Association of non-native Amur honeysuckle (Lonicera maackii, Caprifoliaceae) with other invasive plant species in eastern deciduous forests in southwestern Ohio

Although many invasive plant species negatively impact native plants in natural communities, their relationships with other nonnative plants remain relatively unexplored. In some cases, invasive plant species may be capable of facilitating the invasion of other nonnative species into natural areas, thereby exacerbating their invasive ecosystem effects. We examined whether Lonicera maackii (Rupr.) Herder (Amur honeysuckle), a woody shrub from Asia that is rapidly spreading throughout the midwestem USA, is associated with other invasive plant species, compared to locations where L. maackii is not yet present. Lonicera. maackii is known to detrimentally impact native plant communities and to alter soil nutrients and light levels in invaded areas, indicating that it has the potential to act as an invasion facilitator. Using plots with and without L. maackii in four study sites across southwestern Ohio, we quantified species richness (S), relative abundance (RA), proportion of total species (PR), and diversity (H) of invasive species, compared to native and nonnative species that were not invasive. The presence of L. maackii was significantly associated with an increased number, proportion, and diversity of other invasive plant species, but the relative abundance of invasive individuals did not differ between plots with and without L. maackii. Presence of L. maackii and also distance to roads were explanatory variables that predicted S. PR, RA, and H for invasive species. Overall, the association of L. maackii with other invasive plant species in natural areas indicates the need for continued investigation into the potential role of L. maackii as an invasion facilitator in eastern deciduous forests in the midwestern USA.