Research Task: RB00CKY.1.0
Task Manager: Pat Shafroth
In the dry interior of western North America, riparian cottonwood, willow, and other native species are being replaced by invasive non-native shrubs and trees. Among the most common and abundant are tamarisk (Tamarix spp.), Russian olive (Elaeagnus angustifolia), and Siberian elm (Ulmus pumila). Researchers debate the extent to which these species have had negative effects, but they can alter habitat quality for some wildlife, water use by floodplain vegetation, and the frequency and intensity of wildfires. The objective of this task is to address some of the most compelling research questions related to these and other non-native plant species that occur in riparian ecosystems in the western United States. Some examples follow:
- Long-term, sustainable control of invasive plant species is largely dependent on successful revegetation of a site following removal/control of the invasive. Despite this, revegetation receives relatively little attention in the context of control. Current information has not been well-synthesized, and often, site-specific studies have not been conducted with methodologies that enable rigorous interpretation of results. Many researchers have hypothesized that streamflow regulation can favor invasive taxa and disfavor native riparian vegetation; thus, efforts have been initiated to manage streamflow in ways that favor native taxa. However, these efforts have generally not been monitored to evaluate their efficacy. One objective of this task is to conduct research that will improve the success of land managers who are seeking to revegetate and restore xeric riparian habitats following invasive riparian plant control.
- Tamarisk is now declining in abundance in some parts of its range in the West because of the release and spread of a biological control agent, a defoliating beetle. This situation is presenting opportunities for scientific research that examines the response of ecosystems as an invasive species declines or is controlled. Important questions that USGS scientists are working to answer include: How does water consumption along rivers change as tamarisk abundance and vigor are reduced? What plants will replace tamarisk as it dies back, and are these desirable native species or undesirable weedy species? How are wildlife populations, such as birds, responding to changes in habitat associated with vegetation change? How can land and water mangers best approach efforts to restore floodplain vegetation to achieve their objectives?
- The fate of woody riparian plants is closely tied to flow regime and groundwater dynamics along rivers in the arid western U.S., both of which are expected to change as a function of changing climate. Climate change is likely to substantially alter riparian plant community structure and dynamics, via both direct effects on plants and indirect effects related to stream flow, biotic interactions, and human activities. Of particular interest to land and water managers is whether or not the distribution and abundance of invasive species are likely to increase. Our research addresses several knowledge gaps with respect to climate change impacts on riparian vegetation.
For more information contact Pat Shafroth
U.S. Department of the Interior | U.S. Geological Survey
