The tamarisk, which was brought to the U.S. from Eurasia in the late 1800s for erosion control, windbreaks and decoration, is much detested. Since its introduction, tamarisk ā also known as salt cedar ā has been blamed for choking waterways, hogging water and salting the earth as its range expands, driving out such native trees as cottonwood and willows. In Palisade, Colorado, a state lab is breeding beetles whose sole purpose is to destroy tamarisk. At one point, the University of Nevada published a poster about the plant titled WANTED ā Dead, Not Alive!
āThereās been a concerted effort to demonize tamarisk,ā said Matt Chew, a historian of invasion biology at Arizona State Universityās School of Life Sciences. But he thinks this war is aimed at the wrong enemy.
The tree, he said, is a scapegoat for our struggle with something much bigger and messier than weedy fields: our relationship with water in the West.
The tamarisk has a reputation for hogging water ā but is it warranted?
āThis is one of the constant counts against tamarisk ā that itās wasting water,ā Chew said. āThat particular idea got started in the late 1930s and early 1940s for a very particular reason.ā
Back then, Chew says, the Phelps Dodge Corp. wanted to expand its copper mine in Arizona, but it didnāt have the water it needed for the additional mining and processing. All the water rights to a nearby creek and river had been allocated.
āWhat they needed was an excuse to say there was more water in the rivers so that Phelps Dodge could have more water,ā Chew said. āSo, where are they going to get more water?ā
Phelps Dodge inspected nearby water sources and found lots of tamarisk growing along the banks, Chew said. Mine officials rationalized that if they could prove the tamarisk was draining river water, he said, the mine could potentially get the rights to the āextraā water available by killing tamarisk.
āPhelps Dodge did a bunch of experiments which were later picked up by the Agriculture Department,ā Chew said, adding that Phelps Dodge ended up getting its water rights through other means, but the tamariskās image was destroyed.
As Chew writes in the āJournal of the History of Biology,ā āwith water shortages, economic development during the Depression and copper mining for national defense during World War Two, federal hydrologists moved quickly to recast tamarisks as water-wasting foreign monsters.ā
Since then, researchers have shown that the tree doesnāt use more water than native riparian vegetation, including cottonwoods.
To make matters worse, big changes were occurring in the 1930s and ā40s in the way that water was being moved through the West. Dams and diversions were changing the patterns of flooding, patterns that used to be in sync with the reproductive cycle of more sensitive native plants, such as cottonwoods.
āTo some extent, the way we were managing Western rivers actually created a giant tamarisk housing project,ā Chew said. If the tamarisk is a monster, he said, itās because we created it.
āIf you want good, old-fashioned 17th-century riparian areas in the western U.S.,ā Chew said, āyou canāt take all the water out of the river. You canāt have big irrigated fields. You canāt have huge cities.ā
Anna Sher, an invasive species biologist at the University of Denver and author of the book āTamarix: A Case Study of Ecological Change in the American West,ā agrees that Tamarix (the speciesā genus) isnāt all bad.
Yes, Tamarix can create saltier surface soil that retards other vegetation, and its dense wood can fuel more intense fires. Sher even has heard that a boater drowned in Arizona because rescuers couldnāt get through the dense thickets of tamarisk crowding the shore in time to help him.
But, she says, āI certainly do not hate this plant.ā
It provides nesting spots for the Southwestern willow flycatcher, for example, and she says itās entirely possible for the trees to be a part of the landscape without completely taking over.
āItās only behaving badly because of the way that weāve managed our rivers,ā Sher said.
Although the way we manage our rivers isnāt going to change anytime soon, Sher sees hope for restoring the landscape. Itās called the Field of Dreams hypothesis.
āThe Field of Dreams hypothesis predicts that when you remove the invasive species, thereās an opportunity for the desirable species to come in,ā she said.
Initially, Sher and other ecologists suspected the hypothesis was a pipe dream.
āBut after doing surveys of hundreds of sites throughout the American Southwest, we can see that, on average, native species will come back and theyāll come back proportionally to how much tamarisk has been removed,ā she said. āMore tamarisk taken out, more native plants can come in.ā
There are two conditions required for successful restoration. First, there has to be enough water in the rivers and streams to supply the new vegetation. Second, the public has to remain open to what native plants might come back. They might not be the cottonwoods and willows people hope for.
āItās a new game now with Tamarix here and with the water needs that we have now,ā Sher said, and humans will have to get used to plants that can handle the landscape as weāve shaped it.
Those plants might be drought-adapted shrubs and grasses instead of picnic-worthy trees. And they will most certainly have a tamarisk or two as neighbors.
