Effect of Herbivory on the Growth and Competitive Ability of Reed Canary Grass (Phalaris arundinacea)

• Main Author: Kratzer, Lisa A
• Format: Text
• Language: unknown
• Published: RIT Scholar Works 2014
• Subjects: Herbivory; Invasive species; Phalaris arundiancea; Canada; Branta canadensis
• Online Access: https://scholarworks.rit.edu/theses/8314; https://scholarworks.rit.edu/context/theses/article/9315/viewcontent/LKratzerThesis5_12_2014.pdf

Herbivory plays an important role in plant community structure in many ecosystems through preferential selection, plant regrowth, and seed transport. Phalaris arundinacea, reed canary grass, is a prevalent wetland invasive species consumed by geese, muskrats, and snails. We lack a clear understanding of how herbivory impacts P. arundinacea's invasion potential. Therefore, I sought to understand the effect of herbivory by generalist macrograzers and micrograzers on the competitive dominance of P. arundinacea in created wetlands, especially the degree to which herbivory alters the competitive relationship between P. arundinacea and Typha latifolia (broadleaf cattail). To address this enclosure/exclosure cages were constructed in June 2013. Half of the plots contained only P. arundinacea and half were placed along the edge between P. arundinacea and T. latifolia. In caged treatments, amber snails (Succinea putris) were either included or removed. Control plots without cages assessed the effect of larger grazers. I predicted that herbivory would negatively impact the growth of P. arundinacea, and mixed plots would allow T. latifolia to spread into the P. arundinacea zone. Choice experiments were conducted with Branta canadensis, Canada geese, and S. putris to evaluate their preference for P. arundinacea or T. latifolia. I did not find any significant differences in P. arundinacea growth due to grazing but competition with T. latifolia did impact P. arundinacea. Edge plots at RIT had a significantly reduced growth rate compared to stems from plots containing P. arundinacea only. In choice experiments, geese showed a preference for P. arundinacea over Typha, whereas snails showed no preference. Despite the observed preference, I was unable to demonstrate effects of herbivory in the field. Herbivory appears to play a minor role in P. arundinacea's success as an invasive plant in created wetlands, with other factors, such as competition for light and nutrients of potentially greater importance.