Biology Associate Professor Anna Sher is working to understand how tamarisk alters the environment. Photo: Wayne Armstrong
For 15 years, biology Associate Professor Anna Sher has grappled with tamarisk.
The woody, flowering weed, also known as salt cedar, has been the focus of Sher’s research. She’s traveled the West, studied the ecological impacts and potential solutions and lobbied for change and involvement. She’s heard from the bird-watchers and beekeepers who extol the virtues of the invader, and she’s heard from ranchers and ecologists who clamor for its removal.
“The problem with tamarisk is that it’s able to establish itself and effect other changes to the ecosystem that are harmful to the original plants and animals,” says Sher, who also directs research, herbaria and records at the Denver Botanic Gardens. “It changes the structure of the forest.”
Imported from Asia in the 1800s as an ornamental, tamarisk spread from gardens to natural waterways, boosted along the way by planting programs to control erosion. It spread across the West, and concentrations are now found on an estimated 2 million acres throughout the Western and Southwestern U.S.
Sher’s research has shown that tamarisk is not a particularly formidable competitor as a seedling, but with human help, such as flood-control projects that disrupt flooding cycles, it has thrived. And in areas where it gets a foothold, it doesn’t play well with others.
Thick tamarisk groves change the ecosystem and can drive off native wildlife, including eagles and some fish, says Sher, who co-authored Colorado’s plan to eradicate tamarisk. The plant creates salty soil conditions around it — conditions that are inhospitable to native plants. It can also increase fire intensity and frequency. And tamarisk gobbles up water, depriving farmers and cities downstream.
President Bush signed a bill into law in 2006 directing the government to study and direct management of tamarisk and Russian olive trees, and a DU panel last year called for eradication of tamarisk and other invasives as part of a nine-point plan for a sustainable water future.
Eradication methods include spraying herbicide and unleashing imported insects. But even as scientists develop ways to eradicate tamarisk, there is new debate over whether they should, Sher says. If tamarisk goes, what replaces it? Will native species return to vacant plots now that the soil has been left high in salt? And what about birds that have adapted to tamarisk?
As board president of the Colorado-based nonprofit Tamarisk Coalition, Sher says scientists’ challenge is to understand the role of tamarisk while pushing for research into tamarisk and the effects flood control and other water policies have on natural landscapes.
And the work is more important than ever as demand grows.
“In arid ecosystems, rivers are the veins of life,” she says. “Whatever we do to them has an effect on the entire region.”