Impacts to endangered birds at issue; latest studies show the non-native plants don’t use as much water as previously believed
SUMMIT COUNTY — Land managers looking for ways to control invasive tamarisk trees in the Colorado River Basin may have to search for a new tool.
The U.S. Department of Agriculture has terminated the use of a non-native insect used to destroy tamarisk after concluding that the bug was destroying critical habitat used by the southwestern willow flycatcher, listed as endangered by the federal government. The decision, announced in a June 15 memo, affects biological control efforts in 13 states.
Tamarisk, also called saltcellar, is native to the Mediterranean and central Asian region. It was brought to the U.S. to be used as a windbreak and for ornamental purposes. It quickly spread across at least 1.5 million acres in the arid climate and alkaline soils of the Southwest. In an ironic twist, the endangered flycatcher has taken to nesting in tamarisk.
In the past 10 years, various public agencies launched a costly and labor-intensive effort to prevent the stubborn shrub from spreading farther, and to eradicate it in areas where it’s already established. Initial estimates of tamarisk water use were alarming, which created a sense of urgency.
Additionally, land managers said the plant was displacing native vegetation and hindering recreational access to rivers. Other concerns include impacts to stream morphology that affect habitat for endangered fish. Some studies suggested that tamarisk also can lead to increased flooding.
However, some of the more recent studies on tamarisk show that the plant doesn’t use more water than native willows and cottonwood. Removing tamarisk leads to the growth of other species that use just as much water, the U.S. Geological Survey reported in April. The research shows that many reptiles, amphibians and birds use tamarisk habitat. But it does displace habitat for native cavity nesting birds like woodpeckers.
Along with biological controls, fires and bulldozers have also been used to try and eradicate tamarisk. In its native habitat, the plant is controlled in part by fire and by flooding. It’s rapid spread in the Southwest was partially enabled by fire suppression and because natural stream flows have been altered by diversions.