Decomposition rates and impacts on biodiversity of living Phragmites australis and litter in two sites along Sturgeon Bay, Michigan

Abstract

The purpose of this study was to examine the effects of Phragmites australis (P. australis) on native flora along Sturgeon Bay in Northern lower Michigan. We examined plant species composition amongst both native patches of species (without P. australis) and patches where P. australis was present. Using the Shannon-Weiner index, we found P. australis to have no direct effect on biodiversity on shoreline species. We also quantified decay rates of both P. australis litter and native litter in order to relate P. australis presence to soil characteristics. P. australis lost an average 3.57% of its mass due to decomposition, and native litter lost an average of 7.31% of mass due to decomposition, indicating that native litter decomposes more rapidly than P. australis litter. This suggests P. australis litter could have a greater impact on the plant community than native litter, as it decomposes significantly more slowly. We also examined soil moisture and organic matter content in the native and P. australis patches. The moisture to mass proportion present in the soil for “P. australis patch1” was 0.243, “P. australis patch2” was 0.036, “native patch1” was 0.28 and “native patch2” was 0.154. This data suggests that soil where P. australis is present is less capable of retaining moisture than native patches of dune flora. Data for organic matter content did not show a significant difference between native and P. australis patches but instead a greater variation between the two native patches alone. By cross-examining our three studies, we can conclude that P. australis will not change the species composition and diversity. However, it has an effect on soil moisture, organic content, and decomposition rates on Great Lakes shore communities.