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1 April 2014 Short-Term Vegetation Response Following Mechanical Control of Saltcedar (Tamarix spp.) on the Virgin River, Nevada, USA
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Tamarisk (a.k.a. saltcedar, Tamarix spp.) is an invasive plant species that occurs throughout western riparian and wetland ecosystems. It is implicated in alterations of ecosystem structure and function and is the subject of many local control projects, including removal using heavy equipment. We evaluated short-term vegetation responses to mechanical Tamarix spp. removal at sites ranging from 2 to 5 yr post-treatment along the Virgin River in Nevada, USA. Treatments resulted in lower density and cover (but not eradication) of Tamarix spp., increased cover of the native shrub Pluchea sericia (arrow weed), decreased density and cover of all woody species combined, increased density of both native annual forbs and the nonnative annual Salsola tragus (prickly Russian-thistle), and lower density of nonnative annual grasses. The treated plots had lower mean woody species richness, but greater herbaceous species richness and diversity. Among herbaceous species, native taxa increased in richness whereas nonnative species increased in both species richness and diversity. Thus, efforts to remove Tamarix spp. at the Virgin River reduced vegetative cover contributing to fuel loads and probability of fire, and resulted in positive effects for native plant diversity, with mixed effects on other nonnative species. However, absolute abundances of native species and species diversity were very low, suggesting that targets of restoring vegetation to pre-invasion conditions were not met. Longer evaluation periods are needed to adequately evaluate how short-term post-treatment patterns translate to long-term patterns of plant community dynamics.

Nomenclature: Tamarix (tamarisk).

Management Implications: Short-term reductions in density and cover of Tamarix spp. can be achieved with mechanical control techniques, as applied on the Virgin River, Nevada, USA. These treatments can also reduce total woody plant cover and may provide some reduction in flammable nonnative annual grass density, but have no net effect on total herbaceous density. Thus, treatments can reduce fuelbeds, and the potential for wildfire where fuel reduction is the principal goal of vegetation management. Nonnative annual forbs, Salsola tragus (Russian-thistle) in particular, can increase indicating that control treatments for Tamarix spp. can facilitate secondary invasion by other nonnative species. Treatments can also increase cover of rhizomatous native woody plants such as Pluchea sericea (arrowweed), and native forbs as a group, as well as increase diversity for various plant guilds. Treatments provided no significant benefit to arboreal native plants such as Prosopis spp. (mesquites) nor mesic taxa including Salix spp. (willows) and Populus fremontii (Fremont cottonwood) that may be of greater value to wildlife. The results of this short-term response study are the foundation for understanding longer-term (i.e. 5 yr) Tamarix spp. control efficacy or plant community trajectories, and provide a basis to assess how long the initial treatment effects may persist. In addition, it is unknown how the results of mechanical treatments evaluated in this study compare with those of other approaches (e.g. herbicide, fire, biological control, or combinations thereof). Both short and long term effects, and the relative pros and cons of various control techniques, should be considered when developing any Tamarix spp. management plan.

Weed Science Society of America
Steven M. Ostoja, Matthew L. Brooks, Tom Dudley, and Steven R. Lee "Short-Term Vegetation Response Following Mechanical Control of Saltcedar (Tamarix spp.) on the Virgin River, Nevada, USA," Invasive Plant Science and Management 7(2), 310-319, (1 April 2014).
Received: 5 September 2013; Accepted: 1 February 2014; Published: 1 April 2014

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