Vegetation response to invasive Tamarix control in southwestern U.S. rivers: a collaborative study including 416 sites

Authors

Eduardo Gonzalez, Universite de Toulouse & University of Denver
Anna A. Sher, University of DenverFollow
Robert M. Anderson, University of Denver
Robin F. Bay, University of Denver
Daniel W. Bean, Palisade Insectary
Gabriel J. Bissonnete, U.S. Bureau of Land Management
Berenger Bourgeois, Universite Laval & McGill University
David J. Cooper, Colorado State University
Kara Dohrenwend, Rim to Rim Restoration
Kim D. Eichhorst, University of New Mexico
Hishma El Waer, University of Denver
Deborah K. Kennard, Colorado Mesa University
Rebecca Harms-Weissinger, National Park Service
Annie L. Henry, University of Denver
Lori J. Makarick, Grand Canyon National Park & Natural Resource Stewardship and Science
Steven M. Ostoja, University of California, Davis
Lindsay V. Reynolds, Colorado State University
W. Wright Robinson, Grand County Weed Department
Patrick B. Shafroth, U.S. Geological Survey

Date of this Version

4-12-2017

Citation

2017 by the Ecological Society of America

Comments

Ecological Applications, 27(6), 2017, pp. 1789–1804

Abstract

Most studies assessing vegetation response following control of invasive Tamarix trees along southwestern U.S. rivers have been small in scale (e.g., river reach), or at a regional scale but with poor spatial-temporal replication, and most have not included testing the effects of a now widely used biological control. We monitored plant composition following Tamarix control along hydrologic, soil, and climatic gradients in 244 treated and 172 reference sites across six U.S. states. This represents the largest comprehensive assessment to date on the vegetation response to the four most common Tamarix control treatments. Biocontrol by a defoliating beetle (treatment 1) reduced the abundance of Tamarix less than active removal by mechanically using hand and chain-saws (2), heavy machinery (3) or burning (4). Tamarix abundance also decreased with lower temperatures, higher precipitation, and follow-up treatments for Tamarix resprouting. Native cover generally increased over time in active Tamarix removal sites, however, the increases observed were small and was not consistently increased by active revegetation. Overall, native cover was correlated to permanent stream flow, lower grazing pressure, lower soil salinity and temperatures, and higher precipitation. Species diversity also increased where Tamarix was removed. However, Tamarix treatments, especially those generating the highest disturbance (burning and heavy machinery), also often promoted secondary invasions of exotic forbs. The abundance of hydrophytic species was much lower in treated than in reference sites, suggesting that management of southwestern U.S. rivers has focused too much on weed control, overlooking restoration of fluvial processes that provide habitat for hydrophytic and floodplain vegetation. These results can help inform future management of Tamarix-infested rivers to restore hydrogeomorphic processes, increase native biodiversity and reduce abundance of noxious species.