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The tamarisk leaf beetle now threatens the endangered southwestern willow flycatcher and other birds that have adapted to the non-native tamarisk that grows so thick along the Colorado River.
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Exotic beetles released by the U.S. government to kill exotic trees along the upper Colorado River have munched a destructive path into central Arizona, officials have confirmed, proving to be more mobile and resilient than predicted.

The tamarisk leaf beetle now threatens the endangered southwestern willow flycatcher and other birds that have adapted to the non-native tamarisk that grows so thick along some of the region’s rivers. The beetles can strip a tree of its leaves, ruining it as a home for the birds.

Arizona environmentalists and biologists worry the beetle’s June 8 discovery in Wickenburg dooms many of the remaining flycatchers. Salt River Project has invested millions of dollars and 2,400 acres in mandated habitat protections throughout the Gila River drainage as a condition of raising Lake Roosevelt and displacing old nesting areas.

“We’ll lose that if and when this beetle progresses,” Center for Biological Diversity co-founder Robin Silver said.

“We’ve been kind of hoping this wouldn’t happen, knowing that, likely, it eventually would,” he said.

Some people, like suburban Buckeye’s mayor, are cheering the prospect of a natural thinner for the shrubby tamarisks crowding the Gila River, where thickets of the trees are blamed for flood and fire risks.

But no one knows how much farther the beetles will spread if they find new paths into the Gila River drainage area, which stretches north and east on the Verde and Salt Rivers and south on the Santa Cruz and San Pedro rivers.

An Arizona biologist found beetles and their larvae living in tamarisks on the Hassayampa River, a Gila tributary west of metro Phoenix. The insects had previously moved south from Utah’s Virgin River to Lake Mead and then down the lower Colorado. From there they moved east along the Bill Williams River and its tributaries.

Now they’re within striking distance of the heart of what remains of flycatcher country.

‘A pretty bad miscalculation’

This wasn’t supposed to happen.

When the U.S. Agriculture Department got the U.S. Fish and Wildlife Service’s blessing to release the Asian beetles among tamarisk trees in Utah, the conventional wisdom said the insects could not live this far south. A 2004 release in Moab used beetles from a similar latitude in China and Kazakhstan.

“There was a pretty bad miscalculation,” said Steve Spangle, field supervisor for Fish and Wildlife’s Arizona Ecological Services office.

Research had suggested the aspirin-size beetles would migrate only about a mile a year.

“Once they were released, it just exploded,” said Ben Bloodworth, program coordinator for the Tamarisk Coalition, a Colorado nonprofit watershed restoration group.

The beetles surged by 30 and 40 miles a year, some years possibly aided by unauthorized people moving them. For instance, last year the beetles skipped over a lush patch of Colorado River tamarisk that should have tempted any natural migrants to stop, and instead landed at Lake Havasu.

Those Lake Havasu beetles are the population that Levi Jamison, the Colorado Plateau Research Station biologist who discovered the Hassayampa River beetles, believes seeded the central Arizona invasion.

However the beetles moved over the years, the Center for Biological Diversity and Maricopa Audubon sued to force new flycatcher protections in the face of their advance. This month, just a day after Jamison discovered Maricopa County’s first tamarisk beetles, a federal judge in Las Vegas ordered the Agriculture Department to produce a new plan for helping flycatchers, and to do it this summer.

Agriculture officials declined to comment because of the lawsuit.

Birds adapt to imported trees

The willow flycatcher is a brownish drab insect eater a little smaller than a cardinal, with whitish bands on its wings. The last rangewide survey nine years ago estimated 1,299 territories, most representing a nesting pair, with Arizona and New Mexico containing 978 of them.

It’s unclear how bad the beetles may prove for central Arizona’s flycatchers, Spangle said. Some of the bird’s territories, especially south of the metro area on the undammed San Pedro River, retain native willows where the birds can nest and eat. Others may grow only tamarisk, so the extent of tree die-off will determine ripple effects.

“It really is going to require a site-specific analysis,” he said. “Some stands, if they’re pure tamarisks and the beetle gets in there, it could be significant.”

Research suggests there’s no significant difference in flycatcher nesting success and survival between tamarisks and native willows, Fish and Wildlife biologist Greg Beatty said. Other species such as woodpeckers or hawks may suffer the loss of native cottonwoods to tamarisks, but not the flycatcher.

Americans imported Eurasian tamarisks more than a century ago to plant as ornamentals, windbreaks and riverbank stabilizers. In the Southwest, dams have cut off seasonal floods that germinated and rejuvenated the native willows that historically sheltered flycatchers, leaving tamarisks to crowd the banks.

Like willows, they are spindly with upward-sweeping limbs.

Also known as salt cedar, a tamarisk lifts salt from deep soils and deposits it on the ground when its leaves fall like confetti, further altering the environment to its own alkaline needs. Dense stands in Buckeye have captured river sediments and caused the seasonally dry riverbed to fan out and rise, creating a flood hazard for the growing western suburb.

Some welcome the invading insects

For these reasons and a theory that tamarisks suck up more of the region’s water supply than native plants, governments at every level in recent decades have sought to thin or eradicate them.

“Salt cedars have taken over the river bottom,” Buckeye Mayor Jackie Meck said. “They don’t belong here.”

The thicket pushes floodwater northward, he said, where it carves out farmland and threatens a sewage plant serving 20,000 homes.

It also fuels frequent, hot wildfires.

Tamarisks can sustain several years of defoliation by beetles, and even then only a portion will usually die. So Meck wants to hack and spray a long stretch of the river to remove them all.

Buckeye has cleared 40 acres of it and is attempting to restore native willows and cottonwoods there. Meck wants more: federal permission to clear 18 miles of riverbank. He believes such a clearing of thirsty tamarisks would free up groundwater to restore native plants that flycatchers could also use.

That permission has been years in the asking. Meantime, Meck said, “The beetle will help us.”

Bringing back habitat isn’t easy

Restoring native riverside trees is tricky business in the Southwest.

Most of the rivers are dammed to hold back the spring floods that otherwise sustain and recycle willows and cottonwoods. Instead, river managers release water when farmers need it in summer, a time when it is more likely to help tamarisks.

Simply clearing tamarisks and replanting native trees without altering river management can lead to deserted banks — or a return of tamarisks.

“Tamarisk is symptomatic of the (dam’s) impacts to the landscape,” federal biologist Beatty said. “It didn’t cause them. It’s a product of them.”

Research into the tree’s water consumption does not support the theory that it’s a substantial drag on the supply, he added.

Despite the challenge presented by altered rivers, the Tamarisk Coalition finds hope in emerging techniques for fostering willows. One involves growing them in tall pots so they’ll grow long roots to tap deep groundwater before they’re ever placed on the riverbank. Another involves literal farming of willows, with dedicated irrigation.

“We’ve really tried to get people to do restoration ahead of the beetle,” Bloodworth said, “to actually get some willows in place so that the birds have some place to move to if they need to.”

Environmental coverage on azcentral.com and in the Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow the azcentral and Arizona Republic environmental reporting team at OurGrandAZ on Facebook, Twitter and Instagram.

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