The effects of Japanese hop (Humulus japonicus) invasion and its interactions with co-occurring plants under variable environmental conditions
Huang, Annie H
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https://hdl.handle.net/2142/124584
Description
Title
The effects of Japanese hop (Humulus japonicus) invasion and its interactions with co-occurring plants under variable environmental conditions
Author(s)
Huang, Annie H
Issue Date
2024-05-01
Director of Research (if dissertation) or Advisor (if thesis)
Matthews, Jeffrey W
Department of Study
Natural Res & Env Sci
Discipline
Natural Res & Env Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
Invasion Biology
Invasive Plants
Wetlands
Japanese Hop
Reed Canarygrass
Bur Cucumber
Competition
Wetland Restoration
Abstract
Invasive plant species pose substantial risks to wetland ecosystems by reducing biodiversity and altering ecosystem function. Furthermore, wetlands are even more vulnerable to biological invasions because they are “landscape sinks” that trap sediment, nutrients, and excess water from fluctuating hydrological events. With increasing globalization, ecosystems are more likely to be simultaneously invaded by multiple nonnative species. The invasive Japanese hop (Humulus japonicus Siec. & Zucc.) has been observed to grow over reed canarygrass (Phalaris arundinacea L.) and other vegetation in wetlands. However, there is limited research on H. japonicus, with few studies looking at its ecology as an invasive species, its interactions with other vegetation, and its role in wetlands. To address these gaps, I investigated the impact of H. japonicus on wetland ecosystems, particularly its competition with P. arundinacea. I collected vegetation and canopy cover data in a field study to assess the invasion dynamics of H. japonicus in a restored floodplain forest. Additionally, I conducted a mesocosm experiment to investigate the growth and competitive ability of species, specifically H. japonicus and bur cucumber (S. angulatus L.), against P. arundinacea under different light and water levels. Collected data were analyzed using linear mixed-effect models and non-metric multidimensional scaling to determine factors (light, water, competition) that affect H. japonicus growth and the impacts of H. japonicus on species richness and composition. Results from the field study highlighted the significant spread of H. japonicus and its competitive replacement of P. arundinacea. Shade reduced H. japonicus cover, and in forested transects, species richness was higher compared to open transects, most likely due to the absence of both H. japonicus and P. arundinacea. Along transects, quadrats that had been invaded by H. japonicus differed in species composition from quadrats that had not been invaded. Species composition also differed from October 2022 to October 2023. The results from the mesocosm study supported the finding that shade negatively affects H. japonicus growth. Growth of all species was reduced by high water and low light. Sicyos angulatus was found to be a better competitor than H. japonicus, especially in shaded conditions, due to its higher shade tolerance. The results suggest that creating canopy closure by planting fast-growing native trees can effectively control H. japonicus and P. arundinacea growth, consequently aiding in the preservation of wetland biodiversity.
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