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Title: River flooding and its impacts on large-scale biocontrol of Tamarix in the Colorado and Virgin River system: Moving targets and trajectories

Author
item LEE, STEVEN - Us Geological Survey (USGS)
item SHAFROTH, PATRICK - Us Geological Survey (USGS)
item Ostoja, Steven
item BROOKS, MATT - Us Geological Survey (USGS)
item REED, SASHA - Us Geological Survey (USGS)

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/17/2017
Publication Date: 10/17/2017
Citation: Lee, S.R., Shafroth, P., Ostoja, S.M., Brooks, M., Reed, S. 2017. River flooding and its impacts on large-scale biocontrol of Tamarix in the Colorado and Virgin River system: Moving targets and trajectories. In: Riparian Summit 2017. October 17-19, 2017, Davis, California.

Interpretive Summary:

Technical Abstract: Along riparian corridors throughout the arid and semiarid regions of the western United States, non-native shrubs and trees in the genus Tamarix have replaced native vegetation. Plant communities along rivers with altered flow regimes and flood control have become particularly vulnerable to widespread invasion by Tamarix. In recent years, specialist herbivores (beetles) in the genus Diorhabda have been introduced for the biological control of Tamarix. These beetles can cause substantial defoliation and mortality of Tamarix, paving the way for subsequent changes to plant community composition and structure, and indirect effects on wildlife populations and ecosystem processes (e.g., wildfire, hydrological dynamics, sediment dynamics, nutrient cycling). We have been monitoring vegetation composition, cover, soils and topography along a 50-mile Tamarix dominated stretch of the Virgin River (a major tributary of the Colorado) in southern Nevada since 2009. Biocontrol beetles arrived in 2010 in the upstream part of our study area, and defoliation was extensive by 2012. In December 2010 a large 20-25 year flood event occurred along the river, drastically altering the local topography and vegetation cover creating an opportunity to assess the effectiveness of biocontrol in conjunction with flooding of a free flowing river system. While biocontrol was effective across our study site, those areas that received the largest flood impacts (erosion and/or deposition) had the strongest recruitment and establishment of native vegetation. Flooding is an important part of the dynamics that help shape riparian ecosystems throughout the southwest, yet current regional trends suggest that the frequency of major flood events may be changing. Results from the Virgin River give us insight on how changing flood regimes may impact native plant communities as well as the role that Tamarix biocontrol may have in helping re-establish those communities.