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#           Riparian plant communities remain stable in response to a second cycle of Tamarix biocontrol defoliation      

      October 30, 2020    

Reduced abundance of non-native Tamarix shrubs in western U.S. riparian systems following biological control by a defoliating beetle has led to concerns that replacement plant communities could be dominated by other invasive species and/or not provide some of the ecosystem services that Tamarix was providing. In previous studies, Tamarix decline following biocontrol was accompanied by small increases in native and non-native herbaceous species, with variable responses of woody vegetation. However, none of these studies spanned periods longer than a decade since beetle release. This is an important caveat, given the cyclical nature of plant-herbivore interactions and potential lags in vegetation recovery. We report plant community response to an eight-year-long second cycle of Tamarix defoliation-refoliation in two reaches of the upper Colorado River in eastern Utah, 11–13 years after beetle arrival. Tamarix cover across sites initially declined an average of ca. 50% in response to the beetle, but then recovered. Changes in the associated plant community were small but supported common management goals, including a 47% average increase in cover of a native shrub (Salix exigua), and no secondary invasions by other non-native plants. We suggest that the effectiveness of biocontrol programs must be assessed case-by-case, and on a long-term basis.

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October 2, 2020

####                 Riparian vegetation, topography, and ground cover constituents along the Upper Colorado River near Moab, UT (2010-2017) (ver. 1.1, Jan 2023)              

Fort Collins Science Center

#### Patrick  Shafroth, PhD

##### Scientist Emeritus

Fort Collins Science Center

shafrothp@usgs.gov

970-226-9327

#### Sasha C Reed, Ph.D.

##### Research Ecologist

Southwest Biological Science Center

screed@usgs.gov

928-556-7534

#### Jayne Belnap, Ph.D.

##### Research Ecologist

Southwest Biological Science Center

jayne_belnap@usgs.gov

928-556-7555

## Related Content

October 2, 2020

####                 Riparian vegetation, topography, and ground cover constituents along the Upper Colorado River near Moab, UT (2010-2017) (ver. 1.1, Jan 2023)              

Fort Collins Science Center

#### Patrick  Shafroth, PhD

##### Scientist Emeritus

Fort Collins Science Center

shafrothp@usgs.gov

970-226-9327

#### Sasha C Reed, Ph.D.

##### Research Ecologist

Southwest Biological Science Center

screed@usgs.gov

928-556-7534

#### Jayne Belnap, Ph.D.

##### Research Ecologist

Southwest Biological Science Center

jayne_belnap@usgs.gov

928-556-7555

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