Competitive ability and potential invasion mechanisms of Oplismenus undulatifolius (Ard.) Roem. & Schult. (wavyleaf basketgrass)

Background/Question/Methods

Invasive plant species can enter novel habitats through several mechanisms including superior competitive ability, soil microbe feedbacks, empty niches, or enemy release. Investigating and understanding these mechanisms of invasion success is essential to the management of invasive species and for establishing strategies that can forecast their expansion into naturalized areas A recent invasive species to make its way into mid-Atlantic forests is the shade tolerant perennial grass Oplismenus undulatifolius, which since its first sightings in 1996, has spread to 13 counties in Maryland and Virginia. We conducted a greenhouse experiment determine the competitive ability of O. undulatifolius against Microstegium vimineum, another highly invasive grass species found in Maryland, and a native perennial grass mix of Agrostis perennans, Elymus virginicus and Panicum clandestinum. We also examined the potential roles of mycorrhizal fungal feedbacks and shade tolerance in invasion of O. undulatifolius into forest understories. 

Results/Conclusions

While there was no evidence that O. undulatifolius participated in positive feedback loops with mycorrhizal fungi, there was strong evidence that O. undulatifolius invades forests via exploitation of empty niches. Competition had a negative effect on growth in all species combinations, but O. undulatifolius was affected to a much greater degree than either M. vimineum or the native grass mix. This indicates that post agricultural legacies and overabundant deer populations, which lead to depauperate understories, may be a major facilitator of O. undulatifolius invasion in mid-Atlantic forests.  Growth of O. undulatifolius was marginally higher in the shaded treatment and plants in full sun showed evidence of bleaching and damage, but shade did not affect its performance against competitors. Understanding the mechanisms that underlie invasive species colonization is important to the preservation of native habitat as invasive species facilitate the decline and in some cases loss of native species in susceptible areas.