Invasives to Kill Invasives?

Anyone who has had a wild ride down the Colorado River through the Grand Canyon knows the story.  Even while taking advantage of their shade, and taking photos of the lovely blooms,  boaters cuss the tamarisk (aka salt cedar).

It’s an invader from the Middle East — well actually, it was invited– which puts down deep roots, sucks up scarce water, brings salt up with the water and redistributes it on the surface; it crowds out native vegetation and thereby changes the local ecology: some bugs go, others come; some birds disappear, others appear, and thrive.  On the whole, the river-rap goes, they’d be better gone.  From time to time ruined roots can be seen, the results of acids, fire, shovel and hoe.  Come back again in a few years, like as not, new shoots will be rising out of the river-bank sand to begin again.

Spring flowers on a salt cedar. Photo courtesy U.S. Army Corps of Engineers.

Spring flowers on a salt cedar.
Photo courtesy U.S. Army Corps of Engineers.

Now more money is being poured in, and a potentially risky gamble made: bring in the tamarisk beetle, its natural enemy.

In this corner of America known for its vast landscapes, rugged mountains and deep river canyons, signs of the havoc created by the minuscule tamarisk beetle are everywhere.

For miles along the banks of the Colorado River, hundreds of once hardy tamarisk trees — also known as salt cedars — are gray and withered. Their parched branches look like victims of fire or drought.

But this is not the story of beloved trees being ravaged by an invasive pest — quite the opposite. Farmers, ranchers and the water authorities here are eager to get rid of the tamarisk trees, which are not native to Arizona and which they say suck too much water.  NY Times: Belson

Problem is that the project could be chasing the wrong solution, and bringing on new problems along the way.

Advocates of removing the tamarisk claim that a mature tree can consume more than 200 gallons of water a day. That has tantalized farmers and utilities in search of cheap, plentiful water.

… There is little proof, though, that removing the tamarisk will increase the amount of available water. And if thirstier trees replace it, there could be even less water.

And of course, introducing species to help out with a wee problem here has time and again created another big one over there.

What will the tamarisk beetle feed on once their preferred food dips below population sustainability?

Well, “they are likely to feed on other trees.”

Some of the cleared areas have been replanted with native growths of cottonwood and willow, apparently very beautiful, and beckoning.  But, as far as I can read, no measure of water saved or water lost has been done.  It’s not like cottonwood are little-sippers, for example.

I hope the eradication is going forward slowly and thoughtfully, measuring and watching for the might-have-been-predicted unpredictable consequences.

As Melissa Sevigny has said,  “The tough thing is to turn it around and look at ourselves as the ones who have taken too much from these landscapes. It’s so much easier to point fingers.”

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