SciSun: Salt in the Wound   Leave a comment

Just when you thought everyone knows species don’t belong outside their native environments (watch out for land sharks!), we find that people are still dealing with the effects of non-native species introduction as a method to combat other non-native species that are crowding and out-competing native plants and animals. So despite decades of evidence that no matter how many non-natives are brought into an environment; or why their introduction is considered a good idea at the time; these introductions create imbalance with our environment and never end well. Which is probably why (up to now far, at least), it’s still considered bad form to let lions and elephants and crocodiles run loose on city streets.

Tamarix (tamarisk; salt cedar) is the genus of about fifty species of plants from Africa, Asia, and the Mediterranean that thrive in dry, harsh environments. Introduced to North America in the 1800’s as an ornamental shrub and ‘natural’ method to stabilize soil, particularly on riverbanks and along drainage ditches (something other plants had been doing all along, until they were removed as eyesores), the trees thrived – largely due to lack of competition and because they need little care. Today, tamarisk – also known as salt willow – is one of the most common plants in riverside habitats throughout the Southwest US, spreading through 1.6 million acres and crowding out native cottonwoods and willows. Easily able to out compete other plants through long, strong taproots that collect water from far under the surface – beyond the reach of other plants’ roots – the trees also concentrate salt unearthed from deep ground water and deposit it on the surface, changing the soil chemistry so other plants can’t live.

About the only positive thing you can say about these bosque-bullies is the wildlife habitat they provide – which to be fair, habitat which was traditionally available among the native cottonwoods and willows until they were forced out by the tamarisk. Birds especially, such as the endangered Southwestern Willow Flycatcher (Empidonax traillii extimus), find shelter and protection among the dense branches and thick leaf canopy, cool and shady even in the hottest days of summer. Already facing challenges from rainforest destruction (where the flycatcher spends the winter) and the brown-headed cowbird (another riverside-ruffian), a species that forces other birds out of their nests so it can have a free home, the flycatcher doesn’t need any more problems. Finding fewer and fewer native cottonwoods and willows, but more and more tamarisk plants along the riverbanks, what’s a flycatcher to do but take advantage of the new vegetation and move into the tamarisk thickets. Cottonwood trees are so yesterday, you know.

But government officials and land owners weren’t as flexible as the flycatcher, and by 1900 decided tamarisk was out of control. Not easy to cut down because of their thick, interwoven branches; resistance to fire; ability to survive on very little water; and what seems like a stubborn determination to just not go away, over the decades close to $100 million was spent trying to remove the plants with very little success. Defying even the newest herbicides and chemicals, by the 1970’s it appeared tamarisk had won and in time people started to believe the plants belonged along the waterways, and in fact had always been there. Even the native cottonwood started to get a bad rep as an unwanted plant, which it hasn’t been able to shake despite those ‘Cottonwood – the Trees of our Life’ advertising campaigns.

In 2005, out of desperation, the Department of Agriculture began releasing the only known adversary of tamarisk, the salt cedar leaf beetle (Diorhabda carinulata), directly imported from Kazakhstan, who, apparently starved for native food, was happy to see the tamarisk and wasted no time eating…and eating…and eating, until there were signs the invasive plant was finally under control. In fact, the program was a spectacular success – by some measurements, one of the most successful invasive control programs ever attempted – with one notable problem: Without tamarisk, or cottonwood, or willow, or any other dense riparian vegetation, there’s no place for the flycatcher to nest. Within 5 years much of the streamside habitat had been drastically altered – first by the loss of native vegetation, then through the appetite of the salt-beetle – so that by 2010 the insects, themselves, were beyond control and the program was canceled; but not before the beetle began spreading into areas previously thought out of their range and ability to live, well beyond the experiments’ original boundaries.

Sometimes tamarisk is a challenge to even the best-organized team of goats.

Sometimes tamarisk is a challenge to even the best-organized team of goats.

Plus, other, even more destructive plants are moving in when the tamarisks are gone – weedy plants like Russian knapweed, Russian olive and pepperweed that some researchers have found monopolize even more water than tamarisk, and are proving just as difficult to remove.

Ironically, the best method to control all these invasive species that are sucking up water and invading our native river- and stream-sides is by planting, protecting, and encouraging growth of (wait for it…) the same native cotonwood and willows that were there in the first place, but hundreds of years ago cut down for firewood, building material, and just because they were in the way.  So it seems that the only thing proven by this cycle of native removal and non-native introduction leading to forced controls; and then control of the species that was introduced to control the first original non-native, only to discover the best solution is probably just keeping the native environment as it was; is that maybe people shouldn’t be changing things they don’t understand. Though this one example of the cottonwood and the tamarisk and the salt cedar beetle and the willow flycatcher, that should be obvious. As obvious as knowing you should never add salt, to a wound.


Michonne Says: If those salty-cedar bushes were closer to the rocks, marmots would eat them and they’d be all gone. Marmots love salt. All you have to do is move the salty-cedar bushes closer to the rocks.

Posted October 20, 2013 by ECOVIA eco-adventure® in SciSun

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