Olives in Overdrive: Spatial and Temporal Patterns of Russian Olive Establishment on the San Juan River
Cassidy Goering1*, Cynthia Dott2
1Biology and Environmental Science Departments, Fort Lewis College, Durango, CO, USA
2Biology Department, Fort Lewis College, Durango, CO, USA
Water is the limiting resource in the arid desert regions of the western United States, and invasive species are a persistent problem in these landscapes. Invasive species threaten native species by outcompeting them and by altering the habitat that they encroach upon. Russian olive (Elaeagnus angustifolia) is invasive along riparian corridors across western rivers, and it is unknown what factors can predict Russian olive invasion and establishment. The goal of this research was to identify the establishment requirements of Russian olive along two canyon reaches of the San Juan River in southeastern Utah. A total of 74 Russian olive trunk samples were collected across 15 sites in two canyon reaches of the San Juan River between Bluff and Clay Hills Crossing, Utah. Following tree sample collection, dendrochronology was used to identify the establishment year for each of the Russian olive trees that were sampled. Hydrologic and climatic data were collected from the USGS stream gauge near Bluff and from Palmer Drought Severity Index (PDSI) records for San Juan County Utah. Establishment years were tested against hydrologic and climate variables to identify the strongest predictors of successful Russian olive establishment. Across all of the hydrologic and climate variables tested, lower average flows during the year of establishment and the year before establishment created the strongest predictor omnibus test p-value (p = 0.006). Within this model, lower average flow in the year of establishment was the most significant variable (p = 0.011). Our model supports Russian olive behaving as a later successional species that is responding to overall trends in river flow instead of flashy disturbance events. Russian olive is filling a new niche in riparian river habitats that did not exist prior to damming rivers because natural river systems have a high disturbance frequency. Average low flows could also point to overall drought conditions being a predictor of Russian olive establishment, however this is less likely due to a lack of correlations with the PDSI variables that were tested. As Russian olive is managed across North America, it is essential to know that this tree is responding to a novel ecosystem that did not previously exist. Land managers can continue to manage Russian olive with treatments such as removal, however this does not address the root of the problem: alterations to hydrology due to flow management and drought.