Submitted by: Karin Kettenring, Ph.D. candidate, Applied Plant Sciences, Applied Ecology Lab of Dr. Susan Galatowitsch, University of Minnesota, St. Paul, 612-624-0779
When the last glaciers retreated from this region 20,000 years ago, they scoured out thousands of “potholes” across the landscape. These potholes filled with water from the melting glaciers and the prairie pothole wetlands were born. Prairie wetlands are unique to the Midwestern part of the United States and are significant to the millions of waterfowl that make their annual migrations along this major flyway. Also, the glacial soil in this region was rich and desirable, giving birth to a thriving agricultural economy. There has been a continual struggle between these land uses as waterfowl populations declined drastically during the 1800s and 1900s because of wetland drainage. Since the mid-1980s, there has been an interest in directing the predominantly agricultural landscape back towards its prairie wetland roots. Significant federal and state legislation in the 1980s provided impetus (including funding) for wetlands to be restored.
Thousands of wetlands were restored by farmers with help from conservation organizations and government agencies on farmland throughout the prairie pothole region. Ditches and drainage tiles that drained wetlands were dismantled, and former wetlands were reflooded. Were these efforts successful in reestablishing wetland flora and fauna? Over the past 15 years, ecologists have looked at everything from plant to bird communities to determine if the restorations were successful. Their findings were striking. They found that some species return quickly to restored wetlands, but the characteristic plant species that live around the periphery of wetlands in the seasonally flooded zone, especially sedges, were almost entirely absent from restorations. Sedges may have edges (i.e., triangular stems) but wetland edges are missing their sedges.
These grass-like plants are important to wetlands for a number of reasons. Some scientists think that the seeds may be an important food source for certain birds like sedge wrens and common yellowthroats, and that some upland nesting waterfowl require sedges for nesting. Thus, the lack of sedges could potentially be a big loss for wildlife. Another thing to consider is the plant diversity of the wetland ecosystem. We now know that 5-10 years after a wetland is restored the space where sedges would have grown becomes dominated by reed canary grass. Native species can’t compete with this invasive species and the end result is a wetland with low plant diversity.
In the fall of 2000, as I began my graduate research, I sought to determine why the sedges have not returned to wetland edges by focusing on two questions. First, I wanted to know if the sedges were not returning because the seeds were not getting to the restoration sites. Seeds move by wind, water, and animals. I wanted to determine which seeds were getting to restorations and if any of them were sedges. To answer this question, I placed hundreds of seed traps (craft foam coated with a sticky substance), in wetlands throughout my research site. Thus far, I have found no sedges in my seed traps.
I had a second idea that perhaps the sedges were reaching the restored wetlands but that the conditions were not suitable for them to grow. Some seeds require very specific conditions for growth. Bare mud in a new restoration is quite different from what a seed would experience in a natural wetland. Perhaps that perfect concoction of light, nutrients, and water required for seed growth doesn’t exist in a restored wetland. To determine whether sedges grow in restorations, I placed seeds of 5 different sedge species in plots in restored wetlands. I have found lots of little sedge plants popping up in my pots in the restorations. This is good news to restorationists because it means that if sedge seeds are sown into restorations, they stand a chance of becoming established.
Now that I know that sedge seed will grow in restorations, I am investigating the optimal conditions for seed growth. I am conducting experiments in growth chambers – setting temperature, light, and moisture conditions under a range of conditions to figure out what leads to the best seed growth, so I can determine the best time to put seeds in wetlands to maximize the establishment of this plant. In the end, I hope that the information from my research will result in successful sedge establishment in restored wetlands. Then, we would be one step closer to restoring the edges of wetlands with sedges and creating a diverse plant community.
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