Exotic plants have the ability to modify soil seed banks in habitats they invade, but little is known about the legacy of invasion on seed banks once an exotic plant has successfully been controlled. Natural areas previously invaded by leafy spurge in the northern Great Plains typically have one of two fates following its removal: a return of native plants, or a secondary invasion of other exotic plants. It is unknown, however, if this difference in plant communities following leafy spurge control is due to seed bank differences. To answer this question, we monitored seed banks and standing vegetation for 2 yr in mixed-grass prairies that were previously invaded by leafy spurge but controlled within 5 yr of our study. We found that native plant seed banks were largely intact in areas previously invaded by leafy spurge, regardless of the current living plant community, and leafy spurge invasion history had a larger impact on cover and diversity of the vegetation than on the seed banks. Differences in plant communities following leafy spurge control do not appear to be related to the seed banks, and soil conditions may be more important in determining trajectories of these postinvasion communities.

Nomenclature: Leafy spurge, Euphorbia esula L. EPHES

Management Implications: Leafy spurge is an invasive exotic plant of great concern in the northern Great Plains. Control efforts have been successful in recent years, but previously invaded areas either experience a return of native plants (a desirable outcome), or a secondary invasion of other exotic plants (an undesirable outcome). Little is known about the impact of leafy spurge invasion on seed banks, and if seed banks differ between areas with varying invasion histories and vegetation trajectories following leafy spurge control. Our investigation of these seed banks revealed that native species were common in the seed banks of all invasion histories, and that the seed banks were not significantly different among invasion histories and vegetation trajectories. These differences did not appear to be a reflection of the current standing vegetation, but rather resulted either from seeds that arrived at the soil before the invasion, or that were dispersed to invaded sites from nearby native-dominated areas. We conclude that native plant restoration in areas previously invaded by leafy spurge is probably not hindered by the seed banks, and that seed banks appear to be relatively resilient after leafy spurge invasion and control. However, the ubiquitous presence of the aggressively invasive grasses smooth brome and Kentucky bluegrass may necessitate active restoration efforts that simultaneously reduce invasive grass presence and promote native plant recruitment. Additional experimentation would help determine if popular management methods, such as seed addition, are effective in achieving these restoration goals in habitats that already have intact native seed banks.