Saltcedar (Tamarix spp.) is an invasive plant that is crowding out native vegetation and dominating the shorelines of southwestern rivers and streams. But put a room full of weed scientists and land managers together to discuss how to tame the aggressive plant and you’ll trigger a lively debate about how – or even whether – it should be controlled.
That was the experience during a recent symposium on the biological control of invasive plants that was held in conjunction with the annual conference of the Western Society of Weed Science.
According to a symposium presentation by Dr. Allen Knutson of Texas AgriLife Extension Service, Texas A&M University, saltcedar was introduced in the Southwest for erosion control. It found an accommodating home in the region’s river systems and spread fast with seasonal flooding. Over time, riverside and streamside landscapes of cottonwood, willow, native grasses and flowering plants were pushed aside by wide ribbons of saltcedar.
“Though the full impact of such a drastic change in the natural landscape will probably never be fully understood, there are some well-documented outcomes from the spread of saltcedar,” Knutson said. “Because of its dense growth pattern, it consumes large quantities of water and can impact rivers, lakes and desert waterholes. It lowers groundwater levels and has been known to deplete ponds and streams to the detriment of fish and wildlife.”
In an attempt to restore natural river ecosystems, both targeted aerial applications of herbicides and labor-intensive mechanical operations have been used to remove saltcedar, sometimes with long-term success. Now land managers are adding new biological control agents to their arsenal by releasing saltcedar leaf beetles (Diorhabda elongata) imported from China and Greece. The small insects strip saltcedar of its leaves, while ignoring native vegetation.
“Symposium participants had a spirited debate about whether release of a biological control for saltcedar in the Southwest is a good idea or a bad one,” said April Fletcher of the U.S. Fish and Wildlife Service. “But I believe everyone left the symposium with a greater appreciation of how complex the issues of saltcedar control are, and how many questions remain unanswered.”
Many of those unanswered questions involved the ecosystem of the Southwest. If saltcedar is removed, will native species return? Or have groundwater levels and flooding patterns been changed so much as a result of human activities that the original cottonwood galleries will be unable to grow? If saltcedar stands are controlled, what will happen to wildlife species that now depend on the shrub for nesting sites, including the endangered southwestern willow flycatcher (Empidonax traillii extimus)? Participants also had lots of questions about the potential for unintended consequences from the voracious saltcedar leaf beetle.
“Though we’ve made great progress in controlling some of the nation’s most destructive plants and weeds, the debate over saltcedar shows ongoing research is vital,” said Lee Van Wychen, science policy director for the Weed Science Society of America. “Taking a science-based approach can help us answer critical questions about our natural ecosystems and carefully weigh the impact of the decisions we make.”
For a closer look at symposium presentations on saltcedar, biological control strategies and other topics, visit http://www.wsweedscience.org/Slides/slides.asp.
Editor’s Note: A photo of the saltcedar leaf beetle is available for download at http://www.ars.usda.gov/is/graphics/photos/mar00/k8836-1.htm. A photo of saltcedar is available for download at http://www.invasive.org/species/subject.cfm?sub=6515.
About the Weed Science Society of America:
The Weed Science Society of America, a nonprofit professional society, was founded in 1956 to encourage and promote the development of knowledge concerning weeds and their impact on the environment. The Weed Science Society of America promotes research, education and extension outreach activities related to weeds, provides science-based information to the public and policy makers, and fosters awareness of weeds and their impacts on managed and natural ecosystems. For more information, visit http://www.wssa.net.