Anne Minard for National Geographic News
This story is part of a National Geographic News story on global water issues.
Tamarisk trees are invading, crowding out native trees along rivers in the southwestern United States. But their removal could further imperil the endangered southwestern willow flycatcher, a sparrow-sized songbird.
For decades biologists have tried to remove tamarisk—which grows up to 16 feet tall—manually and with herbicides and other strategies. But they are still losing ground to the sprawling tree. Now, some scientists fear that one of those strategies—an imported, tamarisk-munching beetle—could become a scourge in its own right, wiping out tamarisk trees too quickly for other species in the ecosystem to adapt. Not good for green living!
A Growing Problem?
The controversial tree is from Europe and Asia and was first planted in the United States in the early 1800s to decorate western yards and stabilize soil along rivers. Tamarisk, also called salt cedar because it exudes salt into the soil, spread like wildfire. It now dominates more than a million acres of mostly riverside habitat throughout the southwest, having crowded out native trees and keeping them at bay with the salty soils.
Since the 1940s, biologists have worked to control tamarisk trees wherever they’ve taken hold, with especially aggressive efforts in national parks. That’s because the National Park Service aims to protect native plants and animals from a whole host of threats, including invasive species such as tamarisk.
At the Grand Canyon, the trees are so well established along the main Colorado River that park managers have abandoned efforts there. Tamarisk eradication efforts in Grand Canyon National Park for the past decade have been targeted—successfully—at protecting pristine side canyons from the menacing tree’s creep. At last count, tree crews had removed 275,000 trees from 130 side canyons, out of more than 500, within the park.
“From the beginning we knew we were not getting rid of the source,” said Lori Makarick, Grand Canyon’s vegetation program manager.
But that could change with the salt cedar leaf beetle. The tamarisk-killing bug was introduced to areas far enough from the Grand Canyon that biologists thought they would never make it there. The beetle populations, however, kept spreading. And now tamarisk control could happen too quickly for biologists and tamarisk-loving wildlife to adapt.
The USDA’s Animal and Plant Health Inspection Service (APHIS) began importing salt cedar leaf beetles in the late 1990s from Kazakhstan and other regions where they feast naturally on tamarisk trees.
Starting in 2001, land managers in all the southwestern states—except Arizona and New Mexico—began releasing them into tamarisk thickets. Based on input from the U.S. Fish and Wildlife Service, no beetles were released within 200 miles of nesting locations for the southwestern willow flycatcher, a bird endangered since 1995 that now appears to rely on tamarisk trees, nesting in them even when native trees are still around.
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