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The Yampa River and its associated agricultural water delivery systems are spreading leafy spurge seeds downstream from large areas of infestation that have occupied floodplain areas between Hayden and Craig for several decades. The presence of leafy spurge in these difficult-to-treat riparian environments presents an especially difficult challenge to land managers.
The YRLSP seeks to address this problem through scientific research complementing local knowledge, aimed at the development of effective and sustainable leafy spurge management practices. To this end, the YRLSP developed a relationship with Dr. Dan Tekiela, invasive weed scientist with the Department of Plant Science at the University of Wyoming, who recruited two graduate students—Hannah Kuhns and Chloe Mattilio—to work on three leafy spurge research projects in the Yampa River Basin.
Both Hannah and Chloe have now completed their respective projects. We are happy to report that Hannah successfully defended her thesis in late July 2021, and has received her Master's degree. A copy of her Master's thesis, which also serves as the final report on her project for the YRLSP, can be downloaded HERE.
Hannah also presented a Zoom seminar on a portion of her Master's thesis research, on April 9, 2021. To view the video recording of her very informative presentation click HERE.
In the fall of 2021, Chloe completed Chapter 3 of her PhD dissertation—the final comprehensive report on her mapping application projects for the YRLSP. A downloadable PDF of Chapter 3 is available HERE.
If you are looking for a quick overview of Chloe Mattilio's work with leafy spurge mapping, take a look at the update on the remote sensing mapping and invasion risk modeling applications that she presented at the August 2021 YRLSP Working Group meeting. A downloadable PDF of her PowerPoint presentation is available HERE. For a full discussion and maps of Chloe's work on the remote sensing application, see our Remote Sensing page.
Integrated Weed Management
Leafy spurge is an extremely difficult species to effectively manage and many standard herbicide management options produce less than satisfactory results. In riparian areas, the problem is more complicated because several of the herbicides used to control leafy spurge in upland areas are not labelled for use near water. Because eradication is nearly impossible for well-established invasions, reducing seed production and the resulting spread of seed to new areas is an important use of management resources to protect the Yampa River corridor, irrigated agricultural lands, and associated uplands.
University of Wyoming graduate student Hannah Kuhns, under the direction of Dr. Tekiela, began working on a project in 2019 to quantify the impacts of sheep grazing, herbicide applications, or a combination of the two on leafy spurge seed production. In 2020 Hannah extended her research to include an examination of the effect of various environmental variables on leafy spurge seed germination rates, as well as the potential for root fragments (such as might be eroded from a river bank during spring floods) to propagate in new downstream environments. Collectively, Hannah's investigations provide new insight into the optimum timing and best management practices for the control of leafy spurge populations in riparian areas.
A leafy spurge root propagule sprouts in Hannah's lab.
Invasion Risk Modeling
The leafy spurge invasion in the Yampa River Basin is still in progress—what we see today does not define the potential extent of future infestations. Under the direction of Dr. Tekiela, University of Wyoming graduate student Chloe Mattilio has developed a leafy spurge invasion risk model for Moffat and Routt counties.
A primary resource for this model is the extensive spatial dataset that has been developed in nearby Fremont County, Wyoming. Locations of leafy spurge populations have been recorded by Fremont County Weed & Pest for years, resulting in a robust dataset cataloging over 14,000 individual populations. By correlating environmental data for the Fremont County and Yampa River study area infestations (including soil type, texture, and pH; annual and monthly mean climate temperature and precipitation; location slope, elevation, and aspect; as well as infestation proximity to roads and developed areas), Chloe has built a predictive model for the Yampa River Basin, which will facilitate monitoring potential habitats for the arrival of new leafy spurge infestations in the future.
Using ecological niche model (ENM) algorithms, Chloe created a raster (image) file that predicts habitat suitability for leafy spurge in Moffat and Routt counties, at a resolution of 1km x 1km pixels. Each pixel in the raster represents a unique value along a continuous scale from 0 to 1 (least suitable to most suitable leafy spurge habitat). For ease of display in the YRLSP Interactive Map application, the original raster pixels were then reclassified into four discrete categories of risk, before conversion to shapefile format.
Invasion risk data for Moffat and Routt counties, displayed in four classes of habitat suitability for potential leafy spurge invasion.
Remote Sensing Mapping
University of Wyoming graduate student Chloe Mattilio, under the direction of Dr. Tekiela, has also developed a remote sensing application that contributes to the control of leafy spurge in the Yampa River Basin. Chloe's application detects potential existing leafy spurge infestations using high spatial resolution, multispectral satellite imagery. For further discussion of this application, and to view the current remote sensing map series, go to the Remote Sensing page.