Stomping out an invasive iris in Agate Fossil Beds NM

At Agate Fossil Beds National Monument (Harrison, NE), the beautiful, yet exotic and invasive, yellow flag iris (Iris pseudacorus) is taking over riverine wetlands, becoming a concern for the park’s ecosystem. The plant, originally from Europe, arrived in 1906 with a family of settlers 25 miles south of Harrison. The settlers planted seeds of the iris around the family pond, and slowly over the years the flower has spread along the waterways, traveling east into the park. The plant has out-competed many native plant species, and currently covers nine river miles, causing the river to narrow and deepen in areas of dense growth.
Colorado State University graduate, Jordan Spaak (Biology, 2012), was working for the National Park Service in 2013 when controlling this invasive species became a concern for the Monument. Spaak reached back to CSU to discuss this challenge and began working with Associate Professor Paul Meiman. Spaak took on the project and returned to CSU, to earn a Master’s in Rangeland Ecosystem Science focused on management of yellow flag iris.

Originally studying small plots within the park, Spaak and Meiman studied different combinations of cutting, herbicides and planting native species to reduce iris abundance. They also gathered iris seed for a greenhouse experiment to investigate the effects of temperature and light (full sun vs partial shade) on seedling emergence and growth. Interestingly, when they returned to their field plots to check their progress, they began to notice a loss of the iris in their footpaths, and a new idea formed to manage the species – trampling. This made perfect sense, because upstream and downstream of the monument are working cattle ranches. Iris is much less abundant on these ranches, compared to inside the monument where there have been no domestic livestock for over 40 years.

Spaak and Meiman became very interested in the idea of large ungulates (e.g. cattle, bison or elk) for reducing iris abundance. Herding wild ungulates is somewhere between illegal and extremely difficult, and acquiring permits to bring domestic livestock into the park would have been too difficult and time consuming. So, to test their hypothesis the pair decided to get the public involved and a volunteer-driven citizen science experiment was created. For this experiment, members of the Sioux County High School Future Farmers of America volunteered to help, and students were led to study plots to stomp on the iris plants for 3-5 minutes. Results were almost immediate, with a 70-75% reduction in iris density in the first growing season while the native plant species remained intact.

With the success of the citizen science trampling study, Spaak and Meiman are now working with the NPS and the surrounding community to determine the best course of action to further study trampling but with large ungulates instead of high school students. Ultimately, if trampling continues to show promise, Meiman and Spaak hope that the implementation moves from study plots to large-scale iris reduction.

One day in the future, hopefully a large ungulate will be on the monument and can help with invasive plant management. Currently no decisions have been made, and further research will be needed to determine the best way to manage the trampling. In the end, the final result will be based on what is best for the community and ecosystem as a whole, and Warner College, NPS and the local community will continue to work together to identify the best option.