In arid West, a foreign legion of beetles takes on a thirsty invader
Scientists say the beetles released on Southwest riverbanks could tame the water-sucking tamarisk trees.
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The beetle populations only recently exploded on the Virgin River, following their release two years ago in St. George, Utah, some 15 miles upstream from the gorge. Now they are munching en masse downriver, across the northwestern corner of Arizona toward Nevada, as if feasting along one enormous Vegas buffet line.Skip to next paragraph
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In their wake lies a trail of browned-out, skeletal tamarisk. The bushes are by no means dead – it will take typically four years of defoliation to finally kill them off. Surviving plants aren’t frowned on: the goal is to tame, not destroy, the tamarisk.
What exactly will happen next isn’t fully known. And that’s when the controversy begins. “The very simplistic story is that if we remove the tamarisk, native plants will come back. If that happens, great. But there will be, I believe, a lot of places where that won’t happen,” says Mr. Sogge,
Parts of the Southwest, he says, have such poor hydrology that native plants will not return. Instead, other invaders like Russian thistle could move in, or maybe nothing at all – leaving a dead thicket of tamarisk and a denuded riparian zone.
Those scenarios trouble Sogge, an avian expert whose research has found some 50 species of birds using the tamarisk, which is also known as the salt cedar. Among the birds that nest in these trees is the southwestern willow flycatcher, a federally endangered species.
“We like to have absolute good guys and absolute bad guys. The salt cedar doesn’t fall into that dichotomy,” says Sogge.
Many of these birds used to nest in native willows and cottonwoods and would prefer to nest in them again if those natives revived. Sogge worries, however, that the birds will soon not have the choice of either.
Dudley counters that a lot of these systems are in “sufficiently decent condition that natural germination is likely to occur.”
Early signs from a beetle release on the Colorado River around Moab, Utah, show that tamarisk defoliation is giving native plants a sudden second life. Now, Dudley and his colleagues are scrambling to set up test sites farther downstream on the Virgin to experiment with revegetation efforts once the beetles pass through. The tests could show whether native plants will need human help such as prescribed fire, controlled flooding, or reseeding.
Little push for revegetation
Unfortunately for Dudley, the beetles are marching faster than the bureaucracy surrounding his grants.
Rather than miss his window of opportunity, he has plunked down $20,000 of his own money to keep the study moving, in the hopes he will be reimbursed once government agencies get on the same page.
Now that the beetles have been released, the federal government’s lack of follow-through on revegetation bothers many people involved in the project. Sogge says that once the permit to release beetles was given, the commitment to monitoring work went down.
Dan Bean, insectary manager for the Colorado Department of Agriculture, puts it this way: “What happens with biocontrol is the release and initial defoliation is a big deal. Senators and congressmen VIPs come out and get their pictures taken, and then – it really falls off the radar.”
“There is no big pool of money for revegetation that I know of,” adds Mr. Bean. Instead nongovernmental organizations like The Nature Conservancy are putting up some funds.
Aside from the high costs and low flash of revegetation work, some might prefer that nothing replace the tamarisk, as that would free up the most water, notes Dudley.
So far, areas with defoliated tamarisks are showing some modest gains for water.
“You won’t see the Colorado River go to twice its flow. It’ll be subtle. You could be talking about hundreds of thousands of acre feet,” says Bean. “It’ll have an impact, but I don’t think it will radically change the way we have to worry about water in the Southwest.”