Comparison of the vegetation and seed banks of natural and restored wetlands In the Prairie Pothole Region, Saskatchewan.

Date
2013-01
Authors
Put, Margaret Olga
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Faculty of Graduate Studies and Research, University of Regina
Abstract

In the early 1970s, many wetlands in the Prairie Pothole Region of Saskatchewan, Canada, were drained to increase the agricultural land base. In the early-mid 1990s, Ducks Unlimited Canada (DUC) restored many of these drained wetlands to their original spill elevations, reverting back to the natural hydrological cycles and relying on any existing seed banks to passively revegetate the basins. This study compared the vegetation communities and seed banks of “Restored” wetlands to those of “Natural” (never drained) wetlands after almost twenty years, and considered whether relict seed banks could successfully restore drained wetlands without reseeding typical wetland vegetation species. The vegetation and seed banks of nine Restored wetlands were compared to that of nine Natural wetlands. In each wetland, vegetation composition was recorded as percent cover in three visual concentric wetland vegetation zones, namely the Center, Inner-Typha, and Typha zones. Soil samples were collected from these three zones, and the seed banks were assayed in two ways: by identifying and counting the seeds present, and by identifying and counting the seedlings that germinated. Germination assays wereundertaken for eight months under controlled laboratory settings chosen to replicate natural hydrological conditions. The vegetation of the Restored and Natural wetlands was generally different, although there was overlap between the two groups. Approximately 60% of the taxa were found in common. Diversity comparisons showed that richness was significantly greater in the vegetation of Restored wetlands in comparison to that of Natural wetlands, while the number of seeds was significantly greater in the Natural wetlands. There was not a clear distinction between the seed banks of the two groups, and 75% of the taxa were found in common. The seedling assay results showed that the Restored and Natural wetlands segregated into two groups, but with overlap between them. Among the seedlings, less than half of the taxa were found in common between Natural and Restored wetland groups. This study concludes that wetlands that were drained for approximately two decades and then restored to natural hydrological cycles still retained diverse seed banks, which overlapped substantially in taxonomic composition with those of Natural wetlands. The seed banks cannot account for the differences between the vegetation and seedlings assays of Restored and Natural wetlands. It appears that the vegetation of Restored wetlands is still responding to restored water levels. Differences in the seedlings that germinated may be at least partially explained by the methodology in which the seeds were not separated from the substrate before being germinated. The presence of a diverse seed bank that includes wetland taxa gives cautious optimism that, given sufficient time, native wetland vegetation will reestablish in drained wetlands in which water is reestablished. Grazing could not be quantified in this study, but the accessibility of drained wetlands to cattle may be an important impediment to vegetation recovery and may facilitate weedy taxa. Further research on the effects of disturbances such as grazing and on active management approaches that could support and hasten revegetation is needed.

Description
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Science in Biology, University of Regina. xii. 113 p.
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