Document Type


Date of Degree Completion

Winter 2024

Degree Name

Master of Science (MS)


Cultural and Environmental Resource Management

Committee Chair

Clay Arango

Second Committee Member

Megan Walsh

Third Committee Member

Jennifer Lipton


Invasive species threaten plant community structure and function globally. Riparian areas, the zone near streams where water influences vegetation, are especially sensitive to invasive species colonization, suffering large-scale shifts in community composition. Salix fragilis (crack willow) is a nonnative riparian species abundant in the lower elevation tributaries of central Washington. Some speculate whether this willow should be listed as invasive in Washington, despite a lack of regional supporting evidence. I studied riparian communities dominated by either S. fragilis or native species in the Kittitas Valley and measured biodiversity, quantified differences in solar attenuation, and compared leaf decomposition rates to learn how S. fragilis alters riparian zone structure and function. I found riparian communities with S. fragilis had lower plant diversity, but no difference in solar attenuation between riparian forests with and without S. fragilis. I also found a significant interaction between the presence of S. fragilis and in-stream leaf decomposition rates such that leaves decomposed faster in streams dominated by the nonnative willow. Although S. fragilis alters the structure and function of riparian areas, significantly changing the ecology of riparian forests in the Kittitas Valley, additional data are required to make a final management decision regarding listing S. fragilis as an invasive species in Washington.