This Louisiana study was initiated using exclosures to determine whether mammalian herbivory by nutria (Myocastor coypus), muskrats (Ondatra zibethicus), and waterfowl had a measurable impact on the plant community and whether any evidence suggests that plant species composition is affected by herbivory. Results showed that herbivory by muskrat and nutria significantly decreased standing crop biomass of Sagittaria latifolia and Ammania coccinea but did not significantly affect stem densities of any species. The mean biomass of Scirpus validus and Cyperus difformis indicates that they were affected by the feeding activity of muskrat and nutria. Also, there may be long-term effects of herbivory on species composition on the Sagittaria and flats. Long-term exclosure studies are needed to document such changes. In addition, herbivory by waterfowl may also play an important role in plant community composition in the Atchafalaya delta of Louisiana and should be addressed.
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