Flood dynamics dictate distributions of Elaeagnus angustifolia L. (Russian olive) on a riverine floodplain

Authors: West, Natalie; REINHOLD, ANNE MARIE - Montana State University; POOLE, GEOFFREY - Montana State University; Espeland, Erin

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2020
Publication Date: 9/10/2020
Citation: West, N.M., Reinhold, A., Poole, G.C., Espeland, E.K. 2020. Flood dynamics dictate distributions of Elaeagnus angustifolia L. (Russian olive) on a riverine floodplain. Biological Invasions. 22:3493-3499. https://doi.org/10.1007/s10530-020-02352-z.
DOI: https://doi.org/10.1007/s10530-020-02352-z

Interpretive Summary: Russian olive is an expanding invader along western North American rivers, and land managers currently invest considerable time and money in its control and eradication in riparian areas. As Russian olive has increased in riparian zones over the past two decades, water movement of seeds is also likely increasing, speeding up the invasion front and strengthening invasion impacts. However, we know little about these seed dynamics. Where hydrochory is important, flooding patterns should correlate spatially with invader distributions. We evaluated spatial associations between modeled flood return intervals (that is, the frequency at which areas in the floodplain are flooded) and the distribution of Russian olive populations in a portion of the Yellowstone River floodplain in Montana. Current distributions of Russian olive along the Yellowstone River are highly correlated with patterns of flooding, and resulting population estimates suggest the intervals of flooding frequency identified should substantially increase invasion risks along western rivers. However, linking Russian olive cover to patterns of flooding could allow land managers to better target vulnerable areas and timeframes for management.

Technical Abstract: Dispersal limitation is thought to slow invasions of Russian olive (Elaeagnus angustifolia L.). Hydrochory has been assumed–but not explicitly considered–as a secondary dispersal mechanism. Where hydrochory is important, flood patterns should correlate spatially with invader distributions. We evaluated spatial associations between modeled flood return intervals and the distribution of Russian olive across a 10.81 km2 section of the Yellowstone River floodplain, Montana, USA. Using output from hydraulic inundation models, we mapped inundation zones associated with successive flood return intervals within the 500-year floodplain. We then compared the spatial extent of inundation zones to distribution maps of Russian olive derived from remote sensing. Russian olive was highly spatially associated with frequent flood return intervals: 80% of the Russian olive cover exists within the 35% of the floodplain classified in inundation zones of 10 year or less; Russian olive cover was most dense in 1.5- to 5-year inundation zones. Immigration at these frequencies could reduce invasion lags and consequently shorten management windows. The strong spatial relationship between inundation frequency and Russian olive distribution suggests that predictions of invasion and management timelines may be improved through a better understanding of the dynamics of hydrochory and seed deposition in this system.