The Tamarisk Assumption

It’s a given here in the desert southwest that tamarisk, a tough little red-barked tree that grows along our river banks, is evil. A European immigrant that arrived more than a century ago, it now dominates the banks of our desert streams and rivers, choking out native cottonwoods and sucking up precious water. At least that’s the conventional wisdom.

Tamarisk in Grand Junction

(tamarisk along the Colorado River in Grand Junction, image courtesy Colorado State University)

Here in Albuquerque, we’re spending big bucks to clear it out of our bosque, the woods along the river, based on that conventional wisdom. I’ve been pretty enthusiastic about the results – beautiful open woods, with the cottonwood returned to its regal riverside dominance. But I keep hearing inklings from the science community that we know less about the tamarisk and its role here than we think.

The latest inkling comes from the March-April issue of Southwest Hydrology, a publication out of the University of Arizona.

The article is based on a conference last fall in Grand Junction – the 2005 Tamarisk Symposium – that brought together researchers grappling with the tamarisk issue.

The conventional wisdom, as outlined by USGS plant ecologist Pat Shafroth, is that tamarisk pushes out native vegetation, sucks up more water than the natives, carries fire more easily and is better adapted to the results of fire. The conventional wisdom also suggests that if you simply root it out, natives will sweep in to replace it.

But there’s another side to this story – the suggestion that tamarisk’s spread is simply a response to the way we’ve changed the river systems with dams and other flow regulation. In other words, there is no natural riparian system left, and the salinity, increased fire etc. that we’ve been blaming on the tamarisk is actually a result of the changed hydrology.

It seems clear that the real story is some mix of the two views, with tamarisk not a benign player, but not the cause of all the evils for which it’s blamed. The trick is to sort things out a bit better so we don’t have unrealistic expectations about the benefits to be hand by the eradication efforts now underway.


  1. hmmm….yea, put me in the hating tamarisk category. do they really suggest that tamarisk is potentially a good adaptation to damming, though? I’ve seen many a dammed stream with healthy cottonwood communities and no tamarisk, but perhaps that observation is based on northern riparian communities. Certainly tamarisk overgrowth seems to be a desert phenomenon. I’ve never seen it north of Moab.

  2. The problem with Salt Cedar is the exponential growth. It’s spreading at approximately 20% per year, has been for decades, and there is no sign of slowing. It’s easy to see the potential extents, based on where it is and how it’s spreading.

    The Feds imported it in the early 1900’s for “erosion control” – well, it does that… No we have to conserve because of that so Texas gets its “share”.

    Salt Cedar has no enemies, it has no friends. It just drinks water – one medium sized plant sucks as much water as a family of four. One can argue the transpiration is potentially good, but that’s downwind – not in the existing aquifer. One can also argue that since eradication, river flows have not immediately rebounded. However, given Salt Cedar can suck down the water table 20 feet or more, we have roughly a foot of rainfall per year (only half of which infiltrates), and soil is typically 30% voids, it’s a no brainer it will take a decade or so for water tables (and therefore runoff) to recover.

    I’m looking forward to reading the April 3rd issue (and thanks for the reference) – but the problem of Salt Cedar is not to be confused with dams or any other changes. It’s a monster – and if not yet the biggest monster we have in the SW – due to its exponential growth it will, someday, be. If we don’t address the problem there is no doubt about that.

    Exponential growth – it’s only a matter of time.

  3. Another point – one can observe, below devastating floods that are undammed upstream, salt cedar recovers quite well – putting to rest the potential that it’s a result of “damming”.

    Damming has its problems – especially with regards to cottonwood development etc., but that’s a whole different problem.

  4. Steve –

    As usual, some citations would help, especially for the groundwater model you sketched out. That’s not my understanding of how riparian groundwater systems work, but you’re apparently the expert here.

    Kearsley, at last fall’s AGU meeting: “The imposition of flow regulation in large rivers of the Western U.S.A. not only permitted the invasion by tamarisk into riparian habitats, it continues to contribute to invasion through the effects of elements of the regulated hydrograph.” My understanding from talking to the scientists is that this part of the story is pretty non-controversial – that the lack of the natural flood regime favors tamarisk over cottonwood and other natives that depend on the big spring flood (not a whole different problem – it’s all a part of the same complex phenomenon). This is Shafroth’s point. (If you click the link, you can see his slides.)

    As for the water consumption part of the story, there’s a good deal of research now ongoing (some in our own stretch of the middle Rio Grande – Cliff Dahm from UNM and his students) trying to answer the effect of tamarisk on shallow water tables relative to natives. Your view expressed here nicely encapsulates the conventional wisdom.

  5. John –

    I’ll look for some references, and there would be some truth of spread in the lower bosques accelerating due to the lack of cottonwood regrowth as cottonwoods fail without flooding.

    Before the upstream dams, one year in about ten the Rio ran bank to bank during spring runoff – that would be about 3 miles wide at Montaño. Then again in the summer there might be absolutely no flow there.

    It takes a flood with a water table declining at a slower rate than that which the cottonwood roots can grow downward in order to start one. Plus, the old floods roiled old debris under to keep the bosque fertile – here, as well as the Nile….

    That doesn’t happen anymore.

    I’ve seen the “rebuilt” bosques – they are quite, on the surface, like they used to be – when I rode my little dirt bike through them (without damage, I might add…)

    Still, there is more than one problem with them, and dams are one – something we have to make a choice about. Do we want to restore the bosque, at the necessary expense of flooding downtown every few years??? That’s what it will take, despite what the “lion tamers” will tell us.

    But that’s a different problem than the salt cedar.

    I took a drive one day from Upham to Engle – saw an old oasis at, I think, Jornada… It was full of salt cedar with no surface water to be seen – undoubtedly the ground water was way deeper than one could dig to… It was about 10 miles from the nearest possible planting site – on the Rio. Salt cedar seeds are very small and easily get sucked up into clouds to spread *many* miles.

    There was a lake at an old hotel at La Ventana, a popular hotel, back before the 44 was paved. It’s about 15 miles south of Cuba (NM, for you out of staters). Now, there’s just a stand of salt cedar with one old lone cottonwood by the highway.

    Get out and look at areas not influenced by dams and you will see – the spread of salt cedar has nothing to do with dams. It’s a cancer. Of course it’s hard to see on a bike – you can’t cover that much ground. You need a good offroad SUV (not an Expedition et al). A Land Cruiser is good…

  6. Wrap-up:

    most, if not all, of the restoration ecologists I know say: tamarix bad.

    The hydrology may have changed, but better to replace those plants with a native to which the fauna and other flora are adapted to better preserve resilience.

    Sometimes we can’t get that goal, but usu. that’s around cities at small scales.



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