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

Abstract

North American invasions of Elaeagnus angustifolia L. (Russian olive) are still expanding, and hydrochory could be increasing invasion impacts along rivers. Spatial association between riverine flood-inundation patterns and E. angustifolia distributions suggests a link between seed movement potential and invasion patterns in time and space. Using output from hydraulic inundation models, we mapped inundation zones associated with successive flood return intervals within 10.81 km2 of the estimated 500-year floodplain of the Yellowstone River, Montana, USA. We then evaluated spatial relationships among inundation zones and E. angustifolia distribution. Elaeagnus angustifolia was highly spatially associated with frequent flood return intervals: 80% of E. angustifolia exists within a subset of the floodplain predicted to flood every 10 years or less, with the highest occupancy in the 1.5- to 5-year return zones. Within frequently inundated areas, floodplain occupancy of E. angustifolia was distributed in patterns consistent with likely areas of sediment deposition. Thus, existing predictions of invasion timelines are likely to improve with explicit consideration of dispersal opportunities associated with hydrochory during flooding. In particular, if hydrochory is a significant secondary dispersal mechanism, then seed immigration at flood intervals of 5 years or less could lead to substantially shorter invasion lags than currently predicted.