Rehabilitation of an agricultural wetland: Utilizing seed bank data to inform restoration and management.
AuthorOverlin, Anne Kathleen
AdvisorStringham, Tamzen K
Environmental and Natural Resource Sciences
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Wet meadows are ecologically significant and economically important areas that occupy a relatively small percentage of the landscape. They are at especially high risk because management of these lands for agriculture often require hydrologic modifications and eradication of native dominant species. European and North American studies suggest that after cultivation or grazing ceases, important structural components of vegetation that used to be dominant may not spontaneously re-emerge. Dominant species are important because they control ecological processes that determine wetland function. These statements suggest that once these species are no longer dominant, wetland function is compromised, and restoration of ecological function requires reestablishment of the prior plant community composition. In this study we asked whether formerly dominant species could establish following agricultural abandonment and explored relationships between the seed bank composition with depth to ground water data and biomass accumulation. We hypothesized that resistance to weed invasion is a function of the maintenance of community functional groups, meadow hydrology, and biomass management. A seed bank study of Winters Ranch, Washoe County Nevada was conducted from October 2014 to October 2015. A greenhouse seedling bioassay identified total of 2,416 seedlings and 33 plant taxa were observed in the seed bank, of which eight were native perennial bunchgrasses, 15 native forbs, four exotic grasses, and six were exotic forb species. The average viable seedling densities ranged from 6.8 seedlings/m2 to 147 seedlings/m2. The most common seedlings in the bioassay included Bromus tectorum (cheatgrass), Bromus arvense (Field brome), and Apera interrupta (silky bent grass), which are exotic winter annual species. An important finding was that the seedbank was not necessarily indicative of the aboveground vegetation. Some sampling plots revealed a seedbank dominated by late seral species, such as Deschampsia cespitosa (tufted hairgrass), a native graminoid that historically dominated wet meadows but is now only a minor component if not completely missing from meadows suggesting that some areas have the seed bank potential to return to a late seral state. Other plots were dominated by exotic annuals which were significantly correlated with deeper litter (thatch). These plots were in areas with deeper depth to ground water during the drought suggesting that a lack of decomposition is due to lack of soil moisture. Management ImplicationsManagement of fallow fields, particularly those with altered hydrology (lack of irrigation, diversions, ground water pumping) and slower decomposition will likely result in unexpected weed infestations and require the most effort to restore. Keywords: Agricultural wetlands, decomposition, seedbank, litter, Great Basin, ground water, Juncus arcticus, Carex nebrascensis, Deschampsia cespitosa, Bromus tectorum