Influence of Light Availability and Water Depth on Competition Between Phalaris Arundinacea and Herbaceous Vines

Invasive plant species pose substantial risks to wetland ecosystems, causing a loss of biodiversity and changes to plant community structure and assembly. With an increase in biological invasions, ecosystems are more likely to be simultaneously invaded by multiple nonnative species. The invasive Japanese hop (Humulus japonicus) has been observed to grow over reed canarygrass (Phalaris arundinacea) and other vegetation in field settings. We investigated interactions between the invasive H. japonicus, P. arundinacea, and a native analog to H. japonicus, bur cucumber (Sicyos angulatus), grown under variable environmental conditions in a greenhouse experiment. Species were grown in monoculture and in competition (H. japonicus×P. arundinacea and S. angulatus×P. arundinacea) under two light levels and two water depths. All monocultures grew best in low water and unshaded conditions, with significant effects of light and water on total biomass. Humulus japonicus growth was strongly reduced by high water, whereas P. arundinacea growth was strongly reduced by low light. In competition against P. arundinacea, S. angulatus was a better competitor than H. japonicus, and competitive effects of both vine species were more severe in shaded conditions. Therefore, restoring canopy cover and planting fast-growing, native trees in combination with planting S. angulatus might be an effective method for managing P. arundinacea populations. Studying the environmental conditions preferred by native species over invasive species provides insight into management efforts that allow native plant species to outcompete invasive species in field settings. Understanding the interactions among invasive species helps guide management efforts to prevent their establishment and spread.