[Wikipedia] Invasive behavior: The species was introduced into North America by the late 19th century, and was both planted and spread through the consumption of its fruits (which seldom ripen in England),[15] by birds, which disperse the seeds.[11] Russian olive is considered to be an invasive species in many places in the United States because it thrives on poor soil, has high seedling survival rates, matures in a few years, and out-competes the native vegetation. It often invades riparian habitats where the canopy of cottonwood trees has died. Its quick-spreading root system can make it pest-like. (link added by Mary Ann Machi)