- Managing Seedbank Composition to Enhance Wetland Restoration
Many wetland restorations in the Prairie Pothole Region (PPR) consist of returning the hydrology to a degraded wetland and rely on germination from the seedbank, dispersal, and succession to produce more desirable wetland plant communities (van der Valk 1999, Mitsch and Gosselink 2007). Several years, or even decades, after hydrologic restoration, researchers commonly report that the plant communities in hydrologically restored PPR wetlands can be easily distinguished from native PPR wetland plant communities (Mulhouse and Galatowitsch 2003, Paradeis et al. 2010, Smith et al. 2016). While hydrologic restoration may theoretically result in the development of wetland plant communities indistinguishable from native communities when given enough time, restoring the water regime and relying on succession, the seedbank, and dispersal may not adequately restore severely degraded PPR wetlands within a timeframe reasonable to land managers (Seabloom and van der Valk 2003, Aronson and Galatowitsch 2008). Wetland restoration may also be slowed because wetland seedbanks may be severely depleted following decades of anthropogenic disturbance, and many native wetland species are limited by dispersal (Galatowitsch and van der Valk 1996, Seabloom and van der Valk 2003, van der Valk et al. 2009, van der Valk 2013). Thus, the restoration of wetland plant communities is often enhanced by supplementing the existing seedbank via human intervention (e.g., seeding or transplanting) in addition to relying on natural factors (e.g., germination, dispersal via water movement, wind, or waterfowl and other animals [Wienhold and van der Valk 1989, Aronson and Galatowitsch 2008, van der Valk et al. 2009]).
Knowledge of seedbank composition can help managers to more fully understand a plant community and its ecological history because seedbank composition is not necessarily a direct reflection of aboveground vegetation (Thompson and Grime 1979). Better awareness of seedbank composition prior to wetland restoration may streamline vegetative restoration by allowing managers to recognize native species that may be lacking and identify potentially problematic species earlier in the restoration process. This prior knowledge will allow managers to target specific objectives and utilize scarce resources more efficiently. In our current study, we evaluated the effects of competition-reduction methods on seedbank composition in a degraded PPR wetland that was cropped for several decades but fallowed for most of the last 20 years. Our ultimate goal is to restore this site to a wetland complex possessing a diverse mix of native species typically associated with tallgrass prairie wetlands.
Our study site consisted of an approximately 19-hectare wetland complex located on the Albert Ekre Grassland Preserve in Richland County, North Dakota, managed by North Dakota State University. Following a long history of cropping and fallowing, the site was dominated by annual, introduced, and invasive species, especially Typha × glauca (hybrid cattail) and Phalaris arundinacea (reed canarygrass). We hypothesized that relatively few native wetland plant species would be viable in the seedbank due to the history of conventional agricultural practices employed at this site. Rather, we expected that seeds from the annual, introduced, and invasive species that dominated the emergent plant community would also dominate the seedbank, especially because the site had remained fallow for many of the preceding 20 years. Further, we suspected that competition from these undesirable species would hinder our planned vegetation restoration efforts.
Because conventional farming practices, such as disking, tilling, and applying herbicide, reduce the cover of annual/perennial plants and their contributions to the seedbank, [End Page 12] it can be useful to employ these practices prior to vegetative restoration to reduce competition from the seedbank (Gendron and Wilson 2007, Rowe 2010). To this end, we burned our study site in May 2013 and tilled it three times with a vertical tillage tool. Next, we applied glyphosate once prior to planting with Roundup Ready® soybeans (Monsanto Company, St. Louis, MO) and three times after planting but prior to harvest. We applied glyphosate once post-harvest for a total of five applications in the 2013 growing season (following label recommendations).
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