Factors affecting the distribution of wild rice and the surrounding macrophyte community

TitleFactors affecting the distribution of wild rice and the surrounding macrophyte community
Publication TypeThesis
Year of Publication2003
AuthorsMcGuire MA
DegreeMaster of Science
Number of Pages103 pp.
UniversityUniversity of Wisconsin-Oshkosh
CityOshkosh, WI

A recent decline in wild rice (Zizania palustris) wetlands is cause for concern due to its importance as a food source, refuge for wildlife, and its cultural history. Surprisingly, little is know about the environmental parameters necessary to provide optimal growing conditions for this plant. The goal of this survey was to assess the environmental factors significant in understanding the distribution of Zizania palustris and the aquatic macrophyte community in which it grows and compare it to wetlands where wild rice has been lost. Sixty wetlands in Wisconsin and Minnesota were sampled, with approximately equal numbers displaying dense (19), moderate (23), and sparse (18) wild rice production. Chemical and physical factors, as well as densities of aquatic plants, were measured. Thirty-seven species of macrophytes were identified and recorded. Data were anlayzed using multivariate statistics (CCA) in which the following trends were found. More than one factor appears to be responsible for the distribution of wild rice and the rest of the macrophyte community. Moderate levels of phosphorus appear beneficial to the overall success of wild rice, while free-floating macrophytes show an overwhelming response to increases in phosphorous. The distribution of macrophytes at sample site B (bordering wild rice beds) is strongly correlated and thus interpreted to be primarily driven by pH, with Potamogeton robbinsii and filamentous green algae responding most strongly to its increase. Helathy stands of wild rice exhibit a narrow circum-neutral range of pH (6.13-7.99), which is significantly different from the greater range exhibited by poor wild rice wetlands (6.5-8.5). This pattern was parrlleled when considering depth which suggests that deeper wetlands may be more susceptible to wild rice loss. It was not evident from this study that there were any direct competitors to wild rice. Ceratophyllum demersum does seem to be a likely candidate though if conditions within the wild rice wetland become more eutrophic. Management of existing wild rice wetlands should focus on pH, depth, increases in shore development. Increase of P. robbinsii and filamentous green algae may act as possible indicator species for loss of wild rice.