Academics and Research

DU ecologist and biologist team up for book on invasive plant

Anna Sher, associate professor of biological sciences at the University of Denver, has long been known for her research on the Tamarix tree, an invasive species that proliferates in the American West’s riparian areas. She and Professor Martin Quigley, ecologist and director of the University’s Chester M Alter Arboretum, are editors of the recently released “Tamarix. A Case Study of Ecological Change in the American West” (Oxford University Press, 2013). The two fielded some questions by email about their new book.


Q: Many of us first became acquainted with the Tamarix a few years ago, when it was demonized as a voracious water guzzler responsible for draining rivers and threatening water supplies. Did it deserve this bad rap?

A: Yes and no. Like most trees that grow along our rivers, Tamarix (common names are tamarisk and saltcedar) can use a lot of water, and during a drought year this water “loss” may be felt. However, this does not necessarily mean that cutting down Tamarix trees will give us back the water — also known as “water salvage.” Instead, we encourage people to think about what they need and want from the plant communities that live by our rivers and see if Tamarix is useful or not in that context. Sometimes it is and sometimes it isn’t, water issues aside.


Q: What was your goal in assembling and editing this book?

A: We wanted to pull together all of the aspects of this fascinating plant to demonstrate the complexity of a single exotic species and how it is a part of the transformation of the Western landscape. This re-assembly of vast riparian landscapes has political and even ethical ramifications. We included all perspectives in one volume. It is our understanding that this is the first time anyone has done something like this, combining biological, ecological, historical, management (i.e. practical), political and philosophical elements joined by a single species.


Q: Anna, in the chapter you wrote for this book, your refer to the Tamarix as the “paradox plant.” What makes it a paradox?

A: Tamarix is a paradox on many levels. Biologically it is a paradox because it combines traits of both the mouse and the elephant: producing many offspring and taking advantage of scarce resources (like a mouse), while also being a long-lived species that is highly competitive when mature (like an elephant). These are usually contradictory traits.

Ecologically, it can act as both a passenger and a driver of ecosystem change, taking advantage of our alterations to rivers through damming and diversions. Then, once established, Tamarix accelerates and magnifies these changes, such as soil salinity, drought and wildfire.

Politically and socially, Tamarix is paradoxical by acting as both a unifier and a divider of public opinion. Both conservative and liberal organizations and elected officials came together to promote legislation for managing the plant. In recent years, there has been debate among scientists about when and where it should be removed. Our book brings together all these voices so readers can make their own assessment.


Q: What questions does this book raise for land managers in the West?

A: The big question it may raise is whether tamarisk removal is appropriate in a given place at a given time, and which method will be best for that instance. It is easy to think of problems like invasive species in black-and-white terms, but when we try to use the same approach everywhere, there can be serious unintended consequences. In some places it may be posing a significant fire risk or elevating salinity in the soil or ground water, whereas in other places it is important for bank stabilization or as nesting habitat for birds.


Q: How should we regard the Tamarix today? As a friend or as a foe?

A: Like any organism, Tamarix has more than one role in the ecosystems and river valleys of the American Southwest. It can provide habitat for some animals, or it can be inhospitable to other plants and animals. It can be beneficial to ranchers in providing shade for cattle, or it can make impenetrable thickets that keep the cattle from stream edges. Tamarix cannot be categorized simply, and it continues to stimulate discussion across the whole of the Southwest.


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