Study finds ways to eliminate invasive plants naturally

A $180,000 grant from the U.S. Bureau of Reclamation awarded to the College of Technology and Innovation at Arizona State University and Northern Arizona University (NAU) is supporting a study on the effects of biocontrol and restoration on wildlife in Southwestern riparian habitats. The project determines if the introduction of a biocontrol agent, the tamarisk leaf beetle, influences wildlife populations and communities.

Principal investigator Heather Bateman, assistant professor in the department of human and environmental systems at the college and senior sustainability scientist for ASU’s Global Institute of Sustainability, along with co-investigator Matt Johnson from NAU, hope that the results will help natural resource managers make informed decisions by providing guidance on how wildlife species respond to management actions such as biocontrol. The project is taking place along sections of the Virgin River in Arizona, Nevada and Utah.  

The project studies ways to eliminate non-native species without disrupting wildlife; resource managers must often balance the goals of protecting wildlife species and habitats with control of non-native plants. One of these non-native species is saltcedar, which is the third most abundant tree in Southwestern riparian systems and is considered invasive because of its competitive ability and capability to form monotypic stands. If an area is overtaken by saltcedar, it can have detrimental effects on native plants and habitat quality.

Researchers are looking for ways to control these non-native plants without disrupting wildlife. Some methods used to remove these non-native plants include chemical, mechanical and burning methods – all of which disrupt wildlife and can damage surrounding vegetation. Biocontrol is one method used by managers to combat saltcedar by introducing a natural enemy, such as a leaf beetle, to defoliate the exotic plant and possibly reduce saltcedar density.   

The effectiveness of such a solution has been seen in 13 other states, including Utah, which moved a biocontrol agent from central Utah to southern Utah in an effort to control saltcedar infestations along the Virgin River.

The project comes with risks, Bateman said. The Southwestern willow flycatcher bird is a federally endangered subspecies managed by the U.S. Fish and Wildlife Service and often builds its nest in saltcedar. The use of biocontrol in these areas has become controversial because of the possibility that the habitat of the Southwestern willow flycatcher will be disrupted.

“By partnering with biologists from the Utah Division of Natural Resources, my collaborator Matt Johnson will monitor Southwestern willow flycatcher abundance and nest success in restored sites where biocontrol is present,” Bateman said. “Some researchers have identified a potential dilemma that the biocontrol beetle could defoliate saltcedar where the flycatcher is nesting and cause nests to fail. However, defoliation can occur at different times of the summer, depending upon beetle movement and densities. Therefore, it is important to determine the timing of saltcedar defoliation and flycatcher nesting.”

The project involved over four years of studying and pre-planning. In 2009, the research team defined two areas; sites along the lower Virgin River in Arizona and Nevada, and sites near St. George, UT along the Virgin River where restoration efforts have been made. When the study is complete, they will compare the data of the two locations to monitor changes in riparian systems.

The grant lays out several project tasks that are estimated to be completed by September 2014.

Conceptual models will be developed to represent and relate relevant life history information for the Southwestern willow flycatcher and other focal species as a basis for interpreting wildlife models and reflecting how habitat-wildlife relations change before and following biocontrol establishment.

In order to collect pre-biocontrol data, the research team established 20 sites along the lower Virgin River where they monitored pre-biocontrol conditions for species of lizards, birds and other wildlife in 2009 and 2010. The biocontrol beetle became established in the defined research area in 2011 and spread in 2012. The project will expand preliminary work by trapping lizards and examining fecal pellets for evidence of the biocontrol beetle, monitoring birds for foraging of the biocontrol beetle and measuring vegetation in all areas.  

Researchers of the project have used data loggers in habitats affected by biocontrol to document microclimatic changes in habitat. After saltcedar has been defoliated by biocontrol beetles, the foliar canopy is reduced, causing temperatures to increase and relative humidity to decrease. Preliminary results also suggest that lizard abundance decreases during these defoliated times. Ultimately, the effects of defoliation on microclimate will be analyzed and the study will identify species that will be most strongly impacted by defoliation.

Bateman says the proposal helps to fulfill one of the science needs identified by the Bureau of Reclamation by helping to improve monitoring of the effects of invasive species in watersheds and riparian ecosystems in the Southwestern United States. 

Written by Sydney B. Donaldson