regular cleansing. 
• Scientists fell victim to experimenter's bias in re: "alien plants" carry a presumption of guilt. This bias was part of their mental models*, leading them to conclude that salt cedars invaded and usurped, when in fact, they opportunistically filled a niche created by other causal agents, specifically, human intervention in natural water processes. 

While I certainly don't see evidence of Ms. Lamberton's "sudden change in attitude" (just google on 'salt cedar' to see what I mean), I do see that the BLM is considering its warrior stance against salt cedar, as evidenced by this 2007 paper, Saltcedar, written by Sandra Wyman, rangeland management specialist. In particular, the article explains that the business about a salt cedar slurping up 200 gallons of water a day is impossible.

When one considers that herbicides are often used to tackle the salt cedars, it's certainly worth a pause to weigh the pros and cons of the trees' eradication. Especially when it may be possible to manage the trees - and restore native trees - by allowing traditional spring flooding at appropriate times relative to best times for cottonwood germination.

The  "monstering of tamarisk" applies not just to salt cedars, of course.

"Monstering" or even "halo-making" happens in the health, political, religious, and social worlds, as well.

So-called "common knowledge" gets adopted and goes unexamined by people who, in theory, should know better - if not the actual science, then certainly to know they ought to be asking questions.

The salt cedar story is also a good example of how effective it is to entrench a myth (i.e. drinking 200 gallons of water a day) simply by repeating it so many times. To wit: If  "everybody" says a salt cedar guzzles 200  gallons of water a day, it must be true. There is a blindness to the fact that if individuals add their 200-gallon statement to the mountain of others, they are just making the statement appear more substantive, when in fact, the information is false.

Mental models are comprised of our:  

·        Feelings about ourselves and others,

·        Past experiences,

·        Personalities,

·        Assumptions, and

·        Worldviews.

Our mental models are a representation of how we see reality in this world.

Our mental models determine what we see.

Quote:      “We don’t see things as they are. We see them as we are.” Anais Nin

Sources: Chris Argyris, Roger Schwarz